PS Audio 100C Power Amplifier Review

The PS Audio Model 100C dual-mono power amplifier is rated to deliver 120 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.1 percent total harmonic distortion. Its 4-ohm rating is 200 watts per channel. Although it resembles a number of other basic high-power amplifiers externally, the PS100C incorporates several unusual design concepts that set it apart.

The input stages of the PS100C use matched JEFT’s (junction field-effect transistors), and it has highspeed matched bipolar output transistors. The intermediate stages employ full complementary circuitry, and the amplifier is completely direct-coupled from input to output. Because the open-loop gain of the PS100C is relatively low, the amplifier uses only 12 dB of overall negative feedback, which minimizes slew-induced distortion. Despite the small amount of feedback, the amplifier’s harmonic distortion remains low at any frequency or power output within its ratings.

No electronic current-limiting circuits are used to safeguard the output transistors. Speaker fuses, one for each channel, serve that purpose, and their location in the feedback loop effectively eliminates any distortion that might otherwise result from variations in the fuses’ resistance caused by temperature changes during high-power operation. The speakers are protected against the presence of a DC voltage offset in the output, which might damage the speakers or cause distortion, by an active servo circuit with a 1-second time constant. Even the lowest program frequencies are unaffected by this circuit. The power supply uses a specially wound high-current transformer with a separate 25-ampere bridge rectifier and 30,000 microfarads of filter capacitance for each channel.

The all-black PS Audio 100C is relatively large and heavy for its power rating. It weighs about 40 pounds. The 19-inch-wide front panel, slotted for rack mounting, is 5-3/4 inches high and 3/8 inch thick, and the chassis extends 12 inches behind the panel (not including the 1-1/4-inch-deep heat-sink fins that occupy most of the rear apron). There are an input phono jack and a pair of multiway binding posts for each of the channels.

The amplifier has no external fuses; the two speaker fuses and a power-line fuse are located inside its case. Other than the nameplate, the front panel contains only a rocker-type power switch and a small red led power-indicator light. Price: $1,195.

Lab Tests

Although the PS100C’s heat-sink fins became quite hot during the 1-hour preconditioning period, the rest of the amplifier remained comfortable to the touch. In normal operation the amplifier stayed cool and the heat-sink fins became only slightly warm.

The outputs clipped at 134.5 watts when the amplifier was driving 8-ohm loads at 1,000 Hz. Into 4 ohms, the output at clipping was 209 watts. The 2-ohm clipping power level could not be measured since the speaker fuse blew before clipping occurred. In dynamic power tests, the output was 120 watts into 8 ohms, 220 watts into 4 ohms, and 272 watts into 2 ohms.

The PS100C’s slew factor exceeded 25, its output rolling off smoothly as the frequency was raised to our limit of 500 kHz. The amplifier was stable with reactive simulated speaker loads. Its low-level frequency response was perfectly flat from 5 to 20,000 Hz, reaching —3 dB at 100 kHz. An input of 125 millivolts was required for a reference output of 1 watt, and the A-weighted noise level was — 90.5 dB referred to 1 watt.

Driving 8-ohm loads at 1,000 Hz, the amplifier’s total harmonic distortion was under 0.02 percent from 1 to 50 watts, reaching 0.058 percent at the rated 120 watts. Into 4 ohms, the distortion was typically 0.03 to 0.05 percent up to 50 watts, rising to 0.1 percent at 150 watts and 0.14 percent at 200 watts. Into 8 ohms, the distortion at rated power was under 0.06 percent from 20 to 3,000 Hz, rising to just under 0.2 percent at 20,000 Hz. At half power and one-tenth power, the distortion readings were lower, less than 0.025 percent and 0.016 percent, respectively, up to 3,000 Hz and rising to 0.125 and 0.1 percent at 20,000 Hz.

Comments

The PS Audio 100C more than lived up to our expectations. Although its power ratings are not as high as those of some amplifiers we have used, it can easily drive virtually any home speaker system to very high levels. In the process, it is not likely to generate audible levels of any of the multitude of forms of distortion that have been postulated or detected in the output of amplifiers.

The PS100C impressed us not so much by its sheer power as by its total silence. Of course, the absence of a cooling fan contributes to that silence, yet the coolness of the amplifier’s exterior was striking in comparison with most similarly rated amplifiers. But there was also not a trace of vibration or buzz from the power transformer, to say nothing of the extremely low residual noise in the amplifier’s outputs. In fact, the only external evidence that the amplifier was in use was the tiny red power light on its panel. Strangely enough, the only small criticism we could level at the PS100C concerned the power indicator. It is recessed into a narrow groove extending the full width of the panel and can be seen only when viewed from directly in front. From most parts of the room it was completely invisible, and it is only too easy to forget that the amplifier is running.

In our listening tests, the PS100C sounded essentially like most other high-power amplifiers we have used, which is to say that it had no sound character of its own. Our concept of a good amplifier is one that delivers all the power you will ever need, plus a healthy reserve, with total reliability and with absolutely no added noise, distortion, or other unpleasantness under any operating conditions. By those criteria, the PS Audio 100C is a superb amplifier.

Read all

PS Audio reviews

Read all