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My amp is broken

Discussion in 'Amps and Cabs [BG]' started by Jennifer, Oct 9, 2000.


  1. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    My bass amp fades in and out. It's pretty much out all the time now. Solid state Marshall, circa 1989(?). Please don't tell me I have to buy a new head.
     
  2. It's probably repairable, why don't you take it to a good amp tech? Might just be something like capacitors going bad on the power supply. Probably won't cost much to fix it.
     
  3. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    Yeah, I'm going to have to. I just want to go in there sounding like I kind of know what I'm talking about. I'm hoping that the problem sounds familiar to someone here.
     
  4. White_Knight

    White_Knight

    Mar 19, 2000
    USA
    I don't have hardly any experience with amplifier repair, but when you say that it "fades in and out", what do you mean? The sound (volume, etc.), the entire amp (any running lights or whatnot are also turning on/off), etc.? And by fades in and out I'm assuming that you're talking about the volume, correct?
     
  5. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    Yes, the sound fades in and out. It's been a gradual thing. A month ago, it was doing something similar, thought it may be a cord, so I got a new cord and it seemed to work ok for a while. Then it started to seem to cut out occasionally, and naturally, last Friday at a gig, it was doing it big-time. Changed cords, no fix. Got it back home, turn out is fading, not cutting, in and out. Playing my bass through the PA is ok, so I think it's the amp.
     
  6. White_Knight

    White_Knight

    Mar 19, 2000
    USA
    Well, all I can say to you is to take it to a good amplifier technician. I really don't know what's wrong with it. I was hoping that you were going to say something like "the sound cuts on and off randomly" in which case I'd tell you to make sure that the speaker wire going from the amplifier to the speaker itself is securely connected (I know lots of people who have a problem that has been fixed by just that). However, it sounds like something from inside the amp itself to me. As suggested above: perhaps the capacitors are failing. Or maybe the power transformer is going. At any rate, I'd have it checked out as soon as possible.

    Just checked your profile: is that Marshall a tube amp by chance? Now I have almost nil experience with tube amps but perhaps it needs a re-tube.
     
  7. jcadmus

    jcadmus

    Apr 2, 2000
    Jennifer: When you the amp in for repair, you might also want to take along your bass and demonstrate the problem. I had a tech once who ended up chasing his tail on a problem with my amp -- couldn't duplicate the problem on the bench. It was only after I set up the whole rig and played a few notes that he finally got it.
     
  8. If a tube amp is FADING in and out, the most likley problem
    would be a filament dying out intermittantly. caused usually by bad contact in the tube base. Wiggling the tubes in their sockets will verify and maybe even fix. this also could be a bad solder connection or a failing tube.
    A FADING solid state amp would most likly have a power supply problem. Check the printed circuit board around the power supply section for a broken or cracked solder joint. The power supply section would be where the transformer wires connect and the aluminum can filters are mounted
     
  9. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    Thank you all for your help. RockBottom, welcome to TB! If I have a power supply problem, would the power light go on and off also? I don't think mine is.
     
  10. The pilot light may or may not fade with the sound, depends on where it's hooked up. If it does fade than maybe the power switch could also be bad.
     
  11. One last thing about broken solder joints on circuit boards.
    Any heavy part mounted to a printed circuit board is subject to being broken away from the board by moment loads such as dropping or even setting the amp down too hard. Filter cap cans, heat sinks, and on some amps signal transformers are where to look.(on a TV look at the flyback transformer)
     
  12. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    My husband and I took it apart last night, and I just don't see any broken or cracked solder joints. So, into the shop it goes. Thank you all for your help and I'll let you know the results, if you'd like.
     
  13. MohawkHarry

    MohawkHarry

    May 21, 2000
    Chatham,IL
    I was having the same problem last week with my Peavey
    DPB 300 watt head. Last night I pluged in to see if I could reproduce the problem. I heard a little pop and a puff of smoke rolled out of it. With my gain on 7 and my master on 8
    while playing a low e octave on my Warwick fna. Yep I was pluged into the -10db active imput.
    Why is there a gain knob you can turn up to 10 if this will smoke your amp?
     
  14. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    Well, my problem is fixed now. Turns out there was a bad op amp. Whatever that is. Apparantly, there are several of them in there. The rest of them better not break!