Problems With My Marshall Jmp-1

Discussion in 'Marshall Amps' started by Lutzelodeon, Apr 1, 2019.

  1. Lutzelodeon

    Lutzelodeon New Member

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    Hey guys,

    I have some problems with my JMP-1:
    - Clean Channel is very quiet (not really audible at max volume)
    - OD Channel is audible (low volume though) but if I roll the volume knob on my guitar or slighty touch the strings it starts making cracking noises etc.
    -> Volume is very low in general at max volume

    This just happens when I use the amp for more than (about) half an hour. I can hear the volume fading out really fast in the end. Switched valves among each other - No changes noticable.
    The transformer looks a bit brown on one side - I've read that the JMP-1 has issues with the transformer. Maybe it could be the transfomer?
    The transformer hangs around 62°C when the problem occurs.

    Greetings from Germany,
    Lutz
     
    tce63 and Mitchell Pearrow like this.
  2. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    :welcome: To the forum, I have no experience with this amp, but if you have a known good preamp tube, try it in each position, to check that it isn’t a bad preamp tube, I know you have already tried with the ones in it, but that may be the problem, what power tubes are in it, try putting in your spare set! If you don’t have a spare set, I highly recommend getting a set! Cheers Mitch
     
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  3. Lutzelodeon

    Lutzelodeon New Member

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    Hey Mitch,

    thanks for your answer - I really appreciate it :).
    There are no power tubes, just 2 ECC83 - One is the Clean and one is the OD Channel.
    I could try to use some tubes of my JVM.

    Greetings,
    Lutz
     
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  4. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    That would be a big start, as I said I have no experience with your amp brother! Cheers
     
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