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Product Documentation

General Information

Light Dependent Resistors

light dependent resistor gifWhat Is An LDR?

An LDR is the marriage of a photoresistor with a light emitting diode (LED) in a small sealed package approximately the size of an M&M candy. Each LDR has 2 pairs of wires. One pair connects to the LED while the second pair connect to the photoresistor.

The resistance of an LDR varies in proportion to the brightness of the LED which is in turn dependent on the amount of electrical current running through the LED.  As the LED becomes brighter the resistance of the photoresistor decreases.

Through precise control of input current, LDRs can smoothly regulate resistance over a wide enough range to provide effective high performance audio volume control.

LDRs optically isolate the control circuitry from the audio signal passing through the photoresistor. The audio signal only encounters a variable resistance that is regulated by photons (i.e. light) and not electrons.

All Tortuga Audio preamps utilize LDRs to control volume (i.e. to attenuate the audio signal).

Tortuga Audio LDR module
Tortuga Audio LDR Module

Why Do We Use LDRs for Volume Control?

We use LDRs because the resulting sound quality is amazing. Adjectives like clear, open, unveiled, articulate, and uncolored all apply to the LDR. All while maintaining excellent bass and overall dynamics even in a passive preamp.

If LDRs are so great why then why don’t all preamps use LDRs? Reasonable question. Here’s why not.

The simple reason is LDRs are notoriously difficult to use for volume control. They are inherently nonlinear which means they act differently at different levels of resistance. They are also not consistent from one to the next even within the same make and model from the same production batch. Their performance curves may even drift slightly over time. LDRs also have higher distortion characteristics than most other alternatives although not enough that it really matters subjectively.

For all the above reasons most audio designers have avoided taking on the challenge of using LDRs.

Tortuga Audio took on this challenge several years ago and has not looked back. We overcame these technical challenges. We are currently on our 4th generation of our LDR preamp control technology.

How are LDRs Used for Volume Control?

Volume control with an LDR is conceptually similar to a potentiometer so lets look first at how the common potentiometer (“pot”) is used for volume control.

Potentiometers used for volume control typically have a fixed resistance between 10k and 100k ohms. The audio input signal connects at one end of this fixed resistance and the other end is connected to ground. The output signal from the pot is a third connection to what’s referred to as the “wiper” which slides along the pot’s fixed resistor. This is shown in the diagram below.

basic volume control schematic

The variable resistance above the wiper (the output) is the series resistance (Rseries) and the variable resistance below the wiper is the shunt resistance (Rshunt). The sum of Rseries plus Rshunt equals the rated impedance (10k, 50k, 100k etc. ) of the pot.

The resistance Ratio is defined by the formula: Ratio = Rshunt/(Rshunt + Rseries). This Ratio also happens to be the voltage ratio of Vout divided by Vin such that Vout = Vin x Ratio. A pot’s attenuation level at any point along the wiper can be expressed in decibels which is defined as 20 x log(Ratio). Putting all this together your arrive at dB = 20 x log (Vout/Vin) where Ratio = Vout/Vin = Rshunt/(Rseries + Rshunt).

Thus, when Rseries is zero the volume is maximum (no attenuation) and when Rshunt is zero the volume is zero (maximum attenuation).

With LDRs, attenuation is achieved by varying the resistance levels of 2 separate series and shunt LDRs to achieve specific resistance ratios that correspond to specific dB attenuation levels. While a pot does this mechanically, the resistance levels of both the series and shunt LDRs must be done electronically. Doing so reliably and repeatedly can be a challenging design problem.

Attenuation & Impedance

What is Attenuation?

Attenuation is the opposite of amplification.

When you amplify an audio signal you are increasing its average voltage level. When you attenuate an audio signal you reduce its average voltage level. Volume control and attenuation are terms that are often used interchangeably.

Attenuating an audio signal (i.e. reducing its voltage level) is most commonly done using a voltage divider.

The common potentiometer (“pot”) is nothing more than a type of voltage divider.

How Does Volume Control Work?

Potentiometers used for volume control will have a fixed resistance rating that is typically between 10k and 100k ohms. The audio input signal connects at one end of this fixed resistance and the other end is connected to ground. The output signal from the pot is a third connection to what’s referred to as the “wiper” which slides along the pot’s fixed resistor. The output signal of the pot comes from the wiper.

The resistance above the wiper is the series resistance (Rseries) and the resistance below the wiper is the shunt resistance (Rshunt). The resistance Ratio is defined by the formula: Ratio = Rshunt/(Rshunt + Rseries). This Ratio also happens to be the voltage ratio of Vout divided by Vin such that Vout = Vin x Ratio. Putting all this math together the resulting attenuation expressed in decibels is defined as: dB = 20 x log(Ratio) or if you like dB = 20 x log (Vout/Vin) where Ratio = Vout/Vin = Rshunt/(Rseries + Rshunt).basic volume control schematic

Thus, when Rseries is zero the volume is maximum (no attenuation) and when Rshunt is zero the volume is minimum (maximum attenuation).

Volume control with an LDR is conceptually similar to a potentiometer.

With LDRs, attenuation is achieved by varying the resistance levels of 2 separate series and shunt LDRs to achieve specific resistance ratios that correspond to specific dB attenuation levels. With a pot all this is done mechanically whereas with LDRs it’s done electronically and thus can be manipulated in ways that you can’t with a pot.

Input Impedance with LDRs

Music is alternating current/voltage (AC), not constant direct current/voltage (DC). With DC electricity we use the term resistance. With AC electricity we use the term impedance. Thus, the term “impedance” is a way of talking about resistance when the voltage is composed of an ever changing voltage over a wide frequency spectrum as is the case with music.

In the section above we defined Rseries and Rshunt. The sum of these 2 values is defined as he nominal impedance of both types of volume control.

If we want to maintain a target 20k ohms input impedance, the combined resistance of the series and shunt LDRs must always equal at least 20k ohms. With LDRs we can’t quite achieve this in practice. With LDRs the Rseries and Rshunt values can never be exactly zero.

For practical reasons such as longevity, we limit the minimum resistance level of our LDRs to 100 ohms and the maximum resistance to 100k ohms. In order to also achieve a full attenuation range of 60 dB within this limited range we have to let the impedance level rise when volume is between 0-22%. At higher volumes the impedance is able to remain constant.

This is illustrated in the graph below of a nominal 20k LDR attenuator. The input impedance (green line) starts at 100k at zero volume, drops down to 20k by step 16 (-46 dB) and than remains constant over the remaining attenuation range. Note that the impedance is the sum of Rseries (red line) and Rshunt (blue line) the ratios of which define the attenuation level in dB (black line) at each step.

ldr3x.v2 attenuation and impedance curves

Output Impedance

The output impedance of potentiometers and LDR attenuators is neither fixed nor is it independent from the input impedance. As is clear in the above graph, the output impedance (yellow line) varies with each step in the attenuation.

The output impedance is actually the parallel resistance of the series and shunt LDRs. The output impedance starts at ~100 ohm and remains relatively constant until step 16 and then begins to increase along with the shunt resistance. Output impedance peaks at 25% of the nominal input impedance corresponding to step 59 which is at exactly -6 dB of attenuation.

Used as passive attenuators there’s no avoiding the varying output impedance shown. As a practical matter this rarely poses a problem in real world audio applications.

Adjustable Impedance

What Is Adjustable Input Impedance?

Adjustable Input Impedance is a feature introduced in January 2015 that allows the user to change the default 20k input impedance of Tortuga Audio’s  preamps to any level between 1k to 99k ohms.

Using this feature is completely optional. In most cases leaving the setting at 20k is ideal.  But for those who wish to explore potential improvements, trying alternative input impedance levels is possible with Tortuga Audio preamps.

Why Would I Want To Change Input Impedance?

Some combinations of source (DAC, CD transport, phono stage etc. ) and amplifier may benefit from changing the input impedance of the passive preamp.

Adjustable Impedance allows the user to set up five (5) different input impedance levels and switch between these while playing music without interruption. This flexibility will allow the user to fine tune and select the passive preamp impedance level which is optimal for their source(s) and amplifier.

Increasing the preamp’s impedance will result in a higher overall effective impedance as seen by the source. A higher impedance will make it easier for the source to transfer audio energy (i.e. the music) to the amp because it requires less current from the source.  If your source happens to have a less robust output stage, connecting it to lower impedance devices may result in loss of dynamics and poor bass. Some source components may require say 50k or higher impedance to perform properly.

Why not just set the default preamp input impedance to 100K and be done with it? You may also ask why don’t all amplifiers have 100k versus say 20k input impedance? Raising input impedance higher than necessary can raise distortion levels. This is particularly true of LDR passive preamps where high voltage drops across the LDRs raises their distortion level – although even at 100k input impedance our LDR preamps still sound fantastic.

Input impedance should be sufficiently high to ensure optimal performance but no higher. Raising the impedance even higher probably won’t improve performance and may in fact raise distortion. More is not always better.

There’s no simple formulaic approach to knowing what input impedance is optimal for your system. This is something you have to arrive at through a bit of trial and error using various impedance levels.

How To Set Up Each Impedance Setting

Impedance setting #1 is 20k by default. All Tortuga Audio preamps are shipped with this default impedance. User may change this impedance level to any value between 1k and 99k. Similarly, impedance settings #2 through #5 can each bet set up each with its own impedance level. Multiple settings allow for switching between setting levels while listening to music so you can determine which is optimal for your system.

When you first receive your preamp, only impedance setting #1 will have been configured. Settings #2 through #5 are empty. If you switch to impedance settings #2 through #5 without first configuring them you will get no output from the preamp. This is the #1 most common mistake people make with our preamps. 

Changing the impedance level of a given impedance setting number (1-5) must be done for each impedance setting individually per the steps below. For example, this means you have to follow the entire procedure listed below for impedance setting #2 and only #2. Once you’ve completed the procedure for #2, you can then choose to change the impedance for some other impedance setting number. If you wish all 5 settings to be available, you must setup each setting number separately. 

Below you’ll find the procedure for changing the impedance setting number and/or impedance level. The procedure may differ slightly depending on type of controller board in your preamp.

Instructions For V25 Preamps

StepDescription | For V25 Preamps Only
1Turn on the preamp
2Put Preamp In Impedance Adjust Mode - Press the Mode Button on remote 2 times (once only for single input LDR1.V2 or LDR1B.V2) to display the Impedance Adjust values. The left display shows the impedance setting number (1-5). The right display shows the impedance level (1k-99k) associated with the impedance setting number.
3Select Setting Number - Use the Raise/Lower buttons to select the impedance setting # (1-5) shown in left display that you wish change or set up initially.
4Adjust Impedance Level - Use the Left/Right buttons to adjust the impedance level shown in the right display to desired value (1k-99k)
5Save Changes - Press the Enter button to save the current setting number and associated impedance level. This returns unit to normal volume control mode.
6Run AutoCal To Build New Attenuation Table - Press the Mode Button on remote 5 times (4 only for single input LDR1.V2 or LDR1B.V2) to switch to AutoCal Adjust Mode. Both displays should show zero values. Press the Right Button 3 times in a row to start AutoCal.

Instructions For V2 Preamps With Firmware Versions 2.2.x

StepDescription | For Firmware Version 2.2.x Only
1Turn on the preamp
2Press the Mode Button on remote 2 times (once only for the LDR1.V2 or LDR1B.V2) to display the Impedance Adjust values. The left display shows the impedance setting number (1-5). The right display shows the impedance level (1k-99k) associated with the impedance setting number.
3Use the Raise/Lower buttons to select the impedance setting # (1-5) shown in left display that you wish change or set up initially.
4Use the Left/Right buttons to adjust the impedance level shown in the right display to desired value (1k-99k)
5Press the Enter button to save the current setting number and associated level
6Turn off the preamp
7Enable Auto-Cal by pressing the Enter button. The Auto-Cal process will populate the attenuation table based on the new impedance level for the selected step.
8Repeat steps 1 through 7 for each setting. Each setting number must be configured individually per all the above steps.

Instructions For V2 Preamps With Earlier Firmware 2.1.x

StepDescription | For Firmware Version 2.1.x Only
1Turn on the preamp
2Press the Left button on the remote. The right display will show the currently selected impedance setting (1-5).
3Use the Raise/Lower buttons to select the setting set you want to change or set up.
4Press the Left button again on the remote. The right display will now show the impedance level (1k - 99k) associated with the currently selected setting.
5Use the Raise/Lower buttons to adjust the impedance level to desired value (1k-99k)
6Press the Enter button to save the current setting number and associated level
7Turn off the preamp
8Enable Auto-Cal by pressing the Enter button. The Auto-Cal process will populate the attenuation table based on the new impedance level for the selected step.
9Repeat steps 1 through 8 for each setting. Each setting number must be configured individually per all the above steps.

Using Adjustable Impedance While Listening To Music

Once 2 or more impedance settings have been set up, you can switch between them in real time while listening to music.

Please note that if you switch to an impedance setting that is not defined, the audio output will shut off. Switching back to a defined setting number will switch the music back on.

Consult the instructions above to access the impedance level adjustment display and use the Raise/Lower buttons to switch between 2 or more settings with different levels. You may notice a qualitative difference between levels or you may not. Much depends on the specific equipment in your system and its sensitivity to impedance bridging ratios.

Based on feedback we’ve received from customers and our own experience with adjustable impedance the optimal setting is one that provides sufficient impedance bridging (ratio of amp input impedance to source output impedance) between the source and the amp. Increasing the impedance bridging ratio further usually does not provide additional benefit and can actually have a negative impact on sound quality.

Auto Calibration

LDRs and Calibration

Using LDRs in audio applications is technically challenging because the relationship of current vs. resistance within each LDRs is both highly nonlinear and can vary considerably from one individual LDR to the next. It can also change over time as an LDR ages.

The conventional approach to dealing with these challenges is testing 100 or more LDRs to find matching pairs or multiple pairs. Even when initially matched, LDRs are known to shift their calibration curves over time as they normally age. This can degrade the stereo imaging and sound stage and allow channel balance to drift left or right. Moreover, if one of the matched LDRs fails, the preamp might be rendered unusable.

Tortuga Audio has developed proprietary technology that overcomes these challenges thus making LDRs practical for commercial audio applications. Software driven digital control of the analog LDRs is an essential part of this technology.

Auto Calibration

In May, 2014 Tortuga Audio released its V2 Preamp Controller with adaptive self calibration call auto-calibration or “autocal” for short.This is unique among all known products using LDRs in audio applications.

Autocal eliminates the need to test and match LDRs. It also ensures that the LDRs continue to perform optimally despite any drift that may occur due to the normal aging process of analog devices. Autocal is a closed loop system employing both DACs (digital to analog converters) and ADCs (analog to digital converters) to calibrate each LDR against a multi-step attenuation schedule. Calibration results are stored in memory and then used to accurately control each LDR during normal operation.

In summary, autocal:

  • Is a self-contained software driven self calibration process that doesn’t require any external equipment
  • Automatically calibrates the resistance values of the LDRs against a defined attenuation schedule
  • Ensures that the LDR preamp will continue to perform optimally as LDRs age or drift over time or if an LDR has to be replaced

Running Auto Calibration

For Version V2/V21 Hardware

The following summarizes how the current version of AutoCal works for preamps with the V2/V21 boards. Earlier versions of the firmware may behave slightly differently.

StepDescription
Turn Preamp Off manualPreamp must be plugged into power but turned off
Start AutoCalmanualAutoCal must be manually started. Once started the AutoCal cycle will run to completion and shut off by itself.
displayLeft display will show which LDR is currently being calibrated. Right display will show which step (1-70) is currently being calibrated. If connected, the Status LED will blink rapidly during AutoCal.
sequenceLDRs are calibrated in the following sequence:  #1-right series, #2-right shunt, #3-left series, #4-left shunt. The series LDRs start at step 70 and count to 1. The shunt LDRs start at step 1 and count up to 70.
disconnectAudio inputs/outputs are automatically disconnected when AutoCal starts and reconnected when AutoCal stops
durationA complete AutoCal cycle typically takes around 10-15 minutes but may run faster or slower. A very slow (> 30 minutes) cycle may indicate that an LDR has developed a problem and may need replacement.
via remotePress the Enter(center) button on the remote to start AutoCal
via encoderTurn the Encoder approximately quarter turn to the right to start AutoCal
Stop AutoCalautomaticOnce started, the AutoCal cycle will run to completion and shut off by itself (recommended)
manualAutoCal can be stopped at any time but we recommend allowing the calibration cycle to finish on its own
via remotePress the Enter button on the remote. You may have to press the Enter button more than once
via encoderTurn the Encoder approximately quarter turn to the right
Skip LDRmanualYou can force AutoCal to skip to the next LDR (nor recommended)
via remotePress the Right button to skip from current LDR to the next LDR. If already on the 4th LDR, will shut off AutoCal.
via encoder(not available)
FrequencyIf your preamp performs well there’s no compelling reason to run AutoCal. If you wish to run AutoCal periodically, we suggest once a month or once a quarter.

Auto Calibration Recommendations

We recommend the following:

When To Run Autocal

There’s no fixed requirement for when you should run autocal. You could literally go months or even years without ever once running Autocal. However, we recommend running autocal once every 1-3 months to ensure optimal performance.

Keep Source/Amp Turned Off During AutoCal

During AutoCal, the V2 disconnects the audio signal inputs and outputs from the V2 board. You do NOT have to disconnect your amp from the V2.  However, we recommend you turn off both your source and your amp prior to running AutoCal as a precaution. If your amp remains on when AutoCal starts and stops, sometimes you may notice a brief pop or click sound coming from your speakers when AutoCal starts and stops.

Allow Your LDR Preamp To Thermally Stabilize Before Starting AutoCal

LDR’s are sensitive to ambient temperature changes. Therefore, you should avoid running AutoCal until the V2 has had time to stabilize at room temperature. If  you just relocated the V2 from either a hotter or colder location, we suggest you wait an hour before starting AutoCal.

Avoid Interrupting AutoCal Once It’s Been Started

Interrupting AutoCal won’t harm your preamp but it may result in less than ideal calibration results. If AutoCal gets interrupted, we suggest you rerun AutoCal to completion.

Common Specifications

The following specifications are common to all Tortuga Audio preamps as of May 2017.

