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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…

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…

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…

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PSA's preamps and amps were about to be completely revamped using the Gain Cell technology, which would make the review out of date as soon as it appeared.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…

I used AddDistortion to apply four different…

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…

"Naughty But Nice," my feature article on the subject of euphonic distortion (Stereophile, April 2006), prompted an e-mail correspondence with Earl Geddes, co-originator (with Lidia Lee) of the GedLee distortion metric, which I mentioned in the piece. Geddes asked me for the polynomial coefficients I'd used to generate the four different distortion patterns, from which it emerged that, for three distinct reasons, the GedLee metric figures quoted in my article require correction.

First, I was guilty of a keying error with the GedLee…

Lavry...
I was familiar both with Lavry Engineering's pro-audio components, under its older name of dB Technologies, and with designer Dan Lavry, from his often outspoken, tech-heavy postings on the Internet newsgroup rec.audio.pro. You can find theoretical white papers…