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I recently noticed that my sIII build has been making all kinds of buzzing and humming related to the grounding. The symptoms are essentially a real loud buzz that will lessen when touching the guitar's strings or the amp's chassis and worsens depending on the location of the guitar in the room. My other amp, a Top Hat AC-30 style exhibits this same problem but on a infinitely smaller scale leading me to believe it's definitely something with the sIII. I've checked all my ground connections with a meter but that didn't get me anywhere. Chopstick probing didn't seem to reveal any weird wire placement issues causing the noise. I'm pretty well stumped at this point so am turning to the experts for some advice/ideas about where to go next. Could a bad tube cause this much noise? I've never had one that caused these types of symptoms but haven't tried swapping them yet. I can also post interior pics/voltages if necessary. Thanks!

Assuming you had a good one from the start...

Bad tubes can certainly cause a wretched noise. Easiset thing is to swap a few and see.

Measure and record your voltages. Compare to the original ones you made (you did record them right).

Sounds like it's grounded fine but what happens when nothing is plugged into the input? Do you get the same noises or anything weird? IF you dont, there a chace its equipment so ... do me a favor, can you try another cable & possibly a guitar?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I never recorded the voltages initially as it worked flawlessly from first power up. It didn't get used for a few months as I got crazy busy with work and had little spare time to noodle. Now it's buzzy. It definitely didn't behave this way before. It's almost unusable as it is now.

With nothing plugged into the input it seems to make little noise. I have way too many guitars and I tried it out with at least 5 the only any better then the others was the Les Paul (my only humbucker guitar) but even it exhibited the buzzing, just less severe. And I agree, it does sound like a guitar problem but none of my guitars buzz like this through my other amps leading me to believe there's something amiss with the sIII. I even tore apart my new/old Electric XII thinking there was a wiring or pickup issue (just got it a few weeks back) but everything was perfect. I think I was the first to even pull the pickguard off the thing!

Anyway, thanks for the quick reply! I'll try swapping all the tubes tomorrow evening and if that doesn't make any difference I'll draw up a voltage chart and post pics to see if that can lead us anywhere.

Well, some more experimenting revealed that's it's definitely not tubes and that it's very much related to certain guitars. The odd thing is that the typically noisiest ones I have (3 vintage Jazzmasters) are the quietest, in fact they sound perfectly fine. The Electric XII however is the noisiest guitar I've ever heard through my sIII but it sounds perfectly fine when played through my Top Hat. It's rather frustrating. What kinda weird grounding problems in my house/guitar/amp could be causing this sorta reaction? I'm at a loss really.

Does the amp make any noise without a guitar cord plugged in and with the volume turned up?

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Guitologist at Large
"How does that feel?"

It does make noise with the cord in and volume up. When I turned it on tonight there was some noise coming from the input jack area. I went prodding around with the chopstick and got it to go away by shifting the shielded cable joints a bit but for a little while my guitar cable was actually microphonic. Weird. It's still noisy after getting that to stop though. Typical grounding buzz that goes quiet when touching the chassis or the ring on the cable end. The normal channel is a little quieter then the TMB channel but both just seem too loud. I really don't have time to make a voltage chart right now but I'll definitely do that by the end of the weekend. Oh and I replaced a 12AX7 that was a little bit microphonic but that didn't make much of a difference.

Hi
It may be a stupid question but did you ground the center tap of the 6.3V, close to the ground of the EL84's?
Or if there isnt any connect two 100 Ohm's to the 6.3V an connect both other ends to ground.
This saved my sIII a lot of noise. Also check if you can with a scope for unwanted frequenties it could als be a oscillation with your guitar lead as a antenna. ( I was covering the 1MC band at first....)
Also dont't be affraid to use shielde wire upto the P1, but use good quality.
This should do it. If not ops

GRTZ
Ed

Are you testing this amp out of the box or in one?

Some of these symptoms smack of shiielding. Can you grab a piece of shield material (steel, aluminum) and hold it over the open chassis and try again?

My shop has some wild stray noise and sometimes, I'm trying to trace noises like this only to find it's the environment.

If it makes a difference, install it into a cab with a shield between the cab and the chassis.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

So I put some shielding on the back of the amp and that has helped enough that it's now almost as quiet as my Top Hat. There's a very small audible difference in the amount of buzz but it's hardly what I consider a problem now. I can't hear it at all once I start playing and before it was noticeable. So thanks for the suggestions all!

Now I just need to figure out what to do about my couple of extra buzzy guitars.