Marshall Jmp-1 Strange Flanger Sound Issue.

Discussion in 'The Workbench' started by mrp, Dec 19, 2016.

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  1. mrp

    mrp Member

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    Hi,

    I had been using my JMP-1 for over a decade - stock tubes, OD2 channel - with no issues until recently.

    There was this bad cable that kept producing loud spikes - although I'm not quite sure the JMP-1 wasn't adding up to these as well. After that the JMP-1 started sounding dull, one-dimensional, with poor note definition, and worst of all - with a subtle yet relentless flanger quality to the sound on all four channels.

    Swapping tubes (V1->V2) didn't help at all. Having googled extensively, I assume it's quite an uncommon issue.

    Any help much appreciated.
     
  2. Len

    Len Well-Known Member

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    Replace the tubes rather than swapping them.
     
  3. GT08

    GT08 Active Member

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    A bad power tube will cause this symptom.....and take the bias miles off.
    Change the power tubes and re-bias.
    Always keep spare GOOD tubes (power and Pre) for testing purposes.
     
  4. Jazz P Bass

    Jazz P Bass Active Member

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    That 'Flanger' sound may be your power supply filter capacitors going wonky.
     
  5. mrp

    mrp Member

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    Forgot to mention: I use a solid state Peavey KB/A 50 as a power amp with JMP-1's emulator outs. JMP-1's Headphone jack signal has the flanging as well.


    Thanks, perhaps it's something in that vein.
     

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