The information below provides product documentation on all Tortuga Audio products.

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Tortuga Audio Preamps

General Information

1.Overview of LDR Preamps

LDR Preamp Products

Tortuga Audio’s passive preamp product line-up includes the following current models.

LDRx Passive Preamp

Custom enclosure with 3-5 input single ended with 2 parallel outputs |  internal power supply runs off 120 or 240 VAC mains

LDRxB Balanced Passive Preamp

Custom enclosure 3 input, dual output balanced preamp with additional RCA input/output | internal power supply runs off 120 or 240 VAC mains

LDR3.V2 Passive Preamp

3 input, dual output singled ended preamp in standard extruded aluminum enclosure with external power supply

LDR1.V2 Passive Preamp

Single input, dual output singled ended preamp in standard extruded aluminum enclosure with external power supply

LDR1B.V2 Passive Preamp

Single input, dual output balanced preamp in standard extruded aluminum enclosure with external power supply

LDR3x.V2.1 Preamp Controller Board

The V2.a preamp controller board for building DIY preamp projects.

Passive Attenuation 

Tortuga Audio preamps are unity gain preamplifiers that passively control audio volume by attenuating the source audio signal with light dependent resistors (LDRs) configured as LPad series/shunt voltage dividers. The LDRs are passive analog devices that are actively controlled by a digital control system. The term “passive” in this context means there is no amplification or electronic buffering of the audio signal nor is the audio signal acted upon by directly an external power source as happens in a conventional active preamp.

light dependent resistor gifLight Dependent Resistors (LDR’s)

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. The resistance of an LDR varies in proportion to the brightness of the LED which is in turn dependent on the electrical current running through the LED.  Volume control is achieved by regulating the current (brightness) of the LED within the LDR.

It is notable that the control circuitry never touches the audio signal electrically since the LED regulates with the photoresistor with light (photons) and not electrons.

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

Tortuga Audio LDR module
Tortuga Audio LDR Module

Why LDRs?

In many ways LDRs defy common audio wisdom. They are difficult to design around. They don’t necessarily have the best technical specs when compared to say high quality resistors. They even have higher distortion characteristics than most other alternatives. Nevertheless, LDRs provide the best overall sonic performance compared to all other volume control technologies.

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.

LDRs In Tortuga Audio Preamps

Tortuga Audio preamps utilize 2 LDR’s per channel in an LPad series-shunt configuration. The LDRs are controlled with a digitally driven analog circuit using a processor with proprietary software. Input impedance is maintained at or above a floor setting while simultaneously achieving an attenuation range between -60 and 0 dB. A total of 4 LDRs are used for single ended (unbalanced) stereo applications while 8 LDRs are used for balanced volume control. Additional LDRs are used as on-off switches (in lieu of relays) to select between multiple audio input signals. The LDRs used for attenuation are socketed and thus can be easily replaced (similar to an analog tube) if required due to normal aging. LDRs are expected to have a useful life of approximately 50,000 hours similar to light emitting diodes.

Adaptive Auto-Calibration of LDRs

Using LDRs in audio applications is technically challenging because the relationship of current vs. resistance within 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 requires testing individual LDRs to find matching 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, 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 LDRs is an essential part of this technology.

In May, 2014 Tortuga Audio released its LDR3x.V2 Preamp Controller (the “V2”) which utilizes adaptive auto-calibration technology. Auto-calibration 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. This calibration feature distinguishes Tortuga Audio from all other companies and products that use LDRs for audio volume control. Auto-calibration is a closed loop system employing both DACs (digital to analog converters) and ADCs (analog to digital converters) to calibrate each LDR against an absolute 70 step attenuation schedule. Calibration results are stored in memory tables and then used to accurately control each LDR during normal operation. Overall left/right channel balance accuracy is generally within 0.2%.

Adjustable Input Impedance

In January 2015, Tortuga Audio added adjustable input impedance to its line of LDR passive preamps. Impedance is adjustable between 1k and 99k ohms. The user may configure up to 5 different impedance settings with different impedance levels and switch between these while listening to music. Adjustable impedance is a unique Tortuga Audio feature that allows the discriminating user to optimize the impedance bridging ratio between audio source and amplifier.

Digital Control of an Analog System

Tortuga Audio LDR preamps are software driven digitally controlled analog volume control devices. The digital processor and related control circuitry are optically and electrically isolated from the audio signal. The processor calibrates and stores the software based attenuation schedule, regulates the LDRs for volume control, switches inputs, provides status/display information, and manages user control input via both a remote and a manual encoder located on the front panel. The controls system is driven by proprietary software. As of May, 2014 V2 based preamps can have their firmware updated by the owner via a USB connection to a PC.

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Last updated on Feb 13, 2017

2.Attenuation and Impedance

Attenuation

Volume control with an LDR is conceptually similar to a potentiometer.  Both are voltage dividers that reduce (attenuate) the incoming voltage signal which is how volume is controlled. In LDRs, attenuation is achieved by varying the resistance levels of the series and shunt LDRs to achieve specific resistance ratios that correspond to specific dB attenuation levels. The resulting resistance ratio divides the voltage level of the incoming audio signal according to the formula: Vout = Vin x Ratio.  Alternatively, Ratio is defined as: Ratio = Vout/Vin. The resistance Ratio is also defined by the formula: Ratio = Rshunt/(Rshunt + Rseries). Putting all this math together the resulting signal attenuation expressed in decibels is defined as: dB = 20 x log(Ratio) or if you like dB = 20 x log (Vout/Vin).

basic volume control schematic

All Tortuga Audio preamps use the same 70 step attenuation schedule from ~60 dB to 0 dB. Each step is slightly greater than 0.9 dB up until -5 dB (step 60) at which point the step size is reduced to 0.5 dB for the remaining steps 61 through 70. This reduction in steps size mitigates the very large changes in sound pressure per step as attenuation approaches 0 dB. This attenuation schedule is illustrated in the graph below in the gray trace labeled dB.

Input Impedance

The Ratio discussed above could be achieved for each dB step by a wide range of specific series and shunt resistance values. However, since we also want to maintain a specific constant input impedance the absolute resistance values are constrained insofar as the sum of the series and shunt resistances must equal our target input impedance. If we want to maintain a minimum 20k ohms input impedance, the Rseries and Rshunt must always equal at least 20,000 ohms for each of the 70 steps between -60 dB and 0 dB.

The graph shown for a 20k attenuator shows the impedance level in green across the full 70 step (60 dB) range of the attenuator. The input impedance declines from 100k down to 20k by step 16 (-46 dB) and than remains constant over the remaining attenuation range. The reason the input impedance increases as volume drops below step 16 is because the design limits the minimum resistance of the LDRs to 100 ohm (to preserve their useful life). With the shunt LDR limited to a minimum of 100 ohms, the series LDR has to reach 99,900 ohms in order to achieve -60 dB of attenuation. If the LDRs could safely achieve a minimum of say 10 ohms, then the input impedance curve would be a constant 20k across the entire control range.

ldr3x.v2 attenuation and impedance curves

 

Output Impedance

With this type of attenuator the output impedance is neither fixed nor is it independent from the input impedance. As is clear in the above graph (yellow line), the output impedance varies with each step in the attenuation.

The output impedance is 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 ~5,000 ohms (25% of the nominal input impedance) corresponding to step 59 or -6 dB of attenuation.

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Last updated on Sep 10, 2016

3.Adjustable Impedance

What Is Adjustable Input Impedance?

Adjustable Input Impedance is a new feature introduced with version 2.1 of our passive preamp firmware. This feature allows the user to change the default 20k input impedance of Tortuga Audio preamps to anywhere from 1k to 99k ohms.

Why Would I Want To Change Input Impedance? 

Some combinations of source (DAC, CD transport, phono stage etc. ) and amp may benefit from changing the input impedance of the passive preamp. 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 say 100K? 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.

In most cases the target 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

The Tortuga Audio firmware 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.

Impedance #1 is 20k by default. LDR preamps shipped with the 2.1.0 firmware are already set up this way. 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.

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 setting them up you will get no output from the preamp. 

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 say 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. 

The procedure for changing and existing or setting up a new impedance setting or changing the impedance level in a setting already setup is listed below. There are 2 procedures listed, each slightly different that the other. The first is for V2 boards with firmware version 2.1.x. The second table is for the more recent version 2.2.x firmware.

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.
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.

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 tto 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.

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Last updated on Sep 19, 2016

4.Auto-Calibration

Overview

AutoCal is a significant development in the evolution of LDR based volume control. AutoCal eliminates the need to test and match individual LDRs. Most importantly, together with replaceable plug-in LDR modules, AutoCal ensures that your Tortuga Audio preamp will continue to operate indefinitely.

Auto Calibration (AutoCal) was introduced with version V2 of the LDR3x Passive Preamp Controller Board. The characteristics of AutoCal are as follows:

  • AutoCal automatically calibrates the resistance values of the LDRs in the LDR3x against a defined 70 step attenuation schedule.
  • AutoCal is a self-contained software driven calibration process that doesn’t require any external equipment.
  • AutoCal ensures that the LDR preamp will continue to perform optimally as LDRs age and their performance curves shift over time or if an LDR has to be replaced.

Running Auto Calibration

The following summarizes how the current version of AutoCal works. 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 Do’s and Dont’s 

We recommend the following:

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.

