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'SONY
STR-VX
Series
Circuit
Operation
STR-VX5,
-~-VX6 Power
Amplifier
The left-channel power
amplifier circuit
of the
STR-VX5
is shown
in Figure
9.
In the first stage,
a dual PNP transis-
tor
(Q702)
is connected
to a dual
NPN
transistor
(Q701)
as a current
mirror
for high voltage gain.
The DC offset
voltage
can
be zeroed
by RV701 if
slight DC imbalances
occur.
The
second
stage,
which
consists
of Q703
and Q704,
supplies
more
voltage
gain.
The base-emitter
voltage of Q705 is
regulated
by D701,
D704,
and
R717.
Q705 acts as a regulated current
source
for Q703
and
Q704.
D702,
which
is a
varistor consisting of four diodes con-
nected
in series,
biases
the output
stage in class AB
mode
to reduce
C707
R707
erossover
distortion.
The bias cur-
rent is adjustable
by RV702.
The
complementary
output
stage
consists
of Q706,
Q707,
Q708 and Q709.
The
power
amplifier of the STR-VX6
is
nearly identical to that of the STR-VX5,
except
for the absence
of an input ca-
pacitor,
and
a dual FET
(Q701),
which
configures
a DC
amplifier.
Q703 and
Q704
are
connected
between
Q701
and
the current
mirror
Q702 to reduce
high-
frequency
distortion
caused
by the gate-
drain
capacitance
of Q701.
Q705,
D701,
D702
and R710 are a regulated current
source
for Q701,
and the DC
offset volt-
age is adjustable
by RV701.
Current
gain is supplied
by Q710,
Q711,
Q712,
Q713,
Q714,
and
Q715,
which
are con-
nected in a three-stage
Darlington
arrangement.
Fig.
9.
STR-VX5 Power Amplifier
(Left Channel).
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