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Personal Voice Amplifier Background Hum Trouble

  1. Aug 11, 2012 #1
    Long-time lurker, first post, here goes.

    So I'm working on a personal voice amplifier for a face mask. I have the dynamic mic element ("www.accusonicproducts.com/pdf/G01A009-PFK.pdf2FVVVHLD_Q" [Broken]), which feeds into a 3v class A preamp, through a 100k audio taper pot, to a 6v lm386 amp with the gain set for 200.

    The problem is that there is a very loud buzz present while using the preamp, which is not present while using on the lm386 amp. However, if I put my finger across the pins for the potentiometer the sound clears and be comes noticeably louder and operates correctly.

    The only difference between my circuit and the one schematic I linked to is that I substituted polyester caps in place of the ceramic, I didn't think it would make much difference, but I could be wrong.

    Schematics available on demand.

    I'm at my wits end, any help would be appreciated!
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Aug 11, 2012 #2
    You need to post the schematic and preferably a picture of your circuit. It is hard get what you circuit is by reading.
  4. Aug 14, 2012 #3


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    Staff: Mentor

    Could well be mains hum. You might not have good shielding, or the earth braid might not be connected properly, or might be earthed in the wrong place. You are using coax for all audio leads?

    Examine the audio on an oscilloscope and determine its frequency, is it identical with your mains frequency? Then probably your finger is performing the earthing function.
    Last edited by a moderator: May 6, 2017
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