Sony HP-210 - Page 9

Stage/Control
Positive bias
power supply
D501, D502,
D503
De bias adj.
RV542
Negative-
feedback loop
R557, R556
C547
Drivers
Q505, Q506
Power
amplifier
Q507, Q508
Function
These diodes are forward biased
by supply voltage through R564
and provides stabilized dc volt-
age of about 1.8V, supplying
idling current for Q506, Q606.
Controls the idling current in
Q505, Q506, Q507 and Q508
to eliminate crossover distortion
at small signal levels.
These components provide nega-
tive-feedback voltage from the
output of the power amplifier
to the emitter of Q503.
These transistors operate as
emitter followers to provide
the current swings demanded of
the output stages for full output.
These SONY silicon transistors
have been specially manu-
factured to drive the speaker
system. Output is coupled to
the speakers through C548.
Stage/Control
Power Supply —
Voltage
regulator
Q509, Q510
Function
DC output from rectifier D504,
D505 is filtered by C701 and
applied to series regulator Q510.
Q509 compares a sample of
the output voltage picked off
across R568. A change in
output voltage is detected at
the base of Q509 and there-
fore alters its collector voltage.
Since the collector of Q509 is
directly coupled to the base of
Q510, the change in output
voltage alters the conduction
of Q510 by the amount neces-
sary to maintain the output
voltage constant. An increase
in output voltage causes an
increase in the impedance (de-
crease in conduction) of Q510,
and vice-versa. The dc output
voltage supplied to the tuner is
thus stable.