April 15, 2005AVTAC Pasiphae Transformer Attenuator
Months later, I had the final version in my system. Months after that, with a few hundred hours of listening time logged, I am at last ready to go public with my opinions. As for Parrys outlandish claims, hang on to your hats.
The principle of transformer attenuation
Audio design remains part marketing, part engineering, part science, part whimsy, and part general chicanery. It is the singular individual who would undertake such a vocation, and that about describes AVTACs founder, Dave Parry. His formal training is in computer programming, and his passion is traditional circuit design and tube electronics. The latter he learned the old-fashioned way, from his father.
Neither father nor son is known to suffer fools gladly, and both are large and occasionally ill-tempered men. In such company, solid, time-honored circuit design thrives and bullshit quakes. For this reason, transformer attenuation is a problem tailor-made for the Parry philosophy: a simple, traditional technology that addresses the seemingly simple problem of controlling volume. Every preamp does it, and every stereo needs it.
The standard volume control is the cheap and reliable variable resistor. A resistor simply takes the energy of an electrical signal and converts some of that energy to heat, leaving a signal thats smaller in terms of both voltage and current. If you find comfort in the water analogy for the flow of electricity, the voltage is analogous to pressure, and the current represents the flow rate. Imagine water flowing through a hose at a certain rate and a certain pressure. Make a hole in the hose and some of the water sprays out, leaving in the hose lower pressure and a lower rate of flow. Placing a resistor in the path of an electrical signal accomplishes something similar.
The transformer attenuator addresses the problem of attenuation by using a transformer rather than a resistor to decrease voltage. A transformer can take a high-voltage, low-current signal and convert it into a low-voltage, high-current signal of the same energy (minus some small losses in the transformer). Hence, you get the decrease in voltage that you need to lower volume while losing next to none of the signals energy. Instead of demolishing the signal and then resuscitating it actively, voltage is exchanged for current to achieve the desired result. Impedance between the source and the amplifier are matched in a manner similar to the way the transmission in your car matches the high-rpm/low-torque output of the engine to the low-rpm/high-torque rotation at the wheels. Best of all, the process occurs in a single step using a single passive component.
There are other advantages. Transformers have a primary coil that is coupled with a secondary coil through an air gap, so the signal applied to one coil is physically separated from the output at the second coil. This can decouple ground loops in the system, decreasing noise and hum. Coils can be easily wired in a balanced configuration, hence transformer attenuators are naturally compatible with both balanced and single-ended equipment.
For all of these reasons, transformer attenuators can be found in pro-audio recording studios and concert halls. Unfortunately, transformers must be carefully designed for flat frequency response, and they require that each attenuation step be individually wired for practical volume control. These factors make transformer attenuators large, heavy, and expensive, even as the associated electronic circuits in active preamps keep getting cheaper. For these reasons, transformer attenuation has remained relatively unknown in home audio. Until now.
A first look at the Pasiphae
The name Pasiphae is pretty cool. In fact, almost everything about this product is cool. The name sounds a bit like passive, which is appropriate -- transformer attenuation is a form of passive attenuation. Pasiphae comes from a Greek myth involving bestiality, which I wont go into, and is also the name of Jupiters 15th moon. (Look for other AVTAC products named either for moons of Jupiter or illegal sex acts.) The original Pasiphae prototype had a retro-industrial style of which I was very fond, including a rack-mount faceplate with handles and a nixie tube display that showed the volume attenuation steps numerically. Nixies are vacuum-tube curiosities containing filaments in the shape of numbers that glow orange. Again, very cool. Because these numbers are almost an inch high, they are much easier to read than standard LED displays.
With all this included in the prototype, I suspected that Dave Parry would go all out for the production version. Still, it floored me. The Pasiphae has a thick, CNC-machined aluminum faceplate (no handles) in a tasteful muted silver-white with two nixie tubes per channel, and a series of flush-mount buttons along the bottom. The Pasiphae logo is deeply engraved on a black anodized center strip, and flanked by two large brass knobs plated in 24k gold. The knobs must weigh a pound each. Their super-smooth rotations are coupled to optical rotary encoders. The units dimensions (19"W x 6"H x 21"D) will just fit into a standard stereo rack shelf, and the very heavy (60 pounds) milled-aluminum chassis is supported by five (yes, five) vibration-damped feet of gold-plated brass. The effect is clean, ultramodern, and shockingly handsome.
The downside is that my other components couldnt measure up to the appearance of the Pasiphae. My dCS Delius and Purcell, for example, are awesome megabuck components. Next to the Pasiphae, they looked like something from the Blue Light Special at Kmart.
