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Intermittent "Fizzle-out" on my amp

Discussion in 'Amps and Cabs [BG]' started by 3toes, Sep 29, 2008.


  1. 3toes

    3toes

    Aug 30, 2006
    Charleston, South Carolina
    Endorsing Artist: Lakland Basses
    Every once in a while when playing through my amp, the sound through my cabinets "fizzles" (aka volume drops a LOT and it crackles and pops). It comes back up after a while, but obviously something is up. I've tried new instrument cables, my preamp in my bass has fresh batteries... I do probably need to replace the speaker cables, but usually when those are shorting out you can trouble-shoot it by jiggling them, no such result doing that.

    I've noticed it does it in my bedroom when I'm practicing and the A/C unit outside my bedroom clicks on. Or when setting up for a gig and sound checking with a fan plugged into the same power-strip. And yesterday we were practicing in the guitarist's garage and it was acting up every so often (lord knows what was running in the house). Also note that in my bedroom and yesterday at practice I was not going through a power-strip.

    Is this a case where a power-conditioner or surge protector is needed? Or maybe a new power-cable for the amp-head itself?
     
  2. 3toes

    3toes

    Aug 30, 2006
    Charleston, South Carolina
    Endorsing Artist: Lakland Basses
    Bueller? Bueller? Anyone?
     
  3. spode master

    spode master

    Jan 21, 2007
    First thing to check.

    Clean input jacks, clean output jacks. check cables.

    Sounds like there is a possiblity of failing solder joints.

    Perhaps on the output transistors.

    But could be anything from input jack solder points to, tone pot etc.

    Start with the simple things first.
     
  4. ibnzneksrul

    ibnzneksrul

    Feb 2, 2007
    So Cal
    It sounds to me like the problem is coincident with sags/fluctuations in the AC line voltage, which could mean that the big filter capacitors in your amp's power supply are not doing their job in maintaining the DC voltage levels on the supply rails. Could be cold solder at the caps or perhaps a cap has gone south, but either way unless you're qualified in amp repair I'd have a tech look at it.
     
  5. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    Try the amp in a different building. If the problem doesn't happen there, it's possible that your AC line voltage is just marginal.
     
  6. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    That's an interesting problem. Can you cause the problem by bending the AC cord back and forth, at either end of it as well as at various points along its length? I'm thinking something might have run over it and broken most of its strands somewhere. Maybe you can look for damage on the insulation.
     
  7. spode master

    spode master

    Jan 21, 2007
    I think if the filter caps solder joints were bad, there would be a bad hum apperent when the lead of the cap effectively lifts, out of the circuit.
     
  8. 3toes

    3toes

    Aug 30, 2006
    Charleston, South Carolina
    Endorsing Artist: Lakland Basses
    Nope, messing around with the power cord does nothing.
     
  9. ibnzneksrul

    ibnzneksrul

    Feb 2, 2007
    So Cal
    Possibly, it depends on the design of the power supply and the actual nature of the problem. In any case if I were troubleshooting it I'd look at the output of the bridge rectifier at those filter caps first.
     
  10. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    Set the amp like you usually play it, have your bass plugged in but sitting on a stand, and pick up the amp & give it a few good shakes in the air. Any noises?

    If your speaker cables are flaky, you should replace them anyway just in the interests of best practices and establishing a solid baseline (whoops, sorry) for the problem.

    Other than that, this is probably gonna fall into the Could Be Anything Needs To Be Opened Up category. Unless this model has a history of something always going wrong with it. That I don't know.

    I know I'm repeating what's already been said by others, but if I were looking at it I'd be checking inside for a loose wire or lug or solder joint or even a defective power switch. (Last one's a long shot of course.)
     
  11. 3toes

    3toes

    Aug 30, 2006
    Charleston, South Carolina
    Endorsing Artist: Lakland Basses
    Yeah, I shot an email to ol' Dino at Ampeg. He pretty much said it could be any number of things and I should have a tech look at it :meh:
     

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