Testing an amp ground?

[easilyspooked]

I'm curious about amp grounding, specifically i'd like to know how i can find out if my amp is properly grounded, i'm assuming this is a Use a Multimeter answer, but i don't really understand electricity and i'm a bit slow today.

 

If my amp and my vocal pa are not on the same plug at home, where the wiring is very old and has not yet been redone to modern specs (upstairs has, we're getting there), I get shocked when i complete the circuit by touching my guitar and the mic.

 

I have not previously been shocked at shows, but saturday night we played a new club and I was shocked every time I came into contact with the mic. I asked the sound guy about it and he said it must be my amp, but he was a Terrible sound guy.

 

What's my first step in trying to discover the root of the problem?

 

Is there anything I can do on stage in the moment if the problem arises again (i've heard this is a pretty consistent plague upon musicians)?

 

Thank you very kindly!

[mike42]

You've likely got two separate but related problems. A lack of adequate grounding and something with reversed polarity at the outlet. Reversed polarity is probably what's causing the shock. Good grounding won't fix that problem, but it should keep you from getting the shock - may trip a breaker too.

 

Get one of the LED outlet checkers, 6-10 bucks, at Home Depot, Lowe's, any mid-size hardware store. It'll tell you if the outlets are wired correctly or not. You may also have a polarity problem in some of your equipment. Pretty simple fix usually, but you need someone who knows a bit about wiring to spot it.

 

If your home wiring is two wire only (no ground), you may still have some outlets wired with the polarity reversed. Fixing that might solve your shock problem even without having a ground line. That's not a recommendation to use ungrounded outlets, but sometimes you work with what you got. You should be able to check the ground on a piece of gear by taking a resistance reading between the ground prong on the plug and any exposed metal on, or connected to the chassis. Should read pretty near zero ohms.

[WRGKMC]

They make the 3 way to 2 way AC jack adaptors you can buy all over the place. If you look at tham carefully, theres a metal loop where the nground prong would normally be. What thats used for is, you unscrew the AC jack cover screw then fit that screw through the adaptor eyelet. That will provide a ground for most older home wiring that used the older metal conduit type cabling. That conduit is grounded at the box and can provide some grounding.

 

 

Other issues like your concert, both the PA and you amp may (and usuall do) have properly grounded outlets but the distance to the breaker box and all of the wire nuts used to join wires may have ground leakage. This will cause a difference in potential between the two grounds resulting in a shock.

 

Two things can be done there. One, if your sound guy was any good H'e have put your mic wire on a DI and lifted the ground as a quick fix. Another is to use an isolation transformer on the PA so noone will get zapped, Thats another thing I keep around for gigging. I also have one for my guitar amp and it removes ground induced hum in my studio because I use several different outlets. It also removes posibility of shock.

 

Lastly, if worse come to worse, use a mic condom. (foam wind/pop screen filter) It will keep you from having your mouth zapped by the mic.

[easilyspooked]

thanks guys! i appreciate the explanations!

 

the basement is on the list of places to rewire, and i now do have screwed in cheaters, but i'll definitely be looking at getting a wind screen for on the fly stuff, that's a great idea!

[mike42]

Hope your problem gets sorted out. One thing I would add about the 3 wire adapters. For those to give any protection they have to be screwed into an outlet with an intact run of conduit from the outlet box to the main panel. In my part of the country (Memphis) it's actually pretty rare to see residential wiring in conduit. So most of the time when folks are using those things, even with the screw attached, they're actually not grounded to anything. One of the outlet checkers will tell you if you've actually got a ground connection.