Criteria 
Preamplifier typePassive audio attenuator using light dependent resistors (LDRs) in a series/shunt (L-Pad) configuration
GainUnity (1x) gain (no amplification)
Input impedance20k by default adjustable between 1k and 99k
Bufferingnone
Audio Signal IsolationNo active manipulation of the audio signal. Audio signal optically isolated from LDR controls but may share common ground.
Total Harmonic Distortion1% or less
Channel BalanceWithin 0.5 db over full attenuation range
Attenuation Range-60 db to 0 db in at least 70 discrete steps plus muting
FusesNo internal or external fuses
Control systemV2 - 8 bit PIC microcontroller running at 4 MHz
V25 - 32 bit ARM microcontroller running at 72 MHz
Circuit boardsNickel immersion gold PCBs with blue solder mask
SolderLead free solder with 3% or higher silver content
ROHSCompliant or exempted
Ambient ConditionsStable, dry indoor environment only with ambient temperature within 60-90 degree F
Trigger OutOutputs a 12 VDC signal when unit is turned on. Signal can be used to turn other devices on/off that are equipped with a Trigger Input.
Encoder ControlRotary stepped multi-function volume control (front panel) with integral push button switch
Remote ControlInfrared control via standard silver Apple remote | 38 kHz NEC protocol
Apple Remote Pairing

What Is Remote Pairing?

Remote pairing is simple process to “teach” your Tortuga preamp how to talk to your Apple or Tortuga (legacy) remote.

Do I Need To Pair My Remote?

Chances are the answer is NO!  A remote is included with each Tortuga Audio preamp and that remote will already have been paired with your preamp.

If you purchase a Tortuga Audio DIY premap controller without also purchasing a remote then you will have to purchase your Apple remote separately and pair it with your controller.

When Is Remote Pairing Necessary?

Every Apple remote has an internal ID number. There are 256 possible ID numbers. The purpose of the ID number is to allow the use of different remotes for different products. You may have an Apple remote to your Apple TV in addition to your Apple remote for your Tortuga preamp. Without ID numbers it would be chaos with both devices reacting to any remote. Usually, pairing is only required with a new remote. Rarely it may also be require after a major firmware upgrade.

Can I Change the ID of my Apple Remote?

The answer is yes but the only reason for doing so is if you have two Apple remotes for two different devices and both remotes happen to have the same ID number (one chance in 256). The Apple remote ID can be changed by simultaneously pressing both the Menu and the Enter/Center key on the Apple Remote for 5+ seconds and then releasing. This will change the ID number to some new value. After changing the ID you will then have to pair the Apple remote with your Tortuga preamp.

Does Remote Pairing Apply to my Tortuga Preamp?

Starting with version 1.0.9 of the LDR3x.V2  firmware the Apple Remote can (and sometimes must) be paired with the preamp unit in order for the preamp to recognize and respond to the Apple Remote’s commands. This is only relevant to the LDR3x starting with the V2 model and also with the LDRx, LDRxB, LDR3.V2 & LDR3.V2K models. Prior to version 1.0.9, the Tortuga preamps would respond to any Apple or Tortuga legacy remote without pairing which occasionally created conflicts with other equipment.

How Do I Pair My Remote With My Preamp? 

Pairing your remote with your Tortuga preamp is a fairly straight forward process that can be accomplished in less than a minute. Below you’ll find a step by step guide on pairing your remote.

StepActionHow
1Turn on the preampPress/release the Encoder button or briefly connect/release J2-ES to J2-G on the LDR3x board
2Enable “pairing” modePress in & hold the Encoder button for at least 20+ seconds (suggest 30 seconds to be safe) and then release. If you have a DIY LDR3x preamp controller board without an Encoder, you can emulate the Encoder press/hold by connecting J2-ES to J2-G (ground).
3Confirm preamp is in pairing modeUpon release of the Encoder button (see step 2 above), the DM1 display module and/or the Status LED will start blinking rapidly.
4Pair the remoteBy pressing any key on the remote except the Menu(Power) key. Pressing the Center/Enter button is preferred. This will stop the rapid blinking and return the preamp to normal volume control mode.
5Confirm the pairingPress the raise/lower keys on the remote. If the pairing was successful the preamp should now react normally to the remote. You are done!

Trouble Shooting

“I press/hold the Encoder push button for 20 seconds and release and the display blinks for only a second or so and then stops”  – This means you didn’t hold the Encoder push button in long enough. If you hold it in for greater than 10 seconds but less than 20 it resets the preamp’s channel balance which is indicated by brief (1-2 seconds) blinking.

Remote Control Scheme Versions Explained

3 Control Scheme Versions

While there is only 1 version of the silver Apple remote itself, there are 3 slightly different control scheme versions depending on when your preamp was built and shipped, which version controller your preamp has,  and which version of firmware your preamp has.

tortuga audio apple remote control buttons

 

 

Version V25

Version V25 applies only to preamps using the Tortuga Audio V25 controller board which was released starting April 1, 2017.

There are 2 ways to tell if your preamp is using the V25 controller.

  1. Product Name – Your preamp has the V25 suffix in the product name, i.e. LDR1B.V25.
  2. Firmware Splash – Approximately 5 seconds after you plug power into your preamp the firmware version will display briefly. If you see a 4 digit number then you have a V25 version preamp. If its’ not a 4 digit number you have a V2 board (see below).

Version V22

Version V22 applies to all Tortuga Audio preamps with the V2 controller board shipped starting May 15, 2016

You can determine which firmware version you have by watching the display when you plug in or turn on power to the preamp. As the preamp boots up it will first display 3 numbers. These numbers will be either 21X or 22X where “X” is a subversion.

If you still have a 2.1 version you are encouraged to upgrade your firmware to 2.2 which is arguably a better organized and more intuitively easy control scheme compared to the earlier 2.1 version.

Version V21

Version V21 applies only to Tortuga Audio preamps with the V2 controller board shipped prior to May 15, 2016 which have also not already been upgraded to version 2.2 firmware.

Key Differences Between Version V21 and V22

The release of V22 Apple Remote control scheme marked significant changes from the earlier V21 scheme. The V25  control scheme is almost the same as the V22. These changes are summarized below.

Auto-Repeat – With the 2.2 firmware, all buttons on the Apple Remote  will auto-repeat if held down. This was not the case with the 2.1 firmware. Single button presses should be deliberate yet brief to avoid unwanted auto-repeat.

Balance Adjustment – Balance adjustment is now the primary function of the left/right buttons along with volume control via raise/lower buttons.

Control Modes – The previous Mute(play) button has been repurposed as a Control Mode button with the control modes listed below. Each press of the Control Mode button will switch the preamp to the next mode and update the display accordingly. Once you’ve cycled through each control mode, a subsequent press will return the preamp to the default volume control mode as indicated by a brief blinking of the display. Pressing the Enter button at any time while in any of these control mode will return the preamp to it default Volume Control Mode.

  • Input Adjustment Mode
  • Impedance Adjustment Mode
  • Display Adjustment Mode
  • Max Volume on Input Change Mode

Once you press the Control Mode button the preamp is no longer in volume control mode. You switch between different control modes by repeatedly pressing the Control Mode button. To exit and return to volume control mode, simply press the Enter button at any time….or…continue to press the Control Mode button until you cycle back to volume control mode as indicated by a brief blinking of the display.

Power On/Off – The Power On/Off button is now dual purpose. A brief press will mute/unmute the preamp. A press/hold will shut the unit off.

V25 Control Guide

V25 Apple Remote Control Scheme

The following information applies to the use of the Apple Remote for controlling Tortuga Audio preamps built withe the V25 preamp controller which was officially released April 1, 2017.

The Apple Remote shown below is Apple’s standard “silver” remote. It’s a simple 7 button IR remote from which more than only 7 control functions are derived. The control functions of each button will vary depending on the control mode the preamp is in as explained below.

tortuga audio apple remote control buttons

 

 

Control Modes

There are six (6) control modes with Volume Adjust mode always being the default.

In addition to the default Volume Adjust mode the 5 other control modes are:

  • Input Adjust
  • Impedance Adjust Mode
  • Display Adjust
  • Max Volume on Input Change Adjust
  • AutoCalibration Start/Stop

Navigation between the control modes follows a few simple rules as follows:

  • Each press of the Control Mode button switches the preamp sequentially to the next mode.
  • The 6th press returns the preamp back to its default Volume Adjust mode.
  • Pressing the Center/Enter button at any time returns the preamp to its default Volume Adjust mode.
  • When the preamp is in Volume Adjust mode, pressing the Center/Enter button will cause the display to briefly flash acknowledging the command and that the unit is in Volume Adjust mode.

Remote Control Functions

Each of the remote control functions and control modes are shown below in two different formats; a graphic version with a mock-up of the dual displays, and tabular list version (click on version tab to select).

remote_2.2_turnon
remote_2.2_turnoff

v25 apple remote volume adjustment
remote_2.2_muting
remote_2.2_balanceadjust
v25 apple remote control modes
remote_2.2_inputadjust_slow
remote_2.2_inputadjust_fast
remote_2.2_impedanceadjust
remote_2.2_displayadjust
remote_2.2_maxvolumeadjust
v25 apple remote autocalibration mode
Function/ModeStatusButton(s)Description
Turn OnOffMenuPressing button turns the unit on.
Turn OffOnMenuThere are 2 ways to turn off the preamp.

1-step turn off - Press/hold the Menu button and then release. Note that if held down too long unit may turn back on and if held down too briefly will result in muting the preamp but not turning it off.

2-step turn off - First mute the unit by briefly pressing the Menu button. When the volume has fully ramped down to zero, a subsequent press of the Lower button will turn off the preamp.
Volume MutingOnMenuBrief press of Mute button will mute or unmute the unit. The volume will ramp down to zero when muted. When unmuted the volume will ramp back up to its prior setting.
Volume AdjustOnUp/DownRaises and lowers the volume by 1 step for each press. Holding down the buttons will cause the command to repeat.
Balance AdjustOnLeft/RightShifts the channel balance 1 step to the left or right a maximum of 20 steps either way. Each step changes channel balance by ~0.5 dB. As channel balance continues to skew towards a given side (left or right), the combined volume level of both sides will automatically adjust to maintain the same overall volume level.
Input Adjust - Slow ModeOnMode, Raise/Lower & Left/RightPressing the Mode(play) button once will switch the unit into Input Adjust mode. The right display will show the currently selected input number. The left display will show the prior volume level associated with that input when it was last selected.

Music will continue to play on current input channel while while the preamp is in Input Adjust mode and you make your input selection.

Use the raise/lower buttons to adjust the input to desired number.

Press the Center/Enter button to activate the newly selected input and return to volume control mode.

If you select the same same input as your're currently listening to, nothing happens upon pressing the Enter button and returning to volume control mode.

If you select a new input, pressing the Enter button will cause the existing input signal volume to ramp down, the new input to then be connected, and the new input volume to ramp back up.
Input Adjust - Fast ModeOnMode, Left/RightPressing the Mode(play) button once will switch the unit into Input Adjust mode. The right display will show the currently selected input number. The left display will show the prior volume level associated with that input when it was last selected.

Unlike the Slow Mode described above, the Fast Mode immediately changes the input without first muting the volume.

Use the left/right buttons to change inputs immediately.

There will be a brief 200 millisecond delay in fast switching the inputs which will hardly be perceptible.
Impedance AdjustOnMode, Raise/LowerPressing Control Mode (play) twice will switch the unit into Impedance Adjust mode. The left display will show the impedance setting number (1 through 5) and the right display will show the impedance level (in xxK ohms) associated with the currently selected impedance setting number.

Use the raise/lower buttons to change the impedance setting number (1-5). Use the left/right buttons to change the impedance level for the currently selected impedance setting. Press the Center/Enter button to exit Impedance Adjust mode and return to volume control.

Changing the impedance setting number will instantly change the preamps impedance to the level associated with the setting number provided that this setting and its associated level have already been run through the auto-calibration process.

If you switch to an impedance setting number (1-5) that has not already been initialized through auto-calibration then selecting it will result in the audio being turned off. This is the single most common error users make when working with the Adjustable Impedance feature.
Display AdjustOnMode, Raise/Lower & Left/RightPressing Control Mode (play) three (3) times will switch the unit into Display Adjust mode.

BRIGHTNESS ADJUST

The right display will show the brightness level number between 0-15.

Use the raise/lower buttons to change the brightness level. Press the Center/Enter button to exit the Display Adjust mode and return to volume control.

TIMEOUT ADJUST

Timeout allows you to cause the display to turn off at the selected number of seconds after prior command input via the remote. Timeout only works when in Volume Adjust Mode and is disabled when the preamp is in any other control mode.

The left display will show the timeout number between 0 and 99 seconds. If set at 0 the display timeout feature is disabled. The minimum timeout setting is 5 seconds.

Use the left/right buttons to adjust the timeout to desired level. Press the Center/Enter button to exit the Display Adjust mode and return to volume control.
Max Volume On Input Change AdjustOnMode, Raise/LowerPressing Control Mode (play) four (4) times will switch the unit into Max Volume On Input Change mode. The left display will be blank. The right display will show the maximum volume allowable when switching to a new input or when the unit is first turned on. This can be adjust between 1 and 99. The initial default value is 50. This protects your audio gear (speakers!) from accidentally going to full volume when switching to an input they may have been at or near full volume when previously selected as would be the case if the preamp was being used in a home theater bypass scenario.

Use the raise/lower buttons to change the max volume on input change level. Press the Center/Enter button to exit the max volume on input change adjust mode and return to volume control.
Auto-CalOnMode, RightPressing Control Mode (play) button five (5) times will switch the unit into Auto Calibration mode

Both displays will initially show 0 upon entering the auto-cal mode.

Press the Right button 3 times to enable auto-calibration. The right display will show the count up as you press the button.

Once enabled the unit go through several stages of calibration. The first stage involves making 4 adjustments during which time a 4 digit number will be displayed typically ranging from 1500-1850. If the preamp does not cycle through these 4 adjustments within say 30 seconds or so that's an indication one or more LDRs may be having a problem. If there's a problem the numbers will either continue to increase or decrease steadily until hitting some upper or lower limit and then remain fixed.

The unit will the proceed to cycle through each of 4 LDRs showing the LDR number in left display and the calibration step number in right display. There are 99 calibration steps for each LDR. Upon completion of 4th LDR, unit will terminate calibration, briefly shut off the preamp, and then start the preamp again normally.

At the beginning of each LDR's calibration the step number will likely remain at step 1 for a while. That's normal. After no more than a minute the step count should proceed upwards. Sometimes the step count goes quickly and other times it may slow down quite a bit. This is normal.

If the calibration step process slows down and stops or never proceeds beyond step 1 and does not proceed after a minute of waiting that is a fairly definitive indication that the LDR whose number displayed in the left display has gone bad and needs replacement.

You can skip over an LDR any time during autocal by pressing the right button. If you skip past the 4th LDR, autocal will terminate.

 

V2 (Rev 2.2) Control Guide

V2 Controller | Firmware Version 2.2.x

The specific Apple Remote functionality described below is applicable to any V2 based LDR preamp that has firmware version 2.2.0 or later. Any V2 based preamp can be upgraded from the earlier 2.1 firmware to version 2.2.

tortuga audio apple remote control buttons

 

Remote Control Functions

The Apple Remote is a simple 7 button IR remote from which more than only 7 control functions are derived. The control functions of each button will vary depending on whether the preamp is turned on or off and depending on the current control mode of the preamp.

The remote control functions are explained below 3 different ways included visual display, as a list of control functions and as a list of control buttons.

remote_2.2_turnon
remote_2.2_turnoff
remote_2.2_volumeadjust
remote_2.2_muting
remote_2.2_balanceadjust

In addition to the default volume control mode there are 4 additional control modes that are enabled using the control mode select button. Each these 4 control modes are explained below.
remote_2.2_selectingmode
remote_2.2_inputadjust_slow
remote_2.2_inputadjust_fast
remote_2.2_impedanceadjust
remote_2.2_displayadjust
remote_2.2_maxvolumeadjust

Function/ModePowerButton(s)Description
Power/MuteOffPower/MutePressing button turns the unit on.
Power/MuteOnPower/MuteBrief press will mute or unmute the unit. The volume will ramp down to zero when muted. When unmuted the volume will ramp back up to its prior setting.

Press/hold of the button will turn the preamp off.
Volume AdjustOnUp/DownRaises and lowers the volume by 1 step for each press. Holding down the buttons will cause the commands to repeat.
Balance AdjustOnLeft/RightShifts the channel balance 1 step to the left or right. Maximum of 9 steps either way. Each step is slightly less than 1 dB.
Input AdjustOnMode, Raise/Lower & Left/RightPressing Control Mode (play) once will switch the unit into Input Adjust mode. The right display will show the currently selected input number. The left display will show the prior volume level associated with that input when it was last selected.

Music will continue to play on current input channel while while the preamp is in Input Adjust mode.

SLOW MODE

Use the raise/lower buttons to adjust the input to desired number/source.

Press the Center/Enter button to activate the newly selected input and return to volume control mode.

If you select the same same input as your're currently listening to, nothing happens upon pressing the Enter button and returning to volume control mode.

If you select a new input, pressing the Enter button will cause the existing input signal volume to ramp down, the new input to then be connected, and the new input volume to ramp back up.

FAST MODE

Use the left/right buttons to change inputs immediately.

Using the fast mode will change inputs immediately without first muting the volume. The volume will change to the level last associated with the newly selected input.

There will be a brief 200 millisecond delay in fast switching the inputs which will hardly be perceptible.

If you are switching from a low volume to a high volume source you may hear a brief surge in volume of the previous input during the change over. This is normal and due to the fact that we use LDRs as on/off switches and they turn off slowly. Units with regular relays should not experience this volume surge during fast switching.
Impedance AdjustOnMode, Raise/LowerPressing Control Mode (play) twice will switch the unit into Impedance Adjust mode. The left display will show the impedance setting number (1 through 5) and the right display will show the impedance level (in xxK ohms) associated with the currently selected impedance setting number.

Use the raise/lower buttons to change the impedance setting number (1-5). Use the left/right buttons to change the impedance level for the currently selected impedance setting. Press the Center/Enter button to exit Impedance Adjust mode and return to volume control.

Changing the impedance setting number will instantly change the preamps impedance to the level associated with the setting number provided that this setting and its associated level have already been run through autocal. If the setting has not been initialized through autocal then selecting it will result in the audio being turned off.
Display AdjustOnMode, Raise/Lower & Left/RightPressing Control Mode (play) three (3) times will switch the unit into Display Adjust mode.

