Bryston 11B - Page 3

Low Filter
The inflection point of the rumble
filter has been chosen at 31.7Hzto
correspond to the lowestsignal fre¬
quencies likely to be found in re¬
corded music, and to a suggested
revision to the RIAA recording curve
for LP discs. For these reasons, and
for the more important reason of
avoiding low frequency transient
overshoot, ringing and phase mis¬
alignment, the low filter is a
“minimum” type, with a 6dB/octave
slope below cutoff. This is quite
effective in reducing subsonic
woofer-wooble and its attendant
intermodulation effects, however,
since the most problematic turntable
and warp-induced rumble frequen¬
cies, in the area of 2-5Hz, are
reduced an average of about 20dB
or a factor of 100 in terms of power
demand. The low filter switch is
active in the In’ position, and
affects only the phono inputs.
Mute Switch
The listener often is called
momentarily away from critical lis¬
tening, to answer the phone for-
example, and wishes to reduce the
gain for a short time without disturb¬
ing the volume control setting. The
mute switch reduces preamp gain
by 20dB. Thus the music may still
be heard, but at a background level.
This is also useful for changing
records, cueing the stylus manually
to a particular song, cleaning the
stylus with a brush, etc. The mute
switch is active in the 'In’ position
and affects only the main outputs
without disturbing the tape outputs.
Mono Function
Occasionally a system will display
some offset in gain favouring one
channel over the other due to slight
differences in speaker efficiency,
differences in room loading, or a
somewhat off-center listening pos¬
ition dictated by room decor. Thus it
is convenient to "mo.no” the signal
to obtain the most unambiguous
center image, convenient to adjust¬
ing the balance control. For reasons
of simplicity, rather than having a
separate switch for this function,
the "Mute” switch also connects
the two channels in Mono.
Obviously, the listener may wish to
advance the volume control to pro¬
vide sufficient level for establishing
center image. Do not forget to
reduce the volume control again
before deactivating the mute
switch in this case, or you may be
startled by the sudden increase in
sound level. The balance control is
a tailored inflection type which has
very gradual action near the center
of rotation for fine adjustments to
the left-right balance of the stereo
image.
Turn On Delay
The Model 12B contains an output
relay with an approximate 3-second
delay at turnon, to allow any transient
thumps to settle. The relay opens
instantly when the preamp is switch¬
ed off to prevent any power-supply
decay artifacts from appearing at
the outputs. The relay is hermetically
sealed in an inert atmosphere to
completely eliminate contact con¬
tamination and provide nearly infinite
lifetime (rated in tens of billions of
cycles). This same relay is employed
in the automatic amplifier disconnect
function which is part of the head¬
phone circuit, and in the protection
mechanisms connected into the
power supply. Whenever the pre¬
amplifier is under power, and the
relay is open for any reason, the
green pilot light on the front panel
changes to red. (Since the power-
supply filter capacitors are quite
large, the red LED indication will
fade slowly after fhe preamp is
switched off).
Accessory Outlets
The 12B includes three 3-prong
grounded, 120 volt receptacles on
the rear panel, two switched, one
unswitched. Please observe the
caution printed below the re¬
ceptacles regarding maximum
power draw from these outlets.
Large power amplifiers, especially
including the Bryston Models 3B
and 4B should not be plugged
into these receptacles. To do so
may damage the preamp’s power
switch. It is permissible to plug the
Bryston 2B-LP into these outlets,
however, or any class AB amplifier
up to 50, (or class A amplifier up to
15) watts per channel. In general, it
is inadvisable to switch large power
amplifiers on and off by the switch
in a preamplifier, for the above rea¬
son, and also because it is likely to
cause a fluctuating voltage-drop on
the preamplifier's line cord, which
in worst case conditions can
become an audible problem.
DC Power-Supply Output
On the rear panel of the Model
12B (and 11B) there is a DIN con¬
nector which provides ±24V DC of
regulated power. This is provided
for future Bryston products, such
as equalizers, electronic crossovers
and the like, which will be available
with or without power supply, for
reasons of economy. This output is
fully protected, and contains a circuit
which opens the output relay auto¬
matically if excessive current is
drawn.
The Twelve-B has been designed
from a rational, function-oriented
ideal of maximum musical accuracy,
with an absolute minimum of use¬
less gadgetry or extraneous con¬
trols. The signal-handling circuit is
novel and fundamentally correct,
both electrically and more important,
sonically. We believe you will find a
renewed sense of awareness of the
listening pleasure in your music
collection, played through your
Bryston preamplifier. All your signal
sources will sound cleaner and
more muscially transparent than
you may have experienced before.
Please do not hesitate to write us
if you have any questions or com¬
ments about any of our products.
Your opinion is of paramount im¬
portance to us.
Af \ \ - Y
V J
LTD.
LTEE
57 WESTMORE DRIVE, REXDALE, ONTARIO, CANADA M9V 3Y6 TELEPHONE: 416-746-1800, TELEX: 06-989548
IN THE U.S.A. TELEPHONE 802-223-6159
Printed in Canada