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Thread: Preamp noise

  1. #1

    Confused Preamp noise

    I have a preamp design I normally used this design but all of a sudden after building it again after a year of not using the design I hae an issue.

    When I turn the volume nob up a little you hear music and then a little more then there is a load thump in the speaker then silence and thats using the 100k. If I use a 10k pot I can hear the music when the nob it turned all the way down just the same which isn't suppose to happen and I still get a load thump with a squeak this time but if I turn it up more I still get music the volume doesn't seem to change much though if any at all.

    IF remove the pot and connect the wire leaving the negative of c1 and the output the music plays clean and nice I cant seem to get any adjustments using a pot though and Im using new pots, 50k high quality pot and generic 100k pots.

    Can anyone help diagnose this issue.
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  2. #2
    .... Silvio's Avatar
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    Hi ENZY, Try changing the capacitors around the opamp (C1,C2,C5,C9) see how it goes, it also could be a ground loop issue.

    Check also the pcb for any dry joints and cleanliness. Try washing it with some solvent like acetone or cellulose thinner.

    Cleanliness and good sound joints are important in pre-amp stages as signal paths have very low currents.

    Check your input jack plugs and sockets for cleanliness these tend to develop some tarnish with time

    See also that your ground connections are clean and tightened well.

    I hope that helps

    Regards Silvio

  3. #3
    I would wonder also if your amplifier and preamp share common grounds if there could be any ground loop issues as stated by Silvio? Good luck.

  4. #4
    Quote Originally Posted by Easyamp View Post
    I would wonder also if your amplifier and preamp share common grounds if there could be any ground loop issues as stated by Silvio? Good luck.
    Yes they both share the same ground, all the caps were changed to the original values I had and same issue.

  5. #5
    Hello Enzy, it may be a long shot but can you power your preamp from a battery, so as to separate the supplies? Obviously you’ll still have the grounds connected but this will alleviate any possible ground loop issues from the preamp and amplifier. I will do this if I have any noise issues as test, but I generally try and have separate taps to run preamp circuitry so I don’t have to think about ground loop issues. I can’t remember if you already tried to power and operate the preamp separate from the amplifier with an isolated tone or music source, but I would try this also to verify it’s operation. Cheers

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