BRIGHTNESS ADJUST

The right display will show the brightness level number between 0-15.

Use the raise/lower buttons to change the brightness level. Press the Center/Enter button to exit the Display Adjust mode and return to volume control.

TIMEOUT ADJUST

Timeout allows you to cause the display to turn off at the selected number of seconds after prior command input via the remote. Timeout only works when in Volume Adjust Mode and is disabled when the preamp is in any other control mode.

The left display will show the timeout number between 0 and 99 seconds. If set at 0 the display timeout feature is disabled.

Use the left/right buttons to adjust the timeout to desired level. Press the Center/Enter button to exit the Display Adjust mode and return to volume control.
Max Volume On Input Change AdjustOnMode, Raise/LowerPressing Control Mode (play) four (4) times will switch the unit into Max Volume On Input Change mode. The left display will be blank. The right display will show the maximum volume allowable when switching to a new input or when the unit is first turned on. This can be adjust between 1 and 70. The initial default value is 35. This protects your audio gear (speakers!) from accidentally going to full volume when switching to an input they may have been at or near full volume when previously selected as would be the case if the preamp was being used in a home theater bypass scenario.

Use the raise/lower buttons to change the max volume on input change level. Press the Center/Enter button to exit the max volume on input change adjust mode and return to volume control.
Auto-CalOffEnter, RightPress Enter button to enable auto-calibration. Unit will cycle through each of 4 LDRs showing LDR number in left display and step number in right display. There are 70 calibration steps for each LDR. Upon completion of 4th LDR, unit will shut disable auto-cal and shut off display.

You can skip over an LDR any time during autocal by pressing the right button. If you skip past the 4th LDR, autocal will terminate.
Pre-CalOffLeft, RightCaution! Do not attempt the Pre-Cal process unless you have both the proper precision resistors and have carefully studied the pre-cal documentation.

Pre-Cal requires the removal of all 4 LDRs and temporarily replacing them with a set of precision resistor modules with both 100 ohm and 100k ohm resistors. Use the 100 ohm resistors first. Also, Pre-Cal requires dual display modules. After the pre-cal resistors are installed, proceed to place the unit into Pre-Cal mode.

First place unit in Auto-Cal mode. Then press the Left button 3 times to switch unit to Pre-Cal mode. When the calibration factor on the display stabilizes, press the Right button to switch to the next LDR/resistor. Repeat for next 3 100 ohm LDR/resistors. Then switch all 4 precision resistors over to 100k. Repeat the process of stabilizing the display value and pressing the Right button four more times. At the conclusion of this process you will have pressed the Right button 8 times. The eight time will end the Pre-Cal process and blank the display. The results of the pre-calibration will be save in memory.
ButtonPowerModeFunction
EnterOffAuto-Calturns auto-cal on/off
On
Volume Adjustdoes nothing except blinks display
OnInput Adjustturns on selected input and returns unit to volume control
OnImpedance Adjustreturns unit to volume control
OnDisplay Adjustreturns unit to volume control
OnMax Volume On Input Change Adjustreturns unit to volume control
RaiseOffInfo Displaymove info display up 1 step
OffAuto-Calpress 3 times to enable Pre-Cal Adjust
OnVolume Adjust
increase volume 1 step (0-70)
OnInput Adjustselect next input (increasing) | rolls over to 1st at max input
OnImpedance Adjustselect next impedance setting (1-5) | rolls over at top
OnDisplay Adjustincrease brightness level one step (0-15)
OnMax Volume on Input Change Adjustincrease max volume 1 step (1-70)
LowerOffInfo Displaymove info display down 1 step
OnVolume Adjustdecrease volume 1 step (0-70)
OnInput Adjust
select next input (decreasing) | rolls over at bottom
OnImpedance Adjust
select next lowest impedance setting (1-5) | rolls over at bottom
OnDisplay Adjustdecrease brightness level one step (0-15)
OnMax Volume on Input Change Adjustdecrease max volume 1 step (1-70)
LeftOffPre-CalIf unit is in AutoCal, pressing the left button 3 times in a row will put unit into Pre-Cal mode
OnVolume Balance Adjustshifts volume balance 1 step to the left (max 9 steps)
OnInput Adjustswitch to next lowest input (fast switch mode)
OnImpedance Adjustincreases impedance lvel by 1k
RightOff
Auto-Cal switches auto-cal to next LDR, shuts off auto-cal if already at 4th LDR
OffPre-Cal switches pre-cal to next LDR (required), 1st 4 steps are 100 ohm, 2nd 4 steps are 100k ohm
OnVolume Balance Adjustshifts volume balance 1 step to the right (max 9 steps)
OnInput Adjustswitch to the next highest input (fast switching mode)
OnImpedance Adjustincreases impedance level by 1k
PowerOff
n/aturns unit on
Onn/aquick press – mutes volume

press/hold - turns unit off
ModeOn1st pressselects Input Adjust mode
On2nd pressselects Impedance Adjust mode
On3rd pressselects Display Adjust mode
On4th pressselects Max Volume on Input Change mode
OnAdditional pressrolls over to 1st position – Input Adjust mode
V2 (Rev 2.1) Control Guide

V2 Controller | Firmware version 2.1.x

The specific Apple Remote functionality described below is applicable to any V2 based LDR preamp with earlier version 2.1.x firmware. Owners are encouraged to update their firmware to latest version of 2.2 after which you should refer to Apple Remote 2.2. section above.

You can tell which version firmware you have but viewing the display when power is applied to the preamp. If 3 digits are displayed in sequence in the right display then you have version 2.1 firmware. If 3 digits are displayed simultaneously using both displays then you already have some version of 2.2 firmware.

Apple remote buttons

 

 

Apple Remote Controls

The Apple Remote is a simple 7 button IR remote from which more than only 7 control functions are derived. The control functions of each button will vary depending on whether the preamp is turned on or off and depending on the current control mode of the preamp.

The control functions of the Apple Remote are shown in the 2 tables below. The first table describes the control functions and modes. The second table summarizes how each control button relates to the control function.

Control Functions/Modes

Function/ModePowerButton(s)Description
Power On/Offn/aPowerPressing button toggles the unit on and off
Volume AdjustOnRaise/LowerRaises and lowers the volume by 1 step for each press
 Volume MuteOnMuteToggles the mute status of the unit
Brightness AdjustOnEnter, Raise, LowerTo place unit into Brightness Adjust mode:

  • Older LDR3x.V1 – Press Mute to first mute the unit. Adjust brightness while unit is muted.
  • Newer LDR3x.V1 – Press Enter button while in Volume Adjust mode
  • LDRx, LDRxB, LDR3.V2, LDR3.V2K, LDR3x V2 and V2.1 –  Press Center twice while in normal Volume Adjust mode to switch unit to Brightness Adjust Mode.

Right display shows brightness level between 0 and 15. Use Raise/Lower buttons to adjust brightness. Press Enter button again to confirm/save new setting, exit Brightness Adjust mode and return unit to Volume Adjust mode.

Input AdjustOnRight, EnterPress Right button to switch to next input. Unit will immediately mute and right display will show selected input. Press the Enter button to lock in the selection, un-mute the unit, and return unit to Volume Adjust mode.
Balance AdjustOn Mute, Left, Right, EnterPress Mute button to first mute the unit. Then press Right button switch unit to Balance Adjust mode. Displays will blink. Right display will show double digit value. Balance towards right channel will show in right digit. Balance towards left channel will show in left digit. Use Left and Right buttons to adjust balance as you like. Press Center button to lock in balance adjustment, un-mute the unit, and return the unit to Volume Adjust mode.
Balance ResetOnMute, LeftPress Mute button to first mute the unit. Then press Left button to reset Balance Adjust to neutral. Unit will automatically un-mute and return the unit to Volume Adjust mode.
Auto-CalOffEnter, RightPress Enter button to enable auto-calibration. Unit will cycle through each of 4 LDRs showing LDR number in left display and step number in right display. There are 70 calibration steps for each LDR. Upon completion of 4th LDR, unit will shut disable auto-cal and shut off display.
Impedance AdjustOnLeft, Raise, Lower, Enter Press the Left button to display the current Impedance Number (1-5). Press the Left button again to display the Impedance Level (1k-99k) associated with the current Impedance Number. Press the Left button repeatedly to toggle between displaying the Impedance Setting number and its associated Impedance Level.To switch to a different Impedance Number (1-5) use the Raise/Lower buttons while displaying the Impedance Number. This will immediately switch the preamp over to using the Impedance Level associated with the Impedance Number you selected. If you switch to an Impedance Number that has not been  installed yet (has not been run through an Auto-Cal cycle), the audio output will likely shut off due to an absence of calibration settings for that Impedance Number/Level.If you wish to change the Impedance Level associated with the currently selected Impedance Number, switch display to Impedance Level (via Left button), then use Raise/Lower buttons to adjust impedance between 1k and 99k. The default setting is 20k. To lock in this new setting you must first press the Enter button and then run Auto-Cal for that new Impedance Level. If you do not run Auto-Cal immediately after changing the Impedance Level of the currently selected Impedance Number, the Impedance Level will not actually change.
Pre-CalOffRaise, RightCaution! Do not attempt the Pre-Cal process unless you have both the proper precision resistors and have carefully studied the pre-cal documentation. Pre-Cal requires the removal of all 4 LDRs and temporarily replacing them with a set of precision resistor modules with both 100 ohm and 100k ohm resistors. Use the 100 ohm resistors first. Also, Pre-Cal requires dual display modules. After the pre-cal resistors are installed, proceed to place the unit into Pre-Cal mode.First place unit in Auto-Cal mode. Then press the Raise button 3 times to switch unit to Pre-Cal mode. When the calibration factor on the display stabilizes, press the Right button to switch to the next LDR/resistor. Repeat for next 3 100 ohm LDR/resistors. Then switch all 4 precision resistors over to 100k. Repeat the process of stabilizing the  display value and pressing the Right button four more times. At the conclusion of this process you will have pressed the Right button 8 times. The eight time will end the Pre-Cal process and blank the display. The results of the pre-calibration will be save in memory.

Control Functions Summarized By Button

ButtonPowerModeFunction
EnterOffAuto-Calturns auto-cal on/off
 OnVolume Adjustdoes nothing except blinks display
 OnInput Adjustlocks in selected input, blinks display, and returns unit to volume adjust
 OnBalance Adjustlocks in channel balance, blinks display, and returns unit to volume adjust
 OnBrightness Adjustlocks in brightness level, blinks display, and returns unit to volume adjust
 OnImpedance Adjustlocks in changes to Impedance Number/Level, blinks display, and returns unit to volume adjust
RaiseOffInfo Displaymove info display up 1 step
 OffAuto-Calpress 3 times to enable Pre-Cal Adjust
 OnVolume Adjustincrease volume 1 step (0-70)
 OnBrightness Adjustincrease brightness 1 step (0-15)
 OnImpedance Adjustincrease impedance setting (1-5) or level (1k-99k)
LowerOffInfo Displaymove info display down 1 step
 OnVolume Adjustdecrease volume 1 step (0-70)
 OnBrightness Adjustdecrease brightness 1 step (0-15)
 OnImpedance Adjustdecrease impedance number (1-5) or level (1k-99k)
LeftOffn/adoes nothing
OnBalance Adjustmoves channel balance 1 step left
OnImpedance Adjusttoggles between display of impedance number (1-5) and level (1k-99k)
RightOffn/adoes nothing
OffAuto-Calswitches auto-cal to next LDR, shuts off auto-cal if already at 4th LDR (not recommended)
OffPre-Calswitches pre-cal to next LDR (required), 1st 4 steps are 100 ohm, 2nd 4 steps are 100k ohm
OnInput Adjustmutes the unit and switches unit to next input
OnBalance Adjustmoves channel balance 1 step right
PowerOffn/aturns unit on
Onn/aturns unit off
MuteOffn/adoes nothing
OnVolume Adjusttoggles muting – mute ramps volume down to zero, un-mute ramps volume up to prior setting

 No Auto-Repeat

The Apple Remote does not repeatedly send commands if you hold down the Raise or Lower buttons to adjust volume. Therefore each Raise/Lower button press increments/decrements the volume by 1 step count only.

Pre-Cal & Impedance Adjust Functions

  • Pre-Cal and Impedance Adjust functions were added on 1.15.15 along with the release of version 2.1.0 of the LDR3x firmware.
  • These functions are not present in earlier versions of the firmware.
  • All LDR3x.V2.1 boards and LDR preamp products shipped on or after 1.15.15 include 2.1.0 or later versions of the firmware.
  • All Tortuga Audio preamp products with USB connections can be updated  with latest version of firmware to add these functions.

Apple Remote Bug:

  • Units affected:  All LDR units shipped on or after 10.1.13 but before 12.7.13
  • The Bug: Pressing the Left or Right button again after having switched to a new input (but before having confirmed the change via pressing the Enter button), will either put the unit into Balance Adjust Mode (if you pressed the right button again) or will Reset the Balance (if you pressed the left button again).  The reason this happens is switching inputs mutes the unit and when muted the Left/Right buttons control Balance Adjust Mode/Reset.
  • The Work Around: When switching inputs you can only press the Left or Right buttons once and then must immediately confirm and lock-in the new input by pressing the Enter Key. Repeat this cylce until you’ve selected the desired input.
  • The Fix: All LDRx units shipped on or after 12.7.13 have corrected software where pressing the Left or Right button will immediately switch over to the next input such that hitting the Enter key to confirm and lock-in the input change is no longer required.
Control Knob (Encoder) Guide

The Rotary EncoderTortuga Audio encoder.

LDR3.V2 passive preamp - black anodized front - side viewIn addition to having remote control, all Tortuga Audio preamps are also controllable via a control knob on the front panel.

Unlike conventional preamps which use a potentiometer, the control knob on a Tortuga Audio preamp is attached to a rotary “encoder”. An Encoder is special type of rotary switch which generates switching impulse patterns which differ whether its turned clockwise or counter-clockwise. These switch impulse signals are interpreted by the preamp’s control unit to raise or lower volume etc. The Encoder is also equipped with an integral push button.

Also unlike a conventional potentiometer, the Encoder has no hard stop rotational limits. It will turn an infinite number of times in either direction. Going from zero to full volume will take approximately 2 full rotations of the Encoder. It’s possible to spin the Encoder faster than the control system is capable of detecting. Continuing to turn the encoder in the same direction once volume has reached minimum or maximum levels serves no useful purpose but is not harmful.

Encoder Control Functions

The Encoder has the following functionality:

Power On:  When unit is off, a momentary push/release of the Encoder will turn the unit on.

Power Off:  When the unit is on, a push/hold for between 2-5 seconds followed by release will shut the unit off.

Mute: When the unit is on and Un-Muted, a momentary push/release will Mute the unit.

Un-Mute:  When the unit is on and Muted, a momentary push/release will Un-Mute the unit.

Volume Raise/Lower:  Turning the encoder clockwise will raise the volume while turning the encoder counter-clockwise will lower the volume. Once zero or max volume is reached, continuing the turn the Encoder in the same direction serves no purpose.

Input Select:  For units with multiple inputs, a push/hold while also turning the Encoder (left or right) will put the unit into Input Select Mode and allow selection of the desired input by turning the encoder. The selected input will take effect upon release.

Balance Adjust:  A push/hold of the Encoder between 5-10 seconds followed by release will place the unit into Balance Adjust Mode and allow adjusting the left-right channel balance by rotating the encoder in the desired direction. Once you’ve adjusted the balance, a brief push/release will lock in the new balance setting and return the unit to normal Volume Control Mode.

Balance Adjust Reset:  A push/hold of the Encoder for greater than 10 seconds but less than 20 seconds followed by release will reset the Balance Adjust to zero upon release.

Remote Pairing:  A push/hold of the Encoder for greater than 20 seconds followed by release will place the unit into Remote Pairing Mode. Subsequent pressing of any key on a compatible remote will “teach” the unit the ID the remote and thereafter the unit will respond to that remote.  Remote Pairing Mode can only be enabled with the Encoder.  Please refer to the section above on Remote Pairing for more detail.

Auto Calibration Start/Stop:  When unit is off, a quarter-half clockwise turn will toggle Auto Calibration on or off (introduced with V2 software build 1.1.2 on 7.15.14).

Firmware Updating Instructions

Overview

Updating your preamp’s firmware requires the use of a bootloader program running on a PC together with the latest firmware “hex” file. You download both the bootloader and the firmware file from our website. Then you connect your PC to your preamp via a USB cable. To execute the actual upload process you run the bootloader program, apply power to your preamp and then use the bootloader to upload the firmware hex file into your preamp.

Once set up, the firmware upload/update process typically takes less than 15 seconds.

Detailed instructions on the firmware update process are provided herein.

What is the Bootloader?

The (mikro)Bootloader  is a small PC based software application that you use to establish USB communications with, and upload new firmware into, the V2/V25 preamp.

Unfortunately the Bootloader is a PC/Windows only application. There’s no MAC version currently available. We are not anti-MAC, but the supplier of our programming tools stubbornly refuses to provide a MAC version of the Bootloader program while providing no reasons for not doing so. Go figure.

The Bootloader program is a simple executable file (mikroBootloaderUSBHID.exe). Unlike conventional software, it does not have to be installed/registered into your PC. The program file simply has to reside somewhere on your PC. We suggest you download it to your PC desktop. The first time your run this program (by double clicking on it) it will create a small text file named “settings.ini” in the same directory. No special drivers are needed. It doesn’t install or change anything in your PC. If your PC has a USB port, you should be good to go.  We know the Bootloader works with Windows 7, 8 and 10. It may also work with  older versions of Windows but we haven’t tested that. To remove the Bootloader program from your PC simply erase both the  mikroBootloaderUSBHID.exe and settings.ini files from whatever directory you put them in.

Download The Bootloader

 

About USB Cables – Important!

The #1 problem that people encounter when trying to update their firmware is the inability to make a connection. In most cases this is caused by their USB cable.

Most of us have several USB cables laying around because we have cell/smartphones and other devices that use USB cables for charging. Unfortunately, many of those USB cables are for charging only and lack the ability to transmit data.

Charging only USB cables will not work with the bootloader and firmware update system!

You need to use a proper USB “data” cable that has the conductors for the D+ and D- USB data signals.

Firmware updating will not work without a proper USB data cable.

