We control volume with light
Tortuga Audio designs & builds
LDR-based preamp controllers & related buffers
- No mechanical devices
- No potentiometers
- No stepped attenuators
Just a resistor and a photon
Home audio gear since 2012
What is an LDR?
A Light Dependent Resistor (LDR) is a composite part that integrates a photoresistor (a.k.a. photocell) with a Light Emitting Diode (LED) to create a new and uniquely useful component type – a true variable resistor controlled by a small electric current.
Our LDRs are manufactured by Advanced Photonix, a division of OSI Optoelectronics — one of the largest optoelectronic component manufacturers in the U.S., with over 50 years in photonics and optical sensor design.
How LDRs behave
LDR resistance varies inversely with the light intensity emitted by the LED. Higher control current results in lower resistance. But this relationship is not constant as is evident by the changing slope in the performance curve shown for a typical LDR. This is called “nonlinear” behavior and it’s one major reason why LDRs are challenging for audio designers.
Another key design constraint is the available control range. We are limited to operating our LDRs between 100 ohms and 100,000 ohms to ensure longevity and stable repeatable behavior.
Modular construction
Since LDRs have a finite life and sometimes fail prematurely, we chose to put our LDRs into plug-in modules that are easily replaceable rather than solder them in permanently. We have gone through 2 LDR module design iterations resulting in the earlier V2 module and the current V3/V4 module both shown below.
About the distortion
LDRs produce higher harmonic distortion than alternative volume control technology. This is a valid measurement and we don’t dispute it.
Two points to consider. First, LDR distortion is predominantly second-order harmonics — the same type of “musical” distortion that is deliberately cultivated in tube equipment and is perceived as neither harsh nor electronic. Second, the distortion numbers are well below the thresholds of human hearing’s ability to detect. Moreover, they sit far below the distortion levels of the speakers and room that ultimately produce the sound you hear.
In practice, this is a measurement without a musical consequence. What LDRs give up in measured THD, they give back in the absence of mechanical contact degradation, wiper noise, and channel mismatch — the harsh, grainy, mechanical artifacts that actually degrade music. The distortion LDRs do add is the subtle second-order kind, the character that listeners consistently describe not as coloration but as naturalness — clean, clear, organic, and free of the electronic signature that plagues most active and many passive designs. For us, and for the owners whose words you see below, that’s a trade-off worth making.
You don’t have to take our word for it. Every Tortuga Audio preamp ships with a 30-day in-home audition policy. Try it in your system. Trust your ears.
What owners hear
14 years of owner reviews. No editing. No cherry-picking. These are their words.
- LDR3000T owner comments
“I am truly gobsmacked by this preamp.”
“The difference it makes to the sound is astonishing. I echo what others have said: clarity, purity, sound stage. But I particularly agree with “clean”. It’s really unbelievably clean. And natural. Very very natural sound. And the one thing that I don’t think others have mentioned but which is really striking in my system is the bass. Huge extra bass depth and slam…”
- LDR3.V25 owner comments
“There have been many goosebump moments.”
“…let me be clear. I love it! First listen after completing assembly was to LPs, with the turntable feeding into the Meitner’s phono section and from the Tape Out (fixed level) jacks into the Tortuga. Sound quality is noticeably better than through the Meitner’s own line stage, top to bottom, with a veil removed and better controlled bass very apparent. There have been many, many goosebump moments, with familiar albums often taking on a new beauty thanks to the Tortuga’s superb performance. Make no mistake, this is a relatively inexpensive preamp with exceptional accuracy that does not in any way add to or subtract from the original recording, IMHO.”
The ePot.V4 system
Five generations and 14 years in, the V4 is our latest complete preamp controller — volume, input switching, display, and remote control — built around our LDR attenuation engine and designed for builders who want the electronics done right.
Features
The epot.V4 board
The V4 board is the heart of every Tortuga Audio preamp.
Passive or active? Your system decides.
The passive vs. active debate is better understood today to be less about which is inherently better than recognizing and adapting to a given system’s strengths and weaknesses. Turns out most systems work fine with passive attenuation without an active gain stage or impedance buffer. For when you need a bit more isolation or dynamic performance, we offer a clever little solid-state add-on buffer board that gets the job done. And a tube based buffer option may also be in the offing later this year.
Passive preamp
- Shortest possible, least adulterated signal path — nothing between source and amplifier but a pair of LDRs
- No active component or power supply to color the signal
- Ideal when your source has a strong output stage, cables are short, and amp input impedance is high
Active preamp
- Low, fixed output impedance regardless of volume setting
- Drives long cables and lower-impedance amp inputs without signal loss Isolates your source from your amplifier
- Eliminates impedance matching concerns
- Greater system flexibility — works well with virtually any downstream equipment
Built for builders
Tortuga Audio sells modules and components that allow a builder to create their own passive or active preamplifier.
We design and manufacture the electronics — the controller, the LDR modules, the display, the buffer board — and you bring the craft. Our customers build preamps into chassis they choose, wired and finished to their own standards. If you know how to solder, read a wiring diagram, and want control over every detail of the final build, this is your platform.
Please note that we DO NOT sell comprehensive turnkey kits. There are no detailed step-by-step instructions or pre-drilled enclosures. However, we do provide extensive technical resources by way of an online product documentation knowledge-base.
Articles & resources
We’ve been designing LDR-based audio controllers since 2012. We’ve published articles cover the technology behind our products, how LDRs work, and what makes them different. No hype — just what we’ve learned building them.
The guy behind the Tortuga
I started Tortuga Audio in 2012 soon after experiencing first hand what light-dependent resistors could do for audio. Fourteen years later, and I’m still exploring the possibilities. I design everything from a small shop in central Oregon, and I still get a kick out of shipping gear to someone who actually wants to build something with it or hear it in their system.
Sometimes I even get inspired to design, build and sell a few finished preamps and buffers because we can’t all be makers all the time.
