Mesa Tremoverb grounding problem

[JdelRio]

I bought a second-hand Mesa Tremoverb a couple of months ago but I am getting electric shocks from microphones when I touch them with my lips whilst playing guitar. Also, when I lightly touch my guitar strings I get a clicking sound through the amp. I've tried different guitars, jack leads, power cables, plug sockets in different buildings and still get the same thing. The weird thing is that in the manual there is a Ground switch on the back of the amp, but I don't have it! Its the only difference between my amp and the manual diagram. I am in the UK using 240v power if this makes any difference...

[Don Moose]

This is something I'd email Mesa about ... if they had an email address available.

I hope that 130V MOV is gone, too - or is replaced with one that's at least 270V.

I'm going to suspect the ground lead from the power inlet has come loose or is otherwise making bad contact - check the connection at the plug and at the chassis.

I'm also going to wonder if the inlet was wired reversed (Hot <-> Neut exchanged). Hot is supposed to go to the fuse. Does your RadioShack equivalent (Mapex?) sell outlet tester devices? After you verify your favorite outlet, connect the tester to internal side of the amp's power input and see what it thinks.

If all that looks OK, you can clip in a 0.01uF 1KV film cap from Neut to GND and measure the voltage between your chassis and mic. I would not try the Hot side. This is supposed to be a TEMPORARY fix for a temporary situation (these are called 'death' caps, cause if it's connected to Hot, and dies short, and the socket's GND connection is bad, you get mains voltage on the chassis - don't use this on a mains socket you haven't tested as properly wired).

Hope this helps!

[Enzo]

I could be wrong, but a lot of export stuff does not include the ground switch. All the PVs for example. I'm not sure a ground switch is legal in the UK.

ANd am I wrong: 240 is balanced power? THat is no hot and neutral, both wires are hot?

But the earth wire might not be intact. Measure resistance from the earth pin on the mains plug to the amp chassis. Obviously when the amp is not plugged into the wall.

[JdelRio]

Thanks guys. I followed your advice and looked inside the amp. It was actually really simple - the earth wire had broken where it was soldered to the chassis, so I just re-soldered it and now its fine! Thanks for making the effort to help me. Cheers.

[Don Moose]

Thanks for making the effort to help me.

That's why we're here, Man.
Have a beautiful day.