looking for an op-amp with AGC

Discussion in 'Analog & Mixed-Signal Design' started by bug13, Jul 24, 2018.

  1. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    Hi guys

    Is there an op-amp with AGC built in? Or how can I implement one if not too difficult. Some how I can't find any op-amp with AGC built in, maybe I am looking at the wrong place???

    I have multiple analog audio feeds with different signal strength going into a switch, I want constant output.

    Thanks guys!!

    IMG_4029.JPG
     
  2. danadak

    Well-Known Member

    Mar 10, 2018
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  3. sghioto

    Active Member

    Dec 31, 2017
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    Last edited: Aug 1, 2018
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  4. sghioto

    Active Member

    Dec 31, 2017
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    " If " the signal levels are fairly constant why can't you adjust each input to the same level?
    SG
    EEE low tech limiter.png

    [​IMG]
     
    Last edited: Aug 2, 2018
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  5. Audioguru

    Expert

    Dec 20, 2007
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    Maxim make a MAX9814 mic preamp IC with AGC.
     
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  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Won't active AGC inevitably introduce compression and hence give distorted audio? Or isn't that a concern?
    Have you considered a passive mixer, with pots to adjust relative channel volume levels?
     
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  7. Audioguru

    Expert

    Dec 20, 2007
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    Automatic Gain Control adjusts the gain. If its attack and release are too quick then it causes symmetrical odd harmonics distortion similar to clipping. Usually it has a fast attack and a slow release.

    It distorts the dynamics of sounds. If music is playing then AGC causes the level of background sounds to be modulated by loud drum or bass beats. During a beat the level of background sounds is suddenly reduced then the level slowly comes up to normal but the next beat also suddenly reduces their level. On some songs the background music cannot be heard if there is loud drum or bass beats.

    Some people think that AGC is needed for speech but I think it messes up speech.

    In this circuit where inputs with different levels are switched on and off, when a lower level signal follows a high level signal then the beginning of the low level signal will be low level until the release time of the AGC slowly increases it.
     
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  8. PeteHL

    Member

    Dec 17, 2014
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    There is a circuit in a book in my library with the title "Audio Automatic Gain Control". The book is Vol. 3 of the Encyclopedia of Electronic Circuits (Rudolph Graf), from some time ago. This was originally in Pop Electronics 1968 (!).

    The circuit includes MC3340 audio attenuator, an op amp (741), JFET 2N5485, and about 20 discrete passive components.

    As I don't have a scanner, I would have to compose the schematic from the page. If you think that this might be what you would want, I could compose in LT spice or one of the other drawing programs that I have.

    Regards,
    Pete
     
  9. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    Hi @PeteHL, thank you for your kind offer, I will most likely just use the MAX9814 or amplifier circuit with 3 different adjustable gains as other member suggested
     
  10. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    That’s an educational read, thanks!
     
  11. bug13

    Thread Starter Senior Member

    Feb 13, 2012
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    yes, I think that may be a better solution
     
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