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pre amp help needed

  1. #1
    Neil Groves Neil Groves is offline

    pre amp help needed

    Hi Guys, well i just got around to finishing my colour organ and all is now fine when i apply a line level signal, i now wish to add a pre amp at the front end so i can select either mic or line to drive the circuit, i don't know much about pre amps in terms of input/output voltages but i am assuming with a mic insert, i am dealing with a few micro volts? i need to raise this to a couple hundred millivolts using an op amp since i have one half of a dual op amp unused on my board, i can't seem to find a circuit online surprisingly, could someone point me in the right direction please?

    Neil.

  2. #2
    audioguru audioguru is offline
    A microphone has an output of about 10mV when it is about 10cm in front of your mouth and you are talking in a normal conversation level.
    Then the preamp needs a gain of about 200 so that a volume control can adjust its level up or down.

    Use a low noise audio opamp for the preamp.
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    Last edited by audioguru; 13th April 2012 at 02:46 PM.
    Uncle $crooge

  3. #3

  4. #4
    audioguru audioguru is offline
    The website does not work anymore.
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    Uncle $crooge

  5. #5
    Mosaic Mosaic is offline
    Yes it works fine.
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  6. #6
    Mosaic Mosaic is offline
    Here is the circuit image from the website....sans all the explanations about its operation.
    Attached Images
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  7. #7
    audioguru audioguru is offline
    I made comments on the schematic.
    Attached Images
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    Uncle $crooge

  8. Thread Starter #8
    Neil Groves Neil Groves is offline
    ok thanks guys, a project for the weekend me thinks.

    Neil.
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  9. #9
    audioguru audioguru is offline
    An entire weekend?
    2 minutes to design the circuit and maybe 5 minutes to build it.
    Then 2 minutes to get the generator and 'scope warmed up.
    The actual test takes a few seconds.

    Drink wine or beer for the remainder of the weekend.
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    Uncle $crooge

  10. Thread Starter #10
    Neil Groves Neil Groves is offline
    lol....your forgetting you are way more experienced than me, i try to take my time and learn something along the way.

    thanks Audioguru.

    Neil.
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