Though essentially a two-man operation based in Athens, Greece, Ypsilon Electronics has been, since 1995, turning ears and eyes throughout the audiophile world with purist, hand-crafted electronics whose sound seems to defy characterization. Even under audio-show conditions in difficult hotel rooms, and often driving unfamiliar loudspeakers, the sound of Ypsilon electronics seems to evaporate in ways that few products manage, leaving behind less residue and more music.

That may sound like fan hyperbole, but it's what I immediately heard a few years ago, when I first encountered Ypsilon gear at a hi-fi show. Though the company was then new to me, nothing I've heard since, at shows or at home, has deviated from that very first impression.

Ypsilon models look beautiful, even dramatically so, in their cases of thick, milled aluminum, and perhaps that's what first drew to them the reviewers and civilians who attend audio shows. What kept them there was the sound, or the lack thereof.

Many listeners tempered their initial enthusiasm with caution: A sound that good must be based on sonic tricks that only time will reveal. I found myself almost wishing that to be true, given what Ypsilon products cost. But having spent a great deal of time with Ypsilon's VPS-100 phono preamplifier ($26,000; I reviewed it in "Analog Corner" in August 2009 and March 2011), I'm convinced there are no tricks.

As is often the case in high-performance audio, less artifice comes at a high price. Ypsilon's products are very expensive, and deceptively simple in design. The PST-100 Mk.II will set you back $37,000. If you don't need the active stage, the completely passive PST-100 TA can be had for $26,000. (The active tubed stage can be retrofitted at the factory.) But either way, and considering that a preamplifier's basic job is to switch and route low-level audio signals without adding to or subtracting from any signal fed to it, these are high prices to pay for what is, essentially, nothing.

Of course, there's more to a preamp's job: It must also provide signal attenuation and, usually, gain, as well as an output impedance low enough to drive cables and interface with a power amplifier of high input impedance.

A Purist Approach
Over the past year or so, a few impressively neutral, dynamic, quiet, wide-bandwidth tube preamplifiers have passed through my listening room that rival the quiet and tonal neutrality of my reference, the solid-state darTZeel NHB-18NS. The best solid-state and tubed preamps these days are more sonically alike than different, though of course the subtle differences are the basis on which listeners who can afford such products choose.

Ypsilon's co-owner and chief designer, electrical engineer Demetris Backlavas, believes that the key to a preamplifier's sound is the means by which it attenuates the signal it's fed. Instead of the more commonly used resistor attenuation, Backlavas uses what he says is a very linear, 31-tap transformer that Ypsilon winds in-house. By comparison, he says, attenuators that use even the finest-quality resistors tend to sound grainy and discontinuous because the in-series resistor converts voltage into current, while the parallel resistor turns current back into voltage.

Not that Backlavas and his partner, Andy Hassapis, didn't try to build a better resistor-type attenuator, using a variety of materials. The problem, according to Backlavas, is that, in order to resist, a resistor must be made from a bad conductor of electricity. Copper and silver are good conductors and small-value resistors can be made from these metals that, not surprisingly, can sound very good. Unfortunately, it's impossible to use copper and silver to make high-value, wideband resistors because of the parasitic inductance that goes along with the need to use coils of very many turns. In addition, resistor-based attenuators waste signal energy by turning the attenuated energy into heat.

Nonetheless, Backlavas admits that attenuators of reasonably high quality can be built using carefully chosen resistors. You're probably listening to such a device as you read this. And, as anyone who has spent time listening to transformers (and Backlavas has spent more time listening to them than most) knows, even those with identical specs can sound remarkably different from each other, and some can ring unpleasantly or sound bad for a variety of reasons.

In fact, transformer-attenuated preamplifiers—or, more precisely in this case, autoformer-attenuated preamps, in which the primary and multi-tap secondary overlap—aren't new. Hobbyists have advocated and built them over the years, but few are commercially available. The advantage of such an attenuator over one that uses resistors is that energy is transformed and not lost as heat. Backlavas gave an example: starting with a source impedance of 1200 ohms, attenuating the signal 10dB (or 3.16 times), produces an output with lower voltage and higher current and an impedance of 120 ohms (1200/3.16²), which has an easier time driving loads, unlike the less amplifier-friendly results produced by a passive-resistor attenuator.

