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I was playing an outdoor gig in North Texas last Saturday evening, and about halfway thru I lost what seemed to be about 50-75% of my volume level in my amp (Marshall AS100D, playing a Jumbo Takimine Acoustic). At first I thought it was my battery in my guitar's pickup, but I replaced it with no improvement. I then switched channels on my amp, also no improvement. I finished the gig with my vol levels for master and input way higher than I've ever played.

As we were packing up we all noticed there was significant dew moisture on all our gear, cases, etc. I then wondered if that was the source of my volume loss. I brought my equipment home and turned a low speed fan on it to dry out anything that might have built up inside the amp. I plugged everything in Sunday afternoon and it was much better that the night before, but not quite back at 100%. I also played a second guitar thru the amp that had not been outside the previous night, and there was no difference, so I do believe it is amp related.

Does anyone know what might have caused this?

  • Did you use the same cable? Was the drop in volume instant or gradual? Might also be worth thinking about migrating this to the electronics stack exchange. And a photo of the internals may be useful for spotting things like swollen caps / corrosion etc. – Dave Engineer Apr 28 '15 at 12:41
  • Edited to make reading easier. – Karen Apr 28 '15 at 19:35
  • Eva-dry 500 silicon beads in a renewable encasement work really well for my little stuff I don't know about outdoors but it might help if that in truth is the problem – user10164 Apr 29 '15 at 9:47
  • I put my stuff in tuppawear with them to minimize outside effects a small box might suit your purpose – user10164 Apr 29 '15 at 9:48
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True, it could be a drop of water on a bit of circuitry somewhere but in reality the circuitry is inside the box so doubtful water actually fell into it (unless it was angled up or something ?).

The air's pretty damp when there's dew about of course so it could be condensation, but the Amp ought to have been warm enough to resist that quite resoundginly.

Guitar leads can do all sorts of weird things if they get damp though. Have you tried a different lead ?

Were you using distortion? If so, did it go quiet but still distorted, or go quiet & clean as if you'd turned the gain or guitar volume down ? That would give you an indicator as to whether the issue is before the pre-amp or after it.

If stayed distorted: The issue is after the preamp which is where the voltages are a bit higher. I doubt it'd be water-related there as this stuff gets quite warm- unless a load of water fell into the amp or something.

If it went clean : That implies the amp is getting less level- could be the guitar (butyou tried another ) or lead or moisture getting into the lead socket.

I guess the tricky part is such things could be caused by moisture but could be lots of other things too like a dry soldr joint or loose valve or fuse etc.

If in doubt, continue with the drying-out. Maybe a dehumidifyer might be an idea ?

ps. nice amp !

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