HELP! - weird amp problem

James Maxwell · Post by **James Maxwell** » 3 Jun 2012 11:22 am

Hey guys,
I have a Peavey "Special" amp, not a "Special 112" or anything like that. It is simply called a "Special". It is similar to this amp: http://bb.steelguitarforum.com/viewtopi ... a67e2b35c7 , except mine is all stock.

I am having a weird distortion problem. Even on my clean channel it sounds like this: http://www.youtube.com/watch?v=MewoRxLER6Q .

Any ideas of what the problem is?

James Maxwell · Post by **James Maxwell** » 3 Jun 2012 12:07 pm

Also, I am plugged straight into the amp, no volume pedal. Both inputs sound this way. i have also tried a six string guitar and it sounds the same.

If it helps, Here are some pics of the circuit board:
https://docs.google.com/open?id=0B8TUmW ... kU2X0REc28

https://docs.google.com/open?id=0B8TUmW ... FQ1dk9zR1E[/url]

Dave Grafe · Post by **Dave Grafe** » 3 Jun 2012 1:31 pm

It's not really very practical to diagnose malfunctioning electronic gear via Youtube and Internet, James, somebody who actually knows what they are doing needs to look at it in the real world

David Nugent · Post by **David Nugent** » 3 Jun 2012 2:37 pm

James..It may be stuck on the overdrive channel, do you have a footswitch available (most two button switches with a 1/4" plug should work)? You might try hooking one up to the designated jack and see if that solves the problem... When I purchased the unit pictured in the link that you posted the opposite was true, the overdrive channel would not come on. Once I located a footswitch and hooked it up, the problem was solved.

James Maxwell · Post by **James Maxwell** » 3 Jun 2012 3:23 pm

David, I do have a foot switch but both channels are bad

Mike Wheeler · Post by **Mike Wheeler** » 4 Jun 2012 5:52 am

James, it is hard to be accurate when listening to a video, but, my opinion is that you have a power supply problem. I suspect at least one dying filter capacitor. At any rate, the amp needs to go to a qualified amp tech for diagnosis.

Remember those amps have a few years on them, so components have aged and the ones most vulnerable to aging are the caps.

Also, I wouldn't wait too long getting it to a shop. The problem could get worse quickly and cause a more expensive failure. In fact, you might consider sending the chassis to Peavey...they are very reasonable and do excellent work.

Stephen Cowell · Post by **Stephen Cowell** » 4 Jun 2012 10:50 am

Take a short guitar cord and bypass the effects loop on the back... just plug it into the in and out. This is one common problem area.

James Maxwell · Post by **James Maxwell** » 4 Jun 2012 6:35 pm

Stephen, I will try that and let you know, thanks

James Maxwell · Post by **James Maxwell** » 5 Jun 2012 5:50 pm

Well my amp doesn't have an effects output on it, but I tried a cable from pre amp out to pre amp in, and it still sounds distorted.

Bob Tuttle · Post by **Bob Tuttle** » 5 Jun 2012 7:46 pm

Bad speaker maybe ???

Steve Ahola · Post by **Steve Ahola** » 5 Jun 2012 8:52 pm

I think that your best bet is to find an authorized Peavey repair shop in your area and pay him to diagnose the problem. Does the amp get loud? In that case the problem is not with the output section (4 discrete output transistors in a TO3 case made by Motorola!) Off the top of my head it sounds to me like something is messed up in the preamp circuit.

Most shops these days have a flat rate for a basic diagnosis. If you want to try to diagnose it yourself get a can of Freeze Spray and hit all of the semiconductors one at a time while a friend plays guitar. (Not a joke- when I was working at Pacific Stereo in the 70's some of the less talented service techs would go through cases of freeze spray which would often pinpoint an intermittent problem as a particular component started to overheat.)

I know a really good Peavey amp tech in the midwest if you want to ship it to him- or take a road trip!

Steve Ahola

Stephen Cowell · Post by **Stephen Cowell** » 6 Jun 2012 6:59 am

James Maxwell wrote:Well my amp doesn't have an effects output on it, but I tried a cable from pre amp out to pre amp in, and it still sounds distorted.

OK, first easy thing down... this is the most common problem, either eff loop or pre-out/in jacks' normals get dirty.

Listening to the video carefully, it's very compressed (from the camera) but I can hear a buzz on that last note. Normally that would be a speaker, especially with a solid-state amp (no arcing generally). And, conveniently, the easiest thing to do next is sub out the speaker. I'm with Bob Tuttle on this one.

Steve Ahola · Post by **Steve Ahola** » 6 Jun 2012 11:53 am

Stephen Cowell wrote:And, conveniently, the easiest thing to do next is sub out the speaker. I'm with Bob Tuttle on this one.

I agree with that completely. A tip: you can get a 1/4" stereo female coupler phone jack (AKA a barrel coupler) from Radio Shack and use it to temporarily connect the speaker in one combo amp to the output of an amp head or another combo amp. With one end of the coupler connected to the speaker use a guitar or speaker cable to connect it to the speaker output jack.

BTW the mfgs tell you to never use a guitar cable as a speaker cable. But a guitar cable will work just fine as long as the current does not exceed the capacity of the inner conductor (typically 18GA or more in decent quality cables.) A 25' extension cord of 18GA wire is rated for up to 7 amps at 120vac so for just temporary or "low impact" use a good guitar cord should work fine. I've gotten into a lot more trouble using a speaker cable for a guitar.

Note to self: put colored heat shrink tubing on jack barrels for my speaker cables.

One important warning: if a guitar cable should crap out when using it as a speaker cable it could create serious damage your amp.

Steve Ahola

P.S. On second thought a problem with a preamp would usually create problems with only one of the channels. So if the problem was with the amp it would probably be further down the circuit which handles both channels- like the FX loop. (I hear so much crap and distortion on the video that I'm not sure what is from the amp and what is from the camera.)