Ypsilon PST-100 Mk.II line preamplifier Page 2
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 737 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 1028 are 1.5dB each. The final three steps (3537) 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 resistorand, 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 functionsdon't misplace it. Fortunately, it, too, is milled from a hefty chunk of aluminum. If you sit on it, you'll know itand 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 panelless than optimally convenient, but not a real problem.
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 amplifierthan 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 Deccathe 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 heardand 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 contactits texture and tonalitywith 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.