Design of self-excited audio amplifiers based on spectrum-shifting

In order to avoid the generation of amplifiers whistle, the method of spectrum-shifting is used to move the audio signal, in this paper, The design of a spectrum of audio frequency low-noise removal circuit, Circuit by the low-noise preamplifier, low pass filter, analog multiplier, quartz crystal filter and PA power amplifier, After assembly, debugging and testing, the system do not produce self-oscillation and successfully remove the whistle sound. more importantly, there is no distortion of sound signals and the system gain of sound reinforcement reach 6-10dB.