| The
following article appeared in
Issue No.22
Winter 1994-95
"David Rich, as an engineer, is one of the biggest fans of Chris
Russell as an engineer, so David should have written the review of
Chris's latest-and-greatest preamp. Because of various intramural
errors - all of them my fault - David never had a chance to do so,
and therefore, since "the buck stops here," I am closing
up the breach.
The BP20 replaces the 11B and 12B series in the Bryston line and
represents a complete rethinking on the part of Chris Russell of
just how a preamp should go together. The basic Bryston gain-stage
topology, using operational amplifiers made up of discrete components
and +24 V power supplies, has not changed (at least as far as I
can see), but the physical layout and construction of the unit are
new and different. The main chassis is pancake-flat (barley 1 1/2"
high); the power-supply transformer is a separate external unit
with an "umbilical cord." The PC boards have been redesigned,
the signal paths simplified, and a ground plane incorporated. Each
of the two channels has two XLR balanced and one XLR balanced output,
five unbalanced inputs and two paralleled unbalanced outputs, plus
a tape loop. That provides a lot of interface flexibility. There
is no selector switch (a debatable signal-path simplification),
only a toggle switch for Tape/Source selection. A balance control
with 12 o'clock detent is next to the continuously variable volume
control. The construction details are absolutely beautiful: parts
quality is high.
Two favorable characteristics become apparent in the course of
my measurements: (1) there was no "better" channel, the
two being absolutely identical in distortion and noise, and (2)
the balanced signal path distortion was just as low in distortion
and noise as the unbalanced. This uniformity was new in my experience.
On the other hand, the balance control at the detent was off by
0.7 dB at unity gain with 2 V out (XLR in/out).
The THD + N versus level measurements yielded outstanding results.
With either unbalanced in/out or XLR in/out, the 20Hz and 1kHz distortion
dropped to a minimum of -97dB shortly before the clipping level.
The 20kHz curve showed a small amount of dynamic distortion but
only above 4 V and 8 V out (unbalanced and balanced, respectively),
so it is of no significance. Maximum undistorted output was approximately
14 V unbalanced and 28 V balanced - I think that should be sufficient
for any application, don't you? The curves were absolutely linear
(i.e., noise-dominated), the noise floor appeared to be no better
and no worse than I had seen in other topnotch preamplifiers, give
or take a couple of dB. Channel separation, one of the stumbling
blocks with a compact chassis and a balance control, was much improved
over the 11B. Under worst-case conditions (balanced was worse than
unbalanced , unity gain worse than full gain), the separation was
70dB or better (up to 85dB) at nearly all frequencies. Messing with
the balance control made things worse at the highest frequencies;
54dB at 20kHz was the most screwed-up reading I was able to obtain
that way. This is still highly acceptable performance.
The Bryston BP20 is only the second preamplifier we have tested
- the first was the Krell KRC-2 that will accept both balanced and
unbalanced inputs and deliver both balanced and unbalanced outputs.
If that's what you need - and in certain highly elaborate audio
systems you almost surely will - the Bryston outperforms the Krell
in most respects at 38 cents on the dollar (unless you feel the
Krell's CMOS remote control alone justifies the other 62 cents).
As a purely unbalanced front end the Bryston has some rivals, though
no indisputable superiors, and its look-and-feel make it a delight
to use in any event."
We invite you to experience the Bryston SST2 Series amplifiers
20 Year Warranty - A Generation of Music
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