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Audio Amplifier Negative Feedback

June 14th Fact-of-the-Day

A small amount of the output signal from an audio amplifier can be fed out-of-phase back to the amplifier input to decrease distortion, reduce noise, improve transient stability, and extend the frequency response. The penalty is reduced gain, because the input signal strength must be increased enough to offset the negative feedback if the amplifier output level is to be the same. A typical audio power amplifier, for example, might have 5 percent intermodulation distortion (IMD) without negative feedback. If 1/5th the output voltage (or current) is fed back to the input out-of-phase (14 dB of negative feedback), the intermodulation distortion generally will be reduced be a factor of about 5 to approximately 1 percent. Unfortunately, if the feedback is increased sufficiently to reduce the intermodulation distortion to zero, the amplifier gain also will be zero. ©2005 Martek International All rights reserved.


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