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Last updated on Sep 11, 2016

5.Common Specifications

 

All Tortuga Audio LDR preamps have the following specifications in common:

  • Preamplifier Type: Passive stereo attenuator
  • Input/Output Buffering: None
  • Attenuation Technology: Resistive attenuation via light dependent resistors in series/shunt (L-Pad) configuration
  • Attenuation Range/Increments: Discrete 71 steps (70 + mute) between -60 dB and 0 dB (see Attenuation & Impedance)
  • Gain: Unity gain (1.0x) – no active amplification
  • Audio Signal Isolation: Audio signal optically isolated from from control power but may share common ground
  • Total Harmonic Distortion: 1% or less
  • Left/Right Channel Deviation: 0.4 dB or less
  • Control System: 8 bit 16 MHZ software driven digital microcontroller which controls all analog circuitry & communications
  • Printed Circuit Boards: Nickel immersion gold PCB with  blue solder mask
  • Lead Free Silver Solder:  Lead free  3% or greater silver content solder
  • ROHS: Compliant or exempted
  • Operating Ambient Temperature: Stable, dry indoor environment with ambient temperature within 60-90 degrees F
  • Trigger Out: Outputs 12 VDC signal when unit is turned on
  • Encoder (Panel) Control: Rotary 30 step/rev mechanical encoder with integral push button switch
  • Remote Control: Infrared remote | 38kHz | NEC protocol
  • Control Functionality: 
    • Power On/Off toggle
    • Volume Raise/Lower
    • Mute/UnMute
    • Channel Select
    • Channel Balance Adjust
    • Channel Balance Reset
    • Display Brightness Adjust
    • Auto Calibration Start/Stop
  • Control Device Details: 
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Last updated on May 13, 2016
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Remote & Encoder Controls

1.The Apple Remote

tortuga audio apple remote control buttons

The Apple Remote

All Tortuga Audio preamp products use the elegantly simple Apple remote shown above for remote control. The sections below describe how to use the Apple remote to control your Tortuga preamp.

2 Control Versions

While there is only 1 version of the silver Apple remote itself, there are 2 slightly different control scheme versions depending on when your preamp was built and shipped and depending on which version of firmware your preamp has.  These version are 2.1 and 2.2. (sometime also referred to as 2.1.x and 2.2.x).

Version 2.1

Version 2.1 applies only to V2 and V2.1 Tortuga Audio preamps shipped prior to May 15, 2016 which have also not already been upgraded to version 2.2 firmware.

Version 2.2

Version 2.2 applies to all Tortuga Audio preamps shipped starting May 15, 2016

Which Version Do I Have?

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 3-4 numbers. These numbers will be either 2.1.x or 2.2.x 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.

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Last updated on Sep 19, 2016

2.Version 2.2 Remote Control

tortuga audio apple remote control buttons

Applicability

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.

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 graphically, and as a list of functions and as a list of control buttons.

Graphical Summary
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

List of Controls
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.
List of Buttons
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

 Key Changes From Version 2.1 (as of revision 2.2.5)

The key changes from the earlier 2.1 Apple remote control scheme include:

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.

The 4 control modes include:

  • 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.

Other Changes In 2.2

  • 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.
  • Improved control integration between preamp boards for balanced audio configurations
  • Enhanced stability through numerous tweaks under-the-hood
  • Better protection against spurious infrared noise sources that might cause false control input

Regarding the Tortuga Audio legacy remote

The 2.2 firmware series has retained the ability to use the Tortuga Audio legacy remote in addition to the Apple remote. However, the Balance and Balance Reset buttons are no longer active on the Tortuga remote. Also, all of the 6 input select buttons now function the same as the Control Mode button on the Apple remote. The Tortuga remote still retains the functionality of its Mute button. Please note also that the auto-repeat feature of the Tortuga remote work differently than the Apple remote insofar as the Tortuga remote issues auto-repeat commands much sooner and faster than the Apple so use only deliberate and quick button presses with the Tortuga remote.

 

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Last updated on Sep 10, 2016

3.Version 2.1 Remote Control

 

Apple remote buttons

 

Applicability

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.

Control Buttons

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.
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Last updated on Sep 10, 2016

4.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.

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Diagnostics & Maintenance

website area under construction
We are working on an easy to follow diagnostics procedure which will be added here when it’s ready. Meanwhile, here’s a highly abbreviated summary of the 2 most common problems.

As with  tubes in a tube amp, the most likely cause of a true hardware problem with your Tortuga Audio preamp is a failed or out of spec LDR. Fortunately, the primary LDRs are plug-in modules that can be easily removed and replaced.

The second most likely problem with you Tortuga Audio preamp is neither a hardware nor a software problem but a simple matter of having switched the impedance setting (1-5) to a number that has not yet been set up. The symptom is no audio output. This is due to the attenuation table being empty. To correct this problem change the impedance setting back to setting #1 which is the original default setting. Please refer to the General Information section of this documentation for more info on Adjustable Impedance.

1.Pre-Calibration

Caution - Read Carefully!
Done correctly, PreCal works. However, DO NOT attempt to PreCal your preamp unless you’ve carefully studied the instructions below and have the required resistors or pre-calibration modules. If you’re not generally comfortable tinkering around with electronics or are not DIY (do-it-yourself) oriented, we suggest you not attempt PreCal. Performing PreCal incorrectly will not permanently damage your preamp but it will very likely make your preamp unusable until such time as you perform the PreCal process correctly.  If you attempt to perform PreCal on your preamp and you mess it up, Tortuga Audio is not responsible for correcting the problem. 

What Is Pre-Calibration (“PreCal”)?

PreCal is a method of calibrating the four LDR channels on the LDR3x preamp controller using 100 ohm and 100k ohm precision calibration resistors in order to improve the overall accuracy of the auto-calibration results and thus the performance of the preamp. Without PreCal the auto-calibration measurement circuit and normal control circuit will be less accurate.  These inaccuracies are an inherent part of any electronic measurement circuit and is why calibration is a normal part of setting up and using measurement electronics.

Does my Tortuga preamp require PreCal?

PreCal is a normal part of Tortuga Audio’s commissioning process for each LDR preamp starting with the release of version V2.1 of the LDR3x preamp controller board on January 5, 2015. If you already own an LDR3x.V2.1 board or any Tortuga preamp product shipped on or after January 5, 2015 your board/preamp has already gone through PreCal and repeating the process is not necessary. 

If you own a V2 version of the LDR3x or any Tortuga preamp built with the V2 board, then your preamp will likely benefit from PreCal. PreCal only needs to be performed once.

How do I perform PreCal on my preamp?  

Done correctly PreCal only takes a few minutes. While the  following instructions would benefit from pictures, at present there is only text so please read carefully and do not proceed unless you are sure you understand each instruction.

Orientation (critical!)

Looking at the V2.1 board, the “front” of the board is the end with the large rectangular controller chip, and conversely the “back” of the board is the end with the 4 LDRs. The following instructions assume you are facing the front of the board looking towards the back where the LDRs are located. Going from left-to-right, the 4 LDRs are identified as follows:  RV4   RV3  RV2  & RV1.  These identifiers are printed on the circuit board.  The PreCal sequence is #1-RV3, then #2-RV4, followed by #3-RV1 and finally #4-RV2.

Required Equipment (critical!)

  1. Dual display modules are required. While you might get away with just a single display module it’s too easy to get confused so we don’t recommend it.
  2. 4 0.1% accuracy 100 ohm resistors connected to female square pin sockets on each end
  3. 4 0.1% accuracy 100,000 (100k) ohm resistors connected to female square pin sockets on each end
  4. Alternatively to 2) and 3), you an purchase a set of precision PreCal modules from Tortuga Audio.
  5. Apple Remote

PreCal Procedure

StepActionHow
1Disconnect audio inputsRemove all input/output interconnects from the preamp
2Connect preamp to powerAllow unit to boot up - wait until the display stops showing numbers
3Confirm preamp is offThere should be no numbers showing on the displays
4Remove the LDRsPull out each of the 4 LDRs and set them aside in the same order that were installed. At this point you’ll notice the 4 square male pins to which each LDR module had been attached. The 2 back pins are involved in the PreCal process while the 2 front pins are not.
5Install the 100 ohm resistorsIf you are using your own resistors, connect the 4 100 ohm resistors across the 2 back pins of each of the 4 LDR pin headers. If you are using Tortuga Audio supplied PreCal modules plug the 4 modules in such that the larger/fatter resistor is facing towards the rear of the board and the smaller/skinny resistor is facing forward.
6Start auto-calPress the Center/Enter button on remote or give the Encoder a quarter to half a turn. Unit should commence auto-cal with displays showing status.
7Switch to PreCal modePress the Left button on the remote deliberately 3 times in a row pausing briefly between each press (prior to rev 2.2.3 firmware press the Raise button). You can tell the unit is in PreCal mode because the display modules will show different info than is typical of auto-cal. At this point PreCal will be on LDR #1-RV3. The left digit on the left display module will show “1”. The right digit on the left display module together with both digits on the right display module form a 3 digit number indicating the calibration factor needed to read 100 ohms. By way of example, if the 4 digit display shows 1950 this means LDR #1 requires a -5% correction factor. If it shows 1132 then this means LDR #1 requires a +13.2% corrector factor. You don’t need to record these values. They are saved in the units’s memory.
8Allow #1 LDR’s (RV3) correction factor to stabilizeEven though the 3 digit number will most likely continue to change up or down it should stabilize within a min/max range rather than continue to count up or count down endlessly. It should stabilize within just a few seconds. If the number continues to increase (or decrease) continually for more than 10 seconds without reversing the cause is most likely improper grounding of the audio signal ground from the controller board to system star ground. If this happens remove power from the unit to shut if off and diagnose/correct the problem before attempting PreCal again. While this is unlikely to happen with a finished preamp product, this type of grounding problem is not uncommon with DIY versions of the LDR3x preamp controller board due to the DIY’er not grounding the unit properly.
9Switch to #2 LDR (RV4)Press the Right button on the remote to switch to the next LDR. The left digit on the left display will change from #1 to #2.
10Allow #2 LDR correction factor to stabilize(see #8)
11Switch to #3 LDR (RV1)Press the Right button on the remote to switch to the next LDR. The left digit on the left display will change from #2 to #3.
12Allow #3 LDR correction factor to stabilize(see #8)
13Switch to #4 LDR (RV2)Press the Right button on the remote to switch to the next LDR. The left digit on the left display will change from #3 to #4.
14Allow #4 LDR correction factor to stabilize(see #8)
15Switch to #1 LDR (RV3)Press the Right button on the remote to switch to the next LDR. The left digit on the left display will change from #4 back to #1.