Firmware Update Procedure – Short Version

Here’s the short version of how this works.

  1. Preparation
    • Remove power from your preamp (unplug the power cord)
    • Download the updated firmware file from our website to your PC
    • Download the Bootloader program from our website to your PC
    • Connect your PC to the preamp via the USB cable provided with your preamp
  2. Start the Bootloader program
  3. Apply power to your Tortuga preamp (this starts a 5 second timer during which you must do the next step)
  4. Click the “Connect” button on the Bootloader program
  5. Browse for and select the firmware (hex) file you downloaded in step 1)
  6. Click on the “Begin Uploading” button on the Bootloader program.

With step 6) the actual uploading of the firmware takes less than 5 seconds. You’ll see a progress bar. It will be obvious when it’s done. When it’s done you can disconnect the USB cable from the preamp and proceed to use the preamp normally.

The information that follows below elaborates on the above steps.

Step 1 – Preparation

Remove Power From Your Preamp

This is key and often confuses people so read carefully. The Bootloader is only able to connect to your preamp during the 5 seconds after power is applied. If the connection hasn’t been made during that 5 second start-up period you have to remove power and try again. By “connection” we don’t mean physically connecting the USB cable. “Connection” means step 4.

Download Firmware File & Bootloader Program

The latest firmware file and the Bootloader program can both be found here [link to be added].

The firmware file is referred to as a “hex” file because it’s a text file wherein the code is formatted using a specific hexadecimal protocol and file uses a .hex file type suffix.

The Bootloader program is a small Windows executable (.exe) application file. You only need to download it once and keep it handy somewhere on your PC.

Connect The USB Cable

Finished Preamps

All finished Tortuga preamps require a USB cable with type A male connectors on both ends. The cable is supplied with all finished Tortuga Audio preamps. Connecting the cable does nothing by itself. Your PC should not react.

DIY Boards – Micro-B Socket

If you have an older V2 LDR3x DIY board with a micro-B socket board soldered to the J8 header on the board you’ll need a cable with a male A end and male micro-B USB end. An LED light on the micro USB connector breakout board on the V2 will light up once it’s connected to your PC.

DIY Board – Tortuga USB Connector

If you are using a Tortuga USB connector cable with the female end connected to the J8 header make sure you have the female end connected such that the red wire is next to microcontroller end of J8 header and not the end with the white dot.

Step 2 – Start the Bootloader program

When the Bootloader program starts it will look more or less like the pic below. At this point it won’t be doing anything except waiting.

bootloader_1

Step 3 – Establish the USB link to the preamp

Connecting power to your preamp starts the 5 second bootloader connect window.

You should notice the following changes to the mikroBootloader program once power is applied to your preamp:

  1. The little USB symbol to the right of “1 Wait for USB link” should turn red
  2. The Device window should display “LR3x.V2 Board” or “LDR.V25” or similar
  3. The MCU Type window should display “PIC18” or “STM32F” or similar
  4. The History Window should say “Waiting MCU response…”

At this point you will have 5 seconds to establish a USB link between your PC and preamp by pressing the “Connect” button next to “2 Connect to MCU”. If all goes well, the “Connect” button text will change to “Disconnect” and the History Window will now say “Connected” as shown in the pic below. If you run out of time, don’t panic, just remove power again, wait a few seconds and then reapply power to the preamp which restarts the 5 second Bootloader timer.

bootloader_2

Step 4 – Choose the firmware (.hex) file

Select your firmware file by pressing the “Browse for Hex” button next to “3 Choose HEX file”.  This will open a file dialog box. Find your downloaded .hex file stored on your PC and click the “Open” button. At this point the firmware is ready to be uploaded into the preamp board.

bootloader_3

Step 5 – Upload Firmware To Preamp

Press the “Begin uploading” button next to “4 Start bootloader” to upload the firmware into the preamp. The previous firmware build will first be erased and then the updated software build will be written to the preamp’s microcontroller chip. This erase/write operation is very fast and should take less than 5 seconds to complete.

You should get a “Success” message. Click the  “OK” button to close the message box. Note the new messages in the History Window. Upon a successful write, the Bootloader program will automatically disconnect from preamp and the preamp will reboot which takes 5 seconds.

You are now done and can close the Bootloader program, disconnect the USB cable, and enjoy your updated preamp.

bootloader_4

V25 Firmware

For V25 Preamps Only

The firmware below is for V25 based preamps only. If you have a V2 based Tortuga Audio preamp model, please refer to similar info specific to the V2.

Determining Your Current Firmware Version

How do you know what firmware version you have? The firmware version will flash briefly on the display roughly 5 seconds after power is applied to your V25 preamp. To be clear, the firmware versoin does NOT display when you turn on the preamp but only when you apply power to the preamp.

The firmware version will be a 4 digit number like 1015. If you don’t see a 4 digit number show up on all 4 digits of your dual 2-digit display you do not have a V25 based preamp.

Firmware Updating Instructions

Please refer to the section under Firmware Updates entitled Firmware Update Instructions for detailed instructions on how to upload firmware to your preamp.

Upgrading To Rev 1012 (or higher) the First Time

The first time you upgrade to version 1012 (or higher) from version 1011 (or lower) your preamp will go through an automatic re-initialization process related to changes in how impedance adjustment is done and how the resulting attenuation table data is stored.

Users may specifically skip Rev 1012 and upgrade to whatever latest subsequent revision there is above 1012 but this one-time re-initialization process will still apply.

This is a one-time process but must be allowed to run to completion to become effective. If interrupted, the automatic re-initialization process will repeat itself the next time your preamp is powered up until the process is allowed to run to completion.

Duing this re-initilziation process your existing impedance settings will be deleted as will the 100-step attenuation tables associated with each of those settings. Various numbers may be displayed during this process. When the first phase of the re-initilization process is complete your preamp will then automatically enter the second phase where it automatically runs through a calibration cycle associated with impedance setting #1 which is set by default at 20k ohms. When the calibration process is completed your preamp will reboot and then turn itself on after which it will be available to be used normally.

Users with balanced preamp will need to repeat this process with both V25 boards. When updating the left board there will be no information displayed. Please allow at least 15 minutes after uploading the firmware to allow the automatic re-initialization process to complete even if no information is displayed.

With this upgrade, setting/level #1/20k will no longer be available to be edited by the user as before. Only settings 2-9 will be available to the user to setup and adjust input impednace between 1-99k ohms.

Please consult Version 1012 under the V25 Changelog below for more information on how impedance adjustment works starting with Version 1012.

Latest Firmware Versions

 

V25 Changelog

The following table lists all changes to the V25 firmware since initial release including any proposed near term changes.

Rev/Date
Description
1016 - 11.05.17* Change (auto-repeat) - The faster Apple remote auto-repeat response introduced with 1014 has been slowed down for all buttons that can auto-repeat except for the Raise & Lower buttons.
* Change (turning off preamp) - The old way of turning off the preamp by press/holding the Menu button has been removed. The reason for this is the Menu button was serving two functions - toggling the mute status (brief press), and turning off the preamp (a longer press/hold). Too often this led to ambiguous results. Starting with 1016 the Menu button is now solely for muting/unmuting the preamp.

Turning off the preamp is now an unambiguous 2-step process:
1) Mute the preamp by briefly pressing the Menu(Mute) button
2) When the preamp is muted (volume @ 0), press the Lower button to turn it off.
1015 - 10.18.17
This revision is included for consistency but does not affect any features or operations other than maintaing compatibility with V25 boards with different size EEPROM chips. Upgrading to this version if you already have 1013 or 1014 is not necessary or useful.

* New - Added the ability to detemine whether board's eeprom hardware chip uses 16 or 24 bit addressing. Early V25 boards had larger size eeproms that require 24 bit addressing (3 bytes). Subsequent boards have smaller eeproms that only require 16 bit addressing (2 bytes). Each time firmware boots address size is determined as first step in initializing.
1014 - 10.16.17* Tweak - This update improved the responsiveness of the controller to inputs from the Apple Remote and also corrects a minor error in how the preamp responded to repeat commands when user held down the certain buttons on the remote. As a result of this update the controller reacts faster to Apple command especially repeat commands when buttons are held down. Time will tell if the faster response is desireable to end-users or if it proves to be too rapid and may need to be slowed down a tad in a future update.
1013 - 9.21.17
(internal release only)
* Fix - Preamp would not display volume after initializing the board in the event the default #1/20k setting/level had not been calibrated.
1012 - 9.20.17
!! MAJOR UPDATE !!
Please read info carefully.
Release 1012 represents a major change to how adjustable impedance is handled. Upgrading to 1012 will cause your preamp to erase and reset all existing impedance settings and calibration data followed by automatically running calibration at the new fixed default of setting #1 @ 20k. The update will not be completed until this calibration step is completed. Please allow up to 15 minutes to allow the updating, resetting and calibration process to complete. The unit will reboot and restart after completion. Try not to turn off power or otherwise interrupt this process or else it will repeat from the beginning until allowed to fully complete.

** Changes with 1012 **
1) Impedance settings increased from 5 to 10.
2) Impedance setting #1 is now fixed at the default of 20k and can no longer be changed by user. Only settings 2-10 can be setup and modified by user.
3) The display will now blink when user selects an impedance setting number and level combination that has not already been run through calibration.
4) Switching the unit to any setting/level combination that is not calibrated will result in no output from the preamp.
5) Changing an impedance setting/level will not be saved or go into effect until after calibration is run. Press the Enter/Center button on remote after completing a change and then proceed to run calibration as the next step. It's up to the user to ensure calibration is run as the final step. If calibration is not run immediately after making a setting/level change, the unit will revert to last known valid setting/level. If no other settings/levels have been configured the unit will revert to default #1/20k.
6) As before, each setting/level change must be done individually and then processed through calibration to become effective and/or available. User can not make multiple simultaneous changes to settings/levels and run them all through calibration together.
1011 - 7.17.17* New - Added controls for Mono feature - double press Enter button toggles mono on/off. User must press enter button on remote 2 times in a row within 1 second to toggle mono mode. Requires presence of an LDR module in the V25's mono switch socket. If this feature doesn't work in your V25 preamp after uploading this firmware revision there's about a 99.999% chance your preamp does not have a mono switch LDR installed.
* Tweak - Minor mods to certain timer routines to improve overall operation
1010 - 7.5.17This revision was almost entirely related to commissioning, calibration and testing of the V25. Not an urgent revision for end users so this revision was only posted when 1011 was released.
* Fix - Enabled ability to stop cal via encoder turn - had been disabled in prior builds
* New - Added automatic precal for use with new precal board (not for use by end user)
* New - Added ability to jump to next LDR during autocal using right button
1009 - 6.28.17* Change - Skips the Input Adjust menu on units with only a single input.
1008 - 6.20.17* Tweak - Reset display to 0-0 after cal is completed. Was showing 4-1 which could be confusing
1007 - 6.14.17* Fix - Muting via Encoder press/release was immediately unmuting once volume ramped down to zero rather than staying at zero and remaining muted.
* Fix - Max volume limiter on turn-on or input change was not limiting the volume to the user adjustable max limit value
* Fix - When changing input the volume was not changing to the volume level last associated with the input when it was previously selected
1006 - 6.6.17* New - 2 way serial data link is now operational between master and slave boards so it's now ok to connect master J7.TX1 & J7.RX1 to slave board's J7.RX2 & J7.TX2 respectively. Prior to 1.0.0.6 making the connection to slave.J7.TX2 would cause master board to stop working properly. (relevant to multi-board/balanced configurations only)
* Fix - Input switching via encoder was not getting through to attached slave boards. (relevant to multi-board/balanced configurations only).
* Fix - All boards were defaulting to 6 available inputs regardless of how many inputs were actually installed and available. This remains the default for DIY V25 boards regardless of installed inputs but V25 boards installed in finished preamp products now have defined input # limit.
1005 - 5.23.17* Fix - Volume last associated with input was not displaying properly when changing/selecting input
* Change/New - Now have 2 ways to turn off preamp

Old Way (modified) - Briefly press/hold Menu button. Volume ramps down and then
turns off rather than just abruptly turning off

New Way - First mute unit (press Menu without holding it down). When
volume muted (display blinking, right display = 0), press Lower button to
turn unit off.
1004 - 5.18.17* Change - Only master board can output diagnostics via uart
* Fix - Unit would mute immediately upon being turned on via encoder
* Fix - Current impedance settings' cal (attenuation) tables were being erased when impedance changed to a different setting number
* Fix - Eliminated brief volume surge when turning off preamp with music playing.
* Change - Shunt LDRs are now left on at around 200-300 ohms or roughly 2 ma idle current when the unit is turned off. This ensures close to zero audible output when unit is off if music source and amp are still on. Impact on LDR life negligible since 2 ma is only 10% of rated current capacity of LDR.
* Change - slowed down serial communications to display module to avoid possible comm errors - precautionary only
1003 - Initial Release Fix - Revised precal process for 6 fixed resistance levels of 100R, 500R, 5k, 10k, 47k and 100k
Fix - bug in the Trigger out logic
Fix - bug in the impedance select/adjust
1002 - (internal only)* Change - made precal harder to accidentally start (precal not documented for users)
* Fix - several bugs related to calibration involving VRef and Vlo adjustments
during cal and properly saving same.
1001 - (internal only)* Change - removed standalone cal routines related to VRef - now use fixed initial values.
* Fix - corrected bug in cal index initialization
* Tweak - cleaned up cal index routines
1000 - (internal only)* Initial internal post-development release

V25 Roadmap

The following table lists all currently planned major changes to the V25 firmware.

New CapabilityDescription
Calibration DiagnosticsIf problems are encountered during autocal of the LDRs the V25 will identify which LDR is having a problem and a specific diagnostic code will be displayed which can be used by the owner to resolve the problem
Hands-off calibrationAutocal will operate automatically on a fixed schedule in the background when the preamp is turned off. If user turns on the preamp during an autocal cycle the cycle will immediately stop and the preamp will turn on and operate normally.

User can still opt to initiate and observe the autocal process manually.
OLED graphical displayAlternative 256x127 pixel monochrome graphical OLED (organic LED) display module in lieu of existing dual 2-digit 7-segment displays. User can choose via a jumper on the V25. Requires purchase of OLED display module.
Wireless communicationsBy plugging in an off-the-shelf WiFi module the V25 will be able to communicate via WiFi to local devices including smartphone apps for control.
Control via smartphoneControl V25 via iPhone and Android phones. Requires development of Wireless Communication first and also development of custom apps for both the iPhone and Android line of phones.
V2 Firmware

Latest Firmware Version | V2 & V2.1

Use the appropriate firmware version for your model. If you select the wrong version for your preamp no harm will come to your unit. However, it may not work properly and will you will need to upload the correct version and try again.

DIY V2 Board

Download the following version for use in the DIY version of the V2/V2.1 board.

LDR3.V2 & 3-input LDRx Preamps

Download the following version for use in the LDR3.V2 model and the 3-input LDRx model preamps.

LDRxB and 4-input LDRx Preamps

Download the following version for use in the LDRxB model and the 4-input LDRx model preamps.

LDR1.V2 and LDR1B.V2 Preamps

Download the following version for use in the single input LDR1.V2 and LDR1B.V2 preamps.

Which Firmware Version Do I Have?

How do you know what firmware version you have? The 3 digit firmware version will display briefly in the right display ~5 seconds after power is applied to your V2 preamp.

Firmware Updating Instructions

Instructions for uploading firmware to your preamp can be found here.

V2 Changelog

The following table lists all changes to the V25 firmware since initial release including any proposed near term changes.

Rev/Date
Description
2,2,8 - 8.23.16Not a critical update. Update is relevant only if you wish to be able to use the Encoder while the display timeout feature is enabled. The workaround is just use the remote.

* Fix: Encoder control inputs failed to wake up the display after it timed out and turned off.
2.2.7 - 8.16.16This update optimizes the operation of the manual encoder which hasn't received much attention for quite some time now. Volume control via the encoder is now smoother and more granular with each volume step more clearly corresponding to the encoder's position detents (stopping points). It also adds back the missing encoder balance adjust feature which somehow got left out when we released version 2.2.0 firmware.

You might have noticed we skipped version 2.2.6. We implemented phase reversal in version 2.2.6 but this applies only to our LDRxB balanced preamp model and requires some special hardware modifications to the LDRxB for phase reversal to work. Please contact us if you're interested in the LDRxB and balanced preamp phase reversal.

Importance? For most users this is not a critical update. If you notice anything amiss while using your encoder for either volume control or input changing, this update should resolve the problem.

* Change: Made encoder turning interrupt driven rather than poling to improve control response
* Fix: Restored missing balance adjust control functions to Encoder
* Tweak: Improved encoder decode logic for smoother stepping synced with detents
* Tweak: Reduced encoder input change threshold from 5 to 2 steps when using encoder to change inputs
2.2.5 - 6.16.16This update corrects one minor bug (balanced preamps only) and adds 2 new features. It's not a critical update.

* New: Fast Input Switching - When in Input adjust mode user now has option to do use fast switching between inputs by using the Left/Right buttons on the remote rather than the normal Raise/Lower following by Enter. When using the Left/Right buttons the inputs transition within less than a second without any muting/unmuting. When using fast switching the volume will immediately go the volume level last associated with the selected input.
* New: Display Timeout - When in Display adjust mode user can now optionally set the time (in seconds) before display turns off after last user input. Adjustment is between 1 and 99 seconds using the Left/Right remote button. Setting timeout to zero (0) disables the timeout feature. After updating you should check this setting since it may not be zero (off) by default.
* Fix: The new press/hold Menu button turn-off feature introduced in version 2.2.3 was not working properly for balanced units.
2.2.4 - 6.10.16This version was shipped in only 1 preamp and included the "Fix" referenced in version 2.2.5 above.
2.2.3 - 5.30.16This update added back some features that didn't make the jump from 2.1 to 2.2. Most importantly it brought back muting as a stand alone feature.

* Change: When on, pressing menu button mutes/unmutes the unit, while holding it down turns unit off
* Change: Added blinking display for when unit muted
* Change: Added Panel LED flash to acknowledge when user switches control modes (for DIY users with no displays)
* Fix: Corrected a bug which prevented channel balance from working the same in both directions
2.2.2 - 5.24.16This was an an internal revision and only relevant to initial commissioning of new boards/preamps

* Fix: Board ID init was defaulting to V2 instead of V21 on new blank boards
2.2.1 - 5.22.15* Fix: Addressed numerous bugs with the initial 2.2.0 release
* New: Firmware will take ~15 seconds to initialize the first time user upgrades to any 2.2.x version from any prior 2.1.x version. This is a one-time only process.

