Problem with PRS "30" - any ideas?

saf_1

Member
Messages
667
I've got a PRS (Sewell designed) "30" 1x12 combo. This is not the "SE" - it is the handwired, US made amp. All tube, 30 watts, 4xEL84 power section. Lately, it has developed a hum - or more appropriately a buzz - that is audible when the amp is first turned on, but grows progressively louder and louder the longer it's on. The odd thing is, it only does it when I have a guitar plugged into it. If I just turn it on and let it sit, with no cable in the input jack - no buzz. I can turn it up, mess with the tone controls - nothing. Dead quiet. As soon as I plug in a guitar though, instant buzz. Doesn't matter which of my five guitars I use, or whether it's single coils or humbucking p'ups - same buzz. I've tried using different types of cables (normally use George L's), bypassing my pedalboard and plugging in directly - same buzz. The amp almost never leaves my guitar room, and has not been abused. Just started this out of the blue. The only thing I've done recently, is swap out the original JJ power tubes, for a matched set of EI Golds that I had laying around (which I know were all good tubes - had them briefly in another amp at one time). It's not a hum like a microphonic tube, it's a buzz - like a short or something not grounded correctly - except that it progressively gets louder, the longer the amp is on. Anyone have experince with a problem like this, or have any suggestions? This one has me stumped.
 

saf_1

Member
Messages
667
Doesn't crackle like an input jack problem. I'll probably swap the tubes just to be sure, but if it was a tube, I would think I'd hear it, regardless of whether or not I had a guitar plugged in.
 

saf_1

Member
Messages
667
Swapped out all tubes - no change... still buzzing. Stops when I touch the bridge of my guitar, or the phone jack on the end of the speaker cable where it plugs into the guitar. This happens on all guitars, and with every cable I've tried - so it not a guitar or speaker cable specific issue. Sounds like there a ground problem somewhere. Input jack on the amp? Any other ideas?
 

Garthhog

Member
Messages
135
Poor ground connection between your guitar and the amplifier from the sound of it. Make sure that the sleeve connection to the amplifier chassis is not completely open. There will be significant resistance if you take the measurement with one end of the cable plugged into the amp and the other not plugged into anything. Also make sure that the instrument cable you are using has not bit the dust.
 

saf_1

Member
Messages
667
Poor ground connection between your guitar and the amplifier from the sound of it. Make sure that the sleeve connection to the amplifier chassis is not completely open. There will be significant resistance if you take the measurement with one end of the cable plugged into the amp and the other not plugged into anything. Also make sure that the instrument cable you are using has not bit the dust.
I've tried a variety of cables - which all work fine with other amps - so it's not a cable issue. I'll check the input jack on the amp, per your recommendation, and see what happens. Thanks for the suggestion.
 




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