Re: AGC circuit to try?

Paul Galburt - K2AYZ

This circuit is an audio envelope detector - it provides a dc voltage that corresponds to its input audio voltage. This is then applied as a gain control signal to a "voltage controlled amplifier" of VCA (the audio path) that is not shown. There are several solutions to implementing a good VCA, not all are trivial.

This sort of detection can be used to implement a "feed forward" AGC which effective "programs" the gain reduction based on the input level, or a "feed back" or closed loop AGC which acts to prevent the VCA output from exceeding some threshold. Each method has advantages and disadvantages. Which this particular usage is cannot be determined without seeing more of the circuit.

Hope this helps,

Paul K2AYZ

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