What is the difference between feedback and howling?

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What is the difference between feedback and howling? [Copy link]

Feedback and howling have their own differences! Let's use an audio amplifier to illustrate these two issues. Feedback is added to most amplifiers in order to reduce the distortion of the amplifier, and this type of feedback is negative feedback relative to the output signal. Since the introduced negative signal and the input positive signal cancel each other out (only a small part), the signal distortion and noise at the output end are greatly reduced, thereby improving the sound quality (the specific working principle will be analyzed in another article). Since it is negative feedback, it will not cause howling. If howling occurs, it must be that the polarity of the feedback signal is connected in reverse, just change the polarity and connect it! If positive feedback is artificially introduced into the above amplifier, then this audio amplifier will produce howling and become an audio oscillator. When we debug various high and low frequency amplifiers, we need to use high and low frequency oscillators (also called high and low frequency signal generators) made according to this principle. Feedback is divided into positive feedback and negative feedback. Positive feedback will produce howling, while negative feedback will not cause howling. On the contrary, it will improve the output signal and reduce distortion. But there are exceptions. For example, when the negative feedback is too strong and passes through a capacitor or inductor, it will produce a leading or lagging phase shift. This phase-shifted signal has the same polarity as the input, so it will also produce howling! Positive feedback has more uses than negative feedback, such as the signal generator mentioned above. The regenerative radio used by radio enthusiasts for experiments. The local oscillator and beat frequency generator in a superheterodyne radio or receiver. The synchronous oscillator for synchronous detection. The modulated oscillator, frequency-selective oscillator, special crystal oscillator, clock oscillator, etc. in the transmitter are countless. Through the analysis in this article, it is clear what feedback is and what howling is.