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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-…
Sidebar 3: Specifications
Description: Solid-state, two-channel "Hybrid class-A" power amplifier with class-D switching ("SDAT") output stage. Inputs: 2 pairs line-level (1 pair RCA, 1 pair XLR). 4 WBT multiway binding posts. Power output: 150Wpc into 8 ohms (21.8dBW), 225Wpc into 4 ohms (20.5dBW), 275Wpc into 2 ohms (18.3dBW). Frequency response: 10Hz-20kHz, ±0.5dB. THD+N: <0.2% at full rated power into 8 ohms (1kHz). Input sensitivity for full output: 1.15V. Input impedance: 100k ohms. Voltage gain: 30dB.
Dimensions: 17" W by 4.5" H by 14" D. Weight: 35 lbs.
Serial number of…
John Atkinson returned to the PS Audio HCA-2 in January 2006 (Vol.26 No.1):
When Kalman Rubinson reviewed PS Audio's HCA-2 for the December 2002 issue (Vol.25 No.12), he enthused over the sound of this 150Wpc, $1695 power amplifier, but I was bothered by some anomalous measured performance. The amplifier was less linear, particularly at high frequencies, than I had expected. Fig.1, for example, shows how the amplifier's THD+noise percentage varied with frequency at 2.83V into 8, 4, and 2 ohms. Acceptably low in level into the higher impedances and at midrange and low frequencies, and…
Robert Deutsch wrote about the HCA-2 in January 2006 (Vol.29 No.1):
PS Audio's HCA-2 power amplifier was originally provided to me as a companion to their PCA-2 preamp, which I was set to review. That review was abandoned when we got word that PSA's preamps and amps were about to be completely revamped using the Gain Cell technology, which would make the review out of date as soon as it appeared. I'd grown quite fond of the HCA-2 in my casual listening, and I was interested in how it would compare with the PS Audio GCC-100. To keep things on as level a playing field as possible, the HCA-2…
In 1977, just as I was about to take my first faltering steps in hi-fi journalism, the UK's Hi-Fi News ran two articles, translated from French originals by Jean Hiraga, that seemed to me and many others to turn the audio world we knew upside down. The second of them, "Can We Hear Connecting Wires?" was published in the August issue and is the better remembered because it introduced many English-speaking audiophiles to the contention that cables can sound different. The earlier article, published in the March issue, was less earthshaking but still an eyebrow-raiser of considerable force.…
The AddDistortion utility I've written to apply different patterns of nonlinear distortion can be downloaded from my website. I invite anyone who wishes to satisfy themselves on the subjective effects to try it for themselves. The software processes mono 16-bit/44.1kHz WAV files only, but the two channels of a stereo source signal can easily be separated, and the distorted versions recombined, by using either a software editor or two other utilities available on my site: ChannelIsolate and ChannelCombine, which do as their names suggest.
I used AddDistortion to apply four different…
Sidebar: Crunching the Numbers
To add a desired pattern of nonlinear distortion to a signal, you must first calculate the required polynomial expression relating output amplitude (y) to input amplitude (x), which takes the general form
y = ax + bx2 + cx3 + dx4 + ...
where a, b, c, d, etc., are parameters that determine the pattern of nonlinearity. This equation, called the transfer characteristic, is often plotted as a graph with input voltage along the horizontal axis and output voltage along the vertical axis.
The values of the parameters can be calculated from…