At this point you have completed pre-cal with 100 ohms and need to switch the resistors from 100 ohm to 100k ohm before proceeding to next LDR.

Until switchover to 100k ohm resistors is completed at least for LDRs #1 and #2, the numbers show on display for #1 LDR will continue to change. Ignore the display until resistor switchover to 100k is done on all four LDRs.
16Switch resistors from 100 ohm to 100k ohm on all LDRs starting with LDRs #1 and #2.Once all resistors have been switched over to 100k ohm the display values for LDR #1 will begin to stabilize. The longer you took to switch over the resistors the longer it will take for LDR #1 to stabilize.
17Repeat steps 8 through 14Same procedure as before but this time with 100k resistors for each of LDRs #1 through #4.
18Quit PreCal processWhen LDR #4 has stabilized, press the right button on the remote one more time. This will save the PreCal results in memory, turn off PreCal and shut off the preamp. This completes the PreCal process.
19Replace LDRsRemove the four precision resistors or resistor modules and reinstall the four LDRs
20Run AutoCalPress the Enter button and allow the unit to go through a complete AutoCal cycle. Once AutoCal is finished, you are done.
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DIY Components & Kits

2.LDRx.V2 Preamp Controller

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Last updated on May 13, 2016

2.1.V2 Overview

ldr3x.v2 replaceable ldr modulesWhat’s New With The V2?

The biggest change in the V2 compared to the V1 is the introduction of Auto Calibration as well as replaceable LDR Modules. Auto Calibration 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.

A DIY 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 is marketed to the do-it-yourself (DIY) audio enthusiast who wishes to build their own preamp. The V2 builds on the experience and success of the popular 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 that the user can either solder to the V2 board or locate external to the board via user provided wiring.

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

The LDR3x.V2 is part of the Tortuga Audio family of LDR based passive preamps. Please refer to documentation under LDR Preamps – Common Info for more information that applies to all Tortuga Audio passive preamps including the V2 preamp controller board.

Unbalanced Audio (single board)

A single V2 board operates as a standalone passive preamp for single-ended unbalanced 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:

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Last updated on May 13, 2016

2.2.V2 Specifications

 

The specifications for the  LDR3x.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. See optional IO3 input relay 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 micro USB port on the V2 board.
  • USB Port:  Micro 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. See Auto Calibration for more detail.
  • 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

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Last updated on Feb 08, 2017

2.3.V2 Controls

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
J2-IR – IR Receiver

The LDR3x.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.

J2-ST – Status LED

J2-ST is an output signal that when connected to an LED provides status information on the LDR3x. 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.

J2-ES, J2-Ea & J2-Eb – Encoder Inputs

These 3 inputs are for interfacing the LDR3x 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. Additional info on the Alps EC11 series encoders can be found here. 

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.

Essential Function Requiring Encoder J2-ES Connection

There is one control function that can only be done via the Encode switch or other switch connected via J2-ES. This control function involves teaching the LDR3x.V2 the ID of the Apple Remote after the ID has been changed to avoid conflicts. Please refer to the section above on the Encoder for details on the control functions and operations provided by a rotary encoder connected to ES, Ea and Eb.

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Last updated on Aug 18, 2016

2.4.V2 Balanced Audio

Master & Slave Boards

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

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2.5.V2 Wiring

Please note that this section underwent substantial revision as of 9.20.14 resulting in numerous changes to prior guidance. Owners of V2 and V2.1k versions of the LDR3x preamp controller board are encouraged to read this section carefully.

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?

V2 Audio Signal Grounding is Essential 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

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.

Screw Terminals vs. Solder Pads

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

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. 

Balanced Signal Grounding

By definition, balanced signals are not referenced to ground. Nevertheless, as explained above, both the left and right audio signal grounds on the V2 must be connected to star ground to ensure proper functioning of Auto Calibration.

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

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2.6.Status LED

Models LDR1, LDR3, LDR6, LDR3x.V1 and LDR3x.V2  have a Status LED feature or optional output that can be connected to a Status LED. The Status LED conveys the following information:

Off:  Unit is turned off but may or may not be connected to power.

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.

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3.LDR3.V2K Preamp Kit Assembly

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3.1.Kit Overview

LDR3.V2 passive preamp - internal assembly

LDR3.V2K Single Ended RCA Kit

The LDR3.V2K Passive Preamp Kit (the “kit”) is a 3 input, 2 output (parallel) single-ended audio preamp with RCA type input/output jacks.

The kit consists of the components and subsystems listed below. There are additional items supplied with the kit but they are related to one or more of these items.

  • Enclosure Box
  • Mounting Board
  • Front Panel
  • Rear Panel
  • Preamp Controller Board
  • IO Board
  • Display
  • Star Ground
  • USB Cable
  • Power Supply

The photo above provides a side view of everything mounted on the Mounting Board along with the rear panel (sans front panel, enclosure box and power supply). Please note that the above photo shows a different IO board than is used in the kit and the rear panel shows the optional upgrade to Cardas RCA jacks but the kit is conceptually identical to what is shown.

The kit assembly instructions provided herein are far from comprehensive and is in the form of descriptive narrative text with a few supporting pictures and diagrams. We hope to add videos and photos in the future.

Once fully assembly and wired properly the preamp kit will function without any tuning or adjusting. Without a doubt the biggest challenge most of you will have is getting the wiring right.

The kit assembly process is summarized in the following sequence:

  1. Attach display bar to mounting board
  2. Attach display modules to display bar
  3. Add cables to display modules
  4. Attach encoder to display module cable
  5. Attach preamp controller board to mounting board via standoffs
  6. Attach IO board to preamp controller board via 90 degree pins and screw terminals
  7. Install RCA jacks in rear panel
  8. Install power jack in rear panel
  9. Install 12V trigger jack in rear panel
  10. Install USB cable in rear panel
  11. Install star ground standoffs and bus bar wire
  12. Wire everything together
    1. Plug display ribbon cable to preamp board
    2. Solder audio signals from RCA jacks to IO board
    3. Solder audio ground wire to left channel RCA jacks – other end to star ground
    4. Solder audio ground wire to right channel RCA jacks – other end to star ground
    5. Solder audio ground wire to left channel preamp board – other end to star ground
    6. Solder audio ground wire to right channel preamp board – other end to star ground
    7. Solder power ground to power jack – other end to star ground
    8. Solder 12V trigger ground to 12V trigger jack – other end to star ground
    9. Attach power ground wire to preamp board screw terminal – other end to star ground
    10. Attach power positive wire to preamp board screw terminal
    11. Attach 12V trigger positive wire to preamp board screw terminal
    12. Plug IO ribbon cable between preamp board and IO board

The sections the follow below provide additional detail regarding the above assembly sequence.

LDR1B.V2K Balanced XLR Kit

The LDR1B.V2K balanced kit is essentially the same as the LDR3.V2K kit except for the following differences.

  1. The balanced kit uses 2 rather than just 1 LDR3x.V2 preamp controller boards
  2. The balanced kit has a balanced input (1) and balanced outputs (2 in parallel)
  3. The balanced kit has no input switching relay

The descriptions and assembly instructions below are specific to the LDR3.V2K but are almost entirely relevant to the LDR1B.V2K as well. Without a doubt the balanced kit is more complex insofar as balanced audio is inherently more complex when it comes to the wiring of the XLR inputs and outputs.

In wiring a balanced system, one LDR3x.V2 board is designated as the master and becomes the board for the right channel only. The second LDR3x.V2 board is designated as the slave and is for the left channel only. Builders need to pay close attention to the wiring diagram below which shows these differences.

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3.2.Preamp & IO Boards

ldr3x.v2 passive preamp controller board - top view
preamp board
IO3.2 Input Relay Board - Top View
IO3 board (not to scale)

Please note that we have changed the IO3 board slightly by eliminating the two 3-screw terminal blocks J1R and J1L and have replaced these with two sets of 3-pin headers which are soldered in place. These pins go into the J1R and J1L screw terminal blocks located on the preamp controller board.

Components

The preamp and IO board consists of the following items:

  • LDR3x preamp controller board
  • IO3 input relay board
  • 2 3-pin headers
  • 4 aluminum standoffs
  • 8 metal screws
  • long IO3 control ribbon cable

Assembly Instructions

In summary, the preamp board mounts to the mounting board via 4 standoffs and the IO3 mounts vertically to the preamp board via a pair of 90 degree connector pins. The IO3 control ribbon cable connects the preamp board to the IO3 board.