As handsome as the Pasiphaes front panel is, its rear panel is what gives a sense of what this thing can do. Six stereo inputs are provided. Four are single-ended with RCA connectors, and two are balanced with XLR connectors. The Pasiphae will output to the amplifier(s) in single-ended or XLR, with two stereo sets of each if you fancy biamplification (wow!). There is a standard detachable power cord socket (IEC type), and a mains switch in addition to the front-panel Standby/On switch. Mains voltage can be set to 120V or 240V. A heavy, milled-aluminum remote was included whose signal was so powerful I could control the Pasiphae without even pointing the remote at it. Try not to drop this remote on your foot.
Inside the Pasiphae
I thought the innards of the Pasiphae surprisingly elaborate for a passive device. At its heart are two third-generation, UK-made, Stevens and Billington transformers (one per channel) with mu-metal (antimagnetic) shielded cases sturdily affixed to the chassis with acrylic mounts. These provide 23 attenuation steps from 0 to -52dB in 2dB increments (3-4dB at the extremes), which results in a wiring harness containing 46 wires per channel, each wire soldered to a very large, heavy-gauge circuit board containing an array of nearly 100 reed relays -- honest-to-goodness electromechanical switches operated by microcontrollers. Every component, from the wire to the connectors, is premium audiophile grade. Power to the unit comes from two power supplies, one for the nixie tubes and one for the microcontrollers. Because there is no active power in the signal path, the quality of the power cord has no effect on the sound, for once. (I tried it.)
The manual is professionally designed, clearly intelligible for the most part, and contains humorous touches, although the safety warnings and legal disclaimers are a little overdone. I would expect fewer safety warnings in the manual for a nuclear warhead. Despite the manuals thoroughness, the number and configurability of the features make operating the Pasiphae a rather daunting task. In addition to the usual abilities to mute, select inputs, and control phase and channel balance, three grounding configurations are offered to control system hum. The latter came in quite handy in my system.
Everything -- and I mean everything -- about the way the Pasiphae operates can be configured by the user. This includes the information displayed by the nixies (the selected input, the attenuation steps in positive or negative or absolute values, the time and date in various formats), what happens when the Pasiphae is in standby mode, the sensitivity of the remote, the individual functions controlled by the knobs and buttons, and even the way the indicator light on the front panel blinks (30% dimmed, slowly fading in and out, heartbeat, quick blips -- seriously). Because of the unlimited configurability of the panel controls, they are unlabeled, which has made it difficult to explain to my wife how to work the Pasiphae, let alone remember how to do it myself.
Ease-of-use issues aside, every aspect of the Pasiphae screams cost-no-object. You will not find a better-built or better-looking component, period.
My system runs direct from a digital front end consisting of the Sony SCD-777ES SACD/CD player acting as a transport through a dCS Purcell-Delius combination of upsampler and DAC. My experience has been that the Delius digital volume control outperforms both the expensive aftermarket Dact resistive volume control I tried and a variety of active preamplifiers that have been through my system. As a result, I normally use no preamplifier. My digital cable is the MIT Digital Reference with MIT 350 interconnects running to a KR Enterprise 300bsi single-ended tube amplifier. Speaker wire is Cardas Neutral Reference biwire, and the speakers are JMlab Electra 915.1. I use Transparent PowerLink Super power cords upgraded with Furutech IEC connectors.
Cutting the mustard
Ive been struck before by audio components that use an entirely different technology to do what they do. The difference between a solid-state amplifier and a single-ended triode comes to mind, as does the ion-tweeter/horn-based Acapella speaker compared with standard dynamic speakers. For those used to listening for fine distinctions between different brands that use similar technologies, the shift in the frame of reference can hit you like a hockey puck to the head. So it was with the Pasiphae.
Most components benefit from break-in, and transformers especially seem to follow that rule. The Pasiphae was no exception, though I must say it sounded not too bad right out of the box. Each attenuation step involves distinct windings within the transformers, so the more commonly used volume settings break in first. I put the unit through a couple of months of regular use before getting down to critical listening.
Showcase, a sampler CD from Opus 3 [Opus3 21000], features a collection of beautifully recorded, primarily acoustic tracks. The gospel blues "I Want Jesus to Walk With Me," by Eric Bibb, stands out as exceptionally detailed and musical. Keeping in mind that the Pasiphae was competing not with another preamplifier but with no preamplifier at all, I expected to hear a decrease in transparency. This is emphatically not what I got. Instead of less transparency, there was much more. Bibbs voice was both more detailed and more vivid. The accompanying guitar had significantly more subtlety, with a sense of more information coming through. The presentation as a whole was suddenly snapped into focus and energized. I had the impression that the depth and width of the soundstage were expanded in scale without any bloating of the images. The overall effect was a big improvement in realism. Very impressive.
