ground switch?

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billyg121

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probably a stupid question....could someone explain to me the ground switch on the back of the mark 4 a?
 
In the exact words written by Mesa found on pg. 6 of the owner's manual:

Ground Switch helps reduce or eliminate A.C. noise problems caused by old-fashioned ungrounded outlets. Try both positions A and B, using the one which works best. Otherwise keep the Ground Switch in the Center-Off position to avoid the possibility of annoying "ground shocks" when touching microphones.
 
Ground Switch helps reduce or eliminate A.C. noise problems caused by old-fashioned ungrounded outlets. Try both positions A and B, using the one which works best. Otherwise keep the Ground Switch in the Center-Off position to avoid the possibility of annoying "ground shocks" when touching microphones.


They are illegal in the US for this reason. I think they stopped putting them in in the early 90's. I have a Blue Angel, serial # 29 that has it, but my DC-3 doesn't have it, and it was made in shortly after that.

These are dangerous, and left over from a time when amps didn't have a ground because there was not one available in the plugs of any building. I usually defeat them by removing the so-called 'Death Cap' from the switch.

This is a really great place for a 1/2 power switch or a Pentode/Triode switch. This way you won't have to make any holes in your amp.
 
Mark IVA's already have a full/tweed power option, a class A/simulclass option, and a pentode/triode option. They also have a 3 prong grounded plug on an attached cord.
 
:D All you need is a bottle opener! :D


There are times that I really miss my Mark IV, but I never figured out what to do with R2. Plus, our new bass player is so quiet that my DC-3 kills him.
 
I would definitely leave it in the off position.

Next time you take it to your tech, have him disable it, then you won't have to remember.


I've had the **** shocked out of me quite a few times at gigs in places with no ground, it is really dangerous. Plus it hurts like a *****.
 
I would definitely leave it in the off position.

Next time you take it to your tech, have him disable it, then you won't have to remember. The problem is not with the switch, since you have a ground on your cord, but rather with the capacitor that leads from your switch to the chassis of the amp. If this capacitor fails and starts conducting, you will have 120 volts on the chassis of the amp, which means that it will lead straight up your guitar cord to your strings. This electricity should have no place to go, in theory, but when you touch something else, you will get a nasty surprise.


I've had the sh!t shocked out of me quite a few times at gigs in places with no ground, it is really dangerous. Plus it hurts like a *****.

When I lived on Maui, we played a lot of gigs in people's yards, just a few feet from their pools. While we were out of the way of the splashing, we were still close enough to be standing in water.
 
I once played in a band with a bass player that had an old Ampeg SVT with a "repair" end on the power cord. Everything was alright until we were both touching our guitar strings and somehow bumped elbows. ZZZZAAAPPP! Then he would just do it on occasion to get my attention :lol: . No standing water was involved, and kids, don't try this at home.
 
:lol: Ouch!!!!!!!!


When I was in my Electrical Apprentice school, we did an experiment with a line of people and a broken extension cord.

Basically, we all stood in a line holding each other's shoulders, while the teacher held the bare ends of the hot & neutral wires of a plugged in extension cord. Believe it or not, only the last guy got shocked. None of the rest of us got shocked at all.

If you're amp's power is shorting out, you may not even know it until you touch something that will give the electricity a path to flow through you. This is how a bird can sit on a wire with thousands of volts in it and never get shocked, he is only touching the 1 wire. If he touches another wire though, it is free thanksgiving.
 

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