Note: The one-time initialization process will require you to pair your remote with your preamp
2.2.0 - 5.16.15 Initial upgrade from 2.1 series to 2.2.

* Change: Major restructuring of Apple Remote control scheme based on user input
* New: Auto-repeat providing ease of ramping volume up or down with a single press of the remote
* Change: Balance adjustment is now the primary function of the left/right buttons along with volume control via raise/lower buttons
* Change: Mute(play) button has been repurposed as a Control Mode button with the following control modes:
* Input Adjust
* Impedance Adjust
* Display Brightness Adjust
* Max Volume at Input Change Adjust
* Change: The Power On/Off button is now the Power On/Off-Mute button (off or mute being essentially the same thing functionally)
* Tweak: Improved control integration between preamp boards for balanced audio configurations
* Tweak: Enhanced stability through numerous improvements in code
The following firmware changes apply only to the V2.1 version of the LDR3x board and related products released and shipped on or after Jan 1, 2015 up until May 15, 2016. Please refer to Version 2.2 firmware for all Tortuga Audio preamps shipped starting 5.15.16.
2.1.8 - 7.17.15* Fix: Corrected problem where impedance settings above 65k were being changed after being saved. This problem was preventing users from establishing impedance levels above 65k.
2.1.7 - 2.25.15This revision applies only to balanced (dual Master/Slave board) preamp configurations and can be ignored if you have an RCA/single-end preamp

* Fix: Slave was not saving impedance index after Master changed it
* Fix: Slave Auto-Cal was not reliably shutting off when Master Auto-Cal manually terminated
2.1.6 - 2.21.15* Fix: Added missing master-to-slave commands for adjustable impedance
* Tweak: Minor improvements to code related to switching inputs (to save program space)
* Change: Display now shows both left/right bias during balance adjust
* Deleted: Removed flashing of display on startup and shutdown (to save program space)
2.1.5 - 2.9.15* New: Added adaptive closure error relaxation to auto-cal to prevent hanging
2.1.4 - 2.7.15* Fix - Corrected display of variable impedance info
* Fix - Corrected left over debug code that prevented balanced/dual mono to work properly
2.1.3 - (no date)This version included with first wave of V2.1 boards and LDR3.V2 & V2k preamps
2.1.1 and 2.1.2 Interim internal versions - never released or shipped
2.1.0 - 1.26.15First firmware release with the new V2.1 board

* Change: Extensive overhaul of auto-cal code including decrease of closure error from 1% to 0.2%
* New: Added pre-calibration of board with precision resistors
* New: Added adjustable input impedance - 5 possible settings
* New: Added new info displayed upon power-up and via remote when off
2.x.y - 3 digit firmware version
x - current impedance setting
yy - current impedance level (in thousands) at current impedance setting
yy - internal controller hardware version (20 - V2, 21 - V2.1)
* New: Added code unique to the V2.1 controller hardware
The following firmware updates relate solely to the V2 version of the preamp controller board and related preamp products shipped prior to January 1, 2015.
1.2.0 - 9.15.14Please Note: All LDRx & LDRxB Passive Preamp models (released 9.1.14) were shipped with version 1.2.0 or later firmware.

Change: Adapted for new IO Board used with the LDRx & LDRxB including 4th input
Change: Going forward there will be different versions of firmware for LDR3x.V2 vs. the LDRx/LDRxB.
Tweaks: Miscl changes to improve stability
1.1.9 - 9.1.14* Fix: Corrected left/right fixed bias logic so that V2 builds that did not have any fixed bias defined when built and commissioned will now automatically set fixed bias to zero. Lack of fixed bias definition was causing units to be non-responsive to volume commands after software updates.
* Change: When power is applied, unit will now display 5 numbers. The first 3 digits are the software version. The second 2 digits are the right and left fixed bias settings respectively. For most units the fixed bias values will both be zero.
1.1.8 - 8.18.14* Fix: Removed unused timer2 code from interrupt handling routine. Was possibly interfering with remote.
* Change: Changed balance adjust limit from +/-10 to +/-9 to work within limitations of display
* Fix: Removed adding +1 to left bias upon entering Bal Adjust Mode - bug from 1.1.7
1.1.7 - 8.15.14* Tweak: Cleaned up how left/right channel balance adjustment was handled
1.1.6 - 8.12.14* Fix: Corrected display info during AutoCal
* Tweak: Display now shows all 0's as soon as unit is turned on - removed prior delay.
1.1.5 - 8.5.14This update only relevant to those using V2's in balanced audio configuration.

* Change: Improved robustness of Master-to-Slave serial communicate of volume data in balanced systems.
* Fix: Removed ability of Slave to sometimes ramp volume back up to set point by itself after receiving an Input Change command from the Master.
1.1.4 - 7.29.14* New: Displays 3 digit software build number when power is applied. Each digit shown individually.
* New: Added ability to assign a fixed channel bias to each board during initial build to ensure balance is centered. Some V2 boards exhibit a slight left or right channel bias inherent to the collective hardware bias that is not due to calibration of the LDRs. This channel bias is fixed, stored on the board (not the controller chip) and cannot be accessed or changed by the user.
* Tweak: Minors mods to left/right channel info displays
1.1.3 - 7.19.14* Fix: Slave board was not receiving AutoCal start/stop or Next (skip) command signals. This fix is only relevant to those using V2's in balanced configuration. This was a bug introduced with update 1.1.0.
1.1.2 - 7.15.14This update is primarily relevant to those who only use an Encoder and not the Apple Remote to control the V2

* New: Can now toggle AutoCal on/off with Encoder via quarter/half turn to right
New: Status LED now flashes briefly every 2-3 seconds when AutoCal is active
New: Left display module in dual display system now shows which LDR is in AutoCal (1-4)
1.1.1 - 7.7.14* Fix: Removed blinking of numerical display when changing volume. Status LED still blinks as before. Bug was introduced in 1.1.0.
1.1.0 - 7.6.14* Change: With the release of Rev 1.1.0, we have made the following changes to how auto calibration is run:

* AutoCal now runs only when manually initiated by the user while the V2 is turned off but still connected to power. We do recommend that the V2 be powered but turned off when not in use.
* AutoCal is started by pressing the Enter/Center button on the remote which disconnects the V2 from the audio input and output.
* Once AutoCal is initiated, it runs through one full cycle of LDR calibration in the following LDR sequence: right-series, right-shunt, left-series, left-shunt.
* Upon completing a full cycle, AutoCal shuts off and the V2 is reconnected to the audio input and output.
* While AutoCal is running it can be shut off prior to completing a full calibration cycle by pressing the Enter/Center button again on the remote. The V2 may not react immediately to this AutoCal shut down command and it may have to be repeated. We recommend you not interrupt the V2 during a calibration cycle once initiated. A full calibration cycle typically takes around 10 minutes.
* While AutoCal is running, you can cause AutoCal to interrupt calibration on the current LDR and switch to the next LDR in the cycle by pressing the Right button on the remote. If you switch through all 4 LDRs then AutoCal will shut down thinking its completed a full calibration cycle. This feature is provided as a diagnostic tool only. We highly recommend that you not interrupt AutoCal while its running.
* While AutoCal is running, the V2 will display each volume step (1-70) in the process for each LDR. Thus it will go through 70 calibration steps four times in a row over the course of a full calibration cycle.
* When AutoCal is complete or shut down deliberately, the display will also shut off.
* We recommend you turn your amp off before initiating an AutoCal cycle. Physically disconnecting your cables from the V2 isn't necessary.
* We recommend you run AutoCal monthly but this is simply a recommendation and not a requirement.
1.0.9 - 6.30.14* Fix: This update corrects the IR Remote ID recognition and pairing so that the user can correctly: a) Pair the V2 with either or both the Apple Remote and/or the legacy Tortuga Audio Remote; and b) Pair the V2 with only the Apple Remote or only the Tortuga Audio Remote, and c) Change the ID of the Apple Remote and re-pair (teach) the V2 the new Apple Remote ID. Please note the following specifics:

Going forward, uploading this or any subsequent software build will require the V2 to first pair itself with your remote. This will happen automatically the first time you use either your Apple Remote or your legacy Tortuga Audio remote after uploading new software. However, with the Apple Remote, we recommend you first use the Power On/Off (Menu) button to trigger the pairing. Using the Enter/Center key may not be sufficient by itself. You can confirm that the pairing worked by turning the V2 on and off with your remote.
Once you've initially paired the V2 with your Apple Remote after a software build, you can also pair it with your legacy Tortuga Remote but this second pairing will require that the Encoder Switch be pressed and held in for 20+ seconds and then released to place the V2 into Remote Pairing Mode. The Status LED and/or Display Module should blink rapidly indicating it's in Remote Pairing Mode. Pressing any key on the second remote will then complete the process. At that point the V2 should respond to either remote. The same procedure is true if you initially paired the V2 with your Tortuga Remote and also want to add the Apple Remote.
If you find that the Apple Remote you're using with the V2 is conflicting with some other Apple product (TV, MAC etc. ), you can change the ID of the Apple Remote by holding down both the Menu and Center buttons simultaneously for 5+ seconds. At that point the V2 will no longer respond to your Apple Remote because it has a new ID code. To teach V2 the new ID code, you'll then have to press and hold the V2 Encoder Switch for 20+ seconds to place the V2 into Remote Pairing Mode. Press any button on the Apple Remote (other than the Enter/Center button) and the V2 should now respond to your Apple Remote with its new ID code.
Please note that the legacy Tortuga Audio Remote has a fixed ID that can't be changed.
1.0.8 - 6.26.14* Fix: Removed a bug that, when the unit was turned off, caused the Status LED to light up when the Left or Right (Input Change) button was pressed on the Apple Remote.
* New: Pressing the Center/Enter button on the Apple Remote will start/stop (toggle) AutoCal. If it's in between cycles, an AutoCal cycle will commence. Likewise, if AutoCal is already running, it will shut off AutoCal. Please note that this does not enable/disable AutoCal generally, it just toggles a single AutoCal cycle. This was a hidden feature to aide in testing/diagnostics but we decided to release and document it.
1.0.7 - 6.20.14Notice: All units shipped on or after 6.20.14 now include rev 1.0.7 or higher and also include Rev 2 or higher of the bootloader. Rev 2 of the bootloader keeps audio disconnected during the 5 second bootload period after power is applied to the board. This avoids possible relay buzz and possible random audio output when power is applied to the V2. Any amp connected to the V2 should be powered down (or muted) prior to the V2 being connected to power.
* Change (AutoCal): Unit now wait 5 minutes after being turned off before starting AutoCal cycle and also waits 5 minutes after completing an AutoCal cycle before starting the next cycle.
Change: The minimum volume setting upon turning on the unit changed from 20 to 1 so that volume will now resume wherever it was previously for a given input prior to input change or unit being turned off but only between the limits of step 1 and a max of step 35.
Fix: Corrected timer used for enabling display brightness adjustment. Deliberately pressing Enter twice in a row should put the unit into "brightness adjust mode". If the unit doesn't change modes, suggest you slow down the speed of pressing Enter twice.
Tweak: Added 1 second delay after turning off the 12V TriggerOut before proceeding with turning off the V2. Give triggered amp more time to shut off.
Tweak: Several other miscl. edits intended to ensure audio output is minimized when unit is turned off.
1.0.6 - 6.9.14* Fix: added automatic unmuting of volume when Enter button pressed after changing input (bug introduced in prior build)
* Fix: limited starting volume to step 35 (of 70) when changing input (volume level associated with each input is saved when input is changed)
1.0.5 - 6.9.14* Fix: removed display of data on display module each time power applied to V2 board - problem introduced in build 1.0.4
1.0.4 - 6.8.14* Fix: corrected slow blinking status light when unit is off that was introduced in build 1.0.3
* Fix: corrected current input being left on when unit is off that was introduced in build 1.0.3
1.0.3 - 6.2.14* New: added master/slave communication for balanced audio including hardware/timer interrupt driven UART send/receive
* Fix: removed 1.0.2 auto-cal tweak - had stopping auto-cal cycling
* Tweak: removed numerous unused variables & and related code
Tweak: consolidated all flag initialization into single procedure
Tweak: numerous other post development/release clean-up & housekeeping mods
1.0.2 - 5.29.14* Tweak: (for diagnostics only) added ability to switch to next LDR while in auto-cal using left or right button when unit is off
* Tweak: forced initialization of step value 1 to prior stored value when switching to next LDRs during auto-cal
* Fix: unit now only responds to remote input when unit is on (if statement had been cc'd out)
Tweak: turned off debug info being sent to UART
1.0.1 - 5.17.14* Change: Input impedance raised from 10k to 20k
* Fix: Input relays remain off until after Enter command confirms new input choice
* Tweak: changed sequence of items related to unit turn on/off procedures
1.0.0 - 5.15.14* Baseline V2 software build | only 1 unit shipped with this version

 

Components & Kits

V25 Specifications

V25 Board Overview

The V25 Preamp Controller (Rev A) was released in April, 2017.

The V25 is a digitally controlled passive analog 2 channel audio attenuator with integral input switching that uses light dependent resistors (LDRs) for both attenuation and input switching.

The V25 is classified as a “passive” attenuator insofar as there is no active processing of the audio signal and no direct connection to or manipulation of the audio signal by a power supply. Despite the sophistication of the V25 design, all the the audio signal “sees” is a voltage divider composed of 2 LDRs in a classic series/shunt L-Pad configuration that emulates a potentiometer.

The V25 board is shown below with annotation of the key components and control interface points.

V25 preamp controller overview

V25 Specifications

Criteria 
Attenuation typePassive series/shunt (L-Pad) voltage divider using two (2) light dependent resistors (LDRs) per channel | total of 4 attenuation LDRs for attenuation.
Attenuation Range-60 db to 0 db in 99 in ~0.5 dB steps plus 1 additional muting step.
GainUnity (1x) gain | no amplification, processing or active manipulation of the audio signal | audio signal optically isolated from control system
BufferingNo input or output stage buffering
Input impedanceNominal 20k by default. User may configure up to 9 additional impedance settings each adjustable between 1k and 99k and switch between the settings with live music to optimize input impedance for their system.
Number of Channels2 independent channel stereo
Multi-channel Attenuation2 or more V25 boards can be daisy-chained to provided mutl-channel attenuation with 2 channels per board
Channel Balance AccuracyWithin 0.5 db over full attenuation range
Channel IsolationEach channel 100% isolated and independent from the other within the V25 board | audio signal grounds must to tied to a common star ground point external to the board
Audio Signal GroundNo connection of signal grounds to power ground within controller, however, audio signal ground must share common ground with power supply via an external star ground point in order for LDR self-calibration feature to function properly.
Audio Inputs | Single Ended1 board accommodates up to 6 switchable single-ended stereo (2 channel) inputs
Audio Inputs | Balanced2 boards accommodate up to 6 switchable balanced stereo (2 channel) inputs. With 2 boards it's possible to configure a mix of single-ended and balanced inputs.
Audio Input Switching/IsolationInput switching is done with LDRs | typical 50 ohm resistance when on | in excess of 5 megaohms when off | no relays in signal path.
Audio Output Switching/IsolationOutput signal switched on/off with LDR. Isolation between inputs and output when switched off in excess of 10 megaohms.
Total Harmonic Distortion1% or less
Power Input7-30 volts DC rated at 0.5 amp via J1
Power Regulation2 stage regulation | 5 V 1st stage low noise switch mode regulator followed by 3.3 V low noise 2nd stage linear regulator
ProcessorARM M3 Cortex 32 bit microcontroller running at 72 MHz
Control Input | RemoteAccepts control inputs from infrared silver Apple remote or equivalent remote using 38 kHz NEC protocol and Apple commands | infrared commands received via infrared receiver module attached indirectly via display module or directly to J3 pins.
Control Input | EncoderAccepts control inputs from rotary stepped encoder with integral push button switch | encoder attached indirectly via display or can be attached directly to J3 pins.
Control Input | UARTAccepts control inputs from external device using UART serial protocol and specific command codes (available upon request).
Display | 7-SegmentDual 2-digit numerical 7-segment LED type display with adjustable brightness | each 2-digit display is a physically separate module connected via ribbon cable | connects to board via J3 2x5 pin header
Display | OLEDGraphical OLED display (future) | connects to board via both J3 2x5 header and J9 2x7 header | future option that will require firmware update, optional OLED display plus setting display type jumper on J7.DISP.
Display | Status LEDStatus LED light | connects to board via J7
Mono ModeOutput switchable between stereo and mono mode via LDR switch | applies on to single-ended audio
FirmwareCustom interrupt driven application code written in the C language
Firmware UpdateFirmware can be updated via a resident bootloader that communicates with an external PC based HID bootloader application. User can download firmware update files from company website.
USB PortStandard 5 pin USB port allows processor to communicate with external HID bootloader application for updating firmware.
WiFi ModuleFuture ability to plug in a simple WiFi module via J6 that will allow the V25 to be controlled via smartphone app | will require WiFi module, firmware update and fully operational OLED display
Trigger OutOutputs a DC voltage signal when unit is turned on. Signal can be used to turn other devices on/off that are equipped with a Trigger Input. Trigger voltage level is equal to DC voltage level supplied to the board.
Printed Circuit BoardHigh quality nickel immersion gold solder pads with blue solder mask
Ambient RequirementsBoard must be operated in a stable, dry indoor environment only with ambient temperature within 60-90 degree F
ROHSCompliant or exempted
Physical DimensionsLength: 5.7 inches
Width: 2.7 inches
Corner Holes Center: 0.145 inches from edges
Corner Holes Diameter: 0.15 inches
Top clearance: 0.7 inches
Bottom clearance: 0.5 inches

 

V25 Single-Ended Wiring

RCA Jack

RCA jacks are used for single-ended audio. Single-ended audio means there’s only a one audio signal referenced to ground per channel.

Single-ended RCA jacks wiring is relatively simple. There are 2 connections to the RCA jack: 1) The center pin carries the actual audio signal; and, 2) The outer shell connects to system ground. This is shown symbolically below but the symbol closely mimics an actual typical RCA jack.

