discosi Posted July 8, 2008 Share Posted July 8, 2008 Hi everyone, I recently had a gig where the singer was getting a small shock when his lips touched the microphone whilst playing his guitar. I've had this happen before and both times it's been a touring American band with American plugs ( and appropriate transformers for UK). All our 'Sound' & 'Stage' power is on the same phase (electrically), is it due to the American plug? Would taking one rubber foot off the mic stand create an earth thus getting rid of the shock or should I just put a foam pop-shield on the end of the offending mic? Any ideas / suggestions welcomed please, Cheers Si Link to comment Share on other sites More sharing options...
J Pearce Posted July 8, 2008 Share Posted July 8, 2008 Are they using centre tapped ground transformers (building site style)? If so it is just possible that their earth could be up at 55V with respect to your earth. That's enough potential to create a spark, and enough to give a shock when on moist lips. Link to comment Share on other sites More sharing options...
johndenim Posted July 8, 2008 Share Posted July 8, 2008 I have had this before on a '58. A very strange '9v battery on the tongue' type feeling!I thought that it may have been a fault on the mixer but after changing the mic cable the fault was gone.....Interesting. John Denim.ps, sorry I'm no help si! Link to comment Share on other sites More sharing options...
paulears Posted July 8, 2008 Share Posted July 8, 2008 The mic stand idea won't work - too many plastic bits in between, aren't there? The critical thing is that for a shock to be felt you have volts where volts shouldn't be. First thing would be to PAT the kit. In my view, this is one area where testing is vital - equipment with two pin mains and often no grounding in the design. It's more difficult as you have to work out where the problem really is. The guitar usually the earth, via the strings, but if the amp is groundless, then with valve kit it's not impossible to find he ground floating at about half mains voltage. The mic body will be a real ground, and the tingle is worse because it goes through the lips. However, it should not be there. You need somebody who knows what they are doing to sort this one. Is the amp up to our specs, or not? Is it a real fault - if so this could be a terminal one, or is this just a case of the transformer isolating the earth rather than maintaining one? Could just be ok equipment combined in a manner that becomes not ok. Applying earth connections willy-nilly is probably a bad idea, as you could potentially make things even less safe, depending on the configuration, and how you manage the grounding. A good one to give to somebody else, me thinks! Link to comment Share on other sites More sharing options...
fatfrog Posted July 8, 2008 Share Posted July 8, 2008 I'd second what paul has said, However I'd also inspect all the cabling and connectors visually as well, U'd never know what u might find!!! Alan Link to comment Share on other sites More sharing options...
Shez Posted July 8, 2008 Share Posted July 8, 2008 There's a pretty comprehensive thread about this over on the sound on sound forum here. One thing I would mention as it's a pet bug of mine - it's almost never the mic that's the problem even though people / guitarists are usually very quick to blame it. It's almost invariably the guitar amp, most commonly caused (with UK kit at any rate) by clueless guitarists lifting the earth in their amp under the mistaken impression that doing so will cure mains hum problems. For any guitarists reading this: NEVER EVER lift the protective mains earth - it's there to stop you dieing! Link to comment Share on other sites More sharing options...
KevinE Posted July 8, 2008 Share Posted July 8, 2008 I agree, the cutting of mains earths to avoid hum loops is pretty endemic and widespread in the world of touring musicians. Guitar amps are particularly susceptible to ground loops as the guitar pickup inputs are unbalanced and very high sensitivity and musicians often put the integrity of their sound above their safety. The use of switch-mode power supplies increases intrinsic leakage current through the earth conductor which needs to be in tact just for this reason alone! Floating chassis are easy to generate and must be avoided, the results are exacerbated by poor screen conductors in mic and instrument leads giving rise to potential differences between conductors on the same system. A 240-110 centre-tap site transformer shouldn't make matters worse as the earth terminal on the inlet and outlets are still conected together and to mains earth as well as the centre tap. They're safer than the usual cheap autotransformers for 110V equipment as these may leave the 110V appliance at 240 to earth under fault conditions or heavy filter-induced leakage. If you install a ground-lift box you should think through the consequences of aquired charges on conductors that have no other leakage path than a musicians lips!! The source of shock may not be the mic itself but the guitar or pedals and the mic is the ground point. The roadie should carry a multimeter and do cold-checks with power off to make sure all conductors exposed to the musicians are bonded together in some way. After all, a little mains hum caused by energetic earth bonding is way better than a dead rock-star, right? Link to comment Share on other sites More sharing options...
