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Horrible scary sound - what happened?

Discussion in 'Amps and Cabs [BG]' started by c-ba55, Sep 29, 2010.

  1. My band was recording when this happened, so I am attaching an edited mp3. This is after a couple of hours of playing, and it was a hot day. About 5 minutes into the song, I start to hear crackling static. (the clip starts at that point). A few seconds later, I lose a lot, but not all, power and the sound is thin and distorted. I edited out the rest of the song and then there is some bass by itself to try and hear what is going on, at 45 seconds in. I change batteries - it's not that. And at about 1:05, play with the new battery. I start out soft, and there is no problem, but when I turn up, the problem is there again.

    After giving the rig a few days to mellow out, I tried it again just now at full volume and everything was fine.

    Can anyone diagnose from the description / clip what happened?

    Attached Files:

  2. Impossible to say for sure. Clearly a loose or poor connection somewhere. A common source for this problem is the effects loop, if your amp has one. The jacks(send/return) have little switches built into them that can act up in time. Try cleaning those, or just insert (and leave)a short patch cable into the send/return jacks. If that doesn't fix it, it's off to the repair shop.
  3. MIJ-VI

    MIJ-VI Inactive Supporting Member

    Jan 12, 2009
    The effects loop jack switches may be oxidized (a common problem if the amp's effects loop isn't used much).

    Try plugging a guitar (or patch) cable into the effects send and return jacks.
  4. Matt Dean

    Matt Dean Supporting Member

    Jan 2, 2007
    SF (North) Bay Area
  5. Wow, thank you internet.
  6. MIJ-VI

    MIJ-VI Inactive Supporting Member

    Jan 12, 2009
  7. Well, like I said, everything acted fine when I tried it out last night. I'll blow some air through it for now. If it happens again, I'll know to try the patch cord thing.
    I'm relieved that:
    a) Y'all isolated the problem to the amp head (vs. the bass, instrument cable, power cord, speaker cabinet, or speaker cable)
    b) it's not something more major, and can probably be solved for $5.
  8. BassmanPaul

    BassmanPaul Inactive

    It would have been helpful for a diagnosis if you had mentioned what amp you were using.
  9. MIJ-VI

    MIJ-VI Inactive Supporting Member

    Jan 12, 2009
    We don't know those things yet.

    As Paul has mentioned knowing the make and model number of your amp would be helpful...
  10. It's a Thunderfunk 550. It does have an effects loop (in fact it has two - one after the limiter but before the EQ and another after the whole preamp but before the power amp), and also an aux in / tuner out. And it has a DI out, a 1/4" instrument out, two 1/4" speaker outs and two 1/4" speaker outs. And a headphone out.

    The first part of the clip, was running through my effects pedals, which sit between my bass and my amp input (not through the effects loop). And in fact one of my effects pedals does have a bad jack I need to fix. The last part of the clip though, I plugged the bass straight into the amp.
  11. MIJ-VI

    MIJ-VI Inactive Supporting Member

    Jan 12, 2009
    Have you been able to reproduce the noise and try patching both effects loops?

    A bad solder connection or pot could be the culprit too, but on a premium grade amp like the one you have oxidized effects loop jack switches are a more likely suspect.
  12. bass4worship

    bass4worship Ready For Freddy, let rock Supporting Member

    May 4, 2009
    Sebring, Florida
    Sound more like your bass than amp. Had that happen to me and turn out to be my battery connector.
  13. Happened again, and I was able to do a little more isolating. It is not the bass, or any of the cables (including not the speaker cable). It is not the preamp (the post EQ DI works fine). So it is either the power amp or the cabinet. This bums me out because I got both the amp and the cabinet recently on talkbass. I think it takes a few minutes of playing before it kicks in, which is why I thought it passed the test when I just played briefly. So now that I 'know' that, I'll play for a few minutes to get it to happen, and then swap to a different cabinet and then with same cabinet, different amp.

    Today was a cold day and it happened almost right away, versus last time it was a hot day and happened after a few hours. So it is probably not a thermal issue.

    Plugging a cord into the effects loop appeared to work for a minute, but ultimately did not.
  14. Arrachion


    Feb 24, 2008
    The audio sounds like a bad pot to me.
  15. MIJ-VI

    MIJ-VI Inactive Supporting Member

    Jan 12, 2009
    If a cracked solder connection is what's causing the problem, then cold, contracted metal may make for an even more intermittent electrical contact.

    Have you contacted the amp's manufacturer for advice? The sounds you've recorded may be indicative of an issue which has cropped up before.

    MONOLITHLOUD Commercial User

    Jun 9, 2010
    Owner, MONOLITH Loudspeakers & Effects
    brute force is the key for something like this. upon powering your amp on if it seems fine, take your fist and give the top of the amp a good thump, if you get the sound you are speaking of, you have dirty jacks, bad pot or a bad solder connection. the smallest amount of vibration can cause this to happen in an amp. tiny cracks occur and they are fine for minute then they cause the crackling from the slightest of vibration.

    i know it may sound like hitting your amp is a bad idea, it is not, because the slightest thump can recreate your problem. i get amps in my shop all the time where the customer tells me their amp is making this or that sound and of course when i get in my shop, it doesnt do it. so, i thump the thing and it shows its face. that way i know i can disassemble the amp and locate the bad connection. good luck man.
  17. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Michael Manring had the same thing going on at this clinic.
  18. Clark Dark

    Clark Dark

    Mar 3, 2005
    I had the same problem with my Mo'Bass. I cured it by not allowing the cable to dangle from the input jack. I now rout my cable up through the rack handle and bring it "over the top" so the plug has no downward pull. No mo' problems.
  19. And the winner is monolithloud. I did a little more testing. It is not the cabinet, it is not the power cord. It can be brought on by giving the amp a smack. So there is some connection loose/dirty in the amp somewhere.
  20. GregDunn


    Jan 8, 2009
    Turn the amp off. Shoot some tuner cleaner into the fx loop jacks, then run a phone plug in and out of each of them a few dozen times.

    I have an amp which periodically gets oxidation on the fx loop jacks, and because signal is going through those all the time even if nothing is plugged into them, any sort of dirt or crud can interrupt your signal. Pounding on the top of the amp would sometimes fix it, sometimes not. This is an easy thing to do and might save you a lot of hassle.
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