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Peavey Amp Repair Question

Ampig

Ampig

Feb 9, 2000
1,261
351
Manteo, North Carolina
#1
I was just given an old Peavey Mark III combo amp. It has been sitting in attic with no climate control for years. When I turn it on (no instrument plugged in) it howls like a wolf. I disconnected the front control panel so that just the main power supply, preamp and amp are in the circuit and it still howls. Any ideas on what the problem might be?
 
#5
Just remove the cover and jam a screwdriver into the works. Make sure its plugged in as you'll want an immediate response as to the efficacy of your actions.

On a more sober note, if you're serious about a repair, I can drop it off at Alpha Music / Norfolk or any repair shop of your choice. My buddy Bill lives in Toano Woods and more than happy to ferry it to me (I live on the southside). Let me know if I can be of assistance.

Warning: repair costs may outstrip the actual value of the component. Prolly cost you ~$65 (bench fee) to find out.

Riis
 
#6
As stated there could many causes for this problem. Here's one of the strangest I've run into that had similar symptoms.
This may not be the problem, but....

In some combo type amps this may be caused by the basket of the speaker not being grounded. If the baffle board extends up to within a short distance of the preamp and the wood of the baffle board absorbs moisture becoming semi-conductive, there will be a "feedback" loop established between the output of the power amp and the input of the preamp. If the speaker basket is not grounded, grounding it MAY solve the problem.

The basket would be grounded by running a wire from the (-) terminal to the basket. Most speakers will have a basket that is grounded by the hardware of the speaker terminal.

mech
 
#7
mech said:
As stated there could many causes for this problem. Here's one of the strangest I've run into that had similar symptoms.
This may not be the problem, but....

In some combo type amps this may be caused by the basket of the speaker not being grounded. If the baffle board extends up to within a short distance of the preamp and the wood of the baffle board absorbs moisture becoming semi-conductive, there will be a "feedback" loop established between the output of the power amp and the input of the preamp. If the speaker basket is not grounded, grounding it MAY solve the problem.

The basket would be grounded by running a wire from the (-) terminal to the basket. Most speakers will have a basket that is grounded by the hardware of the speaker terminal.

mech
Click to expand...

Sounds to me like the quickest way to rule this out would be to disconnect the internal speakers and/or remove the head from the cab and trial it with an external speaker cab.

Riis
 
#9
Ampig said:
Hey Zoober! What's shakin' neighbor?


I've pulled the amplifier out of the cab and it still does the same thing.
Click to expand...

Life's good but your amp situation doesn't sound so hot. Might want to check with Peavey and find a local authorized repair center. Think there's a couple down this way (Norfolk / VB). Actually, I have two buddies who both live on Thacher Drive (back behind Fleet Bros.) who'd be more than glad to help with the choreography...but they don't know that, yet.

Riis
 
#10
I had this problem with the Peavey MarkIII head. Does the amp roar and the compression light come on, even with the amp at low volumes? My problem was caused by a defective speaker cable (ok, an instrument cable used as a speaker cable) shorted inside the phono jack. Hope this helps.
 
#12
Ampig said:
It's a combo amp with an onboard 15". I could disconnect it and use an outboard cabinet for testing though.
Click to expand...

Good idea. Most onboard amps can become outboard amps with the removal of a few screws. If repair costs are prohibitive or the repair itself is just too much of a PIA, you can always snag another (I'm thinking a la Hartke 1400) for low-dough, velcro it into place, and **presto** instant practice amp.