J Pearce Posted July 8, 2008 Share Posted July 8, 2008 ...A 240-110 centre-tap site transformer shouldn't make matters worse as the earth terminal on the inlet and outlets are still conected together and to mains earth as well as the centre tap...Yep; my point was that I have seen (more than once from foreign touring groups) the low leg (or neutral) of a 55-0-55 transformer bonded to the 240V neutral/earth, creating a second earth at 55V... I don't think I was fully with it when I replied or I would have pointed out the more obvious (and more common) floating chassis, lifted earth etc. Sorry all! Link to comment Share on other sites More sharing options...
fogg Posted July 8, 2008 Share Posted July 8, 2008 I have had thie problem when I've been playing bass and I have used the DI out on my amp. If there is phantom power on the channel that my bass DI is plugged into I get a shock from the mic when my lips touch it. I have looked at the amp and checked all earths and everthing looks fine. Not usually a problem if the desk has individual phantom power as I can turn it off. But my mix wiz doesn't so I have just learnt to sing slight away from the mic. Works for me! Link to comment Share on other sites More sharing options...
Stuart91 Posted July 9, 2008 Share Posted July 9, 2008 A guitarist friend of mine bought a wireless pack for his instrument as a way to avoid shocks. Of course, going wireless opens up another Pandora's Box of technical issues, especially if you are touring abroad, but the consequences are a good bit less lethal! Link to comment Share on other sites More sharing options...
dbuckley Posted July 9, 2008 Share Posted July 9, 2008 Had a vocalist complain to me once he was being shocked on the lips by the mic. Had me going this one. The cause: his shoes generating static when he walked on the astroturf the event company had placed on the stage ... Link to comment Share on other sites More sharing options...
paulears Posted July 9, 2008 Share Posted July 9, 2008 A nice foam windshield will cure Mr Fogg's problem. Showing my age, I often wondered why when SM57s first came out they usually had a Shure open foam windshield on them for vocalists - a pretty useless filter, but good for stopping shocks! Link to comment Share on other sites More sharing options...
Peter F Posted July 9, 2008 Share Posted July 9, 2008 A nice foam windshield will cure Mr Fogg's problem. Showing my age, I often wondered why when SM57s first came out they usually had a Shure open foam windshield on them for vocalists - a pretty useless filter, but good for stopping shocks! This is bad advice. What seems to be being overlooked is that these electric shocks are potentially life threatening. Putting a bit of foam over the end of a mic is not a cure. What happens when the guitarist adjusts the microphone position with his hand? You get electric shocks from microphones when there is a voltage difference between the earth/ground of the microphone and the earth/ground of the guitar you are holding. You can measure this fault using a voltmeter between the mic and guitar. You cure the fault by tracing where the earth is not connected. Almost invariably this will be the guitar amp or in the chain of backline power leading to the guitar amp. Find a known good earth (PA distro maybe), check for continuity from guitar backwards through the amp and mains leads, extensions. Please do not treat these "tingles" as just one of those things. They can and have killed people. Peter Link to comment Share on other sites More sharing options...
PoppaDom Posted July 9, 2008 Share Posted July 9, 2008 A nice foam windshield will cure Mr Fogg's problem. Showing my age, I often wondered why when SM57s first came out they usually had a Shure open foam windshield on them for vocalists - a pretty useless filter, but good for stopping shocks! This is bad advice. Peter Disagree with such a sweeping statement. The cause of these shocks could be attributed to a number of things, some more life threatening than others!I too have had performers getting static shocks caused by them grounding themselves when they made contact with the microphone. This was caused by them standing on arcyrilic and charging themselves up. Nothing life threatening in this situation and paulears advice stands very true IF the shocks are being caused by static. Poppadom Link to comment Share on other sites More sharing options...
KevinE Posted July 9, 2008 Share Posted July 9, 2008 I'm more with Peter F on this one! I agree static does crop up from time to time but especially this damp weather it doesn't occur so much and an audience in a room will soon increase the humidity enough to prevent it. Even correctly wired set-ups can lead to shocks, on account of the aforementioned floating chassis's thanks to the myriad of double-insulated (double leaky...?!?) equipment. Even pro PA desks are coming now double-insulated with compact switchmode PSU's and heavy filtering, meaning you lose a common signal star grounding point. Add the DI boxes, GL isolators, earth lift switches, laptops etc and you soon get a nightmare of mixed potentials. Link to comment Share on other sites More sharing options...
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