Buzzing sound that goes away when touching the strings?

[Hardtailed]

What could be the cause of that?

I thought it might be bad grounding so I used my DMM and measured the resistance from the ground side of the guitar lead all the way to the groud lug on the power connector, and it came under 0.1ohm, so my path to ground is good.

All checked all my ground connection inside the amp, all seems good.

It does that with both of my guitars and the "real" Marshall doesn't do it, just the clone.

Any help would be appreciated!

For the record: I used "2-star" grounds, with the OT center tap joined with the first filter cap ground. Then I had a ground buss on the board (instead of soldered to the back of the pots) where all the grounds go (no loop possible) which is joined with the 2 other filter caps to the 2nd filter cap's bolt.
Power valve are grounded straight to the chassis via 1ohm resistors for biasing purpose.

[tubeswell]

My guess is grounding or shielding. Grounding hum doesn't need much potential difference to cause it - a few mV in the wrong place.

Does it happen with no guitar? (i.e. when you touch just the amp chassis, does it go away?)

Does it happen with all guitars? (in which case, it could be grounding; - or could be that none of them are shielded very well?)

Or if it happens with only one it most probably definitely is poor shielding.

Is the cable bad?

[Hardtailed]

Tried a different cable... same thing

Both of my guitars are the same, with my bass it's even worse: the buzzing doesn't go away when touching the strings.

I'm thinking it might simply be my wall outlet...
I don't have any memories of that problem when I tried it at first, and I was in a different room.
Plus, I used it live last week and don't remember having any problem.

I'll move it to another room and see what that gives!

[Don Moose]

That's a good thought - a dimmer, flourescent (even a CFL) or a cieling fan speed control can throw all kinds of hash.

I do think you should check the ground connection on your input jack, though.

Hope this helps!

[mooreamps]

All of these guys are correct. It's an open ground, somewhere.


-g