audio power circuit

This machine uses two sets of power supplies to supply power to the front and rear stages respectively, as shown in Figure 2-29. The front stage includes an input relaxation voltage amplification
stage, which uses a higher power supply voltage and is stabilized , which can effectively avoid the coupling of the front and rear stages through the power supply. The generated communication
sound is beneficial to improving the signal-to-noise ratio. A higher front-stage voltage also helps the voltage amplification stage provide a higher driving voltage to the power
amplifier output stage. Since the upper and lower circuits of the power amplifier output stage are completely symmetrical, the ripple voltages flowing through the load are equal in size but opposite in direction, and can be completely offset. Therefore, a power supply method is adopted where the power supply is output directly
after rectification and filtering without voltage stabilization . Using this method,
the output tube can obtain a larger instantaneous current without clipping. Since the output circuit is composed of a three-stage Darlington circuit,
the output voltage closely follows the collector potential of the voltage amplifier stage VT7 (VT8). As long as the output tube VT14 (VTis) is not
saturated , the output terminal will have a high enough voltage output. . Compared with a power amplifier powered by only one power supply , it not only reduces
the power consumption of the output tube, improves the overall efficiency and power utilization, but also helps reduce the open-loop output impedance. This kind of circuit has
the advantages of a bootstrap circuit, but the disadvantage of having a bootstrap circuit is essentially positive feedback.