That said, of course, transformer attenuators have their own problems that must be solved before they can produce good sound. The core material must have low hysteresis (hysteresis being like unwanted "magnetic memory") at both low and high frequencies, and linear magnetic permeability with flux and frequency. c

So, in audio as in life, execution is as important as design—and the PST-100 Mk.II is, per Backlavas, a "fairly simple design."

The volume control output transformer, "painstakingly designed and optimized," is custom-wound at Ypsilon on an amorphous double-C core, itself chosen via listening tests. The impedance of the output stage, which is hardwired with fine, custom-drawn silver wire, is around 600 ohms. The active stage is essentially a small, single-ended amplifier.

However, there is more to know about this microprocessor-controlled circuit, which features both active and passive modes of operation. In active mode, high-quality silver-contact relays route the input directly to the transformer volume control, up to step 6. The controller then routes steps 7–37 through the active stage, to produce a maximum gain of 17dB.

When the PST-100 is set to passive mode, its active stage never kicks in. (The PST-100 is available in a less-expensive TA version that only operates in passive mode.) Instead, the signal is routed only to the transformer volume attenuator, bypassing the active stage altogether, with step 31 producing 0dB (unity) gain. In order to drive the transformer efficiently, the manual suggests not running the system in passive mode with sources whose output impedance exceeds 3k ohms.

Regardless of mode, attenuation is 3dB per step up to step 5. Between steps 5 and 10, each step is 2dB, and steps 10–28 are 1.5dB each. The final three steps (35–37) offer 1dB of attenuation each.

In addition to transformer-based attenuation, the PST-100 features 6CA4 tube rectification, choke supply filtering, and a zero-feedback active stage based on a carefully selected Siemens C3m pentode tube configured as a true triode and transformer-coupled to the output. The power supply uses Mundorf and Jensen four-pole electrolytic caps, chosen based on listening tests.

Designer Demetris Backlavas told me that, other than the silver-plated relays and transformer, the only components in the PST-100's signal path in active mode are a resistor bypassed with a Silmic2 capacitor in the cathode, and a grid stopper resistor—and, of course, the C3m tube. He also told me that he'd kept control circuitry to an "absolute minimum" in order to avoid high-frequency noise, and that, to avoid introducing noise, control signals within the preamp are static and not clocked.

No knobs, no switches
The PST-100 Mk.II's chassis, milled from thick panels of satin-finished aluminum, has no switches or knobs. The remote control handles all functions—don't misplace it. Fortunately, it, too, is milled from a hefty chunk of aluminum. If you sit on it, you'll know it—and if you don't, you'd better get to the gym.

On turn-on, an LCD screen on the front panel lights up, and for 30 seconds identifies the unit as the "Ypsilon PST-100 Mk.II," after which it changes to "Volume 00, Input 1 CD." At that point, or whenever you set the volume to "00," you can use the remote's topmost button, labeled "S," to toggle between the PST-100's active and passive modes; your selection is indicated on the display. At any volume level other than "00," this button acts as a Mute control. The next button down extinguishes the rather bright screen, while the center two buttons control volume, and the lower pair handle source selection. The inputs are preprogrammed with identifying labels (CD, Phono, Cinema, etc.) that can't be changed.

On the rear panel are six pairs of chassis-mounted inputs, five of them RCA jacks. Input 6 is unbalanced XLR. Next to the inputs are RCA and unbalanced XLR outputs. A pair of Tape Out RCA jacks is located above Input 4's RCA jacks. As on the VPS-100 phono preamp, the PST-100 Mk.II's On/Off switch is on the rear panel—less than optimally convenient, but not a real problem.

