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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PSA's preamps and amps were about to be completely revamped using the Gain Cell technology, which would make the review out of date as soon as it appeared.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…
Follow-Up, from July 2006 (Vol.29 No.7):
"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…
Sony Classical's head of engineering, David Smith, is a man whose opinions on sound quality I have come to respect. So when David e-mailed me a year or so back, enthusing over a new DAC he'd heard, I paid attention. When Lavry Engineering contacted me about reviewing their DA2002, I didn't need much persuading.
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…
As I write these words, I am about to drive to Goshen College in Indiana to record my fourth CD for Cantus, the unaccompanied male choir from Minnesota. One thing I have learned from my previous three recordings of the group is that when singers let it all hang out, lesser CD players and digital processors lend the mid-treble a shouty quality, almost a "rattle." Some of this is real—I hear it when I'm in the hall with the singers. But with the Lavry fed by a Mark Levinson No.31.5 transport, my 2003 Deep River CD (Cantus CTS1203) sounded as sweet in this respect as Cantus had live. Perhaps…