Riis
 
#13
always test from the simplest problem first to the hardest last... or the cheapest to fix to the most expensive to fix!! ;)

Hey Zoob?? Do you actually live in VB, VA.?? and all your life?? then bout what age group are you in?? wife and I lost track of a girl we had been pretty tight with from there.. her mom has a house not to far from the beach even.. thus all the 20 questions.. she would be late 30's - early to mid 40's maybe... very nicely blessed, brashy as the come... her name was Cindy Weaver.. she worked for OkiData in atlanta for a while and lived in marietta, ga. for a bit.. LadyDawn (my s.o.) said something about she went back to VB for a while right when we moved from nashvegas to the columbia area..

as for Ampig's plight?? I would almost be willing to guess that it is a bad 1k-10v resistor coming from a 40ufd cap that is coming off what is called a hum buster circuit from the big transformer of the power supply side of it to the output stage of the amp.. if that resistor is bad, "which most likely it is", then thus your noise...

now I am not a tech!! I know just enough to get your's and my arse in deeper shite then we're already in!!! my advise would be to take it to someone that knows what they're doing and pay them for an hour of diag time..

peace and blessings,

Bluey
 
#14
mech said:
As stated there could many causes for this problem. Here's one of the strangest I've run into that had similar symptoms.
This may not be the problem, but....

In some combo type amps this may be caused by the basket of the speaker not being grounded. If the baffle board extends up to within a short distance of the preamp and the wood of the baffle board absorbs moisture becoming semi-conductive, there will be a "feedback" loop established between the output of the power amp and the input of the preamp. If the speaker basket is not grounded, grounding it MAY solve the problem.

The basket would be grounded by running a wire from the (-) terminal to the basket. Most speakers will have a basket that is grounded by the hardware of the speaker terminal.

mech
Click to expand...

Meaning no disrespect, this post makes no sense to me at all! I can't remember ever seeing a speaker with a grounded frame!

Paul
 
#16
blueyes said:
Hey Zoob?? Do you actually live in VB, VA.?? and all your life?? then bout what age group are you in?? wife and I lost track of a girl we had been pretty tight with from there.. her mom has a house not to far from the beach even.. thus all the 20 questions.. she would be late 30's - early to mid 40's maybe... very nicely blessed, brashy as the come... her name was Cindy Weaver.. she worked for OkiData in atlanta for a while and lived in marietta, ga. for a bit.. LadyDawn (my s.o.) said something about she went back to VB for a while right when we moved from nashvegas to the columbia area..

Bluey
Click to expand...

I've been here 21 years (originally from Western MD / Western PA) and live about 15" from the oceanfront. The name doesn't ring a bell but some big ol' knockers might. My wife (a local) and I are both 50++. I'll file the name away for the moment.

Riis
 
#17
Lady Dawn just got in from work.. the very first thing she asked when she walked through the door was had you guys heard of or knew who Cindy was.. she has just corrected me telling me that her age would be late 40's maybe even early 50's... hmm... she was very much vibrant and alive... but hey maybe your wife would know since she is a local.. ld asked me to ask.. they were very close.. ld had to sing at a friend's wedding the same time I had been working a few months as a roving / walking musician at opryland.. so I fixed her up an accompaniment tape of half a dozen songs that she preformed... Cindy showed up on one of her whims from hotlanta so they drove down to muscle shoals together and I worked that weekend.. well I pulled my shifts... you know how it is.. when the cat's away the mouse will stay behind and nibble on his cheese!! **rofalol** I think I worked for Rock Solid Sec. both nights.. the Brian Setzer orchestra and maybe the Henry Rollins Band.. or Sublime and 3 Doors Down... can't honestly remember Black Flag and Smashing Pumpkins.. it was a few years ago.. but Dawn did ask me to inquire ya know how it goes..


Peace and Blessings,

Danny
 
#18
BassmanPaul...I can't remember ever seeing a speaker with a grounded frame!
Click to expand...

They're not common but do exist. Grounding the speaker frame is something that often has to be done to OLD tube guitar amps to prevent oscillation. Current is induced into the frame by the voice coil. The chassis are not fully enclosed and the circuits are open to the speaker. The high impedance circuits pick up the induced current and there is a feedback loop.

The Peavey combo bass amps are of a similar construction and I believe I've seen grounded basket speakers in some of them over the years.

mech
 

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