Sublime nonsound
If the Ypsilon phono preamp is any indication, the PST-100 Mk.II requires a very long break-in period. There's a lot of wire in those transformers. Even after the PST-100 had spent a few months in my system, I still wasn't sure it had fully broken in by the time I had to write this review. But even raw out of the box, the PST-100 Mk.II produced that Ypsilon "nonsound" heard at audio shows throughout the world. Still, the sound continued to open up and become more dynamic as time passed, but with little change in its tonal balance or transient performance.

While I listened in both active and passive modes, the latter's output, even with the attenuator well down from its 0dB maximum level, was more than enough to drive my Musical Fidelity Titan amp and my relatively sensitive Wilson Audio MAXX 3 speakers In passive mode, there was literally nothing but the silver relay and the step-down transformer between the incoming signal and the interconnect to the power amplifier. The PST-100 sounded about as close to the source as can be imagined. All sources, analog or digital, were steps more transparent, three-dimensional, and closer to sounding "live"—or at least closer to the source going directly to the amplifier—than I've otherwise heard in my listening room.

One of the last records I played before switching from the darTZeel to the Ypsilon was a 45rpm, single-sided, four-LP reissue of Jascha Heifetz's recording of Bruch's Scottish Fantasy and Vieuxtemp's Violin Concerto 5, with Sir Malcolm Sargent conducting the New Symphony Orchestra of London (RCA Living Stereo/Classic LSC-2603-45-200G). While it's considered to be one of RCA's best Living Stereo recordings, it's licensed from the UK and was originally produced by Decca—the engineer was the great Kenneth Wilkinson. The recording of Heifetz's violin is particularly exquisite, and a good test of a preamp's ability to convey instrumental attack, textures, and harmonic structures, not to mention precise imaging and dimensionality.

The PST-100 Mk.II managed all of those things with a purity, delicacy, and verisimilitude that surpassed the performance of any preamplifier I've heard—and I've heard and owned some very good ones. When Heifetz plays spiccato (light, staccato bowing), each time his bow bounced off a string, the Ypsilon reproduced the character of that physical contact—its texture and tonality—with glistening transparency and physical dimensionality. The only word appropriate to describe my first hearing of this album through the PST-100 Mk.II is thrilling. This familiar recording sounded more "real" than I'd ever heard it, with Heifetz more clearly delineated in space in front, and the orchestra arrayed behind him.

Against the darTZeel
After the PST-100 Mk.II had been installed, two EMI Classics recordings arrived, in a recent reissue by Esoteric Remasters (SACD/CD ESSE-90048): Otto Klemperer and the New Philharmonia Orchestra performing Franck's Symphony in D, at Abbey Road Studios in 1966 (originally EMI 5276); and Schumann's Symphony 4, recorded at the famed Kingsway Hall in 1960 (EMI 2398). I was familiar with these works, though not these recordings of them, but after numerous plays I had a pretty good handle on their sounds. The Kingsway recording was more spacious, and done from a mid-hall perspective, but both are very fine "vintage" symphonic recordings, and the 2010 transfer from analog tape to DSD, made at the JVC Mastering Center, was pristine.

Specifications

Description: Tubed preamplifier with remote control, transformer-operated volume control, and switchable passive mode. Tube complement: 6CA4, C3m. Inputs: 5 unbalanced line-level (RCA), 1 unbalanced (XLR). Outputs: 1 unbalanced (RCA), 1 unbalanced (XLR), 1 buffered Tape Out (RCA). Frequency response: 9Hz–100kHz, –3dB. THD: not specified. Signal/noise: not specified. Channel separation: not specified. Maximum output: not specified. Input impedance: 50k ohms. Output impedance: 150 ohms.
Dimensions: 15.6" (400mm) W by 7" (180mm) H by 16" (410mm) D. Weight: 55 lbs (25kg).
Serial Number Of Unit Reviewed: 017.
Prices: $37,000; completely passive PST-100 TA, $26,000. Approximate number of dealers: 8.
Manufacturer: Ypsilon Electronics, Y8 AG. Athanasioy Street, Peania 19002, Athens, Greece. Tel: (30) 210-66-44-588. Fax: (30) 210-66-44-812. Web: www.ypsilonelectronics.com