RCA jack schematic symbol annotated

Wiring RCA Jacks to the V25

The recommended way to wire single-ended RCA inputs/outputs to V25 is shown below in two diagrams below.  The first is a more abstract schematic representation while the second looks closer to actual wiring to the boards. In either diagram we only terminating a single input and a single output to the left and right channels.

Before diving in with wiring your V25 boards, we strongly recommend you study these diagrams until you understand the wiring scheme represented here.

V25 preamp controller single-ended wiring schematicThe wiring diagram shown below is consistent with the schematic shown above and is provided to show where the wires need to be connected on the actual V25 boards. Note that this is only for a single input so the input is connected to the solder pads labeled RI1 and LI1 on each board. For additional inputs you would terminate the wires to solder pads RI2 and LI2 etc.

Alternatively you could also make the same terminations via the J5 pin header or some combination of the J5 header and the solder pads.

Lastly, 2 solder pads are provided on the V25 board for both the output (RO and LO) and the signal ground (RG and LG). This redundant pads are solely for convenience.

V25 preamp controller single-ended wiring diagram

V25 Balanced Wiring

Multi-Board Audio Data Link

The V25 is designed to allow multiple V25 boards to be daisy-chained together for multi-channel audio. The top most board in a daisy-chained multi-board scenario is designated the master and other downstream boards are slaves.

As the names suggest, the master V25 board is in charge and receives control inputs, drives the visual display, and passes commands over to first slave board in the daisy-chain. The first slave board then passes commands on to the next slave board.

The master and slave boards are powered individually from a single common power supply and communicate with each other via a simple 2 wire serial data (UART) link.

Any V25 board can be the master. No special jumpers or settings are required.

Dual Board Balanced Audio

Balanced stereo audio requires two V25 boards with the data link connected between them and the audio inputs and outputs wired as described herein.

Master To Slave Control Connection

The master/slave designation is determined by how the communications link is connected between the 2 boards. The 2-wire serial data link on the master board is always connected to pins TX1/RX1 and the serial data link at the downstream slave board is always connected to TX2/RX2. This is shown in the diagram below.

If there are multiple downstream slave boards the same TX1/RX1 to TX2/RX2 connection pattern repeats between each paird of slave boards. In this fashion each downstream slave board is subservient to its upstream neighbor.

External Control of Master

Users can opt to control the master V25 via any external control device equipped with a UART port by connecting the external control’s TX/RX signals to the master’s RX2/TX2 pins respectively.

Users should refer to the V25 UART Commands section found elsewhere in the online production documentation for more details on the UART commands and protocol.

V25 master slave serial data link diagram

Balanced Wiring | 3 Pin XLR

Balanced XLR wiring is unavoidably more complex than single-ended RCA.

First, you are dealing with three (3) terminations per channel; two signals (pin 2 and pin 3) plus one shield/ground (pin 1). Next, you have both male (output) and female (input) type connectors each of which reverse the position of pins 1 and 2 with respect to the other while pin 3 remains thankfully unchanged. Last, but not least, some diagrams show the pins in a front view while another may use a rear view.

For purposes of your sanity and this guide, assume all XLR connectors herein are rear view only.

XLR 3 pin wiring
Balanced Audio Wiring

Connecting balanced audio signals and ground to the V25 can be challenging for the simple reason that it’s a bit complex and thus it’s easy to make a mistake.

The correct way to wire balanced audio to the V25 is shown below in two different diagrams. The first is a more abstract schematic representation while the second looks closer to actual wiring to the boards. In either diagram we only terminating a single input and a single output to the left and right channels.

Before diving in with wiring your V25 boards, we strongly recommend you study these diagrams until you understand the wiring scheme represented here. The wiring scheme is summarized in the following bullet points:

  • Master board handles the A/+ phase of both the right and left channels
  • Slave board handles the B/- phase of both the right and left channels
  • All grounds (including the pin 1’s) get wired to a single common “star ground” point somewhere within the enclosure

V25 preamp controller - balanced audio wiringThe wiring diagram shown below is consistent with the schematic shown above and is provided to show where the wires need to be connected on the actual V25 boards. Note that this is only for a single input so the input is connected to the solder pads labeled RI1 and LI1 on each board. For additional inputs you would terminate the wires to solder pads RI2 and LI2 etc.

Alternatively you could also make the same terminations via the J5 pin header or some combination of the J5 header and the solder pads.

Lastly, 2 solder pads are provided on the V25 board for both the output (RO and LO) and the signal ground (RG and LG). This is simply for convenience.

V25 preamp controller balanced wiring

Display, Encoder & IR Receiver

7-Segment Display Assembly

The display assembly provides visual (numerical) status information and indirectly connects the user control input devices (encoder & infrared receiver) to the V25 board. The 7-segment DM1 display assembly is shown below (front and rear views).

DM1 dual display assembly

The 7-segment display assembly is composed of the following parts.

  1. Master Display Module – populated with chip, capacitor, conductor, resistor plus 2 digit display on reverse side
  2. Slave Display Module – 2 digit display only
  3. Encoder – rotary encoder with integral push button switch
  4. IR Receiver Module – 3 pin infrared receiver device (must be soldered to master display module)
  5. Ribbon Cable #1 – 2×5 pin cable connects master display module to slave display module
  6. Ribbon Cable #2 – 2×5 pin cable connects display assembly (via master) to the V25 board
  7. Cable #3 – 4 pin cable connects Encoder to master display module

7-Segment Display Module

The 7-segment display module is a  dual-digit display that uses LED type 0.58″ high 7-segment displays to show numerical data. The figure below show the front and rear view of a master display module. The front view of a slave display module looks essentially identical to a master display module.
DM1 7-segment display front and back annotated

A pair of display modules are needed to properly display information for the V25 preamp controller. The master handles the low-level display processing and the slave acts as an extension to the master. The V25 board handles the high-level display processing.

When a pair of master-slave display modules are mounted in an enclosure, the master shows the right channel information and the slave shows the left channel information. They should be mounted in the enclosure accordingly.

The master module connects to the V25 board via a ribbon cable to J1 on the master display and to J3 on the V25 board. Note that red stripe on the ribbon cables connecting to the display modules must be aligned with the side of the J1 and J3 headers that has the white dot.

V25 preamp controller 7-segment display connection

Encoder Module

The encoder module is rotary encoder with integral push button that’s mounted on a small printed circuit board. The encoder circuit board has a 4 pin header labeled A, B, S and C which correspond to the master display module’s J2 pin header labeled A, B, S & G.

A & B are the encoder’s 2 rotary switches used to determine direction of turn and pulse counts and S is the push button. A, B & S are all referenced to G which connects to the V25’s ground.

Tortuga Audio encoder.

Infrared Receiver Module

The infrared receiver module (“IR module”) is a single integrated infrared receiver with 3 pins as shown below. The IR module mounts to the master display module via solder pads IR1 such that the front of the IR module (the face with the bump) faces same direction as the display module digits.

LDR3x IR Receiver module pins/wiring

V25 USB Port

USB Port

The V25 USB port is header J8.  Although J8 is visible and labeled on the topside of the V25 board the actual pin header itself is located on the underside of the board as shown below.

The J8 USB port uses the standard 5 pin USB connections as follows:

  1. Vbus – the +5V line
  2. D-(minus) – the negative data signal
  3. D+(plus) – the positive data signal
  4. N/C – no connection
  5. G – ground

When connecting to the J8 USB port it’s extremely important to make sure that the Vbus/+5V line is connected to the #1 pin. Reversing the USB connection to the J8 port and then connecting a powered USB device will destroy the V25 board.

V25 preamp controller USB port connection

V25 UART Commands

External Control

The V25 Preamp Controller Board can be controlled by external control devices such as an Arduino board or any other programmable device with standard UART serial communications hardware or the equivalent in software.

When an external controller is employed the external controller’s UART transmit (TX) and receive (RX) signals are connected to the V25  Master Board’s RX2 and TX2 pins respectively.

In order to have reliable UART communications the user should be mindful that both devices share a common ground.

V25 master slave serial data link diagram

UART Protocol

The UARTs used by the V25 are built-in to the V25 processor’s hardware, utilize data receipt interrupts, and are considered extremely accurate and reliable.

The V25 employs the following UART communications protocol.

  • Baud Rate: 115,200 bps
  • Stop Bits: 1 stop bit
  • Parity: none
  • Data bits: 8
  • Flow Control: none

V25 UART Control Commands

The control commands available to an external controller are defined in the table below.

Collectively these commands should allow for the comprehensive control of the V25 even in the absence of any visual feedback from the V25.

The user accepts all risks in using an external controller and these commands to control their V25 controller.  

Command ValueCommand NameDesciption>
0_power_toggletoggles the on/off state of the controller
1_turnonturns controller on if it's off otherwise ignores
2_turnoffturns controller off if its on otherwise ignores
3_raiseresponse depends on controller mode - by default it raises volume 1 step
4_lowerresponse depends on controller mode - by default it lowers volume 1 step
5_leftresponse depends on controller mode - by default it shifts volume balance 1 step to the left
6_rightresponse depends on controller mode - by default it shifts volume balance 1 step to the right
7_enter* volume adjust mode - blinks display
* other modes - locks in any changes and reverts to default volume adjust mode
8** reserved **don't use
9** reserved **don't use
10** reserved **don't use
11_menu_volswitches controller to default volume adjust mode
12_menu_inputswitches controller to input adjust mode
13_menu_displayswitches controller to display adjust mode
14_menu_volmaxswitches controller to max volume on input change adjust mode
15_menu_impedswitches controller to impedance adjust mode
16_menu_calswitches controller to auto calibration mode
17_mute_toggletoggles mute state of controller
18_mutemutes the volume if not already muted
19_mute_switchmutes controller, then switches to new input (slow mode only), and then unmutes controller
20_unmuteunmutes the volume if it's currently muted
21_refreshrefreshes display based on current mode
22_showdisplay info associated with current mode
23** reserved **don't use
24** reserved **don't use
25** reserved **don't use)
26** reserved **don't use
27** reserved **don't use
28** reserved **don't use
29** reserved **don't use
30** reserved **don't use
31_send_vol* 2 bytes : command + value
* value = volume level 0-99
32_send_volbias* 2 bytes : command + value
* value = volume bias between -20 and+20
33_send_volmax* 2 bytes : command + value
* value = max volume upon input change between 1 and 99
(99 essentially defeats this safely feature)
34_send_input* 2 bytes : command + value
* value = input number between 1 and 6
35
_send_imped_index* 2 bytes : command + value
* value = impedance index number between 1 and 5
36_send_imped_level* 2 bytes : command + value
* value = impedance level between 1 and 99
(must run autocal after changing level before change becomes active)
37** reserved **don't use

External Control Integration

To effectively use the UART control commands the use must be mindful of the overall V25 remote control scheme. For convenience the V25 Apple remote control scheme is shown in the table below.

For example, in order to change inputs, an external controller must first place the V25 into input control mode and then issue the appropriate raise, lower, left, right,  and enter commands consistent with instructions for changing input as described below.

Function/ModeStatusButton(s)Description
Turn OnOffMenuPressing button turns the unit on.
Turn OffOnMenuThere are 2 ways to turn off the preamp.

1-step turn off - Press/hold the Menu button and then release. Note that if held down too long unit may turn back on and if held down too briefly will result in muting the preamp but not turning it off.

2-step turn off - First mute the unit by briefly pressing the Menu button. When the volume has fully ramped down to zero, a subsequent press of the Lower button will turn off the preamp.
Volume MutingOnMenuBrief press of Mute button will mute or unmute the unit. The volume will ramp down to zero when muted. When unmuted the volume will ramp back up to its prior setting.
Volume AdjustOnUp/DownRaises and lowers the volume by 1 step for each press. Holding down the buttons will cause the command to repeat.
Balance AdjustOnLeft/RightShifts the channel balance 1 step to the left or right a maximum of 20 steps either way. Each step changes channel balance by ~0.5 dB. As channel balance continues to skew towards a given side (left or right), the combined volume level of both sides will automatically adjust to maintain the same overall volume level.
Input Adjust - Slow ModeOnMode, Raise/Lower & Left/RightPressing the Mode(play) button once will switch the unit into Input Adjust mode. The right display will show the currently selected input number. The left display will show the prior volume level associated with that input when it was last selected.

Music will continue to play on current input channel while while the preamp is in Input Adjust mode and you make your input selection.

Use the raise/lower buttons to adjust the input to desired number.

Press the Center/Enter button to activate the newly selected input and return to volume control mode.

If you select the same same input as your're currently listening to, nothing happens upon pressing the Enter button and returning to volume control mode.

If you select a new input, pressing the Enter button will cause the existing input signal volume to ramp down, the new input to then be connected, and the new input volume to ramp back up.
Input Adjust - Fast ModeOnMode, Left/RightPressing the Mode(play) button once will switch the unit into Input Adjust mode. The right display will show the currently selected input number. The left display will show the prior volume level associated with that input when it was last selected.

Unlike the Slow Mode described above, the Fast Mode immediately changes the input without first muting the volume.

Use the left/right buttons to change inputs immediately.

There will be a brief 200 millisecond delay in fast switching the inputs which will hardly be perceptible.
Impedance AdjustOnMode, Raise/LowerPressing Control Mode (play) twice will switch the unit into Impedance Adjust mode. The left display will show the impedance setting number (1 through 5) and the right display will show the impedance level (in xxK ohms) associated with the currently selected impedance setting number.

Use the raise/lower buttons to change the impedance setting number (1-5). Use the left/right buttons to change the impedance level for the currently selected impedance setting. Press the Center/Enter button to exit Impedance Adjust mode and return to volume control.

Changing the impedance setting number will instantly change the preamps impedance to the level associated with the setting number provided that this setting and its associated level have already been run through the auto-calibration process.

If you switch to an impedance setting number (1-5) that has not already been initialized through auto-calibration then selecting it will result in the audio being turned off. This is the single most common error users make when working with the Adjustable Impedance feature.
Display AdjustOnMode, Raise/Lower & Left/RightPressing Control Mode (play) three (3) times will switch the unit into Display Adjust mode.

BRIGHTNESS ADJUST

The right display will show the brightness level number between 0-15.

Use the raise/lower buttons to change the brightness level. Press the Center/Enter button to exit the Display Adjust mode and return to volume control.

TIMEOUT ADJUST

Timeout allows you to cause the display to turn off at the selected number of seconds after prior command input via the remote. Timeout only works when in Volume Adjust Mode and is disabled when the preamp is in any other control mode.

The left display will show the timeout number between 0 and 99 seconds. If set at 0 the display timeout feature is disabled. The minimum timeout setting is 5 seconds.

Use the left/right buttons to adjust the timeout to desired level. Press the Center/Enter button to exit the Display Adjust mode and return to volume control.
Max Volume On Input Change AdjustOnMode, Raise/LowerPressing Control Mode (play) four (4) times will switch the unit into Max Volume On Input Change mode. The left display will be blank. The right display will show the maximum volume allowable when switching to a new input or when the unit is first turned on. This can be adjust between 1 and 99. The initial default value is 50. This protects your audio gear (speakers!) from accidentally going to full volume when switching to an input they may have been at or near full volume when previously selected as would be the case if the preamp was being used in a home theater bypass scenario.

Use the raise/lower buttons to change the max volume on input change level. Press the Center/Enter button to exit the max volume on input change adjust mode and return to volume control.
Auto-CalOnMode, RightPressing Control Mode (play) button five (5) times will switch the unit into Auto Calibration mode

Both displays will initially show 0 upon entering the auto-cal mode.

Press the Right button 3 times to enable auto-calibration. The right display will show the count up as you press the button.

Once enabled the unit go through several stages of calibration. The first stage involves making 4 adjustments during which time a 4 digit number will be displayed typically ranging from 1500-1850. If the preamp does not cycle through these 4 adjustments within say 30 seconds or so that's an indication one or more LDRs may be having a problem. If there's a problem the numbers will either continue to increase or decrease steadily until hitting some upper or lower limit and then remain fixed.

The unit will the proceed to cycle through each of 4 LDRs showing the LDR number in left display and the calibration step number in right display. There are 99 calibration steps for each LDR. Upon completion of 4th LDR, unit will terminate calibration, briefly shut off the preamp, and then start the preamp again normally.

At the beginning of each LDR's calibration the step number will likely remain at step 1 for a while. That's normal. After no more than a minute the step count should proceed upwards. Sometimes the step count goes quickly and other times it may slow down quite a bit. This is normal.

If the calibration step process slows down and stops or never proceeds beyond step 1 and does not proceed after a minute of waiting that is a fairly definitive indication that the LDR whose number displayed in the left display has gone bad and needs replacement.

You can skip over an LDR any time during autocal by pressing the right button. If you skip past the 4th LDR, autocal will terminate.
V2 Overview

ldr3x.v2 replaceable ldr modulesNew Feature | Auto Calibration

The V2 introduces Auto Calibration as well as replaceable LDR Modules. Auto Calibration is a self-contained system wherein the V2 fine tunes the attenuation table of the 4 primary LDRs based on each LDRs actual measured performance. This ensures that the LDRs continue  to perform optimally over time despite potential performance drifting as these analog devices age normally. Even if one LDR fails prematurely or degrades beyond the reach of Auto Calibration, it’s a simple matter to plug in a new LDR Module similar to tubes.

Preamp Controller Board

The LDR3x.V2 (the “V2”) is a preamp controller in the form of a populated 2.5 inch by 4.8 inch printed circuit board that forms the core of a passive preamp or as the attenuator/controller of an active preamp. The V2 builds on the experience and success of the V1 board.

Insofar as the V2 lacks a power supply, controls or enclosure it is neither a complete finished audio premap nor is it a comprehensive kit.

Once connected to an external power source (not included), the V2 can accommodate one (1) single-ended audio input without any additional equipment and up to three (3) inputs when interfaced with an external input relay board (not included). 

The V2 is sold with an uninstalled infrared receiver module required for remote control. The IR receiver module can either solder to the V2 board, located external to the board, or mounted to the DM1 Display Module master board. 

The V2 can be controlled by the Apple Remote or Encoder or both. Neither are included with the V2 and must be purchased separately. Control inputs that are enumerated and explained in sections below.

The V2 is part of the Tortuga Audio family of LDR based passive preamps.

Unbalanced Audio (single board)

A single V2 board operates as a standalone passive preamp for single-ended unbalanced inputs. By itself it can handle a single input. When mated with the Tortuga Audio IO3 input switching board it can switch between 3 different inputs.

