What causes that shock you get sometimes from your Mic while playing your guitar/bass?

[Roswellian]

Over the last few weekends, one of the guitards in my band has complained that he gets shocks when he touches the mic and his guitar.

 

I set up the a very simple PA; a Mackie 808s Powered mixer with no other stuff added on. Shure beta 58s and old reliable mic cables and speaker cables. He plays through and older Peavey and has a petal board. He claims he has never had a problem before. I know I have never had a problem before. We were all using the same power source, a single grounded circuit via a 14 Gauge extention chord. I don't get shocked, the other guy on acoustic guitar doesn't get shocked... why does the other guy get shocked and how can I fix it...?

[WRGKMC]

Ground loop.

 

When your amp and PA are on different outlets, the ground wire resistance between that outlet back to the service box is different for each.

 

Power takes the path of least resistance. If you have a shorter, more conductive path on say your guitar rig, and the PA amps chassis has a higher voltage potential on its ground, when you touch that mic, that voltage wants to get to ground through the shortest path possible and if that happens to be you, you will feel it.

 

Again, its all in how unbalanced the two grounds are. If one outlet has a poor ground, the zap is going to be much greater. Add to that the poor quality, extension cords, ungrounded cords and power strips where guys break the ground off, and outlets at clubs that are beat to crap, you really have to be careful. Your guitar strings are connected directly to frame ground. If the frame isn't grounded, you have no path to ground besides through another piece of gear.

 

Older amps even had a ground reversal switch which would swap around the hot and cold wires. You get that switch wrong and its lights out.

 

Best thing you can do is carry one of those little AC plug checkers and make sure the outlets are good. The rest can be done with an inexpensive AC meter. Check between your strings and Mic to make sure there's no voltage there. If there is then either something's not grounded right or you need to get things on the same power outlet so they are sharing a common ground.

[isaac42]

I'd also check to see if some idiot has clipped off the ground prong on one or more pieces of gear.

[onelife]

Is this happening in different locations?

 

Maybe you can get him to try it without the pedalboard to help isolate the ground fault.

 

[onelife]

You may also consider the possibility of phantom power getting to him via a defective or improperly wired mic cable.

 

Do you normally use phantom power with that setup? If so, you could try switching it off or replacing the mic cable.

[WRGKMC]

You may also consider the possibility of phantom power getting to him via a defective or improperly wired mic cable.

 

Do you normally use phantom power with that setup? If so, you could try switching it off or replacing the mic cable.

 

That's probably stretching possibilities. The mic wouldn't work if it was wired wrong and DC voltage voltage isn't going to shock you like an AC ground loop carrying up to 20 amps or more.

 

Phantom is 12~48 volts DC but the current is super low ranging from .8 to 4 milliamp's for most mics. It self adjusts its current up to maybe 20~30ma max. Even if the cable was wired wrong, you'd still need to touch both leads, each in a different hand with no load from the capsule.

 

The current from a 9V battery is 100 times stronger then what is used for phantom power and with a battery you only feel the current when you touch the leads to your tongue. Could that hurt someone? Maybe if they had a pace maker, but musicians handle 9v batteries all the time and don't keel over on stage when they touch them.

 

With no load from the capsule, again you'd have a dead mic and its unlikely you'd have the cover off an XLR jack where you could get to the leads. (XLR's don't plug in right with the cover off) and if you were running mic cords with the end caps off, and licking the connections with their tongue you probably deserve getting a reminder that the chord is in bad shape and needs to be replaced.

 

I've touched live phantom supplies plenty of times doing repairs and never felt as much as a tingle. Of course I'm a Technician and would never suggest anyone doing that. Its just the likelihood of you being shocked by phantom is super low. If some how you did get a catastrophic failure between AC and DC supplies to get enough current through the phantom lines, the smoke pouring out of the mixer would make it difficult to even find the mic on stage.

 

Just kidding. I'd sure there's some mixer out there some jackass has rewired to be dangerous and still have it working. You could be hit by lightening too just as easily too. Its just not going to happen on a normal setup with a normal cord even if it is wired wrong. The worst you would do is blow the mic up or the mixers phantom supply with the leads backwards. in any case you'd have a dead mic if its not providing the right voltage and polarity.

 

 

[greennn01]

Best thing you can do is carry one of those little AC plug checkers and make sure the outlets are good. The rest can be done with an inexpensive AC meter. Check between your strings and Mic to make sure there's no voltage there. If there is then either something's not grounded right or you need to get things on the same power outlet so they are sharing a common ground.

[WRGKMC]

An old trick you can use is to connect a .33uf or .5uf cap in series with the bridge wire. This is enough capacitance to prevent lethal exposure to current and still provide hum elimination. Its not a complete fix because any other grounded components, metal bridge plates, switches, guitar jacks, or pots with metal knobs will still be fully grounded. The only way you could possibly remove the ground completely is with a 1:1 isolation transformer. You could actually do that with a pair of DI boxes and run your signal low impedance from your pedal board to amp and run the boxes with the ground lifted. In effect you would plug into the DI box, run the XLR out to the second DI box at the amp and then connect the Hi Z jack to the amp. Passive DI boxes work bi directionally and this kind of setups are often used in studios where a guitarist may want to sit in the control room to track and have the amp in the studio miced up. Running low impedance prevents signal loss on a long run like that.

 

Of course you could just go wireless and never have to worry about it.

[RoadRanger]

He plays through and older Peavey

My guess is that's not grounded properly through its power cord. Is it a three wire cord? Does that amp have a polarity switch? I'd get it properly checked out before someone dies unless guitarists are particularly plentiful around there .

[WRGKMC]

I did have an instance last winter where the lead singer was getting zapped on a mic. In that case it was static electricity. She was wearing leather soled shoes and it built up a heavy charge from the rug in my studio.

 

The fix was simple. I had some stuff called Brillionize. Its an anti static glass polish I used as a tech that prevents static. I put some in a spray bottle and lightly sprayed the rug and the problem disappeared instantly. You can do the same thing with water and a little fabric softener in a spray bottle.

 

This kind of shock only occurs in cool and very dry weather, not hot humid summer days. It can feel just like a ground loop though. My company used to sell anti static mats that were grounded. Companies that work with expensive electronic gear, Mainframe computers, Copiers, Circuit board repair facilities etc. would buy them to prevent damage from static discharge.

[Mr Temporary]

I've done the cap & resistor thing on the string ground, and that works. Having had some nasty shocks in the past, I tend to like to have a little extra protection. That being said, it's better to have the power setup correctly in the first place, although in some bars the power is questionable at best.

 

The usual solution is to shield as best you can then disconnect the ground wire to the strings/bridge. Or install active pickups.