There are 4 holes in the mounting board that match the corner mounting holes of the preamp board. Install standoffs in each of these holes. Place the preamp board on to these standoffs making sure to orient the preamp board is oriented with the end with the large microcontroller chip facing the front of the mounting board (the end with the display assembly). Screw the preamp board on to the standoffs.

The IO3 board attaches to the preamp board via the J1R and J1L screw terminals using the two 3-pin 90 degree connector pins. When completed the IO3 board is mounted vertically on the preamp board. Make sure that all of the screw terminal screws are tightened.

The IO3 control ribbon cable connects from the 5 pin J7 terminal on the preamp board to the 10 pin J2 header on the IO3 board. Make sure the red line on the ribbon cable is oriented on the same side as the white dot on both J7 and J2. Also, since J7 is only a 5 pin header and the cable has a 10 pin connector it’s possible to connect the cable to J7 incorrectly. If you find that the IO3 relay board isn’t working, try plugging the cable into J7 via the other 5 pin row of the connector.

We recommend the IO3 control cable remain unconnected until after the rest of the wiring is completed.

This completes the install of these two boards except for the wiring which is discussed later below.

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3.3.Display Assembly

Components

The display assembly (the “DA”) consists of the following items:

  • pre-drilled right angle plastic mounting bar
  • 2 display modules (master and slave)
  • encoder module
  • ribbon cable from master to preamp board
  • ribbon cable from master to slave
  • 4 conductor square pin cable from master to encoder
  • 4 threaded nylon rods
  • 8 nylon washers and 4 spacers
  • 2 metal screws with nuts

Assembly Instructions

In summary, the display bar mounts to the mounting board and the 2 display modules mount to the display bar. The display modules are connected together with a ribbon cable and the master display module eventually gets connected to the preamp board via a ribbon cable. The encoder connects to the master display module via a 4 conductor cable.

Orient the mounting bar such that the 4 holes are facing you and the bottom leg of the bar is facing away from you. Mount the bar to the front of the mounting board (where there are 2 holes near the front edge) using 2 short metal screws and nuts. It’s easier to put the screws down through the bar/board and put the nuts on the underside of the mounting board.  At this point the display mounting bar should be firmly attached to the front of the mounting board.

There are 2 display modules. One is the master and the second is the slave. They are same size but differ in that the master has obviously more components compared to the slave. The master is the “right” display and the slave is the “left”. They should be mounted on to the mounting bar accordingly.

Be careful not to mount the displays upside down. Observe on each 2 digit 7 segment display that the periods (dots) between the numerals need to face downward when mounted to the mounting bar.

Each display module is mounted on the mounting bar using 2 threaded nylon rods. Thread a nylon nut on to each rod with just enough turns to be firmly on the rod. Place the 2 rods through the 2 bottom mounting holes on the display module from the backside of the display (the side that doesn’t have the 2 digit display) so the rods face forward. Then slip a nylon spacer on to each threaded rod. At this point you should have a nut-board-spacer sandwich with the nut on the back side of the display module.

Take the display module with the 2 threaded rods and put the assembly through mounting bar holes from back to front. At this point the 2 threaded rods should be facing out towards the front of the mounting bar and the bottom edge of the 2-digit 7 segment display should be resting on the edge of the mounting bar. Now thread a nylon nut on to each threaded rod and tighten both nuts until the display module is firmly fastened on to the mounting bar. Use some cutters or scissors to nip off the excess plastic threaded rod. Repeat this process with the slave module on the left side of the mounting bar.

There are 2 short ribbon cables and 1 4-conductor square pin cable

Connect one ribbon cable to pin header J1 on the master board and leave the other end disconnected for now. Note the red line on one side of ribbon cable. The red side of the cable should be on the same side of J1 where you see the white dot.

Connect the second ribbon cable to J3 on the master board and also to J3 on the slave board. Make sure the red line on the ribbon cable is on same side as the white dot on J3 on both boards.

Connect the 4-conductor pin cable to the 4 pins on header J2 of the master board. Note the labels A B S G on J2. Now look at the encoder module. Note that the encoder module has the same labels. Connect the other end of the 4-conductor cable to the matching pins on the encoder module.

At this point you are done with the display assembly.

Front and back view of the display module

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3.4.Rear Panel

Components

The rear panel assembly consists of the following items:

  • LDR3.V2 rear panel
  • 10 RCA jacks
  • power jack
  • 12V trigger jack
  • USB cable
  • 4 black socket head screws with matching black washers

Assembly Instructions

In summary install the 10 RCA jacks, power jack, trigger jack and USB cable into the appropriately labeled holes in the rear panel.

When installing the RCA jacks make sure to sandwich the plastic insulation washers on either wide of the panel hole. Also, make sure to orient the holed tab on each of the thin ground washers such that the tabs line up in the same position (either 12 o’clock or 6 o’clock).

Also, the holes for the RCA jacks are larger than necessary for the standard kit jacks (sized to fit the Cardas upgrade jacks). Therefore, you will want to make sure each standard jack is centered within each hole before tightening the retaining nut.

At this point the assembly of the rear panel is complete but for the wiring which is covered below in a separate section.

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3.5.Wiring

Components

Wiring is where everything comes together and becomes a functional whole. To proceed with the wiring you’ll need….everything!

  • Mounting board assembly with controller board, IO board & display modules installed
  • Rear panel assembly
  • IO3 ribbon cable
  • 2 star ground standoffs & 4 screws

Assembly Summary

(TBD)

Star Ground

Before preceding with wiring, it’s helpful to have a conceptual overview of what you are wiring and why. Arguably the most critical yet often most confusing and sometimes challenging aspect of wiring up audio electronics is the grounding. The approach used in Tortuga Audio designs, including your kit, is called star grounding.

Star grounding embodies two simple ideas: 1) everything that needs to be connected to ground gets its own pathway to the star ground point (no daisy chaining); and, 2) there is only one physical ground point to which everything that needs grounding gets connected.

The schematic below illustrates star grounding as well as how to connect a single channel RCA input/output to the preamp controller board. For the sake of simplicity, the IO3 Relay Board is left out of this illustration. Note how all the individual ground wires are routed to a single ground point, the “start ground point”. Note also that we break one of the rules of star grounding in this graphic. Can you spot it?  With both the left and right RCA jacks we are daisy chaining the grounds rather than running individual ground lines from each jack. This is acceptable in practice and avoid excessive ground wires while still avoiding ground loop issues.

Instructions:

To make your star ground point screw the 2 remaining standoffs to the mounting board. For the LDR3.V2K the star ground holes are located to the right of the preamp controller board. For the LD1B.V2K the holes are located on the left rear of the mounting board. In either model, they should be the only 2 remaining pre-drilled holes in the mounting board.

Next, thread the 2 remaining screws into the top of the 2 star ground standoffs but thread them down only half way (don’t tighten). Strip a roughly 2 inch long piece of wire from the heavier green or black wire provided such that you now have bare wire with no insulation. Twist the wire around each of the 2 standoff screws so that you now have the bare wire suspended between the 2 standoffs and wrapped around each screws at least 1 turn. Now tighten both screws to lock down the wire to the standoff. Snip off any excess wire.

This wire suspended between the 2 standoffs is your star ground point. You are going to attach each ground wire to this star ground wire and solder them in place.

At this point the setup of your star ground point is complete.

LDR3x.V2 audio, power and ground wiring

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

Power Jack Wiring

Orient the rear panel at the back end of the mounting board such that all the termination points of the RCA jacks etc. are facing forward. Locate the power jack on the upper left side of the rear panel. If necessary loosen and rotate  the power jack such that the 3 pins are oriented at noon, 3 o’clock and 6 o’clock and then retighten the retainer nut.

Note that the positive 12V pin is at noon and the ground pin is at 3 o’clock. The 6 o’clock pin remains unconnected.

Using the red wire, connect the noon pin on the power jack to the +12 slot on the J6 termination block on the preamp controller board. Be careful that you don’t accidentally terminate to the 12T slot. Use either the black or green wire, connect the 3 o’clock ground pin on the power jack to the star ground point.

This completes the wiring of the power jack.

12V Trigger Out

(TBD)

Input & Output Wiring

(TBD)

IO3.2 Input Relay Board - Top View

ldr3.v2k kit input/output wiring diagram

USB Port Wiring

(TBD)

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4.Other DIY Components

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4.1.Encoder

Overview

In addition to remote control, all Tortuga Audio preamps are also controllable via a control knob located on the right side of 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.

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).

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4.2.DM1 Display Module

DM1 Display Module - Front and Rear ViewsOverview

The Display Module (“DM1″) is a 1.8 inch x 1.8 inch circuit board (1.55 inch x 1.55 inch holes – #6 screw) with a 0.56 inch tall, 2 digit, 7-segment numerical LED display that can be interfaced with the LDR3x Preamp Controller Board to provide numerical/visual feedback of the volume level and other status information of the LDR3x.

The DM1 board has components on both sides. The forward facing side has the actual 2 digit LCD display while the rear side has all other components including the control interface pin-headers  J1, J2 and J3 discussed below.

