Composite power
amplifying V132, V112
AC negative feedback
R121, R108, C105
Mirror image constant current source V104,
V107, VD102, VD103
L I N
Difference amplifying
level V102, V103
Voltage
amplifying
level V105
Composite power
amplifying V133,
V113
Speaker
V101
V115
Mute
Relay
Temperature
compensation
level V106
Figure 3.2.5.1 Power amplifier and protection circuit diagram
The two groups AC 35V voltage outputted from the first sublevel winding of transformer, after
rectification and filtering of 8 In5404 (VD100
VD107) diode and 2 electrolytic capacitor (15000uF/63V,
C108, C109), positive/negative 53V power is achieved to supply power for left/right channel.
The two groups AC 17V voltage outputted from the second sublevel winding of transformer, after
rectification and filtering of 4 IN5404 (VD111~VD114) diode and 2 electrolytic capacitor (4700uF/35V,
C141, C142), positive/negative 23V power is achieved to supply power for SL/SR/C channel. For other
IC and operational amplifiers, after voltage regulating of 3-end voltage regulator L7812 (N101), L7912
(N102), positive/negative 12V power is achieved to supply power for other IC.
1, L, R channel power amplifying circuit
L, R channel power amplifying circuit: L, R main power amplifying circuit of AV321T (RU) is
composed of discrete component, the composed block diagram is shown as the following figure 3.2.5.1
(take L channel for instance):
～
3.2.5 Power amplifier board and protection circuit
L channel signal, through R101, R103, C101 coupling, is sent to B electrode of differential
amplifying stage V102, V102 and V103 compose the differential amplifying circuit of single-end input
and single-end output. Audio signal is outputted from C electrode of V102 to B electrode of voltage
amplifying stage, then to composite power amplifying stage after voltage amplifying.
V104, V107,
VD102 and Vd103 compose mirror constant current circuit. VD102, VD103 provide V104, V107 with
constant base electrode current. Emitter electrode resistance of V104 decides working current of
differential amplifying stage, emitter electrode resistance of V107 decides working current of voltage
amplifying stage. V132 and V112 compose multiple unit tube amplifying to make final stage of power
amplifier have powerful current amplifying ability, and they compose positive half cycle amplifying
waveform. V133 and V113 compose negative half cycle amplifying waveform. The function of
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Summary of Contents for AV311T
Page 1: ...service manual AV311T...
