The Steel Guitar Forum

I have a mid-80s Peavey Studio Pro solid state guitar amp. This amp has a volume (pre EQ) and a master volume (post EQ) and has a 3-prong grounded plug. The amp has a buzzing sound which increases and decreases with the pre-EQ volume. The buzzing occurs without a guitar plugged in and decreases if I touch one of the amp strap bolts on the top of the amp or the input jack. If I plug a guitar in the buzz is also much less because of my hand on the strings. I ran a continuity test to confirm that the bolts are electrically grounded to the 3rd prong on the plug. Could this be a shielding problem or something else? There isn't any shielding currently in the amp. Thanks.

When your hands are on the guitar strings while plugged in, is the buzz inaudible or just less? How is the buzz while plugged in but not touching the guitar?
If your hands on the strings eliminate the buzz, replace the input jack. The jack is a closed circuit, grounding the input of the amp until plugged in. If that part of the jack is not working, the amp will buzz like crazy until plugged in. Otherwise, I would probably suspect an open ground before the pre-EQ volume.

How comfortable are you inside an amp?

Thanks for the reply Dave. Touching the amp strap screws on the top has the same effect as touching the input jack which is the same as touching the strings when I plug in. In all cases the buzz is signicantly reduced, if not entirely eliminated. Other than that, the amp sounds fine. This is a 20 watt amp and not worth much, so I would be comfortable in poking around inside with a meter. Let me add that I'm still very much an amateur tech at best.

Contact our techs at 1-877-732-8391, ext.1420 at Peavey.

Mike Brown
PeaveyUSA

David, you were right. The "shorting" input jack was no longer shorting. I was able to bend the inside shorting blade with some needle nose pliars which fixed the problem. These jacks only cost a couple of bucks so I'm going to replace both of them before I put the amp back together. This will be the first thing I check if I run into this buzz/hum problem again. I know other amps also use this type of input jack such as Evans and Fender. This turned out to be an easy and cheap fix. Thanks for your help.

Glad I could be of service! I would definitely recommend replacing them whenever you can get around to it. If they are soldered into the board and you feel little extra froggy one day, replace the jacks with good 'ole switchcraft jacks (shorting type, of course) and wire them to the board.