Denon PMA-725R - Page 10

BE PMA.S2 SAF 2S Re a a a a Te ETT,
FUNCTION OF NEW CIRCUIT
1. CHARACTERISTIC OF THIS CIRCUIT
The junction temperature of power amplifier output transistor always varies by an ambient temperature and music signal.
Occurrence
of
junction
temperature
varying
causes
in
change
of
bias
current,
unstable
function,
thus
pure
music
signal
playback is unable to do.
To maintain fixed bias current and to make pure music signal playback possible is the purpose of this circuit. This circuit
holds stable bias current condition within a few seconds after turning on the power.
2. BLOCK DIAGRAM OF BIAS CONTROL CIRCUIT FUNCTION
As explained in Fig. 1, detects a voltage across the emitter resistors (RE) of TR1, TR2. Converts the detected voltage and
comparing with the reference voltage to make the bias current value in stable state. Actually, these functions are performed
by 1 chip IC.
. oo 1 Chip IC
TR1, TR2: Output transistor
RE : Emitter resistor
Fig. 1
3. POWER SUPPLY FOR ACTUATING CONTROL CIRCUIT
TR - [ 5, > ToIC (V*) The circuit (IC) controlling bias current actuates by
Power supply circuit floating.
RE Output Accordingly, the power supply is also needed to be
floated.
In this circuit, as indicated in Fig. 2, output is common
TRe
to
provide
+,
—
power
system
and
supplies
to
IC.
Fig. 2
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