BRYSTON 8B-ST AND 5B-ST

By Peter Aczel - Editor and Publisher, The Audio Critic

Regular readers of this journal know that a Bryston power amp is always a completely predictable performer. There are very few audio equipment brands about which I can say they are as good as money in the bank, but Bryston is one of them. Chris Russell's basic amplifier circuit concept, frequently discussed in our pages, has changed very little over the years; in this instance it has undergone some refinements. Chris's engineering associate Stuart Taylor (ST) is recognized as a layout guru, and has come up with entirely new physical layouts for these multichannel amplifiers in order to simplify the signal paths and bring distortion, hum, and noise down to new low levels. Another improvement has to do with what Bryston calls their input buffer-with-gain, also designed tolower distortion and noise, but certainly not a major change. In all essentials, a Bryston is a Bryston is a Bryston - just specify how many channels you want on one chassis and how much power per channel. Whatever configuration you choose, you'll have an amplifier on the leading edge of the art.

The rated power per channel of the 4-channel 8B ST and 3channel 5B ST is the same: 120 watts into 8 ohms. My measurements showed 150 watts to be available at extremely low distortion: between -96 and -98dB (barely over 0.00 1%) at any audio frequency. Into 4 ohms the output did not quite double but reached 225 watts with -90 and -96 dB distortion, the least good figure being the 20 kHz reading (-90 dB = 0.003%). The THD + N curves were entirely noise-dominated and indicated extremely low noise even at only 10 milliwatts output ( -61 and -64 dB, depending on the load). With two channels bridged, I measured 400 watts into 8 ohms with distortion that dipped as low as -100 dB at 1 kHz and -93 dB at 20 kHz.

The PowerCube test (see Issue No. 20 pp. 16-17, for a complete explanation and illustrations) painted a pretty decent picture, with 39.5 V into 8 ohms/0degrees (195 W), quite gently declining voltage into all the purely resistive loads down to 1 ohm, and always slightly higher voltage into the reactive loads than into pure R. Into 1 ohm/0degrees there was still 22.3 V (497 W) available.
(Remember - the PowerCube uses 1 kHz bursts of 20 ms duration, limiting the amplitude at 1% distortion.) For better performance you would have to go to one of the mega-power-supply amplifiers. With two channels bridged, the PowerCube slopes much more steeply, since 2 ohms and 1 ohm loads are not a good match to the bridged output stages, but there are still no anomalies into reactive loads. Into 8 ohms/0degrees the PowerCube reading was 72.5 V (657 W) in the bridged mode.

Needless to say, the frequency response of each Bryston channel is dead flat. At approximately 1 watt into 8 ohms I measured 0.0 dB deviation from 10 Hz to 2 kHz, 0.04 dB at 20 kHz, and -0.22 dB at 50 kHz. Channel separation as measured at the same output level is OK but not great: 40 dB at 20 kHz, increasing by 6 dB per octave at decreasing frequencies, reaching 64 dB at 1 kHz and 90 dB at 20 kHz.

The obvious comparison that comes to mind here is with the McIntosh MC7106, which is a 6-channel model listed at $3500.00. The Bryston amps do quite a bit better on the PowerCube, indicating a power supply advantage, but the McIntosh is even lower in distortion (though not at 20 kHz in the bridged mode) and slightly higher in power output before clipping. The noise floor is a very close contest, but in channel separation the McIntosh wins. The Brystons both have balanced (XLR) inputs in addition to the standard RCA phono jacks; the McIntosh does not. On the other hand, the McIntosh is dead silent mechanically and electrically, whereas both Brystons have a slight mechanical hum coming directly from the power transformer, especially when cold, and produce small but audible on/off thumps through the speakers. As for warranties/guarantees, Bryston is way ahead with their free and unconditional 20-year deal, but the McIntosh amp offers more complete electrical protection against failure and abuse. On balance, I'd say the audio purist will lean toward the Brystons and the convenience seeker toward the McIntosh, but overall it's a win-win situation.

In any event, I rate both the Bryston 8B ST and the Bryston 5B ST in the tip-top category of power amps.

We invite you to experience the Bryston SST² Series amplifiers

20 Year Warranty - A Generation of Music