Even at zero it's loud
September 10, 2010 9:04 PM   Subscribe

My 80's peavey standard 260 solid-state amp head keeps on amplifyin' when both volumes are turned all the way down, which is disturbing. Can anyone shed light on why? YANMAmpRepairGuy.

I don't think this has always been the case, although maybe it has & i just didn't notice because i turn the volume down on the bass rather than fiddling with the amp. It is similar to this though this is not the EXACT schematic of my model, it is all peavey offers. The capacitors were swapped out last year; the new ones are slightly off spec & they are screw-terminal whereas the oem were soldered in. I know I will have to bring it to an amp guy if i want to keep using it; just trying to assess whether it will be worth even the bench fee or whether i should write it off & focus my energy and money on a replacement. thanks much for your thoughts!
posted by Rube R. Nekker to Grab Bag (8 answers total)
Do the volumes do anything when you turn them? Do they make crackly noises? It could be as simple as worn out potentiometers.

It's also possible that a short was created when replacing the capacitors, but looking at the schematic, there is no obvious place where this would cause both volumes to remain at full volume.
posted by Anoplura at 9:19 PM on September 10, 2010

If your amp has the effects and normal channels does the issue happen with both channels? Did the problem start after you got the caps swapped out?

Kind of a weird problem. Do the tone controls work? Grounding problems can cause weird things and if the circuit ground to the controls got lifted/cut/disconnected/etc it could have the effect of basically turning all the controls all the way up. Maybe something happened when you got the caps replaced or something like a wire worked loose over time. Or if the pots are soldered to a board one of the connections on the pots broke. Pots soldered to boards can put a fair amount of stress on the board (and their legs), especially if the nuts holding them to the chassis were loose. And pots are mechanical devices and will eventually fail. Just throwing ideas out their but if I was working on the amp I'd start there, absent specific knowledge about this series of amps.

So it's probably fixable. But is it worth fixing? If it's an amp you otherwise like the sound of and would keep for a relatively long period of time it might be worth it. If it's an amp you use because you have but aren't particularly excited about it might not be worth fixing.
posted by 6550 at 9:30 PM on September 10, 2010

Response by poster: Anoplura, yes, the volume still does go louder, and yes, it's crackling like all get-up.

6550, I think it's happening with both channels, but i'll have to go back & recheck ... tone controls do work. one of the jacks has not worked since i got it, it is one of the ones that blends the two channels but i can't remember if it's on the clean side or the effects side. I don't remember it right after the capacitor work; the first time i recall the volume being weird/crackly/wonky is a few months ago when I (okay don't kill me) ran my iPod shuffle through it. Was running an active device through it what caused a problem?
posted by Rube R. Nekker at 9:44 PM on September 10, 2010

Best answer: The iPod would drive the amp with a (potentially) much higher signal than a guitar. I'm not as familiar with solid state guitar amps as vacuum tube amps, but with a solid state it might be possible that it burned out one or more transistors. Although looking at the schematic I don't really see how that would lead to both volumes not working or being basically full up.

Okay, taking another look at the schematics and with the mention of the crackling on the volumes, a crackling sound could indicate there is DC voltage across the pot. Usually amp makers try to avoid DC across pots in audio circuits just for that reason, so often capacitors are used to block DC from pot. It's unlikely but maybe possible that the too high input ended up exceeding the voltage ratings of the blocking caps, then making them leaking, allowing DC across the pots.

Just throwing some ideas out there. Troubleshooting can be hard enough with the amp in hand, but I hope you can get it figured out.
posted by 6550 at 10:41 PM on September 10, 2010

Best answer: I'm gonna bet you like the tone, because you are talking about saving it. That means you want to save it. Attempt to save.
posted by Ironmouth at 11:05 PM on September 10, 2010

Best answer: It sounds like you have one or more bad potentiometers. They go bad over time. I suggest replacing them all. I suggest you replace them all. I'm not familiar with Peavey amps of that era, but there weren't too many oddball parts being used in the 80's, so you should be able to find drop-in replacements without too much trouble, or spending more than $25 total.

FWIW, the ipod could/would not have harmed the amp. The amp has a high impedence input which basically only cares about the voltage of the input source. While the ipod is capable of putting out a higher current, for driving head phones, it's voltage will be similar (~3v) or lower than the peak output of a bass guitar.

Also, bad capacitors, or incorrectly installed capacitors can definitely cause crackling in the volume knobs, but wouldn't cause the volume problem unless the schematic for the amp is question was drastically different from the one linked to. Even then, I'm pretty sure if would have to be at least 2 different capacitors shorted out in order to get crackling AND the volume issue.
posted by Anoplura at 12:29 AM on September 11, 2010

Best answer: I would get a can of DeOxit, your local Guitar Center should carry it. (Guitar Center link to the stuff I use). It's about 15 dollars a can, and worth every cent. The company that makes it sell other products too that I have tried that work well for what they are advertised for, but the D5S-6 spray is a multipurpose miracle-in-a-can.

I have saved/repaired MANY potentiometers using this stuff, as well as a few input/output jacks, mixing boards, etc etc. EVERY person that uses electronic/electrical gear should have at least a can of the basic general-purpose spray (D56-S). Just spray some on the pots (don't be shy) and vigorously turn them up/down back/forth for a few minutes, spray again, and let dry.

I bought an older 24-track mixer at a garage sale for 10 bucks, half the faders didn't work at all and the rest were 'scratchy;' I sprayed them down liberally with some D56-S, slid them all up and down for awhile, and the board ended up working like it was new.

Oh, and I doubt that running your iPod through it did any damage, I used to run my cassette walkman through my amps all of the time, often with the volume at least 3/4 of the way to max on my walkman and never had an issue.
posted by peewinkle at 12:59 PM on September 11, 2010 [1 favorite]

Response by poster: confirmed that volumes on both channels exhibit behavior.

mine is different from the pdf in that there's no master masters in the middle.

6650, yes, possibilities were exactly what i was hoping to collect.

ironmouth, absolutely. dunno if it's so much tone as all-round punker badassery (i believe the vocal model was greg ginn's guitar amp in early black flag). it has stood up remarkably well with both a loud-drummer-2-screeching-guitars-metal band & a fuzz-psych-punk band considering it's only 130w. the effects side makes dreamy surfrock-dub sounds that i hope to utilize in a future project (ok you got me that's tone.) just a question of where it's going to go on the ol' money-guzzling priorities list.

anoplura, your input is invaluable. & peewinkle, i am familiar w/ this technique & will look into it.

thank you all for your help, putttin' me at ease with the rougue sound engineering techniques i employ & not telling me to dtmfa. *sob* i lubb you mefi! r.r. nekker
posted by Rube R. Nekker at 1:38 PM on September 11, 2010

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