Bryston 9B ST
5-channel power amplifier. Tested sample on loan from manufacturer.
In amplifier design, Chris Russell and Stuart
Taylor are a combination like Joe Montana and Jerry Rice in the
NFL of the 1980s-as good as it gets. The basic Bryston power-amp
topology (the one that made David Rich call Chris "a ridiculously
good engineer" in a long-ago issue of this journal) has changed
only slightly over the years. The main improvements in the present
line have to do with physical layout and how the gain is shared
between the stages, the net result being a lower noise floor.
The ST suffix following the model number credits Stuart Taylor
for the improvements. I have already reviewed the 3-channel and
4-channel ST amps in the line (see Issue No. 24); the 9B ST is
their 5-channel model and the flagship of the line (at least until
a higher-powered version now in the pipeline is released).
This is truly a gorgeous piece of equipment.
No wonder Bryston likes to exhibit it with the cover off at the
various shows. The layout is of the utmost architectural beauty
because of its uncluttered simplicity. Five self-contained, independent
mono modules are arrayed side by side, each fully operational
by itself. Only the line cord and the on/off switch are shared.
Each module offers unbalanced, balanced, or high-gain (+6 dB)
balanced operation via a 3-position input selector switch. The
inputs accept RCA, XLR, and standard phone plugs. The transformers
generate no mechanical hum off the chassis, not even the slightest,
and there are no on/off thumps through the speakers, ever. The
only clue to power on/off is the five-LED front-panel display.
The overall impact of the amplifier in use is that you are in
totally competent, totally professional hands and nothing untoward
can happen. Both the visual and functional aspects of the 9B ST
contribute to that impression.
On the lab bench the measurements are equally
impressive. This is one of the very few amplifiers yielding identical
distortion-versus-output curves at any frequency. The 20 kHz curve
tracks the 20 Hz and 1 kHz curves so closely that the three, when
superimposed, look like one curve. No "dynamic distortion"
here! Into 8Ohms the curves bottom out at -90 dB, into 4Ohms at
-88 dB. These minima are at the precise clipping point, which
is 125 W into 8 Ohms and 200 W into 4Ohms. Needless to say, the
distortion is entirely noise-dominated, the ruler-straight curves
(is that an oxymoron?) declining 6 dB for every 3 dB increase
in power output, starting at -50 dB with 10 mW out into 8 Ohms.
I have seen slightly lower distortion figures but I have never
seen greater consistency.
The PowerCube of the 9B ST painted a highly
satisfactory picture as regards dynamic power and current limiting.
This measurement, which no other American audio magazine performs,
tests short-burst power capability into reactive (i.e., real-world)
loads. For a detailed explanation, see Issue No. 20, where the
test was first introduced. Into resistive (0 degree) loads of
8 Ohms/4 Ohms/2 Ohms/l Ohm, dynamic power of the measured channel
was 211W/350W/516W/574W. Into capacitive (-60 degree/-30 degree)
and inductive (+30 degree/+60 degree) loads, dynamic power was
slightly up at 8 Ohms/4 Ohms/2 Ohms (ideal) and at least not sagging,
though not up, at l Ohm (acceptable). Those are good numbers considering
the continuous power rating of 120 W per channel into 8 Ohms.
Crosstalk between adjacent channels at 1 W output
into 8 Ohms also declines 6 dB per octave as the frequency is
lowered, starting at -56 dB and -65 dB at 20 kHz in the two channels
I measured and ending at -105 dB and -104 dB, respectively, at
20 Hz. Of course, the channel separation would be virtually infinite,
were it not for the close proximity of the mono modules. And,
yes, I almost forgot: the frequency response, at 1 W into 8 Ohms,
is ±0.0 dB up to 5 kHz, declining to -0.07 dB at 20 kHz
and -0.46 dB at 50 kHz. Around here, we call that flat.
Bottom line: this is an impeccably designed
and constructed 5-channel amplifier, far from cheap but not shamelessly
inflated in price, since every dollar is in evidence right there
"under the hood." You can undoubtedly have the same
sound for less money but not the same satisfaction.
-Peter Aczel
We invite you to experience the Bryston SST2 Series amplifiers
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