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Reviewer: Glen Wagenknecht
Financial Interests: click here
Sources: Audio Space CDP 8A CD Player, Wyred4Sound Music Server & DAC-2
Preamplifier: Audio Space Reference 2S
Amplifier: Bel Canto 200.4 Tapping TP22
AV Receiver: Pioneer Elite SC-25
Main Speakers: Apogee Duetta Signature, Paradigm Servo 15 subwoofer, Audio Space AS-3/5A
Stands: Charisma Audio Function Stands Target Stands
AV Speakers: JohnBlue M3s
AV Subwoofer: Paradigm PW-2200
Desktop Audio Speakers: Swans M200 MkIII
Desktop DAC/Pre Headphone Amp: DA&T U-2
Cables: Audio Art SE and Classic cable looms, JPS Labs Ultraconductor 2 speaker cables, Madison Audio Lab E3 Extreme 1 Interconnects/Extreme 2 speaker cables, Signal Cable Silver Reference interconnects and speaker cables, digital optical and coax cable.
Resonance Control: Solid Tech, EquaRack Footers, Weizhi Precision Gold Glory footers, Boston Audio TuneBlock2 footers, Audio Exklusiv Silent Plugs, Audio Exklusiv d.C.d. Base and d.C.d. Footers, Superspikes, and Black Diamond
Powerline conditioning: Exact Power EP15A, Noise Destroyer power filtration
Accessories: TrueHarmonix Black Magic CD Mat Herbie’s Super Black Hole CD Mat
Main Room size: 12' x 17'
Home Theatre: 10.5’ x 16.5’£
Review component retail: $1.475

Seeing the light. A passive preamplifier by its nature should be a relatively uncomplicated beast. In its most rudimentary form it breaks down to an input, an attenuator and an output, essentially a straight wire without gain. On paper and by the numbers this should be easy. As many a designer will tell you, it only looks easy. Component choices and system matching can sink it. For system demands there are a few basic rules. A source with sufficient output. Short cables. An amplifier comfortable with the signal it sees. Yes there are a few provisos and pitfalls beyond that but those are the fundamentals. Internal parts become the obvious bottleneck where the potentiometer is the primary candidate for choice of voice.

The venerable oft maligned carbon wiper is the most prolific in use but has lost favor with the high-end crowd. The two most popular upgrades have historically been the stepped resistor and conductive plastic pot, two devices with very different sonic characteristics. If your primary objective was the preservation of dynamic structure, stepped resistors would be the route. Smooth and natural tonal balance? Conductive plastic. Time and the evolution of technology has blurred those lines and the emergence of redundant contacts, exotic conductive materials, digital pots, resistor ladders and tapped transformers have broadened the field of available choices. Now there's another newcomer to the designer’s arsenal which handles the audio signal in a different way and challenges with a very blunt principle that the best mechanical switch contact is no mechanical contact. Welcome to the light-dependant resistor or LDR.

The LDR can trace its history back to the 1870s. Its modern application as photocell or photo resistor in devices from cameras to street lamps has made it so commonplace as to be invisible to the public eye. It's pretty old school for a fresh audio idea. Why so long in coming then? Here I suspect the old 'familiarity breeds contempt' adage. Its proliferation in other areas, its reputation for tolerance variability and the entrenchment of tried and true methods worked against it. The fact that it was never specifically intended for audio applications made it even easier to dismiss. But just a few years back there were some rumblings on the forums as enthusiasts and DIYers cracked the what-if barrier and the LDR preamp began to build a very enthusiastic fringe following. From shared projects to kits and now a fully commercial product, open the curtain and welcome Mr. Sissener of Tortuga Audio on the audiophile stage.

Tortuga Audio is a small Internet-direct company located in Cape Coral Florida that offers "handcrafted audio gear for music lovers" and specializes in LDR passives. Finding my way to the website, I found a wealth of information about the philosophy and implementation of the technology but remained curious about the man behind the company. So I asked Mr. Sissener to introduce himself and Tortuga Audio to the paying public.

Q: Mr. Sissener, how did Tortuga Audio come about and why did you pursue the LDR?
A: I've always been a tinker and curious about how things work. I was one of those kids who took things apart. Sometimes they even went back together again. That was part of the learning. So small wonder I eventually became an engineer. No matter what I was involved with professionally, I continued to tinker on the side. Driven by my love of music and curiosity I eventually began to experiment with designing and building my own equipment—amps & speakers—and tried to figure out what worked and why.

And for good or ill, I'm afflicted with that dubious internal logic that goes "why buy something with that high price tag when I can build it myself and end up with more cool tools after the project is done?" So it should come as no surprise that I have a strong affinity for the DIY community. A few years ago I was completing work on my first tube preamp which I'd built because I was curious about how tubes work. Frankly, I wasn't very satisfied with the results. 

This led me to ask a very simple question that I couldn't find a good answer to. Why (pre)amplify something before you amplify it? I stared at the complexity of my tube preamp with its own power supplies and glowing tubes and realized that it was every bit as complex as the power amplifier which followed it. Did that make any sense? What would happen if I chucked the whole thing and went with just a potentiometer between source and power amp? This started me down the path of passive preamps with various grades of potentiometers and even stepped attenuators. I soon confirmed that in most cases you simply don't need an active preamp to get very satisfying results. In my research on attenuation I eventually stumbled upon the use of light-dependent resistors as yet another alternative. Ever curious I cobbled together a simple series/shunt configuration of LDRs from Silonex and was completely blown away by the difference in sound quality between LDRs and conventional resistive attenuators.