Fully symmetrical power amplifier circuit

The fully symmetrical power amplifier circuit is made by making the input, voltage amplification, driving and power output parts of the circuit into complementary and
symmetrical forms, so that the respective characteristics of PNP and NPN transistors can be fully utilized to achieve
complementary . Make the circuit stability and output fidelity better. The power output stage of this circuit is divided into fully complementary and quasi-complementary.
Since the quasi-complementary output tube does not require higher requirements for opposite polarity pairing, this circuit is more suitable for amateurs to install
.
    The circuit principle is shown in Figure 2-7Q. VTi, VT2, VT4, and VB form a dual differential input
stage with PNP and NPN polarity. VT3 and VT6 are the constant current sources of the two differential pairs respectively. VDi~VD4 are the voltages of the two constant current sources. benchmark. VT7 and
VT8 form a single-ended push-pull voltage amplification stage and serve as the driving stage of the power amplifier stage. VTlo, VT12, VTli, and VT13 form a quasi
-complementary push-pull power amplifier output stage. VTg, RPz, etc. form an output bias circuit. Adjust RP2 to adjust
The static bias voltage and static bias current of the output tube base .
    R3~min and R21xR29, R31 are the negative feedback resistors of the emitters of each camp , which are used to stabilize the operating points of the circuits at all levels.
Keep the circuit working stably.
    Ri' and Ris are security resistors, that is, when VT3 or VT6 is broken down for some reason, R12 and Rl5 can
barely maintain the operation of the differential circuit to prevent damage to other transistors.
    R22, RPi, R17, and c5 form a negative feedback circuit, which determines the closed-loop gain of the whole machine. Due to the setting of the adjustable resistor
) 1. Therefore, the gain of this machine can be adjusted at any time as needed.
    G and C4 are power supply decoupling capacitors to prevent self-excitation caused by power supply coupling.
    Debugging points:
    The midpoint potential of the output terminal can be reached by adjusting R" or R16. Adjust RP2 to make the voltage between the bases of the two tubes VTio-VTit
1. 65~1.8V, and make the quiescent current of the output tube 30~50mA.
    The quiescent current of each tube of the differential input stage is 0.6~1mA, which can be obtained by measuring the voltage on R3~R6. Adjusting
Ru and R16 can change the constant current source current, which means changing the current of each differential tube. The quiescent current
    of Vr7 and VT8 should be around 10mA, which can be calculated by measuring the voltage on the emitter resistors R20 and R21 . If it does not meet the requirements, it can be achieved by adjusting ‰ and R21.