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Help with noisy Mesa Boogie Mark III

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  • #1

    Help with noisy Mesa Boogie Mark III

    Hi All
    I have a Mark III head on my workbench that literally sounds like a thunder storm when the volume is turned up past 3 or 4 - crackles and pops non-stop and there is also a hiss.
    I can still get sound out of it when I plug in a guitar but the volume goes from nothing to high then back to nothing at around 5 or 6, and back to high when the knob is fully clockwise.
    Pulling V1 removes the problem (and all the good sound) but I can't find anything wrong with this tube or the surrounding components. If anyone has experienced something similar I am keen to understand how it was fixed.
    Cheers
    Tags: None
  • #2
    It sounds to me like it may be the volume pot itself. Check it with a meter as you rotate the pot and see if the jumps in volume correspond to jumps in resistance.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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    • #3
      Originally posted by The Dude View Post
      It sounds to me like it may be the volume pot itself. Check it with a meter as you rotate the pot and see if the jumps in volume correspond to jumps in resistance.
      Also check its overall resistance. Many of the pots found in older Mesas have drifted upwards - some by 50% or more - if so definitely install a fresh part. I got this advice straight from Mesa's Mike Bendinelli, chief engineer.
      This isn't the future I signed up for.

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      • #4
        Constantly dealing with noisy pots myself, I normally will spend time with the amp off, or in Standby, and rack the offending control back and forth until my hand is too tired to do it any longer. Sometimes the resistance track in the pot has become pitted and the wiping action of the wiping contacts won't break down the layer of oxidation. From there, assuming it's a pot having an opening at the terminal ends of the assembly, then using contact cleaner, apply a bit to get onto the resistance track as well as the metal rotor that's in contact with the wiping contacts, and exercise it some more to work it in.

        If that doesn't cure it, then you may just have to replace the pot. Or, pull it from the panel, un-solder the leads and take the cover off the pot for further cleaning/inspection.
        Logic is an organized way of going wrong with confidence

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        • #5
          https://music-electronics-forum.com/...ad.php?t=39843

          see post two by the mastermind. My scenario ended up being the amp needed a recap even though it displayed NO problem whatsoever, other than the volume pot issue. Would be worth a shot to at least check this scenario I'd think

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