Electric Shock

[dirtythermos]

When the microphone is shocking me in the lips, does that mean I need to plug my amp into the same circuit/outlet that the mixer is plugged into?

Is there anything I should know before using a long extension cord with my 35 watt tube amp?

I assume that ground-lifting a tube amp is a bad thing?

 

[kid klash]

I hope you're joking... too many musicians have died this way.

When the microphone is shocking me in the lips, does that mean I need to plug my amp into the same circuit/outlet that the mixer is plugged into?

Is there anything I should know before using a long extension cord with my 35 watt tube amp?

I assume that ground-lifting a tube amp is a bad thing?

ALWAYS use a simple tester (small neon lamp, like the type you'll find on the door of a freezer) or similar device to test the potential between your amp (which is connected to your strings through the wiring inside your guitar) and the PA or any other electronic device carrying primary voltage. Older amps (like Fender amps) have a polarity switch on them, which may help. And yes - all the audio gear needs to be on the same circuit, mainly to prevent ground loops.

 

[goldtopchas]

It's a good idea to have, and USE!!! a circuit tester. You can get a simple and cheap one at radio shack. Plug it in and check the outlets. Yes, it's good to have the PA and guitar amps on the same circuit. I always run an ext. cord along with the snake for the mixer.(no, It has never caused any noise problems). Before I started doing this, I learned the hard way.
Once ,we were playing a club that we had been at several times before. I plugged my amp into an outlet(there were several on my side of the stage). When I stepped up to the mic. for the soundman to get a level...BAMMM!!
It felt like someone kicked me in the throat!! I couldn't breath, or speak for a couple minutes. They almost called 911.
The outlet that I happened to plug into was wired wrong.
You REALLY have to watch out for this...There are a lot of "do it yourself" club owners that will save a few bucks and wire stuff on stage. They don't always know what they're doing.

 

[goldtopchas]

PS: I heard that you can put a small value capacitor between your strings and the ground of the guitar to keep it from zapping you. Has anyone else heard of this???

 

[Clive Hugh]

PS: I heard that you can put a small value capacitor between your strings and the ground of the guitar to keep it from zapping you. Has anyone else heard of this???

Check out www.guitarnuts.com it might just save your life, as the man says too many musicians have been killed by this.

 

[ggunn]

Check out www.guitarnuts.com it might just save your life, as the man says too many musicians have been killed by this.

This is really two separate topics.

A little annoying shock from a mic when you are touching the guitar strings can be helped with polarity switches and the judicious application of ground lifts, but always check after each change by holding the guitar and bumping the mic with the BACK of your other hand.

Incorrect wiring is a lot more dangerous. You can get a circuit tester from Radio Shack pretty cheaply, and it could save your life. Especially deadly is the "hot / neutral reversed" configuration.

 

[c7sus]

What I didn't see mentioned is be sure that the outlet is GROUNDED. Test for ground presence by putting your VOM leads across the hot and ground of the outlet.

Ideal and others make little plug-in devices specifically for testing the wiring configuration of U-ground outlets. Less than $20 at Home Depot. It has a series of lights and a legend to explain the situation marked right on it.

You don't necessarily have to be on the same circuit, but you wanna be on the SAME PHASE as whatever other circuit(s) you use.

 

[boingoman]

the judicious application of ground lifts,

.

There really isn't such a thing as "judicious application" of ground lifts, at least A/C ones.

 

[ggunn]

There really isn't such a thing as "judicious application" of ground lifts, at least A/C ones.

I disagree. For example, in my studio the other day, I connected a bass amp from its high Z line out to the mixing board, and there was a major 60 Hz hum on that channel. That bass amp does not have any ground or polarity switches, so I ground lifted the bass amp and the hum went away. There was no safety issue, as the chassis of the bass amp was still connected to earth ground through the shield (hence the ground loop which caused the noise). And yes, I know that there are other ways I could have done it.

Another judicious use: I once had to run a small outdoor stage from a single A/C circuit where the single outlet had no ground pin. I put the power amps on an A/C strip and inserted a ground lift between it and the outlet. I poured about a gallon of water on the ground close to the plug, and I got the tire iron out of my trunk and pounded it into the ground where I had poured the water. I got some speaker wire and used it to connect the ground ring of the ground lift to the tire iron. I ran an extension cord from the same strip to the guitar amps and such. Ditto the mixer. The system was dead quiet and nobody on stage had even a tiny shock problem.

