Vol I on 1987 Head knackered? And Popping Sound on Switch

Discussion in 'The Workbench' started by OdgeUK, Jun 18, 2020.

  1. OdgeUK

    OdgeUK Member

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    Blew the dust off my '79 1987 JMP Head a few weeks ago. I hadn't used it in a long time because the original power rocker switch disintegrated some time ago and it took me a while to get a replacement from eBay and find time to wire it in.

    The switch replacement was no problem (other than reverse wiring it a few times as it was a 6-pin switch and the original was a 4-pin).

    Two things I noticed once it was done and I was testing.


    1) There's a loud audible pop over the speakers when switching the new switch on and off. I can't honestly say if this was a problem before, as I rarely used this particular head. Is it likely this is the switch? Or could it be something to do with "Snubber caps"?

    2) There is still some audible signal when the Vol I is on zero. And holy crap does the volume jump when you just tweak it a little from zero. Something is wrong, Do I just go for a new pot and wire it in, or is there some troubleshooting I can do here?
     
  2. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Sounds like a pot that needs a good cleaning and deoxidation and if that doesn't work, time for a new volume pot.

    How long has it been since you last ran it?
     
  3. South Park

    South Park Well-Known Member

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    That popping is a voltage spike is the switch in the right location . Some switch’s make noice
     
  4. neikeel

    neikeel Well-Known Member

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    I think both of the above are correct.
    I have been using Deoxit gold for a while now and it is fantastic in pots. The volume jump maybe the 5nF bypass cap if it is still in place. Snubber caps can help with popping with the HT but unusual with the mains.
     
  5. OdgeUK

    OdgeUK Member

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    Thanks All. It had been quite a few months since last firing it up, maybe even a year or so, but it doesn't 'feel' like a Filter Cap issue. Switch is wired correctly to the best of my knowledge. Will stick some regular switch cleaner that I already have in the pot and see if there is any difference at all and confirm if the bypass cap is in place.
     

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