Display Information

Control ModeLeft Display Module

Right Display Module
Volume Control (default)Left channel volumeRight channel volume
Channel SelectCurrent channelNew channel being selected
MuteCurrent volume settingActual volume. 0 went muted. Displays ramp down/up during mute and unmute.
Balance AdjustCurrent volume2 digits wherein 00 indicates neutral, 90 indicates bias of 9 steps towards the left, and 09 indicates bias of 9 steps towards right
Brightness AdjustCurrent volumeBrightness level between 1 (dim) and 15 (bright)
Auto-CalibrationCurrent LDR being calibrated 1-4Current calibration step 1-70
Pre-CalibrationSetting number (1-5)Alternately, setting number (1-5) and impedance level (1k-99k)

The above display information should correlate with the various control modes and actions outlined in the remote control section of this documentation.

Dual DM1 Display Modules behind dark gray acrylic

Mounting

There are two ways to mount the DM1 module(s). The first is to mount the module the back side of an enclosure’s front panel via standoffs that are either glued or screwed into the front panel. The second way is to mount the modules to the floor of the enclosure immediately behind the front panel  using a plastic (insulated) angle bracket. Ideally, the DM1 is mounted behind a dark gray acrylic plastic lens such that it would be visible while on and effectively invisible when off. A entire front panel made of say 0.25″ thick dark acrylic plastic makes for both an attractive front panel and a natural lens behind which the display modules can be mounted. 

Please Note: Tortuga Audio does not provide any mounting fixtures, templates or hardware. 

DM1 Display Module - Rear View

Control Interfaces

The DM1 is a two-sided board where the front side has the actual 7 segment LED display. There are no control interfaces on the front side.  The back side of the DM1 has all the control interfaces. These are listed and explained below.

J1 – main control header – This is the primary control interface between the LDR3x and the DM1 master board. There is no J1 on the slave version.

If you are connecting the DM1 to the LDR3x board using individual female square pin connectors, there are five “required” signals listed below must be interconnected with corresponding pins on LDR3x J4 pins.

If  you are also mounting the IR Module on to the DM1 master, the IR signal also has be connected. Also, if you are connecting the Encoder Module via the DM1 master then of course the A, B & S pins must also be connected to the LDR3x board. 

For the V2 and V2.1 versions of the LDR3x board, the DM1 J1 header connects to the LDR3x J4 header via a 2×5 pin ribbon cable which connects all 8 signals. Make sure that red stripe on the ribbon cable is on the same side of J1 and J4 that has the white dot next to the headers.

  • Required
    • +5 – power (J4- +5)
    • G – ground (J4- G)
    • CS – display select (J4 – CS)
    • SC – serial clock (J4-CK/SC)
    • SD – serial data (J4-DA/SD)
  • Optional
    • A – encoder leg A (J2-EA)
    • B – encoder lega B (J2-EB)
    • S – encoder switch (J2-ES)
    • IR – infrared receiver (J4-IR or J2-IR)

 J2 – encoder interface header (optional) – This optional header is present on the DM1 master but absent on the slave.  J2 allows interconnecting Tortuga Audio’s Encoder Module to the LDR3x via the DM1.  Pins A, B, S, & G on J2-DM1 must be interconnected with corresponding pins on the Encoder Module.

J3 – slave interface header (optional) – This header interconnects the primary DM1 display to the secondary DM1 (slave) display. Interconnection is via 2×5 pin IDC ribbon cable. Make sure that red stripe on the ribbon cable is on the same side of J3 headers as the white dot.

J4 – slave jumpers – This header is only present and used on the slave version of the DM1 board. J4 pins 1 & 2 and pins 3 & 4 must be jumpered/soldered together respectively in order for the slave module to operate.

IR – infrared receiver mount (optional) – The DM1 master board provides a convenient optional mounting location for the IR Module that is supplied along with the LDR3x board. The 3 mounting holes for the IR Module are located immediately below the J3 header.

Note: The term “optional” used above in discussing the control interfaces means the interface hardware is present but using the interface is optional and therefore not required  for the basic functioning of the DM1 display module.

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4.3.IO3 Relay Board

Overview

The IO3 (input/output) Relay Board can be interfaced with the LDR3x Preamp Controller Board (versions 1 or 2) to enable switching between up to 3 audio input signals. There are 2 versions of the IO3 board: the original IO3.1D and the current IO3.2A. Pictures of both versions are shown below. The key differences are summarized in the following table.

IO3 version 1IO3 version 2
Feature
Solder pads for input/output interface with LDR3x boardYesNo
Dimension2.5″ wide x 1.7″ tall2.84″ wide by 1.4″ tall
Mounting holes4 corner holes3 interior holes
J2 pin interface with LDR3x board1×5 pin header2×5 pin header
Output solder pads21

Please note that the IO3 Version 2 board also has mounting spots/pads(6) for 2 relays plus a Q1 transistor however these items are intentionally not installed or used. These items are not installed or used in the IO3.2 because they introduced an unacceptable level of switching noise when used.

The IO3  Interface

The IO3 interface points are identified in the IO3.1 photo below (not to scale!). Please note that the IO3 is symmetrical in that the left side of the board (as viewed below) handles the right channel and right side of the board (as viewed below) handles the left channel. Thus, left/right channel signals do not intermingle on the board.

IO3 Version 1 Board

IO(3 Relay Board - Annotated

IO3 Version 2 BoardIO3.2 Input Relay Board - Top View

Please note the requirement of installing the (red) jumper wires in lieu of the relays that are not used. Some IO3.2 boards were shipped without these jumper wires. The jumper wires connect the output signals from the J1R and J1L terminal blocks to the the J3/J4 output screw terminals and associated output solder pads.

Wiring Diagram

The diagram below illustrates a typical scenario of connecting the IO3 to 3 single-ended RCA input signals and 2 RCA outputs (in parallel).  

IO3 interconnect diagram

Connecting The IO3 To Version 1 LDR3x Board:  

The diagram below shows how to connect the IO3 to the Version 1 LDR3x board.  J1L and J1R of the IO3 connect to the corresponding J1 terminals of the LDR3x. Be careful to connect left with left, right with right, input with input and output with output. It’s all too easy to make a mistake with the wiring. Also note that with the Version 1 LDR3x the left/right channel grounds are connected together at the J1 terminal of the LDR3x.  Lastly, while not shown in the diagram below, you may alternatively connect J2.IO3 terminals In1, In2 and In3 to the corresponding J1.LDR3x terminals of the same name instead of using J7.LDR3x. However, you still need to connect the +5V power as shown.

IO3 interface to the LDR3x.V1

Modifications Required To The Version 1 LDR3x Board:  

The LDR3x requires certain modifications to work with the IO3. These are simple to do. First, you will need to install (solder in) a 5 pin header in the left side of J7 as shown in the LDR3x.V1 picture below. You also need to install 3 jumper wires between the solder pads as shown below. Just in case the photo isn’t clear on this, the jumpers need be connected as follows: a) between right pad of R20 and left pad of D8; b) between right pad of R22 and left pad of D10; and, c) between right pad of R17 and left pad of D5.

LDR3x Version 1 mods for the IO3

Connecting The IO3 To The Version 2/2.1 LDR3x Board:  

The diagram below shows how to connect the IO3 to Version 2 of the LDR3x board. J1L and J1R align with each other both physically as well as schematically. No modifications are required to he LDR3x.V2 board to connect J2 to J7.
IO3_LDR3x_Version2

Solder Pad vs. Screw Terminals  

Most signals shown above (except for +5V power) can be connected to the IO3 via solder pads instead of using the screw terminals. While not as flexible and maintenance friendly as screw terminals, soldered signal connections are simply more reliable and maintenance free. Please note that the IO3 Version 2 board does not provide solder pads for connecting the audio signals to the LDR3x board.

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Last updated on May 13, 2016

4.4.PS12.5 Power Supply

Caution! Working with common household AC power sources is potentially dangerous, can cause shock, and in extreme circumstances can even be life threatening.  Please use extreme caution when handling AC power sources and equipment. Be safe!
LDR3x power supply - typical assembly

The PS12.5 is a 2 channel power supply in the form of a 1.75 inch x 3.5 inch circuit board together with a separate 1.1 inch tall by 2.5″ diameter toroidal transformer that be interfaced with the LDR3x Preamp Controller Board (versions 1 or 2) to provide either or both 12 VDC and 5 VDC.

The PS12.5 Interfaces: The PS12.5 interface points are identified in the photo below and are each described in the following subsections.
PS12.5 wiring interfaces

J1 – Main AC Power Input: This is where you connect the 115 or 230 VAC main power. The two terminals are labeled H(hot) and N(neutral). If you’re not sure which is which on your power cord use a voltmeter to check the voltage between Hot and Ground and Neutral and Ground. Neutral will have little or no voltage relative to Ground. There’s no J1 terminal for the main power Ground connection. You must solder main power Ground to one of the Star Ground solder pads. There are also solder pads provided for both the Hot and Neutral lines which you can use instead of the J1 screw terminals.

J2 – Transformer Primary Connection: This is where you connect the primary windings of the transformer. The transformers has 2 primary windings and 2 secondary windings as shown below. The primary windings are the 2 Red-Black pairs. You can identify which Red belongs to which Black by using an ohm-meter; the matching Red-Black pair from a winding will have very little resistance. Once you’ve identified the pairs, connect the Red wire of the first winding to J2.Red1 and Black wire of the first winding to J2.Blk1. Similarly, connect the Red and Black wires of the second primary winding to J2.Red2 and J2.Blk2 respectively. These four connections can be made via the designated solder pads instead of the screw terminals.

