Sam Tellig:
I have a way of grating on people's nerves. Ask Marina, my wife. She calls it my "mean streak." I can't help it. I take perverse pleasure in slowly tormenting someone whom I sense is unsure and insecure. Especially about hi-fi.
This took place more than 20 years ago. An audiophile friend had purchased a pair of KEF 104 speakers for a song. He did so at a bank auction following the demise of an area hi-fi shop.
"You bought the speakers. Now you have to drive them," I laughed.
"What do you mean? I have separate components. My power amplifier…
Paul phoned me about two such products: the Model 8.0 preamp (which should be available by the time this article appears), and the solid-state, switch-mode HCA-2 two-channel amplifier, which has been available for several months. The HCA-2 retails for $1695; Paul expects the preamp to come in at about the same price. "I know you love tubes," Paul said. "You'll flip over the HCA-2."
"Why didn't you make a tube amp?" I shot back.
"Funky devices," replied Paul. "Anyway, as you know, transistors are valves, too. They turn the power-supply voltage up and down in direct…
"The amount of current required to switch a MOSFET device is minuscule relative to a bipolar, and their switching speed is superior as well," said Paul. "The HCA-2 switches on and off in a series of pulses. If you have a very quiet passage of music, if there is very little musical signal, the pulses are still happening, but they're on for a tiny period of time. When the musical signal gets louder, then these little pulses get longer. The longer each pulse stays on, the louder the music gets. So by changing the width of the pulse in response to the music, we end up generating the musical…
"In terms of real estate, that's right. When we first started working on this amplifier, the original prototypes used a very small power-supply transformer. It must have been a quarter the size of that moose you see in there now. The amplifier is so efficient that you really don't need this big transformer. At the very end of the listening period, we started playing around with very big transformers. We could measure no difference compared to smaller transformers, but we could sure hear it." Just like the early PS Audio preamps.
"What do you think a larger transformer is doing […
Kalman Rubinson reviewed the HCA-2 in December 2002 (Vol.25 No.12): It is Stereophile's policy not to rush to publish the first review of a product, but to take the time to be thorough, reflective, and responsible. But in the case of the PS Audio HCA-2 amplifier, so many comments have already been published, even in Stereophile, that by the time this review sees print it might seem like old news.
First, PS Audio released a good number of beta samples of the HCA-2 to their website subscribers, and posted many of those subscribers' comments. That created a good deal of consumer…
Music, At Last
Finally, the renovations were complete, the plastic sheets came down, everything was vacuum-cleaned (even the equipment rack), and I settled in to listen to the HCA-2. The HCA-2 didn't sound any different from what I remembered of the brief initial audition, when it was cold and right out of the box. It did sound strikingly clear, pure, and open. Sure, there was the joy of getting close to my music again after months at more than arm's length—but the HCA-2 was magnetic. It made me want to listen to every recording that I was familiar with, to see if maybe there was…
I also played a round robin of amp comparisons that pitted the HCA-2 against the Bel Canto eVo 200.2 and eVo2, Sonic Frontiers Power 3, McCormack DNA-1 Rev.A, and the Classé CAM-350 monoblocks. Of these, the HCA-2 was most similar to the Classés, particularly in their open, grain-free, and spacious upper midrange and treble, although the HCA-2 offered a more close-up soundstage. The Classés had more generous bass at all levels, and seemingly unlimited power. At comparably high levels, the Classés inspired confidence—but while I always waited for the HCA-2 to poop out, it never did. That's…
Sidebar 1: Kal Rubinson's Associated Equipment Analog source: Heybrook TT2 turntable, SME III tonearm, Ortofon SME30H cartridge.
Digital sources: California Audio Labs CL-20 DVD/CD player, Meridian 508.24 CD player, Sony XA-777ES SACD/CD player, Mark Levinson No.360 DAC, Weiss Medea DAC.
Preamplification: Sonic Frontiers Line-3, Nagra PL-L preamplifiers; Audiolab 8000PPA phono stage; TacT RCS 2.0 Digital EQ/Room Correction.
Power amplifiers: Bel Canto eVo2 and eVo 200.2, Sonic Frontiers Power-3, Classé CAM-350 monoblocks, McCormack DNA-1 Rev.A.
Loudspeakers: Revel Ultima…
Sidebar 2: Measurements The PS Audio HCA-2 inverted absolute polarity, and its balanced and unbalanced inputs featured almost identical voltage gains: 30.2dB and 30.4dB, respectively, into 8 ohms, both of these on the high side. As a result, it took only 1V or so to drive the amplifier to clipping. The input impedance at 1kHz measured a high 98k ohms via the unbalanced RCA jack, just under half that figure via the balanced XLR jack.
The amplifier's output impedance was moderate, at 0.2 ohm over most of the audioband, rising slightly to 0.3 ohm at 20kHz. As a result, the…
Because this measurement also includes the contribution of noise, I again wondered if the graph was being affected by ultrasonic noise. However, monitoring the distortion content on an oscilloscope screen indicated that the rise in distortion at high frequencies is indeed due to nonlinear behavior. This is shown in figs.6 and 7. Fig.6 was taken at 1W into 8 ohms. The measured THD+noise level was 0.16%, and the distortion content can be seen to be almost pure third harmonic. However, if the load is halved to 4 ohms and the power increased a little, the third harmonic is joined by higher odd-…