Balanced Audio (dual boards)

By using a pair of boards, the V2 becomes a preamp for balanced audio systems. One board is designated the Master and the second configured as the Slave board via an on-board jumper. The Master V2 interfaces with the Apple Remote and/or Encoder and sends volume level and other commands to the Slave V2 via a 3 wire control cable.

Dual Mono (dual boards)

Similar to the balanced audio described above, a pair of V2 boards can serve as left/right channel mono preamps wherein only a single channel of each board is used. As with mono amps, this approach can further enhance channel separation and thus raise the bar on your audio experience. Each mono V2 preamp board can be located immediately adjacent to its amp thus minimizing interconnect distance. A simple 3 wire cable between the pair of V2 boards is all that’s needed for control.

Options:

V2 Specifications

The specifications for the  LDR3x.V2 (“V2”) preamp controller board include the common specifications plus the following:

  • Input/Output Type: Unbalanced stereo (single V2 board) and balanced stereo (pair of V2 boards)
  • Inputs: Single input to board itself. Can switch/select up to 3 inputs when interfaced with compatible input relay/switching board.
  • Outputs: Single output from board. Can be paralleled externally to accommodate additional outputs
  • Input Control Interface: 0.1 inch (2.54 mm) pitch IDC pin header for connecting to optional IO3 input relay board
  • Audio/Control Interface: 0.1 inch (2.54 mm) pitch mini screw terminal blocks for interfacing with Encoder, Status LED etc. (see info in other sections above for details)
  • Display Module Interface: 0.1 inch (2.54 mm) pitch IDC pin header for connecting to to optional external DM1 display module (purchased separately)
  • Optional Display:  Drives  optional single or dual DM1  numerical display(s) providing volume and status information
  • Control System: 12 bit digital-to-analog circuitry used to regulate the LDRs.
  • Software Update via USB :  Control system software can be updated by downloading latest version from the website and then uploading it into the V2 preamp using a simple upload application (also downloaded from website) that runs on a PC connected to a USB port on the V2 board.
  • USB Port:  USB port for updating control system software if warranted.
  • Auto Calibration:  A self-contained software driven process initiated by the user that recalibrates each LDR to correct for drift/aging of the LDRs as needed.
  • Replaceable LDR Modules: Similar to tubes, LDR modules can be easily unplugged and replaced in the event one fails or goes sufficiently out of calibration to warrant replacement.
  • Control Methods & Functions:  Remotely  controlled via the elegantly simple Apple Remote and also via a rotary encoder with integral push button switch.
  • Power Draw:  On: < 0.4 amp @ 12 VDC | Off: < 0.25 amp @ 12 VDC
  • Weight (unit):  ~ 2.7 ounces
  • Dimensions – As Shipped:  L=8.7″  W=5.4″  H=1.75″
  • Dimensions – Board : The version 2 board dimensions are almost the same as the version 1 board except that the version 2 board is 0.1 inches longer than version 1. Hole spacing is approximately the same. Hole diameter is exactly the same.  The version 2 board requires an absolute minimum of 1.625 (1 & 5/8) inches of vertical space not including any standoffs used in mounting the board to a chassis. Highly recommend that 2 inches of vertical space be allocated for the version 2 board. The is twice the vertical space needed by the version 1 board and is due to an additional piggy-back board mounted on the main version 2 board.

LDR3x.V2 board dimensions

V2 Controls

Control Terminal J2

J2 is a 8 position (only 7 used) , 0.1 inch pitch screw terminal connector located on right end of the LDR3x.V2 board as shown in the picture below.
ldr3x.v2 J2 & IR connections
J2 provides for the optional interfacing of three (3) control/status items:  the Encoder, the IR Module, and the Status LED.

The use of J2 is entirely optional provided the IR Module is mounted directly on to the V2 board and the V2 is controlled solely via a handheld remote.

The J2 Terminal interface points are shown in the following diagram and discussed below in more detail.

LabelType
Function
IRD InputInfrared receiver pulse (required for remote)
+5VpowerPower for externally mounted IR Module
GndpowerElectrical ground
STD OutputStatus LED (optional)
ESD InputEncode Switch (optional control input – on/off etc.)
EaD InputEncoder leg A (volume control & input switching)
EbD InputEncoder leg B (volume control & input switching)
n/cno connection – not used

ldr3x.v2 control wiring diagram

LDR3x IR Receiver module pins/wiring
IR Receiver | J2-IR

The V2 is supplied with a high performance 38 khz infrared receiver module (IR Module). The IR Module is supplied loose and not installed. The IR Module can be mounted on the V2 board in the location shown in the picture above. As a practical matter, it’s more likely that the IR Module will be located external  to the V2 board; typically behind an opening in the front panel of an enclosure. An externally mounted IR Module can be terminated either to J2, or alternatively, can also be conveniently terminated via mounting holes provided by a DM1 Display Module.

The picture to the right shows the IR Receiver and  its 3 pin connections. Incorrect wiring of the IR Receiver will immediately destroy it so be very deliberate when connecting the IR Module to the V2 board. If you locate the IR Receiver external to the LDR3x board, pin 1 must be connected to common ground (J2-Gnd), pin 2 must be connected to +5 volt power (J2-+5V) and pin 3 must be connected to J2-IR. Connecting wires to an externally mounted IR Module pins is an awkward exercise in soldering. We recommend using our DM1 Display Module which provides a mounting location for the IR Receiver on its circuit board.

Regardless of where you choose to locate the IR Receiver, it must have reasonable line-of-sight access to the handheld IR remote. The most common approach is to have the IR Receiver be “looking out” from the front panel of whatever enclosure you use to house the LDR3x.

Status LED | J2-ST

J2-ST is an output signal that when connected to an LED provides status information on the V2. The positive lead of the LED (the longer lead) connects to J2-ST which provides +5 V when the LED is turned on. The negative leg of the LED (the shorter lead) connects to common ground (J2-Gnd). In most cases you’ll want to place a resistor in series with the Status LED to limit current (and brightness) through the LED. We recommend a 10-30k resistor but this will ultimately depend on the specifications of your LED and your desired brightness.
The Status LED provides the following information

  • Multiple Brief Flashes:  Upon unit being powered up or turned on, or anytime the Enter key is pressed.
  • Steady On: Unit is on, is Un-Muted and is in normal Volume Adjust Mode (default).
  • Blinking Slowly: Unit is either Muted or at maximum Volume.
  • Blinking Rapidly:  Unit is in Balance Adjust Mode.
  • Blinking Very Rapidly:  Unit is in Remote Pairing Mode.
  • Brief Flash Every 2-3 Seconds:  Unit is off but is running auto-calibration.

Encoder Inputs | J2-ES, J2-Ea & J2-Eb

These 3 inputs are for interfacing the LDR3x.V2 with a rotary Encoder with integral push button switch. The Encoder switch is terminated to J2-ES.  J2-Ea and J2-Eb are for connecting the “A” and “B” legs of a rotary encoder. The common leg of the rotary encoder must be connected to electrical ground (J2-Gnd).

The LDR3x was designed and tested to work with the Alps EC11 series of encoders and more specifically the model EC11B15242AF although probably any of the EC11 encoders (or equivalent) will work.

Wiring Encoder Backwards:  If clockwise rotation of the encoder results in decreasing volume and counterclockwise rotation increases the volume, then simply swap the Ea and Eb inputs.

Pairing With Remote | J2-ES

There is one control function that can only be done via the Encode switch or some other switch connected via J2-ES. This control function involves pairing the V2 with the Apple Remote. Please refer to the preamp controls section on Apple Remote pairing.

V2 Wiring

Wiring For Optimal Performance

Regardless if you already have a fully functioning V2 board or are just starting your V2 preamp project, the single most important element of a successful V2 preamp build is the proper wiring of the audio, power and ground. We’ve learned much about the V2 since its introduction in May 2014; much of it through feedback from our growing DIY customer base. We advise careful review of, and adherence to, the diagrams and info below in the planning and execution of your V2 project.

Star Grounding

There’s an abundance of info available online regarding audio and grounding. Why? Because poor grounding can bugger up any audio system and it’s all too easy to get it wrong. The most reliable approach to grounding is to use “star grounding”. In simple terms, star grounding means everything that needs to be grounded gets its own dedicated connection to one single common ground point. No daisy-chaining of ground connections. This is clearly illustrated in the diagrams below. Can you spot the daisy-chained violator?

Correct Audio Signal Grounding for AutoCal Operation

The diagrams below show both the left and right (unbalanced) and the + and – (balanced) audio signal grounds each being individually tied to star ground. These connections  are absolutely essential to the proper functioning of Auto Calibration. Moreover, power ground must also be connected to the same star ground point regardless of whether you’re using an external DC power supply or bringing in a 3 wire AC main to power an internal power supply unit.

Unbalanced Audio Wiring

Unbalanced (or “single ended”) audio consists of single left and right channel audio signals which are each referenced relative to ground. The left channel input and output are terminated to J1L-Input (or LI) and J1L-Output  (or LO) respectively. Similarly, the right channel input and output are terminated to J1R-Input (or RI) and J1R-Output (or RO) respectively.

Input, output and ground for both the left and right channels can be terminated via the J1L and J2L screw terminals respectively.  A more permanent and maintenance free alternative to using the screw terminals is to solder the audio input, output and ground via the solder pads adjacent to the screw terminals. These are marked as LI, LO, and LG for the left channel and similarly RI, RO, and RG for the right channel.

LDR3x.V2 audio, power and ground wiring

Balanced Audio Wiring

Two (2) V2 boards are required for balanced audio. The Master handles the right stereo channel and the Slave handles the left stereo channel. The Master handles all communication with the user including command inputs from the remote or encoder and output to the display module etc. There is no user interface directly with the Slave board.

Designating the Slave Board (Left Channel)

All V2 boards operate in Master mode unless told otherwise.  To designate a V2 board as a Slave, the pins of jumper JP1 must be connected together. A 2 pin shunt is provided for this. JP1 is circled in red in the second board above.

Master/Slave Communication

The V2 Master conveys necessary information to the Slave via a 2 wire serial data link and a single wire slave select command line between the 2 boards. These connections are shown in the red circles and arrows in the picture above. Please pay close attention to notes 1 through 4 in the picture above.  Note that T-J13 on Master connects to R-J13 on Slave and likewise R-J13 on Master connects to T-J13 on Slave.
ldr3x.V2 balanced audio master/slave connections

For balanced audio, you will need a pair of V2 boards. The master board is designated for the right channel and the slave board handles the left channel. The + channel terminates in J1L and the – channel terminates in J1R. This is arbitrary but it helps to be consistent to both avoid and help diagnose any problems. We recommend the XLR Pin 1 shields be connected together as “pass through”  so that the whole “Pin 1 problem” is dealt with at your source and amp and not also at the preamp.  A great article on the Pin 1 problem can be found here. 

LDR3x.V2 audio, power & ground wiring (Balanced systems)

Kit Overview

Get Familiar With Your Kit

Before proceeding with actual detailed assembly, we strongly encourage you to read all of information below.

 

LDR3.V25K kit internal assembly

 

Check Your Parts List

Every kit should include a parts list that was used by Tortuga Audio to make sure we included all the parts in your kit shipment.

If you haven’t already done so, we encourage you to go through that checklist to make sure you can find and identify all the parts/wiring. If you believe we left something out please contact us and we’ll be happy to ship you the missing item(s).

Key Sub-Assemblies

Your kit is actually a fairly straight forward build since all the circuit boards come fully populated and tested. Most of the work involves mechanical assembly followed by some wiring. The wiring is probably the most complex part but if you move deliberately through the instructions it should all be clear.

The kit is composed of the following sub-assemblies:

  1. The V25 Controller Board with integrated input switching
  2. The display assembly and its mounting bracket
  3. The mounting board to which items 1) and 2) are to be mounted
  4. The rear panel including the RCA jacks, power jack, trigger jack, and USB jack.
  5. While not an assembly as such, the enclosure box and front panel

The Mounting Board

The Mounting Board is a 5.73″ x 8″ epoxy fiber board make of the same material as a typical printed circuit board. The Mounting board slides into the bottom grove of the Enclosure Box.

The Mounting board comes with 8 pre-drilled holes as shown below (except yours doesn’t have the writing on it). Note the hole patterns to orient the top and front of the mounting board.

Three items get mounted on the Mounting Board: 1) The Display Bracket holding the Display Modules; 2) The Controller Board; and, 3) The Star Ground.

LDR3.V2K kit mounting board

Enclosure Box

The Enclosure Box (the “Enclosure”)  is a robust extruded aluminum box that is 3″ tall by 6″ wide by 8″ deep. It is powder coated with a flat black finish. The Enclosure has a series of internal slots on the sides into which you can slide the Mounting Board. The Mounting Board must use the bottom most pair of slots.

LDR3.V2k enclosure box

Enclosure Feet

Four (4) peel-and-stick black urethane feet are provided that are to be mounted on the underside of the Enclosure approximately 1 – 1.5 inches in from each corner. Once in place these have excellent long term adhesion and will be difficult to remove and move so be careful when attaching them.
Tortuga Audio enclosue feet

Fasteners & Display Bracket

The collection of kit fasteners and brackets are shown below followed by a brief description of each.

Display Bracket

The Display Bracket is a gray plastic L-bracket with 6 pre-drilled holes. The leg of the bracket with 2 holes is used to mount the Display Bracket to the Mounting Board. The remaining 4 holes in the other leg are for attaching the Display Modules to the Display Bracket.

Display Bracket Fasteners

There are 2 zinc coated screws with nuts that are used to attach the Display Bracket to the Mounting Board.

Display Nylon Fasteners

The white nylon fasteners are used to attach the 2 Display Modules to the Display Bracket. There are four (4) threaded rods, 8 main nuts, and 4 spacers. In some cases we may substitute 4 additional nuts in lieu of the spacers.

Panel Screws

There are eight (8) panel screws with washers. These are black socket head sheet metal screws. These are used to attach both the front and rear panels to the enclosure.

Standoffs

There are six (6) aluminum standoffs along with twelve (12) zinc coated standoff screws. The standoffs are used to mount the Controller Board to the Mounting Board and to make the Star Ground.

Front Panel & Encoder Knob

The front panel is a heavily tinted clear acrylic 1/4″ thick panel. When the preamp is turned off the dark acrylic panel significantly limits your ability to see the internal components and for all practical purposes looks like a black panel. When the preamp is turned on the numerals from the two Display Modules are clearly visible while everything else still remains unseen.

The front panel attaches to the Enclosure via 4 socket head screws. There is hole and recess in the front panel through which the Encoder is mounted (Encoder not shown in pic below). The black knurled Fender Telecaster control Knob mounts on to the Encoder as the final assembly step.

LDR3.V2K kit front panel with knob

Rear Panel

The rear panel is a black anodized aluminum panel as shown below. It accommodates 10 RCA jacks (6 inputs, 4 outputs), the USB cable, the 12 VDC power input jack and the 12 V Trigger jack.’

The rear panel connects to the Enclosure via 4 socket head screws with washers.

LDR3.V2 rear panel

RCA Jacks

The kit includes 10 standard RCA jacks as shown below. You may have opted for the Cardas upgrade (not shown here).

standard RCA jacks

Power & Trigger Jacks

The power jack is a 5.5 mm style barrel jack with a 2.1 mm pin. It accepts the barrel plug from the external “wall wart” style 12 VDC power supply provided with the kit. The 12 V trigger jack is a mono 3.5 mm phone jack that provides a 12 VDC signal whenever the preamp is turned on.

Both of these jacks are mounted in the Rear Panel.

Tortuga Audio power & trigger jacks

Internal USB Cable

The Internal USB Cable is provided solely to enable updating of the preamp’s firmware which is done via a USB connection to a PC. This 12 inch cable is mounted internally on the Rear Panel and connects to the J8 header on the Controller Board.

Type A USB port with cable

Wire & External USB Cable

The last part of the kit includes a bag with various wires plus an external USB cable. Like the Internal USB Cable, the external cable is for connecting the preamp to a PC for purposes of updating the firmware.

While there’s no hard and fast rules when it comes to using the wire provided you will find that color/lengths of wire provided will make most sense if your use white wire for audio signal hookup, the red and black wire for power and the green wire for ground connections.

Kit Parts List

Every kit shipped should include a hard copy checked-off parts list. The parts list below may differ slightly from the list included with your kit.

Please drop us a note If you find any noteworthy inconsistencies or if you believe anything is missing from your kit.

QuantityStandard Items
1LDR.V25 Preamp Controller Board
12.95" x 6" x 8" black powder coated extruded aluminum enclosure box
1 0.25" x 2.95" x 6" see-through dark acrylic front panel with hole/recess for encoder and knob
1 0.08-0.10" x 2.95" x 6" black anodized rear panel with cut-outs for jacks, etc.
1knurled black enameled Fender Telecaster style encoder control knob
4peel'n'stick urethane rubber feet
10standard gold plated brass RCA jacks
1DC power jack
112 VDC Trigger Out phono jack
8sets of socket head black oxide sheet metal screws with washers (for front/rear panel)
1external "wall-wart" or "brick" style external 12VDC power supply suitable for 120 or 240 VAC
14 conductor cable for connecting the encoder to the display module
1ribbon cable for connecting the display module to the V25 board
1rotary encoder module with nut and washer
1master display board with IR receiver module soldered in place
1slave display board
1ribbon cable for connecting master display module to slave module
1display module mounting bar - plastic angle
4sets of nylon threaded rods with nuts & washers for the master display module mounting bar
1USB cable for connecting V25 USB port to rear panel
10feet of white #24-26 gauge silver coated copper wire (audio hookup)
1foot of red #20 gauge silver coated copper wire (power hookup)
1foot of red #26 gauge silver coated copper wire (trigger hookup)
1foot of black #20 gauge silver coated copper wire (power hookup)
1foot of black #26 gauge silver coated copper wire (trigger hookup)
3foot of green #20 gauge silver coated copper wire ( audio ground hookup)
10.060" x 5.7" x 8"  FRP mounting board
6#4 threaded hex stand-offs for mounting the V25 board and ground bar to mounting sheet
12#4 screws for the mounting standoffs
2#4 screws for the mounting display bar to board
2#4 nuts for mounting display bar to board
1Apple remote
Optional Items
10Cardas RCA jacks
5feet of Neotech 26AWG UP-OCC Solid Copper wire
Detailed Assembly Instructions

Assembly Overview

Assembly of the LDR.V25K kit is fairly straightforward insofar as all the electronic components have already been installed on their circuit boards. Most of the work is a combination of mechanical assembly, connection of cables, and wiring. The cutting, stripping and soldering of the various wires is probably the most challenging aspect of the assembly process.