One more: If you run a stereo chorus into two guitar amps, frequently you get hum because the shields are connected and each also has an earth ground as well. This can happen even if you plug both amps into the same outlet. Lifting the ground on one or the other amp will usually get rid of the hum, and again, the lifted amp still sees ground through the shield and the other amp's earth pin.

Granted, the use of A/C ground lifts is more likely to cause shocking probs than ameliorate them (rethinking what I said yesterday), but they do have their uses.

 

[Imaduck]

Just to clarify for Dirty since he seemed a bit unfamiliar with all of this, many older Fender amps (and other vintage amps for that matter) control their polarity based on the way the standby switch is switched, and generally flipping it down will put it in par with most electronics, though this isn't standard for all amps so if you're still getting shocked then flip it the other way. Other amps have separate ground switches, so just keep switching it until the shock is done (note that to match other people's amps you need to find a ground setting that will keep all of you safe).

Other than that, you just need to worry about the faulty wiring everybody else was talking about. Any of the testers they mentioned should do the trick.

Also, there is a pretty rare chance that two outlets in the same area may be on different grounds (or lack grounding altogether). This is pretty rare, but in certain cases it could create a voltage difference strong enough to be lethal.

PS -- that cap idea is really cool.

 

[ggunn]

Just to clarify for Dirty since he seemed a bit unfamiliar with all of this, many older Fender amps (and other vintage amps for that matter) control their polarity based on the way the standby switch is switched, and generally flipping it down will put it in par with most electronics, though this isn't standard for all amps so if you're still getting shocked then flip it the other way.

PS -- that cap idea is really cool.

Just to clarify further (I own a couple of old Fender amps), it's not the standby switch you are thinking of. Flipping the standby switch down will put the amp in, well, standby. No plate voltage - no sound. The ground switch selects which pole of the line voltage has a capacitor to the chassis; this switch is usually on the right rear corner of the chassis (separate from the power and standby pair of toggles) and is usually a three position switch (center off) which flips horizontally.

For example see the Fender AB763 Showman circuit:
http://www.freeinfosociety.com/electronics/schematics/audio/fenderab763.htm
The ground switch is at the bottom in the center, and the standby switch is on the lower right.

As to the capacitor idea, I'm not sure what a high pass filter (series capacitance) would do in that application, or why it would reduce shocking, but I can't say that I know for sure it won't work.

 

[foreverain4]

this whole shock thing happend to me last week. i have an old sunn 200s. the plug has no ground on it, but my distortion pedal does. so, i knocked the ground off the power strip that i plug my pedals in to. so, nothing is grounded . well, i just happened to be close enough to my bass player, that one of my dangly strings up by the tuners ( i usually do not clip them off ) touched the bass players arm. needless to say, it made him scream! i lifted the ground on his amp, still to no avail. figured he is still grounded through the xlr plugged in to his DI on the bass head.. how can i make it so my rig doesnt kill someone?

 

[ggunn]

this whole shock thing happend to me last week. i have an old sunn 200s. the plug has no ground on it, but my distortion pedal does. so, i knocked the ground off the power strip that i plug my pedals in to. so, nothing is grounded . well, i just happened to be close enough to my bass player, that one of my dangly strings up by the tuners ( i usually do not clip them off ) touched the bass players arm. needless to say, it made him scream! i lifted the ground on his amp, still to no avail. figured he is still grounded through the xlr plugged in to his DI on the bass head.. how can i make it so my rig doesnt kill someone?

Well, the best way would be to replace the power cable on your amp with a three conductor one, and tie the green wire (which is connected to the round pin on the AC plug) to the chassis of the amp. You should, however not attempt this unless you are comfortable and experienced at working on amps; there are some circuit nodes which can retain lethal voltages for a long time after the amp is powered down and unplugged. An experienced amp tech can do this mod in a few minutes.

You should NEVER cut the ground pin off ANY AC plug. If you must lift (and then you absolutely must know what you are doing and have a grounding plan that takes it into account), then use a ground lift adaptor.

The power strip that has the pin cut off, you should either cut the plug off and replace it with a new 3 pin plug, or you should trash it. It's dangerous.

And trim your strings.

The solution to the situation where some things are grounded and some are not isn't to unground those that aren't, it's to ground everything.