ULTRA AUDIO -- Archived Article

June 1, 2003

Quick Everyone, Sell Your Preamps

The world turns, things change, the old goes out with the old and the new comes in with the new -- but not always. It seems inevitable sometimes that a few annoying relics of a bygone era must hang around, serving no useful purpose.

Even those of you who may think that the dinosaurs are long gone would not be quite correct. A close relative of those Jurassic giants remains alive and is even now turgidly basking on the rocky shores of New Zealand, serving no useful purpose. He is a lizard-like creature called Sphenodon punctatum, and he comes complete with a rudimentary third eye in the middle of his forehead, just like Tyrannosaurus.

There are also modern relics, I’ve recently discovered, among our audio components. Look deeply into your equipment rack and you may find some turgid basking going on in your own living room. It’s usually above the amplifier and below the CD player, and it is called the preamplifier. Examine it carefully, but don’t get too close: Winking display, large volume knob, selector switch, metallic skin, and reptilian torpor. Yep, that’s a preamp all right.

What is it doing there? Routing inputs from your various sources? Yes. Tone control? I hope not. Balance and phase switch? Usually. Volume control? Absolutely. Boosting the signal, as in pre-amplifier? Yes again, but wait a tick. If you plug your record player directly into your power amp, you get nothing -- or next to nothing -- so a preamp, or at least a phono gain stage, is a necessity. Non-phonograph sources such as CD players, however, produce more than enough output to damage grandma’s china if connected directly to a modern power amp. So why, in this case, is any pre-amplification needed?

The reason is that passive volume controls are evil.

Volume controls are usually variable resistors. They apply resistance in the signal path, which dissipates a portion of the energy of the signal in the form of heat. The remaining shrunken wisp of electricity then has lower voltage amplitude, which is that aspect of the signal that encodes the music. Hence, a lower volume of sound comes out of your amp. Many people have become enthralled with the transparency and detail of passive preamps consisting only of a volume control and a selector switch. The downside is that these devices attenuate current along with voltage, and current is required to drive the amp. The result is usually a lack of rhythmic energy, decreased bass fortitude and some loss of tonal vividness.

Preamplifiers solve that problem by boosting the current; in essence, they re-amplify the current part of the signal. Unfortunately, this means that a tiny shrunken signal has to pass through all the circuitry of the preamp gain stages, and a loss of transparency and detail inevitably occurs. I say inevitably, because I’ve had some of the better preamps in my system, and they always seem to add a veil of obscurity. Since my dCS Delius DAC has a digital volume control, I can adjust the volume (and save the china) without benefit of a preamp, albeit at a slight loss of resolution. Despite this, in my system, no preamp has always been better overall than any preamp.

That is, until now.

There is a new species in the jungle, folks. It is hiding in the bushes, keeping a low profile, but in its quiet way it is as threatening to the conventional preamplifier as our furry mammalian precursors must have been to the unsuspecting, walnut-brained, Tyrannosaurus. It is called the "voltage-selector and router" (VSR). In essence, this device uses a transformer instead of a resistor to down-convert the voltage of the signal while up-converting the current. Presto! No need to first destroy the signal and then resuscitate it by passing it through a pre-gain stage. A VSR gives you all the current you need by taking advantage of the power inherent in the original signal.

This is not a new concept, though it is fairly new to the home-audio market. Pro-audio components in recording studios have used transformer attenuators for years, mainly because they decouple DC, eliminating ground loops, and can handle either balanced or single-ended signals. Aside from a few low-cost products from Antique Sound Labs and others that use voltage attenuators known as autoformers (basically a single coil with a movable center tap -- you get voltage down-conversion but not current up-conversion), several true transformer attenuators are available as kits. The only company selling production models that I have been aware of previously is Bent Audio of Surrey, British Columbia. They offer a multifunctional routing and control system called the Tap that can incorporate modules containing transformer attenuators, as well as standalone VSR units. The VSR I auditioned is the Pasiphae, a new product made by a new company called AVTAC (Advanced Vacuum Tube Audio Concepts) based in Ottawa, Ontario, Canada. This is an Ultra Audio world premiere. A full review is coming soon.

The Pasiphae uses high-quality Stevens and Billington (of the U.K.) transformers, one per channel, each of which has 40 attenuation steps created by drawing fixed taps at various points from a single master secondary coil. It has three RCA inputs and one XLR input and will set you back a wallet-flattening $9600 USD. The unit comes in a handsome retro-industrial brushed-aluminum chassis with large knobs flanked on either side by a pair of nixie-tube numerical displays for the channel levels. Nixies are a pre-digital vacuum-tube technology that displays big orange numbers when the appropriate filament is lit within the tube. The visual effect is irresistibly sexy. But the way it looks is beside the point. The sound that came out of that thing was nothing short of astounding.

You would think that with a dCS Purcell/Delius source, the new BC24 hybrid amp from Blue Circle tricked out with rare Siemens tubes, and the monstrously expensive and advanced Acapella Violon speakers in my system, there would be nothing further to add. Nothing could be further from what happened when I plugged-in the Pasiphae. I’m talking about a quantum leap in speed, image definition, resolution, microdetail, dynamics, bass performance, and realism. It really works. I was so amazed I just sat there like an idiot.

Or like Tyrannosaurus rex seeing snow for the first time.

...Ross Mantle

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