AV-501 type power amplifier circuit

The preamplifier is composed of ICl-A and ICl-B, its peripheral components and tone control circuit.
    The input signal is attenuated by the master volume control potentiometer RP and added to the non-inverting input terminal of ICl-A. RP2 is a two-channel balance
potentiometer connected to ICl-A to form a non-inverting amplifier. The actual amplification factor is about 4.6 times 0 ICl- The circuit composed of B is basically the same as ICl-A
, except that the amplification factor is about 19 times. RP3 and RP4 and their peripheral components constitute a variable tone control circuit.
    The power amplifier adopts the currently popular circuit structure and can be divided into three
parts: differential input, voltage amplification and power amplification. VT1, VTZ and VT3 VT4 constitute the differential amplifier input stage. VT5 and VT6 are the excitation stages. VT7, RP5, R24
and C20 form a fixed bias circuit to provide fixed bias voltage for the complementary tube VT8. VT10, VT9 and VT11 to stabilize
the collector current of the power tube. The static operating point of composite tubes VT8, VT10 and VT9.VT11 is adjusted by RP5.
    In order to improve the frequency characteristics and make the circuit operation more stable, the circuit has deeper AC and DC negative feedback. AC negative
feedback is added to the bases of VT2 and VT3 from the output end through a voltage divider composed of R27.C17 and R22 to stabilize
the static operating points of VT2 and VT3. Due to the deep feedback amount and the high stability of the differential amplifier itself, the entire
circuit has good stability6