PS12.5 transformer dimensions & wiring

J3 – Voltage 115/230 Switch/Jumper: This is where you connect an either an external voltage selector switch or wire jumpers to designate the source voltage level as being either 115 VAC (US/Canada) or 230 VAC (Europe etc.) The transformer wiring diagram below shows this schematically. For 115 VAC main supply, connect a jumper between J3.1 and J3.2 and a jumper between J3.3 and J3.4.  What this does is connect 2 Red primaries together and the 2 Black primaries together in parallel. For 230 VAC main supply, connect a jumper ONLY between J3.2 and J3.3. What this does is connect Blk1 to Red2 such that the 2 primary windings are wired in series. These switch/jumper connections can be made via the designated solder pads instead of the screw terminals.

PS12.5 transformer wiring schematic

J4 – Transformer Secondary Connection: This is where you connect the secondary windings of the transformer. The transformers has 2 secondary windings as shown above. The secondary windings are the 2 Blue-Green pairs. Connect both blues to J4-Blu and both Greens to J4-Grn. These four connections can be made via the designated pairs of “Blu” and “Grn” solder pads instead of the screw terminals.

J5-1&2 – DC Outputs: This is where you connect the the DC power outputs. There are 2 output channels in the PS12.5. Depending on which options you chose when you purchased the PS12.5 there may only be power output on J5.1 for the single channel version. If you opted for the two channel version, there will be DC power output on both J5.1 and J5.2. The voltage levels will also depend on which options your chose and could be both 5 V, both 12 V, one 5 V and the other 12 V, or just 5 V or just 12 V on the single channel version. Confused yet? Your voltmeter will help you sort it all out. These DC Output connections can be made via the pair of solder pads adjacent to the left end of the J5 screw terminal block instead of using the screw terminal block.

Star Ground Connections: This is where you connect all of the Grounds in your project to one single common ground point. This avoids ground loops which cause hum in audio systems. The PS12.5 provides 10 star ground solder pads located behind J2 and J3 and 8 additional screw terminal star grounds connection points via J5-3 thru 10. All of these connection points are tied to a common copper ground plane within the PS12.5 board.

Specifications: 

  • Rectification: full bridge with glass passivated ultrafast rectifiers
  • Smoothing: 4700 uF – 25 VDC
  • Regulation:
    • High performance 260 kHz switch mode dc-dc regulator(s)
    • Output voltage & current rating (options)
      • Single channel 12 VDC (400 mA)
      • Single channel 5 VDC (400 mA)
      • Dual channel 12 VDC (2 x 400 mA)
      • Dual channel 5 VDC (2 x 400 mA)
      • Dual channel 12VDC (400 mA) and 5 VDC (400 mA)
    • Nominal input voltage: 115 VAC or 230 VAC (switchable with appropriate external switch)
    • Output voltage accuracy: +/- 2%
    • Load regulation: +/-0.2%
    • Quiescent current: 3-5 mA
    • Isolation: none
    • Short circuit protection: continuous
    • Over/Under-voltage protection: none
    • Cooling:  free air convection
  • Grounding:  10 solder pads, 8 screw terminals
  • Transformer: 10VA low noise toroid with 20% margin | 15 VAC output | 12 inch leads | mounting bolt with pad
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5.Legacy Products

The following information relates to products that are no longer in production.

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5.1.LDR1, LDR3 & LDR6

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5.1.1.Front Panel/Controls

LDR6&1_Fronts_IMG_0409

Encoder: Both models have a single multi-function black/knurled Encoder on the right hand side of the front panel. The preamp is fully controllable via the Encoder as well as via IR Remote.

Status LED: To the immediate left of the Encoder, there is a single unlabeled Status LED which when on is the color blue.

Input Select LEDs:  The LDR6 also has 6 Input Select LEDs which indicated which input is currently selected. These are also the color blue when they’re on.

IR Lens: On the far left of the front panel of the LDR6 there is dark circular IR lens behind which sits the IR Receiver. The LDR3 has a small IR apeture but does not have an IR lens.

General Control & Operation: The LDR1, LDR6 and related variants share common operating and control features. More information on the general control and operation of these passive preamps can be found via the link button below:

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5.1.2.Rear Panel

LDR6&1_Backs_IMG_0356

12 VDC Power Supply: Both models are powered via an external “wallwart” style 12  volt DC switching power supply that comes with a 5 foot cord with 2.5 mm barrel connector that must be plugged into the 12 VDC jack on the upper right of the rear panel. When the power supply is plugged in and energized, the Status LED on the front panel will flash briefly.

12 VDC Trigger Out: When these models are turned on, 12 volts DC will be present on the 12 VDC Trigger Output jack on the lower right of the rear panel. This trigger signal can be used to turn on other components equipped with 12 VDC  trigger inputs; amplifiers being the most common component. The Trigger Output will revert to 0 volts when the unit is turned off.  The 12 VDC Trigger Output requires the use of a conventional 1/8th inch (3.5mm) mono phone plug.

Inputs: The LDR6 in equipped with 6 pair of gold plated brass, singled-ended RCA input jacks. The LDR3 has 3 pair of Cardas rhodium over sliver plate solid brass RCA input jacks.

Please note that the “Phono”  input on the LDR6  is NOT equipped to handle a low level signal directly from a turntable. 

Outputs: The LDR6 in equipped with a single pair RCA output jack. The LDR3 is equipped with 2 pairs of Cardas output jacks wired in parallel (both carry the same output signal).

Note: The right most photo is of the LDR1 (discontinued) and not the LDR3. An updated photo including the LDR3 is coming soon.

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5.1.3.Specifications

In addition to the Common Specifications, the LDR1, LDR3 and LDR6 Passive Preamplifiers were designed according the following additional specifications:

  • Input/Output Type: Unbalanced stereo audio
  • Enclosure Body:  Heavy gauge extruded unibody aluminum | Black powder coat finish
  • Front/Rear Panels: Black anodized 5005 aluminum with raw machined aluminum edging
  • Power Jack: Heavy duty 2.5 mm chrome plated through-hole threaded jack
  • 12V Trigger Out Jack: Heavy duty chrome plated through-hole threaded phone jack
  • External Power Supply: 90-264 VAC input | 12 VDC regulated switching power unit rated @ 1 amp with  2.5mm plug  | Energy Star Level V efficiency | built-in overload, short circuit, EMI filter and thermal protection
  • Internal DC-DC Power Regulator:
    • Before March, 2014 – Linear 5 VDC  regulator for power the controller and LDRs
    • On/After March, 2014 – High performance, low noise, switch mode 5V DC-DC converter for powering the controller and LDRs
  • Power Draw: 12 VDC Supply | Off: 31 ma | On: 135 ma | Auto-Calibration: 200 ma
  • Hand-wired:  Internal point-to-point wiring of power & audio I/O to PCB via Milspec teflon insulated silvered copper wire
  • Common Signal Ground: 12 gauge solid copper ground rod ties all audio signal I/O to common signal ground
  • Feet:  Heavy duty non-slip black polyurethane rubber | it stays where you put it
  • Size (shipped package): L=12.0″  W=10.0″  H=6.0″
  • Size (unit): L=8.25″  W=6.25″  H=3.25″  |  L=21mm  W=15.9mm  H=8.3mm
  • Weight (shipped package): 5 lb
  • Weight (unit): 4 lb

LDR1 Only

  • Audio Connectors: Gold plated brass RCA jacks
  • Inputs: One pair of unbalanced stereo inputs
  • Outputs: Two pair of unbalanced stereo outputs
  • Input Indicators: None

LDR3 Only

  • Audio Connectors: Cardas GRFA-L rhodium over silver plated brass RCA jacks
  • Inputs: Three pair of unbalanced stereo input | Labeled 1, 2 and 3
  • Outputs: Two pair of unbalanced stereo outputs wired in parallel
  • Input Indicators: Three blue LED indicators of current selected input located on the front panel

LDR6 Only

  • Audio Connectors: Gold plated brass RCA jacks
  • Inputs: Six pair of unbalanced stereo inputs | Labeled CD, DVD, DAC, TV, PHO, & AUX (inputs 1-6)
  • Outputs: One pair of unbalanced stereo outputs
  • Input Indicators: Six (6) blue LED indicators of current selected input located on the front panel
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5.2.LDRx.V1 Preamp Controller

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5.2.1.V1 Overview

LDR3x DIY Preamp Controller Board

Please note that the V1 is a legacy product and is not longer supported. It has been replaced by the V2/V2.1 versions.

A DIY Preamp Controller Board: The LDR3x is a preamp controller in the form of a partially populated 2.5 inch by 4.7 inch printed circuit board that is marketed to the do-it-yourself (DIY) audio enthusiast who wishes to build their own preamp.

Insofar as the LDR3x 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 LDR3x 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 LDR3x is sold with an uninstalled infrared receiver module that the user can either solder to the LDR3x board or locate external to the board via user provided wiring.

The LDR3x can be controlled by the Tortuga Audio Remote, the Apple Remote and/or Encoder all of which are optional and not included. The LDR3x also has several unique control inputs that are enumerated and explained in sections below.

The LDR3x is part of the Tortuga Audio family of LDRx passive preamps. Please refer to documentation under LDRx Passive Preamplifier for more information that applies equally to the LDR3x.

Unbalanced (Single-Ended) Audio:  The LDR3x comes in two versions: a Master and a Slave. The Master operates as a standalone passive preamp for single-ended unbalanced inputs. The Master is also used for balanced audio. The Slave is only used with balanced audio.