The Bibb selection goes through some very wide dynamic changes. One minute hes whispering and the next hes shouting. Normally, I find myself reaching for the volume control several times during the piece. The Pasiphae tracked these dynamic changes, but with less harshness and abruptness. In my usual setup, I often have the impression that louder sounds are more tonally vivid and realistic, which makes me tend to want to turn up the volume in the quiet parts. With the Pasiphae, the soft passages were just as tonally rich as the loud, allowing satisfying listening even at low volumes. If anything, soft passages should have a high degree of emotional intensity, and this the Pasiphae was uniquely able to achieve. The dynamic contrasts were rendered nicely, with seemingly boundless energy on loud transients, but the increased intensity of the soft passages made me much less tempted to reach for the volume control during a performance.
What could the Pasiphae do with more complex instrumentation? Showcase also includes a Dixieland version of "Comes Love," by the Swedish Jazz Kings, that is normally not particularly enjoyable through my system. The tune is upbeat with heavy tubas, honky-tonk piano, and all the multifarious instrumentation typical of Dixieland. Inevitably, they are all playing together. The usual effect is one of overcooked jambalaya or [insert stew-like mélange of choice]. The improvement through the Pasiphae was simply stunning. Suddenly, it seemed that every instrument occupied its own airspace. I could allow my ears to roam over the presentation, focusing my attention on any player at will. The more I listened to a given instrument, the more it came forward with all the detail I cared to take in. I realized that my usual system actually smears and jumbles sounds together, while the Pasiphae sorted them out cleanly and naturally.
How did the Pasiphae sort out the soup? With, in a word, speed. The Pasiphae was like adding a nitrous booster to my stereo in terms of the speed of transient delineation. There was no damping, no smearing, no hesitating, no rolling-off. I believe these qualities gave rise to the usually grumpy Thorsten Loeschs borrowing of a certain cats pithy phrase, "insultingly neutral," to describe transformer-attenuator sound. The Pasiphaes speed also had an effect on perceived tempo. The Swedish Jazz Kings track, for example, had more bounce and drive than Im used to, which allowed me to experience the joyful exhilarating effect that Dixieland is supposed to have.
Bass was leaner and meaner compared with my usual setup, going from about 15% body fat in my regular configuration to 5%, with no loss of deep extension. There was no extra emphasis in the bass region, however, such as one hears with many active preamplifiers. Flab-free bass with maximal articulation is a bit of a holy grail for many audiophiles. They should not be disappointed in the Pasiphae.
The Pasiphaes top end, as heard in clarinets and piano in "Comes Love," was evenhanded, with good extension into the very highest registers. Recordings that tended toward brightness through my regular system were tamed to some extent in the top, not because of rolloff but because of better articulation and detail in the extreme treble through the Pasiphae. My only significant critique here would be a bit of extra reverberant energy in the upper mids, although this diminished over time, suggesting a break-in issue. The noise floor, which was a bit higher throughout the frequency spectrum than through my Delius alone, also rode a little higher in that region. The noise floor tends to rise with greater information retrieval from the source, tape hiss being the classical example. In the case of the Pasiphae, this was an easy tradeoff for me to make, given the obvious benefits.
The Pasiphae improved just about everything: speed, microdynamics, focus, ambience retrieval, tonal vividness, and rhythmic drive. Impressive as it was using single-ended cables, I was bowled over when I switched to the balanced outputs of my Delius DAC. As advertised, the balanced configuration did seem to be a natural match for the transformers. They responded with a generally fatter, more relaxed sound while retaining all the good qualities of the single-ended configuration. I loved it.
I did some comparisons by using the Delius digital volume control with the Pasiphae wide open, then switching to the digital volume wide open and the Pasiphae set to produce the same volume. In every case, my beloved digital volume control was bested by the Pasiphaes naturalness, neutrality, and seemingly supernatural detail retrieval. Magnifying-glass-like improvements in soundstaging were again evident. The Pasiphaes presentation was much more palpable, vivid, and focused, focused, focused, even at very low volume. I listened to a lot of CDs during the review period, and heard the above-noted improvements in every genre of program material, from pop rock to classical.
Unique sonic properties
Its worth dwelling on the sonic properties unique to passive attenuation. As mentioned above, standard active preamplification involves attenuation of signal energy followed by a reinforcement or resuscitation of the signal in the current domain. I speculate that, during this process, the very lowest-level information drops out. The very softest sounds simply dont make it. This may be one cause of the so-called "black background" or "low noise floor." This is a good thing when it refers to lack of noise coming from the equipment. However, if the noise floor is artificially low or unnaturally "black," the louder transients seem to pop out of nowhere, resulting in peaky transients and an exaggerated sense of detail. Hyperdetail lends a hi-fi character to the sound that is initially impressive but inevitably becomes fatiguing over time.