When you’re almost done the final assembly will look something like the pic below. You will then slide this assembly into the enclosure and attach the front and rear panels to the enclosure to finish the job.

We believe the instructions and guidelines provided are adequate to assemble the kit successfully but we remain open as always to suggestions on how to clarify and improve this information.

Enjoy your project!

LDR3.V25K kit internal assembly

Install Standoffs & Display Bracket to Mounting Board

There are six (6) standoffs as shown below. 1-2-3-4 are for mounting the Controller Board. 5-6 are for the Star Ground.

Make sure you leave standoffs 1-2-3-4 somewhat loose at this point. You will want some flexibility in these standoffs when attaching the Controller Board later on.

The Display Bracket mounts to the front of the Mounting Board as shown with 2 screws/nuts (ignore those 3 white lines for now). The 2 screws must come up through the bottom of the Mounting Board through the bracket such that the nuts are on the top as shown.

Make sure the nuts are reasonably tight. It’s very difficult/awkward to access these nuts later.

Make sure the Display Bracket face with the 4 drilled holes is facing forward and not backward.

Install Display Assembly to Display Bracket.

To attach the Display Assembly to the Display Bracket attach one Display Module at a time using the following detailed procedure:

  1. Find 2 white threaded nylon rods and screw on a nut to only one end of each rod as shown to the right.
  2. Insert the rod with nut through the back side of one Display Module through each of the bottom two corner holes in its PCB such that the two bare rods are now facing you and the nuts are behind the display PCB.
  3. Slip a white nylon spacer over each rod such that the spacer is now against to front side of the PCB. Some kits may not have spacers and if so use nylon nuts as the spacer instead.
  4. Next thread the bare nylon rod ends through the two holes in the Display Bracket from the backside such that the spacer is now up against the back side of the Display Bracket and the two bare rods are pointing out the front.
  5. Thread a nut on to each rod and tighten until the nut-pcb-spacer-bracket-nut “sandwich” is now snug (see next pic below)
  6. Repeat 1-5 for the other Display Module
  7. Attach the ribbon cable between the master and slave Display Modules.
Tortuga Audio display module mounting
The “nut-pcb-spacer-bracket-nut” sandwich

In some cases the “spacer” will be another nut. In which case make sure you tighten the the 2 nuts on other side of the Display Module before proceeding to mount the displays to the Display Bracket.

Make sure the master Display Module is on the right side and the slave Display Module goes on the left side. The master Display Module is the one with the most electronic components on its PCB whereas the slave has only a single 2×5 pin header and a 2 digit display.

Try to keep the ribbon cable and the Encoder cable attached to the master Display Module while mounting it to the Display Bracket. It’s much more difficult to attach these cables after the master Display Module has been mounted to the Display Bracket.

At this point the Display Module assembly should look something like the picture below. Note that the threaded nylon rods now need to be nipped off using which is easily done with any plyer style cutter.

Install IR Receiver Module

LDR3x IR Receiver module pins/wiringNormally we try to install the IR receiver module on the master Display Module before we ship the kit. In the event the IR receiver module is shipped loose, here are the instructions for mounting the IR receiver module.

The IR receiver module needs to be soldered into the master Display Module (the one on the right) in its lower left front corner as shown in the picture below. The 3 pins of the IR insert into the 3 holes in the master Display Module. You should insert the IR far enough into the holes so that you can bend the IR leads to the left leaving it IR facing out towards you.

Make sure before soldering that there is room to bend the IR Receiver Module to the left such that it does not block or interfere with the adjacent Display Module. 

Make sure you clip off the excess leads of the IR after it’s been soldered in place. Do this now before proceeding because it will be difficult to access them later. 

Tortuga Audio display modules with IR receiver module

Install Controller Board

Mount the V25 controller board on the 4 standoffs that you previously attached to the Mounting Board. Secure each corner with a #4 screw provided.

Note that the pic below does not show the Display Assembly already installed. Note also the 2 Star Ground standoffs near the top of the mounting board.

V25 preamp controller on mounting board

Verify that the screws to the controller board standoffs are tight on both the board side and on the underside of the Mounting Board. 

Star Ground

The 2 remaining standoffs on the Mounting Board are for creating the Star Ground point. All ground connections will terminate at the Star Ground.

Strip off the insulation on a 3-4″ length of either the heavy black or green wire. Thread a #4 screw into both standoffs approximately half way leaving room for the wire between the screw head and the standoff. Suspend the stripped wire between the 2 standoffs as shown in the pic below. Put one full turn of the stripped wire around each screw. Then tighten the screws so that the bare wire is now firmly suspended between each standoff. Use wire cutters to trim off excess wire.

V25 preamp kit star ground

Rear Panel | RCA Jacks

A standard kit RCA jack is shown below disassembled into its parts 1 through 5. Ten (10) of these jacks need to be mounted to the rear panel. The install steps for a single are illustrated in the pic below going from right (#1) to left (#5). Each step is explained below.

 

Step 1 – Insert the RCA jack threads first into the rear panel from the labeled side. Make sure the jack has its white hole alignment washer (not the #2 washer) and that the raised inside edge of the alignment washer is facing towards the rear panel as the jack is inserted.

Step 2 – Slide the white washer onto RCA jack

Step 3 – Thread 1st nut on to RCA jack and tighten it down. Make sure to center the jack in the panel since the panel holes are larger than needed for the standard jacks in order to also accommodate the larger optional Cardas jacks. The threads of the jack should not be touching the panel.

Step 4 – Slide ground ring on with tab facing up towards the top of the rear panel.

Step 5 – Tighten the 2nd nut on to RCA jack while holding the ground tab facing towards the top edge of the panel.

Repeat the RCA jack install steps above for each of the 10 RCA jacks. When completed the 10 jacks in the rear panel will appear as shown below.

V25 preamp kit rear panel

 

Rear Panel | Power, Trigger & USB

After installing the 10 RCA jacks you then need to install the Power Jack, Trigger Jack, and USB port. The pic below shows all three of these jacks installed and wired as viewed from both the inside of the rear panel (left pic)  and the outside of the rear panel (right pic).

All 3 are located on the right side of the rear panel. The Power Jack (12 VDC) is located in the larger top-most hole above the Trigger Jack (12V Trigger). The USB jack/cable mounts behind the rounded rectangular hole.

The Power Jack has  both a nut and a washer. The Trigger Jack has only a washer. Before tightening either orient each jack as with the solder tabs in the 12 o’clock and 6 o’clock position as shown below. Preferably use a socket to firmly tighten each nut. If you don’t have a socket carefully use pliers but be careful not the scratch the anodized finish while doing so. Do not over-tighten the nuts.

The USB jack/cable uses 2 #4 screws. In your kit these may either be machine type screws or sheet metal type screws. Either will work. It doesn’t matter which way the USB jack is oriented.

V25 preamp power, trigger, usb jacks

Power Jack Solder Tabs

Viewed from the rear of the jack, the Power Jack has 3 solder tabs as illustrated below. A heavy red positive (V+) voltage wire needs to be soldered to the top (12 o’clock) tab and a heavy black ground (Gnd) wire needs to be soldered to the right (3 o’clock) tab. The bottom tab is not used.

Solder a 8-10″ length of heavy red wire to the 12 o’clock tab and a 6-8″ length of heavy black wire to the 3 o’clock tab. Twist these wires together once you’re done soldering.

Be very careful that the soldered wires do not cross and touch each other or other tabs/parts of the jack. T

Trigger Jack Solder Tabs

Viewed from the rear of the jack, the Trigger Jack has 3 solder tabs plug a 4th switch tab as illustrated below. A light red positive (V+) voltage wire needs to be soldered to the top (12 o’clock) tab and a light black ground (Gnd) wire needs to be soldered to the bottom (7 o’clock) tab. The left (9 o’clock) tab is not used.

Solder a 8-10 inch length of light red wire to the 12 o’clock trigger out tab. Solder a 6-8 inch length of light black wire to the 6 o’clock trigger out tab. Twist these wires together once you’re done soldering.

Be very careful that the soldered wires do not cross and touch each other or other tabs/parts of the jack.

Rear Panel | Signal Ground Wires

Each standard RCA jack has its own ground tab with a hole in it. You are going to run a ground wire through each of the 5 ground tab holes for the right channel jacks and a separate identical ground wire through the ground tab holes for the left channel. This is shown in the pic below.

Take 2 x 10 inch lengths of heavy green wire and strip 4 inches of insulation off of each leaving the other 6 inches insulated. While making sure you don’t unravel the stranded end, thread the bare wire through each of the 5 tabs. When done, solder each tab to its ground wire.

Before threading the wire through the ground tabs holes, make sure each tab is aligned with the next tab and using pliers twist each tab 90 degrees so the holes in the 5 tabs line up. This will make it much easier to thread the ground wire through the tabs holes. 

Rear Panel | Signal Wires

Cut 9 x 4 inch lengths of signal wire from either the standard white stranded hookup wire or the optional solid Neotech wire.

Take 8 of these wires and strip roughly a 1/4-3/8″ of insulation off of one end only. Take the 9th wire and cut it in half into roughly 2 inch lengths and strip similar length of insulation off of both ends of both the shorter wires.

Starting with the bottom row (left channel) solder a single wire to each of the 3 left-most RCA jacks (the inputs) as viewed in the pic below. On the 4th RCA jack from the left (output jack 1 of 2)  twist the ends of a 4 inch and a 2 inch length of wire together and solder that twisted pair end to the 4th jack. Then solder the other end of the short 2 inch wire to the 5th RCA jack from the left (output jack 2 of 2).  Repeat this sequence for the top row of RCA jacks (the right channel).

 

V25 preamp RCA signal wires

At this point you are ready to proceed with connecting/soldering the rear panel wiring to the V25 board and the Star Ground. To proceed, place the rear panel along the edge of  the end of the Mounting Board with the rear panel’s wiring facing towards you. We suggest you place something heavy like a dictionary behind the rear panel so that it stands up facing you as shown above.

The wiring of the audio signals between the RCA jacks and the V25 board is illustrated below for a single input and output.  Follow the wiring termination schedule below for further details.

V25 preamp controller single-ended wiring diagram

Wire/Cable Termination Schedule

The following table lists each of the wires and cables and where each are to be connected either by soldering, plugging, crimping etc. You should have already partially or totally completed some of these already following the instructions above.

You are strongly encourage to refer to this schedule as a guide and checklist. One all of these connections have been made, you are all but done with your kit.

Wire/CableFromTo
Display Module Ribbon Cable #1Master (right) display module J3 (align red stripe with white dot on board)Slave (left) display module J3. (align red stripe with white dot on board)
Display Module Ribbon Cable #2Master (right) display module J1 (align red stripe with white dot on board)V25 board J3 (align red stripe with white dot on board)
Encoder Cable (4 conductor) | with DM1 Display ModulesMaster (right) display module J2 (pins A, B, S & G)Encoder module J1 (pins A, B, S & C)
Encoder Cable (4 conductor) | no Display Modules (direct from encoder to V25 board)Encoder module J1 (pins A, B, S & CV25 board J3 pins EA, EB, ES & G.
Power Jack | +12V Wire12 o'clock tab | heavy red wireCrimp pin that goes into 0.156" 2 position latching socket so that when socket plugs into the V25 board's J1 power pins the red wire is on the outboard side (next to+Vin label)
Power Jack | Ground Wire3 o'clock tab | heavy black wireStar Ground
V25 Board Ground WireStar Ground | heavy black wireCrimp pin that goes into 0.156" 2 position latching socket so that when socket plugs into the V25 board's J1 power pins the black wire is on the inboard side (next to U4 label)
Trigger Jack | +12V Wire12 o'clock tab | light red wireV25 board J4.Trig (solder)
Trigger Jack | Ground Wire6 o'clock tab | light red wireStar Ground
Rear Panel | Left Channel RCA Signal GroundDaisy chained bare wire through ground tab holes | heavy green wireStar Ground
Rear Panel | Right Channel RCA Signal GroundDaisy chained bare wire through ground tab holes | heavy green wireStar Ground
V25 Board | Left Channel Signal GroundV25 board LG solder padStar Ground
V25 Board | Right Channel Signal GroundV25 board RG solder padStar Ground
Left Input #3Rear Panel left-most bottom RCA jack pin | medium stranded white wire or optional Neotech solid wireV25 board LI3 solder pad
Left Input #2Rear Panel 2nd from left bottom RCA jack pin | medium stranded white wire or optional Neotech solid wireV25 board LI3 solder pad
Left Input #1Rear Panel 3rd from left bottom RCA jack pin | medium stranded white wire or optional Neotech solid wireV25 board LI1 solder pad
Left Output #1Rear Panel 4th from left bottom RCA jack pin | medium stranded white wire or optional Neotech solid wire (see Left Output #2 before proceeding)V25 board LO solder pad
Left Output #2Rear Panel 4th from left bottom RCA jack pin | medium stranded white wire or optional Neotech solid wire (see Left Output #1 before proceeding)Rear Panel 5th from left bottom RCA jack pin | medium stranded white wire or optional Neotech solid wire
Right Input #3Rear Panel left-most top RCA jack pin | medium stranded white wire or optional Neotech solid wireV25 board RI3 solder pad
Right Input #2Rear Panel 2nd from left top RCA jack pin | medium stranded white wire or optional Neotech solid wireV25 board RI3 solder pad
Right Input #1Rear Panel 3rd from left top RCA jack pin | medium stranded white wire or optional Neotech solid wireV25 board RI3 solder pad
Right Output #1Rear Panel 4th from left top RCA jack pin | medium stranded white wire or optional Neotech solid wire (see Right Output #2 before proceeding)V25 board RO solder pad
Right Output #2Rear Panel 4th from left top RCA jack pin | medium stranded white wire or optional Neotech solid wire (see Right Output #1 before proceeding)Rear Panel 5th from left top RCA jack pin | medium stranded white wire or optional Neotech solid wire
USB CableRear Panel | cable is molded to jack end which has been screwed into rear panelConnect 5 pin female header end into the V25 board's J8 pin header located on underside of left front corner of V25 board. Make absolutely sure that the RED wire of the female header is aligned with rear most J8 pin (the pin labeled Vbus).

The Finished Assembly

If you’ve completed all the above steps including all the wire/cable terminations per the above schedule, your finished assembly should look something like the pic below.

You are almost done! The final steps include inserting the finished assembly into the enclosure box, attaching the encoder to the front panel, attaching both the front and rear panel to the enclosure box and attaching the knob to the encoder.

LDR3.V25K kit internal assembly

 

Install Finished Assembly Into Enclosure

The enclosure box has a series of internal slots on both the left and right inner walls. The left and right sides of the Mounting Board will slide into these slots. You need to use the bottom-most slot!

V25 kit enclosure - internal

Slide the display end of the finished assembly into the enclosure box  using the bottom most pair of slots. The pic below shows a finished assembly on the left and and a finished assembly fully inserted into the enclosure box on the right except for final attachment of the rear panel to the box.

V25 preamp kit - inserting assembly into enclosure

 

Attaching Rear Panel

Gently press the rear panel into the enclosure box. Install a black #4 socketed sheet metal screw with washer in each corner of the rear panel making sure you engage the extruded screw hole in each corner of the box. Since the screw holes in the enclosure box are not pre-tapped you will use the screws themselves to create threads in the enclosure the first time they are fully screwed into place. This will take a bit of extra torque on the hex wrench. Subsequent removal and replacement of these mounting screws will be much easier. Snug down the screws but do not over-tighten.

The rear panel area should now look like the pic below.

V25 preamp kit rear panel

Attaching Front Panel

Turn the unit around with the front facing you. Remove the nut and washer from the Encoder and insert it through the back side of the acrylic front panel. The rear side of the front panel will have a milled recess around the hole for the Encoder. Slip the washer and nut on to the encoder and tighten the nut gently yet firmly. At this point the front panel and preamp should look something like the pic below.

V25 preamp kit - front panel install

The last step in the assembly process is to attach the front panel to the enclosure box. Use the same black socket head screws and washers that you used for the rear panel. Do not over-tighten the screws.

If you haven’t already done so, the final step is to attach the knob to the Encoder shaft. The knob has a set screw that must be aligned with the flat part of the encoder shaft. Tighten the set screw firmly. After the set screw is secure check that when you press in the encoder that it doesn’t bottom out against the face of the front panel. If it does, loosen the set screw and pull the knob out “a smidge” and tighten the set screw again.

At this point the front panel area should look like the pic below.

And you are DONE!LDR3.V25K passive preamp kit - front/side view

Troubleshooting

SymptomSuggestions
No response after applying power* Each V25 was fully tested prior to shipping so lack of response to being powered up is unlikely to be due a problem with the board proper.

* The V25 takes approximately 5 seconds to boot up after power is applied at which point it will briefly display a 4 digit firmware revision number and then turn off ready for normal use.

* Double check that 12 volt power is present at the J1 power connector and that the +V is being applied to the J1 pin closests to the edge of the board. Reversing this polarity can damage the power regulaor.

* Double check that wiring to the 12 volt power jack terminals is consistent with the instructions herein.

* Double check that the ribbon cable connecting the master display module to the J3 10 pin header is connected and that the red stripe on the cable is aligned with the side of the header with the white dot on the board.
Unit turns on automatically after applying power* The V25 takes approximately 5 seconds to boot up after power is applied at which point it will briefly display a 4 digit firmware revision number and then turn off ready for normal use.

* If the unit turns on after the boot up and firmware version is displayed then the cause is most likely that the encoder is wired backwards and is sending the board a turn-on signal. Reverse the wires to the encoder and retry.
Righ display works but left display remains off* Check that the ibbon cable is connected between the right and left display J3 headers. Confirm that the red stripe on the that ribbon cable is on on the top side at both ends.
Digits on 7 segment display are partially blank or corrupted* First check the brighness level setting and make sure brightness is set down to 10 or less.

* If problem persists after reducing brightness level, the problem is likely due to a bad ribbon cable between the board and the right display module or a bad ribbon cable betrween the right and left display modules. Replace as indicated.