A class-A amplifier with dynamic biasing

The input stage of this power amplifier is a pair of field effect transistors, which have the advantages of high input impedance, large dynamic range and low
noise . VT3 and VT4 form the second stage of amplification. VT5 provides 1.8mA current to VTl. VT2; VT6 provides 9. The constant current of SmA
is VT3 VT4. Due to the conduction of VD1, even if the current and voltage fluctuate, it will not affect
the reference voltage of VT5 and VT6, ensuring the stability of the current of the two tubes VT1 and VT2. VT9 ~ VT14 form a complementary output stage, and its output current is controlled
by VT8 . VT8 is a constant voltage circuit with small dynamic internal resistance. The voltage of VceC is constant. Adjusting RP2 can adjust the static operating current 6. VT7, C3 R13. VD2 forms a dynamic bias circuit . Its principle is: in the signal When the input increases, VT7 causes the base current of VT8 to decrease, the Vce of VT8 increases, and the currents of VT9~VT14 also increase accordingly. The highest peak value can reach 4~5A, making the push-pull output automatically work in the Class A state, not only Reduce crossover distortion and cross-over distortion, and improve power utilization. The control of dynamic bias is determined by R13. C5 is a large loop negative feedback capacitor that accelerates high-frequency signals. It has a phase advance compensation function that can reduce transients. State distortion and intermodulation distortion, and can prevent self-excitation. The input stage is also equipped with a high-frequency filter network t to filter out some unnecessary high-frequency noise and improve the signal-to-noise ratio.