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    The automatic gain control circuit AGC provides a signal with less harmonics and additional amplification, between certain limits.
    As a result, it eliminates those intensity differences, annoying, and of speech music, which sometimes appear on radio and television.

    Field effect transistors T1 is used as a variable resistance. It’s value can vary from infinity to about 150Ω. It is in parallel with R3 and R4 together with, inducing the amplification of A1. Without FET, gain
    of A1 is about 20 dB.

    AGC Automatic Gain Control circuit diagram

    automatic gain control circuit schematic

    Amplification of A1 and A2 compensates damper losses: total agc circuit gain, with T1 blocked is 0 dB. Signals with a level lower than that set by P1 are amplified by a factor of maximum of 6.9 (= 17 dB amplification).

    AGC components list semiconductors

    D1 = 1N4148
    T1 = BF245C
    IC1 = TL072
    IC2 = TI071

    Automatic gain control PCB

    agc pcb

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    4 Responses to "Automatic Gain Control Circuit"

    1. this function should be integrated in TV from factory.

    2. Yes, TV-ads are really loud sometimes…

    3. Does any one have the pcb in a better quality?
      I want to etch it myself to create some gain control!

    4. Is it possible to modify the input so it takes an electric guitar as input? The impendance is a lot higher. Is it possible to just change the values of some resistors, or does it require a separate buffer?


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