JMP1 - Weak Sound

Discussion in 'The Workbench' started by JPRS, Aug 19, 2019.

  1. JPRS

    JPRS New Member

    Aug 19, 2019
    Likes Received:
    Hello all, greetings form Portugal.

    My preamp jmp1 when in OD 1 or 2 has sound, but its not the usual volume. I have to crank the volume all way up to get a room level volume.

    In clean mode, all cranked up. I only get a very very weak noise when strumming the guitar.

    Sometimes when in OD mode there are some slight volume variations.

    Tried 2 power amps. Same problem

    It is the second time it happens. The firs time after some minutes and rechecking cables it was ok again. But now again, it is definitely no cable.

    any thoughts?

  2. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Aug 2, 2012
    Likes Received:
    Los Angeles
    did you ever get this sorted out?

    There are "pad" buttons for each output. It could be anything though...
  3. ampmadscientist

    ampmadscientist Well-Known Member

    Jun 26, 2014
    Likes Received:
    Start the reactor... Free Mars!
    Welcome to the forum JP :cheers:.

    The symptoms you are describing could be a couple of things.

    A. First change the 2X 12AX7 preamp tubes inside the unit with new tubes, and then re-test.
    B. Plug a guitar cable between send and return, then re-test.
    C. If either of these doesn't solve the problem, it's likely there is a broken solder connection somewhere on the circuit board.

    The unit is static sensitive therefore special soldering equipment and static precautions are required to work on this unit. This is not a joke because 1 static discharge can destroy the unit circuitry.
    This unit should be worked on by a qualified technician recommend Marshall service center.

    Last edited: Oct 3, 2019

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