LDR3x preamp controller circuit board

Tortuga Audio Plans LDR3X Preamplifier Controller for DIY Community

As we work to expand our line of next generation  preamp products  built around light dependent resistors (LDRs), we also plan to soon introduce an LDR based preamp controller board, and related products, for the Do It Yourself (DIY) audio community.

As we’ve previously announced, Tortuga Audio is actively developing a balanced version of its preamp line – the LDR3B Passive Preamplifier. This development work has led us to take a more modular design approach. One such module is the new LDR3X Preamplifier Controller board which will be at the heart of all of our future passive preamp models including the upcoming balanced LDR3B.

LDR3x preamp controller circuit board
LDR3x Preamplifier Controller

The LDR3X Preamplifer Controller has all the functionality of our original stand alone LDR1/LDR6 passive preamps but with the audio input selection hardware, manual encoder, information display and infrared receiver no longer being located on the board itself. Still, the LDR3X can be easily interfaced with all those items and more and retains the software functionality to make it all work together.

What this means to the DIY’er is the ability to build your own LDR passive (or active!) preamplifier using the LDR3X  to achieve input switching, channel balance adjustment, and exceptionally clean and transparent LDR based volume control.

LDR3X can be incorporated into any new or existing preamp where the designer is looking for remote control functionality.

In its simplest configuration, a DIY high performance remote controlled LDR passive preamp could be assembled with nothing more than the LDR3x board, an enclosure, 4 RCA jacks, a potentiometer and some wire.

This LDR3X Preamp Control board has extensive functionality and features as outlined below.

Precision Transparent LDR Based Volume Control 

Each LDR3X will be supplied with a matched set of 4 installed LDRs.

After installation, each LDR3X will be tested over the full attenuation range of  -60 dB in 70 control steps. The first 60 steps are slightly less than 1 dB each with the last 10 steps being more granular over the last few dB (towards max volume).

Results of the in-situ testing are used to program the final left/right channel correction curves into the software which ensures the best possible stereo imaging and sound stage. In this way each LDR3X is a uniquely custom tuned board. Not exactly conducive to low cost high volume mass production but we think the extra time and effort are worth the superior results.

Infrared Remote Control (via included IR receiver): 

  • Power on/off 
  • Volume raise/lower
  • Mute (with smooth ramp down and ramp up)
  • Left/right channel balance adjust
  • Channel balance reset
  • Select input #1
  • Select input #2
  • Select input #3

While the LDR3X does not include its own handheld remote, the IR protocol, address and command codes will be made available to the buyer and can be manually programmed into many of the better programmable remotes such as those sold by Logitech. An optional Tortuga Audio remote will be available and sold separately.

Manual Control (via user provided inputs):

  • Power on/off
  • Mute (with smooth ramp down and ramp up)
  • Volume adjust via 0-5 V
  • Volume adjust via rotary encoder
  • Channel balance adjust/reset via encoder/switch
  • Power on/off via encoder switch
  • Mute via encoder switch
  • Select any 1 of  3 inputs via encoder
  • Select input #1
  • Select input #2
  • Select input #3

Multiple Inputs

By itself, the LDR3X accommodates a single unbalanced audio input.  However, it also provides switchable current sinks for up to 3 external relays. This facilitates interfacing the LDR3X with relay equipped external inputs boards to allow selecting from any of 3 external inputs using controls built into the LDR3X. If more than 3 inputs are needed, manual mechanical input switching is always an option.

Balanced Input Preamp Control 

Balanced input control is achieved by using two (2) LDR3X boards in parallel. One board is designated the master and the second board is configured as the slave via an on board jumper. One board handles the +signal and the other board handles the -signal.

The slave board is “dumb” and serves mostly as an input/output expansion board for the master. Thus the slave board  is without its own microcontroller, power supply and several other non-essential components. A patch cable is provided to connect power & essential signals between the master and the slave.

The master and slave boards for balanced input control will be sold as a matched pair with particular attention paid to ensuring matched attenuation performance between all 8 LDRs on both boards.

Power Supply & 12 V Trigger Out  

The LDR3X requires a 12 volt DC external power supply which powers the unit via an on board 5 VDC regulator. The LDR3X also provides a 12 V Trigger Out that is powered any time the unit is turned on.

Suitable For Both Passive & Active Preamps

The LDR3X Preamp Controller can be readily incorporated into both passive and active preamp designs including both solid state and tube based active preamps.

Scope & Options

The LDR3X board will be sold with or without IDC pin headers on the control inputs and the audio input/outputs.  A separate IR receiver will be included with the board but will have to be mounted and wired externally by the buyer.

Optional items that may eventually also be offered include:

  • Euro-style Phoenix screw terminal blocks (installed in lieu of IDC pins)
  • External 12 VDC power supply (wall-wart)
  • External input relay board for switching between 3 single-end inputs.
  • IR Remote
  • Alps rotary encoder with pushbutton switch

Pricing & Availability

The LDR3X Preamp Controller board is expected to become available in late March and while pricing has not yet been established it’s expected to cost less than $300 excluding options.

It will be sold exclusively through Tortuga Audio’s website/store.

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