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HP Barney Oliver Manual page 14

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Circuit Description
C.
POWER AMPLIFIER
The
prising transistors Q12* and
as their drivers.
provided
resistors R5* and R6* and by currents
from current source Q8
CR9, R22, CR8 and CR6. The power diodes CRI *
and CR2* shunt R5* and R6* at
to avoid
voltage drops in these resistors.
Inductance L1 * protects the output
the effects of
while R8* eliminates any series reson­
ance with this capacity. Diodes
and CR13 provide output current limitation. To-
with fuses F* these
circuit
The output stages are driven
emitter follower
tion in the collector.
The input
consists of a differential pair,
and Q2, whose emitter currents are supplied by
The input signal is applied to the base of Ql
and the feedback to the base of Q2. The output
collector swing of Ql is limited
to
the emitter-base junctions of the second
and Q7.
at d-c and low
The
( > 100 dB). The primary cutoff
at
falls at 6 dB/octave to reach a value of about 60
dB at 10 kHz. Inductors Ll and L2 introduce a
second pole at 16 kHz above which the
falls at 12 dB/octave to about 200
C6 begins to shunt Rl6
off in the amplifier and reducing the loop
cutoff rate to 6
crossover is at about 1 MHz.
The bridged-T comprising C3,
R12 increases the
reduces the external
the low end response rises
before dropping off. In the bass-boost position
C7
and C8
a pole at 16 Hz and a zero at 80 Hz in the external
Thus the gain rises at 6
for the low end roll-off of
most
'Located on chassis. See righthand portion of Power Amplifier
C.
Schematic, Section VI,
5-2
the power amplifier is
emitter follower com-
*, with QlO and
point
through
signal levels
cable loads at very
CR12
output short
which has current limita-
CR2 and CR3
frequencies is the base-
Thus the loop
where
a
end cut-
once more. Gain
Rll, and
below 16 Hz and
at d-c. The
are
complex so
at the low end
with Rl6 and R17 produce
below 80
Transistor Q3
tiometers R4 and
the currents through R2 and R3 supply the base
currents of Ql and Q2.
input terminals shorted
and R4 with the
is
with the volume control at maximum) to give
zero volts out of the
hold for any
volume control
from
D.
POWER SUPPLY
All supply
are available in both
(± 40V) is rectified by diodes
and CR4 in a double full wave configuration.
Filtering is
has a substantial amount of ripple,
but the power
that this
The terminals and leads of C3 and C4 are
not current
is
or to each other. (You'll ruin your
The
floated on the
will show about the same ripple as the latter. Tran­
gain
sistors Ql and Q2 with their associated circuitry
provide
Zener diodes CR13 and CR14 establish the
reference voltages for the
from the cascaded emitter followers Q3-Q5, and
Q4-Q6. The rate of rise and fall of these
tum on and tum off is determined by the
active filters comprising
R15, C7 and transistor
and RIO, C6, Rl4 and
while CR18 compensates for junction drops in
Q6 and Q8. Resistors Rll and Rl2
for the initial
that these currents do not flow through R17,
CR17 and
Oliver Audio Amplifier
The
current to two poten-
which are
control at mini-
terminals open (or
this condition will
capacitors C3 and C4. This supply
negligible hum in the
-WARNING-
Do
not short to
supplies are
supplies respectively.
current limits on the
20V supplies obtained
±
for the
for the -20 V
for
drops in Q5 and
currents in C5 and C6 so
R20, CRIS.
so that
R5 with the
faces (any
under
is such
10V
Rl3
20V
+
C8 , and
Diode CR17

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