LDR3 Passive Preamp


The original LDR3 has been discontinued and is no longer available for sale. The LDR3 has been replaced by the LDR3.V2. 

The LDR3 Passive Preamplifier is a passive (unity gain)  3 input, 2 output  preamp/volume controller that is fully controllable via both a front panel control knob and hand held remote (included).

The LDR3 is part of our LDRx family of passive preamps that employ digitally controlled  audio grade light dependent resistors (LDR’s) for volume control and also for switching line stage inputs.

We believe (and our customers agree with us) that our LDRx technology  renders a truer, cleaner, and more transparent sound than any other volume control technology. The result is astonishing sound at a price that doesn’t force you to choose between an excellent preamp or a new car.

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Built on the same overall internal design and enclosure as its LDR1 predecessor, the LDR3 design  incorporates the following upgrades.

improved switch mode power supplyNew Power Regulator

A high performance internal switch mode dc-dc power regulator that provides cleaner power to the board. Beta testers have reported improved audio quality from this upgrade that manifests as a quieter “darker” background between notes and even better articulation/expression of detail. We don’t like to hype this kind of stuff but we have to say that after some extensive listening with the new power regulator that it’s even cleaner/sweeter than before. Perhaps even more “involving”. Let’s just say it’s better and better is always a good thing.

Cardas GRFA-L RCA jacksCardas RCA Jacks

The RCA jacks on the LDR3 have been upgraded to Cardas GRFA-L’s which Cardas retails (list) at $15.52 each. There are 10 of these in the LDR3. These are beautiful beefy jacks that are rhodium over silver plate over high quality brass. Too bad they’re on the back and not the front!!

Improved Software

There have been some key “under the hood” revisions in the software that improves the overall stability and reliability of the unit.

Subjective Performance


Descriptive words and phrases that are commonly used by both customers and reviewers to describe the LDRx passive preamplifier sound include: colorless, transparent, neutral, articulate, clear, fuzz-free, clean, natural, and high resolution.

Compared To Other Types of Passives

The consensus of customers and reviewers is you can expect performance  that is superior to conventional passive preamps utilizing even the best audiophile grade potentiometers, stepped resistive attenuators or even most transformer based volume controls.

Compared To Active Preamps

Independent reviewers have found that the LDRx passive preamps match the performance of even the finest high-end preamps costing many thousands of dollars more.


All product specifications and related technical information are available in our online product documentation.

Key Features


Passive means there’s no amplification of the audio signal. The simple truth is that most contemporary audio sources (DACs, CD players, phono stages etc.) do not need active pre-amplification prior to amplification. Any audio system that’s compatible with a LDRx passive preamp will sound sound better than most, and as good as even the best, high end preamps available.

High Input Impedance

Tortuga Audio produces the only LDR based passive preamp that maintains input impedance at or above 10k over the full attenuation range. The result is superior dynamics, fuller midrange, tighter bass, and satisfying percussive slam.

LDRs Instead of Potentiometers

Simply put, music sounds better going through LDRs compared to all other attenuation devices including potentiometers, stepped attenuators and even most transformer based volume controls.  LDRs combine a photoresistor with a light emitting diode (LED) into an integrated package.  LDR resistance (and thus volume) is controlled by controlling the light intensity of the LED.

Digital Control

Despite their extraordinary sound, LDRs are both nonlinear and variable and thus make it quite challenging to implement an optimal preamp design using conventional analog means. Therefore, Tortuga Audio employs a software based, microprocessor driven digital design together with proprietary control software to provide a precision matched audio taper schedule.  while maintaining a nominal input impedance of ~10k ohms. To our knowledge, Tortuga Audio’s design is unique in the audio preamp market.

No Moving Parts In The Signal Path

In addition to using LDRs for volume control, LDRs are also used for input switching in lieu of conventional relays or mechanical switches.  The audio pathway within the LDRx passive preamps is thus purely resistive with no moving parts. There’s nothing mechanical to corrode, fail or degrade the audio signal.

Optically Isolated Signal Path

The audio signal is optically isolated from the power supply and the control circuitry. The audio signal only “sees” purely resistive LDRs.  Electrical isolation between multiple incoming audio signals is well in excess of 5 mega-ohms.

Flexible Control

All LDRx preamps are fully controllable via both a infrared handheld remote as well as via the multi-function encoder/switch on the front panel. Moreover, all LDRx units shipped on or after 11.1.13 can also be controlled by the elegantly designed Apple Remote.

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