Current negative feedback amplifier

WDB228 power amplifier circuit, the circuit shall prevail II: structure, input buffer (VTl, VT2) differential amplification; the main
voltage amplification stage (VT3, VT4) also uses differential amplification} VT5 and VT6 form a mirror circuit, and the VT5 collector is connected to the base , so that the collector
signal of VT3 is directly added to the base of VT6. As a result, VT4 and VT6 form a push-pull amplifier stage, which not only has low distortion, but also high gain. In addition, the input buffer has a low-pass filter, and the output terminal has a "Joubert-RC network" to improve the anti-interference and anti-vibration performance; VD3 ~ VD5 are to enhance the temperature compensation capability. However, due to their Cambodian-level design, they are pure Class B The output makes the playback effect very "stone machine", and the sound quality is good at small and medium volumes. At high volumes, the sound is dry and hard1 accompanied by severe crossover distortion . To address this shortcoming, one is to increase the Class A dynamic bias circuit, by increasing the final stage quiescent current to reduce crossover distortion. The other is to change the feedback form of the circuit, changing it from voltage negative feedback to current negative feedback to improve the distortion caused by the mechanical vibration of the speaker.