BGW 150 - Circuit Description; Power Supply Circuit; Amplifier Circuitry; Bridged Mode Circuitry

12310
150 CIRCUIT
DESCRIPTION
Both
channels of
the amplifier
operate
in
the same
manner, and only
the left
channel
will
be
explained.
POWER
SUPPLY
The AC
input
power from P501
passes
through
the Circuit
breaker CB
301. From
CB
301,
the
AC
goes to
the
power transformer
T301.
The output of T301
goes
to a full
wave
bridge
rectifier,
capacitor input
filter
circuit
consisting
of
D301, C302
and
C303
to
give a
positive
and negative
power
supply voltages.
AMPLIFIER
The input
signal from
0301 is
applied to
the
R301
input level
control.
The output
from
R301
is applied
to
the inverting
input (pin
2)
of op
amp
IC103
through the
coupling
network
C101,
R101, C102
and
R104.
This
network provides a
high
impedance to
the amplifier and
filters
out
DC
and radio
frequency
interference.
Q103
and
Q104
divide the signal
into
positive
and
negative
components
respectively.
They are
connected common
emitter
and provide
voltage
gain.
Q110
and Qlll are
connected common
collector to
provide the
current gain
necessary
to
drive
the output
stages,
Q112
and
Q113.
The
output
appears across
flyback
clipping
diodes D103
and
D104,
then passes
through
compensation
networks
L101/R128
and
R130/C117
and thermo switch
S101,
to
appear
at
output jacks
3308.
Switch
S101
opens if
the output
transistors reach
100 degrees C.
To
maintain overall
stability,
linearity, and
low
distortion,
degenerative
feedback
is used
throughout the
amplifier. Voltage
divider R1Q3/C106
and R106
applies the
correct amount of
feedback to
the non-inverting
input (pin
3)
of op
amp IC103.
Except
for the
input,
the
amplifier uses
direct
coupling
throughout. Q106
and
Q107
provide
the current limiting
necessary to
protect
the output stage.
BRIDGED
MODE
When the
mono/stereo
switch
S301
is set
to
mono, it
converts the
right
channel
amplifier
to a unity
gain
inverting
power
amplifier.
5301
Mono/Stereo
switch
grounds the
normal
input to
the
right
channel
and
connects
the
output of
the left
channel
amplifier
to drive
the
right channel
summing point R102.