Balanced Audio: The LDR3x can be configured to handle balanced audio using two different approaches: Master/Slave boards or  Dual Master boards. In either case both boards (Master/Slave or Dual Masters) are custom matched to have identical matching attenuation curves.

Master/Slave Approach:  The Master Board is designated for the Right Channel and the Slave Board handles the Left Channel. Only the Master Board is used for control interfaces. The Master Board is physically connected to the Slave Board via a 2×5 pin IDC ribbon cable and the Slave Board operates synchronously with the Master Board. The Slave Board is identical to the Master Board except the Slave Board doesn’t have its own microcontroller, on board 5 VDC power regulator, J2 or J6 terminal connectors.

Dual Masters Approach: Alternatively, balanced inputs can be accommodated with a pair of specially matched dual LDR3x Masters. The wiring is the same as with the Master/Slave approach, but each Master Board operates asynchronously from the other (the one doesn’t know what the other is doing). The IR Receivers of both units must have clear “line of sight” to the IR Remote. This approach only works when using a Remote. To initially synchronize  the Dual Masters, ramp both LDR3x units down to zero volume, then raise volume to suit using a single Remote as you would with just a single LDR3x. Both LDR3x units will remain “virtually synchronized” with normal raise/lower volume commands from the Remote. Should they become out of balance, repeat the synchronization process.

Options: 

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5.2.2.V1 Specifications

 

In addition to the Common Specifications, the LDR3x.V1 Passive Preamp Controller Board is designed according the following additional specifications:

  • Input/Output Type: Unbalanced stereo (master board only) and balanced stereo (requires both a master and slave board)
  • 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.
  • Audio/Control Interface: 0.1 inch (2.54 mm) pitch mini screw terminal blocks (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)
  • Current Draw: Nominally 20-60 ma and in no case more than 100 ma depending on peripherals such as display module, relay board, and status LED.
  • Size – Unit:   L=4.73″  W=2.5″  H=1.0″
  • Size – As Shipped:  L=8.7″  W=5.4″  H=1.75″
  • Weight – Unit: 2 ounces
  • Weight – As Shipped: 5 ounces
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5.2.3.V1 Controls

LDR3x - Terminal J2 - Control Inputs/Outputs

Terminal J2 – Control Inputs/Output:  J2 is a 10 position , 0.1 inch pitch screw terminal connector for interfacing with user’s control inputs and preamp status output as summarized in the list below and further explained in the following sections.

J2 provides the control interface to control all functions of the LDR3x via  a combination of inputs including push buttons, encoder, IR Receiver, and analog volume pot. It also provides a single status output for driving an LED Status light.

Control via J2 is optional and can be in addition to or in lieu of control via the Tortuga Remote or Apple Remote. Control inputs via J2 and Remote are complimentary and not mutually exclusive with the exception of controlling volume via analog pot input (J2-VO) which disables volume control via both Remote and Encoder (more detail on this exception below).

LabelType
Function
S3D InputToggle input #1 (select = pull to ground – 0V)
S2D InputToggle input #2 (select = pull to ground – 0V)
S1D InputToggle input #3 (select = pull to ground – 0V)
MuD InputToggle mute (mute/unmute = pull to ground – 0V)
IRD InputInfrared receiver pulse (0V = pulse)
STD OutputStatus output (on = pull to ground – 0V, off = 5V)
ESD InputToggle on/off (Encode Switch) (pressed = pull to ground – 0V)
EaD InputEncoder leg A (on = pull to ground – 0V
EbD InputEncoder leg B (on = pull to ground – 0V
VOA InputAnalog volume control input (min vol = 0V, max vol = 5V)

[box type=”alert” style=”rounded”]Errata: Inputs J2-S1 & J2-S3 are mislabeled (reversed) on version Rev 0.B of the LDR3x board.[/box]

The diagram below illustrates how to implement all the control interfaces available via J2. Each of these are discussed below.
LDR3x - J2 Terminal - Control Wiring

J2-S1, S2 & S3 – Input Select:  These three push button inputs allow the user to select from up to 3 inputs. As shown in the diagram above the 3 pushbuttons terminate to J2-S1, J2-S2 and J2-S3 respectively. The other leg of each pushbutton is connected to common ground (J6-G). Selecting from multiple inputs requires the LDR3x be interfaced with an appropriate input relay switching board (not currently sold by Tortuga Audio) and that the input relay switching board be interfaced with J1-In1, J1-In2 and J1-In3 respectively. Input selection via S1, S2 and S3 can also be implemented using a 3-way single pole rotary switch. S1, S2 and S3 are prioritized such that if all 3 switches were to be pressed (pulled low to ground) simultaneously, S1 will win. If only S2 and S3 were pressed simultaneously, S2 would win.

LDR3x - IR Receiver Module mounting location
LDR3x IR Receiver module pins/wiring

J2-IR – IR Receiver:   The LDR3x is supplied with a high performance 38 khz infrared receiver module (IR1). The IR1 is supplied loose and not installed. The picture above left shows the IR Receiver installed on the board. The picture above right shows the IR Receiver and  its 3 pin connections. Incorrect wiring of power to the IR Receiver will immediately destroy it. You have the option of soldering the IR1 into the LDR3x board immediately next to J3. Alternatively, the user may remotely locate the IR Receiver external to the LDR3x board.  If you locate the IR Receiver external to the LDR3x board, pin 1 must be connected to common ground (J6-G), pin 2 must be connected to +5 volt power (J6-+5) and pin 3 must be connected to the J2-IR. To make these connections, you will have to solder (or otherwise connect) extension wires to the IR Receiver pins and terminate these to the LDR3x. 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.

J2-MU – Mute:  This push button input toggles the Mute/UnMute status of the LDR3x. The other leg of the Mute pushbutton must be connected to common ground (J6-G).

J2-ST – Status LED:  This is only output on terminal J2 and when connected to an LED provides status information on the LDR3x. The positive (+ long) end of the LED connects to J2-ST which provides +5 V when the LED is turned on. The negative (-  short) leg of the LED connects to common ground (J6-G). 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.

J2-ES, J2-Ea & J2-Eb – Multiswitch/Encoder Inputs:  These 3 inputs are for interfacing the LDR3x with the Encoder. J2-ES is a push button switch multi-purpose switch (Multiswitch) that can act as a power on/off toggle switch, mute/un-mute toggle switch and balance-mode-select switch. While the MultiSwitch input can be  implemented by itself, it’s intended to be implemented in conjunction with the rotary Encoder which has an integral push button switch. 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 common ground (J6-G).

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. Additional info on the EC11 encoder can be found in the Appendix to this manual.

J2-VO – Volume Control Potentiometer (Pot):   This input allows the LDR3x volume to be manually controlled using a conventional potentiometer (“pot”).  Connect one leg of the pot to 5 VDC board power via J6-+5 and the other leg of the pot to ground via J6-G. The pot wiper (center terminal) should be tied to the J2-VO terminal. 0V = min volume (muted) and 5V = max volume.  Ideally the pot should have a linear taper since the LDR3x already has its own programmed logarithmic audio taper. Since the pot acts as a voltage divider it can be any nominal resistance but we suggest 5K ohm or greater to limit current draw.

Volume control via a J2-VO pot is enabled via jumper JP1 on the LDR3x board as shown in the picture to the right. Jumpering the 2 right-most pins (or just the 2 pins on boards with only 2 pins) enables this volume control mode.

Special Notes

Wiring Pot Backwards:  If clockwise rotation of the pot results in decreasing volume and counterclockwise rotation increases the volume, then simply swap the +5V and Gnd inputs to the pot legs.

Remote/Encoder Volume Control Disabled:  Enabling Volume control via a pot input to J2-VO will disable volume control from both the Infrared Remote and Encoder.

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5.2.4.V1 Audio Input/Ouput

LDR3x J1 Audio Input/Output TerminalTerminal J1:  J1 is a 10 position, 0.1 inch pitch screw terminal connector for interfacing the LDR3x with the user’s audio inputs and outputs plus optional external input relay selection board.

LabelTypeFunction
In1OutputInput selector – sinks relay current to ground when on
In2OutputInput selector – sinks relay current to ground when on
In3OutputInput selector – sinks relay current to ground when on
ncNo connection
ncNo connection
RIAudioRight channel audio input from selected input source
LIAudioLeft channel audio input from selected input source
AGAudioAudio ground/common
ROAudioRight channel audio output to amp
LOAudioLeft channel audio output to amp

Input Selectors: Terminals J1-In1, J1-In2 and J1-In3 allow the LDR3x to be interfaced with an external input select relay board (not provided/sold by Tortuga Audio). Each of these 3 control signals provides an NPN current sink to ground when activated. They can be activated via Remote and/or via control inputs to J2 including Encoder (see sections Control Inputs & Outputs (J2) below for more details).

Unbalanced Input/Output:

Single Input: The simplest configuration is a single unbalanced audio input (via RCA jack) as shown in the diagram below. The Right Input terminates to J1-RI and the Left Input terminates to J1-LI. Similarly, the Right and Left Outputs terminate to J1-RO and J1-LO respectively. The common audio ground terminates to J1-G.

