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After I sent the Sumo off to Santa Fe for measurements, I got a good news/bad news call from JA: "The Polaris you listened to was not only a pre-production sample, but defective as well (footnote 1). Its distortion on one channel was much higher than spec, and one of the TL-circuit trimpots had a bad wiper. A production sample is being Fed-Exed to you as we speak; could you give it a listen and write a followup by Monday?"

The good news? "I saw an Elvis movie on TV the other night!"

I also received a fax from Sumo's Mike Custer, who…

All the measurements were made after each amplifier had been preconditioned by running it at one-third full power into 8 ohms for an hour. This thermally stresses the amp to the maximum, though the Polaris didn't overheat. The Sumo's small-signal frequency response (fig.1) showed no surprises; neither did the shape of a 10kHz squarewave (fig.2). Both indicated a flat response, which is as it should be for a power amplifier. The input impedance at 1kHz was a reasonable 45k ohms while the signal polarity was the same as the other three amplifiers tested (Muse Model…

Description: MOSFET stereo amplifier. Power output: 120Wpc into 8 ohms (20.8dBW), both channels driven, from 20Hz–20kHz with less than 0.05% THD; 200Wpc into 4 ohms (20dBW), both channels driven, from 20Hz–20kHz with less than 0.1% THD. SMPTE IM distortion: less than 0.05% (0.25W–120W, 8 ohms). TIM: unmeasurable. Hum and noise: 105dB below rated output, 90dB below 1W. Frequency response: –0.1dB from 20Hz–20kHz, –3dB from 1Hz–200kHz. Input sensitivity for rated output: 1.3V; for 1W: 130mV. Input impedance: 47k ohms. Damping factor: greater than 500. Risetime:…

Shortly after my review hit Santa Fe, Tom Norton called to say that he'd arranged for Counterpoint to send along another SA-100; evidently, the amp I heard was one of the first hundred off the line, and Counterpoint's John Fermin felt that it might not represent a typical SA-100 as well as a current unit. The new amp arrived a few days later, but just as I was about to listen to it after a few days' burn-in, TJN called back, telling me that Counterpoint had sent it with the wrong input 6DJ8s, and that the new tubes were en route. But didn't Counterpoint subject…

The listening setup consisted of my self-modified Philips CD-50 fed my buffered passive preamp, this connected to the amplifiers under review. Interconnects and speaker cables were Straight Wire Maestro. Speakers were either Spica Angeluses or Thiel CS1.2s; all line-level gear was plugged into the Audio Express NoiseTrapper Plus.—Corey Greenberg

All the measurements were made after each amplifier had been preconditioned by running it at one-third full power into 8 ohms for an hour, which thermally stresses the amp to the maximum. Though the Counterpoint didn't overheat, its heatsinks did get too hot to touch. The review logistics meant that all the measurements were performed on the first sample. I was a little surprised by the Counterpoint's small-signal frequency response; it showed a rising trend in the top audio octave (fig.1), which results in a degree of overshoot on the 10kHz squarewave shape (fig.…

Description: Hybrid stereo power amplifier. Power output: 100Wpc into 8 ohms (20dBW), 170Wpc into 4 ohms (19.3dBW). Gain: 30dB. Frequency response: 5Hz–100kHz. S/N ratio (20Hz–80kHz, ref 85W): 92dB. Distortion (1kHz, 8 ohm load): 1% at 100W, 0.7% at 10W, 0.3% at 1W. Output impedance: 0.9 ohms. Maximum current available: 25A rms, measured 1kHz gated On for 20ms, Off for 480ms, into 0.1 ohms. Damping factor: 8.9, referenced to 8 ohms at 1kHz. Input impedance: 100k ohms, 100pF. Signal polarity: non-inverting.
Dimensions: 19" W by 4.46" H by 12.68" D. Weight: 28…

The Bryston 4B NRB available…