Irritating Buzz... grounding issue vs other?

[turtle441]

I've been reading Leevi's very similar dissussion eagerly, but can't quite figure out what's up with an issue I'm having.  I built a 2-channel Matchless based amp.  Schematic is posted in original discussion here:
http://el34world.com/Forum/index.php?topic=23398.msg251523#msg251523

The amp runs great and I've adjusted the power resistor discussed in the previous thread to a 22k, which has decreased power tube dissipation a bit.  Primary issue that I've had is an annoying buzz.  It's not present when nothing is plugged in (although there is a small amt of 60-cycle hum, it's tiny by comparison).  With any guitar plugged in, I get an annoying buzz.  It's not overwhelming, but enough that when I'm playing in church, it's probably going to be audible over the PA when I'm not playing.

Buzz goes away when I touch the bridge on the guitar.  This happens with multiple guitars, 2 HB-equipped and 1 P90 equipped.  It was the same with 2 different guitar cords.  It goes away if I turn down the guitar volume.  Using my multimeter, I've got continuity from all guitars' bridges to the amp chassis.

It seems like this should be something wrong with the guitar bridge grounding, but with continuity to the amp chassis, that seems unlikely.  The fact that it's present on 2 HB-equipped guitars makes it seem less likely that it's RF interference, although that is a possibility.

I haven't started swapping tubes yet, but given the response to the guitar volume knob, wasn't clear that that would really help.

Any thoughts?

[shooter]

it's probably going to be audible over the PA when I'm not playing.

It goes away if I turn down the guitar volume

that solves the PA issue

A faraday cage is probably not practical at Church 
Is the amp bottom "sealed" ?, aluminum tapped ala fender, or aluminum plate?

take it home, outdoors, good 3 prong extension cord, mp3 player with a 6" male/male and an 1/8 to 1/4 adapter, plug it in and play, still buzz?  If not, move to the country 

[jjasilli]

Try the guitars in other amps, especially at locations other than the Church.


Try the amps and various guitars at locations other than the Church.


Try other AC outlets on separate power lines around the Church.


The Church may have bad grounding which you can check.  Or have a lot of ambient noise.

[turtle441]

Thanks, to clarify, haven’t tried it at church yet.  This buzz is at home.  Doesn’t seem to vary much between my office and garage.

Guitars have been silent with my other amps, so I don’t think that’s it.

I don’t have the top shielded currently.  (It’s in a Deluxe Reverb chassis.). Will try that next.  Wasn’t convinced it was the right move as it was silent without the guitar plugged in.

[jjasilli]

Good to shield.