Marshall techs...need diagnosis after amp accident please

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Sean Doty, Jun 26, 2005.

  1. Sean Doty

    Sean Doty Member

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    Sure could use your expertise.

    I was playing my JTM 45 clone, happy as a clam. Unbeknownst to me...my 3-year-old maxed out the level and gain controls on my Tonebender fuzz pedal on the old pedalboard. I went to hit the Tonebender for a lead break, not realizing she had goosed the controls and this obviously sent an unintended and serious jolt of juice to the front-end of the amp.

    I killed the pedal after a huge shriek, but now, where the amp was absolutely quiet as as a mouse before getting slammed with the maxed out Tonebender, there is an extremely pronounced and audible hiss - completely not normal prior to the Tonebender overdose.

    The amp still plays, but there is this definite hiss, where before it was super quiet. I shut down the amp, immediately after the shreik, let everything cool, then fired it back up again and the hiss is defintely still there.

    ...any ideas on what I damaged?

    Any expertise would be much appreciated,

    Sean
     
  2. EL34

    EL34 Silver Supporting Member

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    The first thing I would try is swapping out the preamp tubes (one by one, starting with V1), then the power tubes if the preamps turned out to be ok. Good luck, and let us know how it turns out.
     
  3. Sean Doty

    Sean Doty Member

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    I'll give it a shot. Hopefully it will be that simple. If it doesn't work, I'm going to call the amp builder tomorrow, see what he suggests....

    I got used to routinely looking at all my amp knobs before throwing the mains because of my five and three year old - I never ever thought to check the knobs on my pedals too....live and learn. Funny enough, they always seem turn the knobs clockwise...the need to dime everything must be genetic.
     
  4. Sean Doty

    Sean Doty Member

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    This is interesting (and semi-good news)

    Just swapped out all the preamp tubes.....no change. Still had the hiss.

    However, I then went straight into the amp - bypassed the pedal board completely, and the hiss is gone. I think I must have fried the Tonebender and that was what was causing the hiss.....now I'm going going to diagnosis the pedals....see where the problem is to be sure (but my guess is it is with the fuzz pedal). I had all the pedals off after my meltdown incident (and they are all true bypass),so something is definietly amiss there...

    I'm just relieved it ain't with the amp!!!
     
  5. Sean Doty

    Sean Doty Member

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    Guys, I think this was false alarm. I definetly isolated the problem with the pedalboard, but all the individual pedals worked fine during the troubleshoot. I put everything back together and the hiss was gone. Even the Tonebender clone is working perfectly.

    My only guess as to what happened is when I went to turn of the fuzz pedal immediately after sending all the dogs in my neighborhood cowering, I must have jostled one of my cable connections (I'm using George-Ls). Perhaps one of my cable connections isn't as tight as I thought.

    It just seems like a weird sympton for a cable connection.

    Anyway, thankfully, my amp seems to be fine, and, my pedals appear fine. I suppose if I ever have the issue again I'll be checking the cables straight away.

    Moral of the story: Lock up your pedal board in the case after each session. Or at least scan the knobs before switching off standby.......peace out.

    Sean
     
  6. TheAmpNerd

    TheAmpNerd Member

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    This wouldn't be the first pre amp tube eaten up by
    pedals.

    It is more common than I like to think, expecially at jams
    where folks bring the pedal and crank the hell out of it.

    Well, there goes another good sounding pre amp tube. : (

    Glad it wasn't a Tele, Mullard, or other....Hi $ tube.
     

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