The Pasiphae retains all low-level information down to the threshold of hearing, with no artificial blackness to the background. As the unit is passive, it generates no noise of its own. The result is that you can hear the atmosphere of the hall even when the music is not playing. The transients never pop out of nowhere. Rather, they develop and decay in a natural, believable way without being cut off abruptly when they reach the noise floor. At the same time, the superb low-level retrieval results in rich detail at all levels.
In his Preamplifier Cookbook, Allen Wright of Vacuum State Electronics coined the term downward dynamic range. According to Wright, downward dynamic range is one of those qualities that separate the preamp men from the preamp boys. I believe it. Another term that nicely sums up these effects would be Harry Pearsons continuousness, which the Pasiphae has in spades. To resort to a tired but apt comparison, the organic effect of the Pasiphae gave CDs a sense of the pleasant continuousness and wholeness associated with vinyl records.
Comparison with active preamplifiers
A valid question at this point would be: Are the improvements Im hearing unique to transformers, or can they be had with other preamplifier technologies? For comparisons, I had ready access to the well-regarded but now-discontinued Sonic Frontiers Line 3. The Line 3 lived up to its reputation for richness and strong bass, and suffused the soundstage with a warmish glow. The AVTAC bested it by a long shot in terms of detail, speed, and soundstaging without adding extra warmth. Again, the neutrality was, well, insulting. The AVTACs bass was strong and tight, though it didnt sound quite as full as the SFs famously strong bottom end. Overall, however, the Line 3 sounded just plain veiled compared to the Pasiphae.
The improvements I heard in my system were duplicated or exceeded in other systems when I took the unit on the road with me to the homes of local audiophiles. The general reaction was amazement, followed by much groaning and quick mental calculations of cash on hand.
It may be that the Pasiphaes extraordinary neutrality, focus, detail, and soundstaging are features unique to passive attenuation, though I cant exclude the possibility that todays costly top-flight preamps would compare favorably -- Boulder, BAT, Conrad-Johnson, and Audio Research come to mind. I have yet to directly compare the Pasiphae with any of these fine products, but given its superb performance in my system, Im sure Dave Parrys not losing any sleep.
The Pasiphae does not as yet come with a phono-stage option, although Parry has said he will entertain custom orders on request. Naturally, like any other source, an outboard phono stage can be run into the Pasiphae.
Some may worry that the Pasiphaes lack of active preamplification will result in insufficient loudness. Dave Parry tells me that while this is theoretically possible in a system with a source of unusually high output impedance and an amplifier of unusually low input impedance, with todays competently designed sources and amplifiers such an occurrence would be rare, to say the least. The Pasiphae drove all the systems I tried it in beyond their clipping limit. If you want to assure yourself of how loud your CD player really is, just plug it directly into your power amplifier and take cover. (Im kidding. Dont do this -- the result could be loud enough to damage your speakers.)
For many audiophiles, the sheer mechanistic elegance and simplicity of the passive approach to volume control will have great appeal. As a bonus, because there is no active power in the musical signal path, there is no need for an expensive audiophile-grade power cord or power-supply filter.
Each Pasiphae is handbuilt, with a variety of custom options (such as custom connectivity) available on request. AVTAC sells the Pasiphae direct through their website; allow three to four weeks for delivery.
The final word
At last a preamplifier is available that, in my system, is better than no preamplifier at all. It is also not an active preamplifier, but an elegantly simple and traditional solution: a single-stage passive device that does everything an active preamplifier does, with built-in balanced capability to boot. The AVTAC Pasiphae is highly configurable and laden with features, many of which go well beyond those normally found in active preamps. To top it all off, the Pasiphae is the single best-looking component I have ever laid eyes on. The nixie tubes are to die for, but Dave Parry says he wont be able to offer this feature much longer -- these curious devices are no longer being produced, and the world supply is rapidly being exhausted.
Just when you think your front end is as good as you want it to be, a product like this comes along to redefine expectations in the upward direction. The AVTAC Pasiphae holds the singular distinction of being the first high-end production transformer attenuator for the home market. I suspect other companies will follow in its lead. For now, dont even think of dropping big bucks on a high-end preamplifier until youve heard the Pasiphae. In terms of build, its a masterpiece; in terms of sound, its a whole new world.
AVTAC Pasiphae Transformer Attenuator
Advanced Vacuum Tube Audio Concepts (AVTAC)
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