Power amplifier circuit composed of TM2001A

It is a low power amplifier circuit with tone control composed of TM2001A. The prestage of the circuit
is composed of equal loudness compensation, volume control, tone control and other parts. RPi and related RC network form equal loudness compensation
circuit. Wei) 2 constitutes the volume controller, Wei) 3~RPs and 1/2TL082 form a negative feedback tone control circuit. The balanced input circuit is composed of
1/2TL082. TL082 is a junction field effect transistor and is used as a high-performance operational amplifier circuit in the input stage. It
has high input impedance and high slew rate.
    VT3 and VT4 form the overload protection circuit of the power amplifier circuit . . When the output tube is overloaded, the output current increases, and the voltage drop of this
current on the 0_25n resistor increases. VT3 is turned on during the positive half cycle of the output current, and VT4 is turned on during the negative half cycle.
The collectors of VT3 and VT4 are connected to pins 18 and 14 of TM2001A respectively, which shunts the base current of the output tube,
limiting the increase of the output current and protecting the output tube. The base-emitter of VT3 and VT4 has an indirect capacitance of 0L , which
is intended to prevent malfunction caused by instantaneous large current.
    VTs, VT6, etc. form a speaker protection circuit, whose main function is to prevent startup shock and midpoint DC offset. Midpoint offset,
word sensitivity is ±2vo, which is introduced by a 4.7kn resistor through bridge rectification to trigger v, L, and VT6 to conduct, causing the relay to close
(or disconnect). The power-on anti-shock is controlled by v, r6 and its base. It is composed of connected i kn resistor and 220t.LF capacitor. When the power
is turned on, VT6 is turned on, the relay is closed, and the speaker is disconnected. Later, due to the charging of the 220rLF capacitor , the base potential of VT6 increases,
'VT6 is cut off, the relay is released, and the speaker is turned on.