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Operation by Detector Circuit Command
Command from the detector circuits pass through
one of D., Do or D, and are applied in the form of
a current flow. Q5 is normally reverse biased
through R1a, but when a large current flows
through on of these diodes, Q, base potential
declines according to the voltage drop at R,a.
Q, then becomes ON, Qu base potential rises and
Qu becomes ON. Co rapidly discharges and Q,
base potentia.l drops, tuming Q? OFF. The relay
releases and the power amplifier output circuit
becomes cut off.
2. Overload Detecto? Circuit
Shorting of the power amplifier load or a load
impedance below the specified value causes a
command to be sent to the relay drive circuit.
This is illustrated in Fig. 9.
Qa emitter is connected to Q, base through R, and
the junction point to Q, emitter. When RL is
extremely small, Iarge current flows in Qa, Q, turns
ON due to the RE, voltage drop, and current flows
in D.. C1 prevents faulty operation due to extemal
norse.
oirplifier
e q
Fig. 9. Basic circuitry of overload detector
3. Center Point Potential Detector Circuit
If a DC potential is produced at the junction point
of the power arnplifier, a command is sent to the
relay drive circuit. Fig. 10 shows this operating
principle.
Qr and Qo compose a differential amplifier. When
the same input is applied to both input terminals
(Q. and Qo bases), no output is present. However,
if there is a difference between the terminal inputs,
the difference is amplified and becomes the output
between the two collectors. During normal opera-
tion, an AC signal only is present at the junction
point. As Cr reactance is sufficiently low, the signal
is not applied to Q3, resulting in an absence of
output at the collector sides.
When a DC potential is produced at the junction
point, it becomes the input of Q. only. If the
voltage is negative, Q. collector current declines.
And at Qo the collector current increases and the
potential drops, causing current to flow through
If the DC voltage is positive, Q. collector current
increases and the potential drops, while at Qo the
collector current decreases and the potential rises.
Current therefore flows through D. .
Fig- 10. Basic circuitry of center point
potential detector
5 . 5 P O W E R S U P P L Y C I R C U I T
The power stage provides voltage independently to
both left and right channels, using 2 separate
power transformers. Separate bridge rectifiers (one
for each channel) and 10,000gF (x 2) capacitors
provide the plus and minus voltages. Positive
voltage for other sections is provided by full-wave
rectification from the same winding on the power
transformer that is used for the left channel, and a
negative voltage from the corresponding winding of
the right channel transformer. Both are supplied
via voltage regulator circuits.
There is only one pair of secondary windings in each the
lcfl and righl channel powcr lrans[ormcrs.
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