LDR3x Unbalanced Single Input/Output Diagram

Advisory!! – Ordinarily for passives, the audio ground can be a simple pass through as shown. However, with some amps and/or sources, a passive preamp may introduce ground loops with commensurate audible hum/buzz from the speakers. If you experience hum with your LDR3x, you should make sure to connect audio ground (J1-AG) to power ground (J6-G) or better yet connect each separately to a single point chassis ground using star grounding method.  

Multiple Input – Manual Switching:  Selecting from multiple inputs can be implemented via a manual double pole rotary switch as shown in the diagram below. Ultimately, the wiring of input and output to the LDR3x is done the same as with a single input except you’re interfacing with the output of the rotary switch instead of the RCA input jacks.

LDR3x J1 Unbalanced Multiple Inputs via Manual Switching

3 Input Relay Board – Automatic Switching:  The LDR3x can be interfaced with an external relay board for remote switching of up to 3 input channels as shown below. With up to 3 relays tied to power supply (typically +5V or +12V), the relays are energized (switched to grounded) by the LDR3x board via J1-In1, J1-In2 and J1-In3 respectively. This approach allows you to use the IR Remote, Encoder, or push button inputs to have the LDR3x switch the input relays.

Please note that Tortuga Audio currently does not provide or sell an input relay board.

Further detail on the various control options are covered in section  Control Inputs & Output that comes immediately after this section.

LDR3x - Unbalanced Multiple Inputs - Automatic Switching

Balanced Input/Output

Balanced Audio XLR Connectors & Wiring: Balanced audio is more complex than unbalanced (single ended). Each balanced channel has 3 (vs. just 2) pin connection; +signal, -signal and ground. The balanced signals except they are 180 degrees out of phase with each other. Balanced audio utilize 3-pin XLR connectors. Depictions of XLR connections can be confusing because the pin numbers look different depending on whether you’re looking at a female (input) or male (output) XLR connection and also depending if you looking at the front or rear of each gender.

3 pin XLR wiring of male/female connectors

Typical XLR Balanced Interconnect Cable Wiring

J1 – Wiring For Balanced Input/Output:  The diagram below shows the balanced input/output connection to the LDR3x for a single input system. For multiple input systems, follow the same guidelines as described above for unbalanced audio. The Master handles the right channel and the Slave handles the left channel. Pin 1 is the pass through audio ground. The input +signal (Pin 2) is connected to J1-RI and the -signal (Pin 3) is connected to J1-LI.  Similarly, the output +signal (Pin 2) is connected to J1-RO and the -signal (Pin 3) is connected to J1-LO. The input/output wiring is the same for both the  right (Master) channel and the left (Slave) channel.

LDR3x Balanced Input Wiring Diagram

J5 – Master/Slave Board Interconnection:  The Master board connects to its Slave board via a 2×5 pin IDC ribbon cable. The ribbon cable sockets connect to the J5 header pins on both boards. Please note the proper alignment of cable to the J5 header as shown in the pic below (only Master board is shown).

LDR3x J5 Master/Slave Interconnect

Caution: Incorrectly connecting the J5 headers from Master to Slave board can cause irreversible damage to either/both boards.
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Last updated on Aug 18, 2016

5.2.5.V1 Power Supply

LDR3x J6 Power Terminal Block

No Power Supply Included: The LDR3x is NOT sold with its own power supply. The user must supply their own 12 VDC or 5 VDC power source to power the LDR3x.

Terminal J6:  J6 is a 4 position 0.1 inch pitch screw terminal connector for powering the LDR3x with either 12 VDC or 5 VDC  power and also provides a 12 VDC Trigger output. Each of the 4 connections is explained below.

J6+12 – Main Power:  The recommended approach is to power with LDR3x with 12 VDC via terminal J6+12 although the LDR3x can also be powered with 5 VDC via terminal J6+5. The 12 VDC power supply can be a switch mode power supply or linear power supply  (see the Specifications below for details). While not required, we recommend a regulated 12 VDC power supply to avoid problems with the 12 Volt Trigger Out.  The LDR3x takes the 12 VDC input and steps it down to a regulated 5 VDC to power the DCU and the LDRs. The regulated 5 VDC is also available as a power source for control devices via terminal J6+5. The 12 VDC is also used to power the 12 Volt Trigger Out feature.

J6+5 – Main/Control Power: When the LDR3x is powered with 12 VDC, regulated 5 VDC is available via J6+5. When the LDR3x is powered with +5 VDC instead of 12 VDC , the user connects a 5 VDC source to the J6+5 terminal. The 5 VDC power soucr MUST BE REGULATED! If the LDR3x is powered via a 5 VDC external power source, the 12 VDC Trigger Output (J6+12T) will not be functional.

J6-G – Ground: The power supply ground MUST be connected to J6-G in order for the LDR3x to function properly.

CAUTION: Reversing polarity (i.e. connecting positive supply voltage to J6-G and power supply ground to J6+5 or J6+12) may cause irreparable damage to the LDR3x!

J6+12T – 12 Volt Trigger Out: When powered by a 12V DC power source, the LDR3x will generate a switched 12V DC trigger output on terminal J6-12T when the LDR3x is turned on. This output can be used to turn on and turn off other audio components equipped with 12 V triggered inputs. This feature is not operational if the LDR3x is powered from a 5 VDC source.

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Last updated on May 13, 2016

5.3.Tortuga Audio Remote

The Tortuga Audio Remote is a legacy product that is no longer offered for sale. It was shipped with the LDR1, LDR3, LDR6 and optionally with the LDR3x.V1 up until May 1, 2014 at which time it was replaced with the Apple Remote.

The Tortuga Audio Remote is a custom 15 key infrared remote transmitter that uses the NEC IR protocol and is powered by 2 AA batteries.

The Tortuga Audio Remote has the following control functions:

Tortuga Audio infrared remote
Tortuga Audio Remote

Power: Toggles the LDRx power on if off, and off if on. 

Raise (Volume Control Mode): A brief press will raise the volume 1 step. Holding this button down will issue repeat commands and cause the volume setpoint to ramp up quickly. When the Volume is at maximum the Status LED will blink slowly.

Raise (Brightness Adjust Mode): When LDRx units with Numerical Displays are Muted, pressing Raise will increase the brightness of the display.

Lower (Volume Control Mode): A brief press will lower the volume 1 step. Holding this button down will issue repeat commands and cause the volume setpoint to ramp down quickly. When the Volume is at minimum the LDRx unit will Mute and the Status LED will blink slowly.

layout of Tortuga Audio remoteLower (Brightness Adjust Mode): When LDRx units with Numerical Displays are Muted, pressing Lower will decrease the brightness of the display.

Mute: Mutes the LDRx if Un-Muted and Un-Mutes it if already Muted. When Mute is initiated, the LDRx volume will ramp down to zero and the Status LED will blink slowly. When Un-Mute is initiated, the LDRx volume will ramp up to its previous setting and the Status LED will be steady on.

Input Select (1-6): The Tortuga Audio Remote has 6 input select buttons labeled CD, DAC, Phono, TV, DVD  and Aux representing inputs 1-6 respectively. When an Input button is pressed, the LDRx unit will immediately Mute the unit and the Status LED will blink slowly. Once the desired Input has been selected, pressing the Enter key will lock in the selection, the Status LED will flash briefly and the unit will Un-Mute and ramp up to the same Volume setting as before but will now be connected to the newly selected Input.

 Balance: Pressing  the Balance button will put the LDRx unit into Balance Adjust Mode. The Status LED will blink rapidly indicated the unit is in Balance Adjust Mode.

 Left/Right (Balance Adjust Mode):  When in Balance Adjust Mode, pressing the Left key will incrementally shift the Balance towards the left channel while pressing the Right key will shift the Balance towards the Right channel. The Status LED will continue to blink rapidly. Once the desired Balance has been achieved, pressing the Enter key will lock in the Balance adjustment and the Status LED will flash briefly indicating the unit is now back in normal Volume Adjust Mode. Note that the Raise/Lower Volume keys remain operational during Balance Adjust Mode.

Reset (Balance Adjust): Pressing the Reset button to clear the Balance Adjust settings  to zero. The Status LED will flash briefly.

Infrared Protocol and Codes: The Tortuga Audio Remote uses the NEC infrared protocol. The specific codes used are listed below and can be easily programmed into most programmable remotes. Each command issued by the Tortuga Audio Remote is preceded by a System Code and followed by a Command Code.

DecimalHexadecimal
System Code[110][6E]
 
Key

Command Code

Balance100h
Power302h
Reset403h
Raise807h
Mute908h
Left1009h
Enter110Ah
Right120Bh
Lower140Dh
Input #1 (CD)160Fh
Input #2 (DAC)1710h
Input #3 (Phono)1811h
Input #4 (TV)1912h
Input #5 (DVD)2013h
Input #6 (Aux)2114h
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Last updated on Sep 19, 2016
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Change Log

9.10.16 – Partially reorganized documentation into separate expandable topics
9.9.16 – Updated section on Adjustable Impedance to be more comprehensive and easier to understand
8.27.16 – Minor edits and reorganization plus added graphic illustration of Apple Remote 2.2 control functions
5.13.16 – Added version Apple Remote 2.2.X plus reorganized entire document
10.21.15 – Amended section on IO3 Relay Module to include IO3 Version 2
4.24.15 – Added section on the DM1 Display Module
4.24.15 – Added section on Adjustable Input Impedance
4.15.15 – Added section on Pre-Calibration
1.15.15 – Updated Apple Remote section to reflect control functions released with version 2.1.0 firmware
7.13.14 – Updated and rearranged most sections to reflect recent changes.