Getting zapped by my mic...advice, please!

RnRD

Ok, so last night's gig was marred by my microphone zapping me with an electrical shock at regular intervals.

Leaving aside the obvious flaw in my mic technique (sorry to say I am one of those "mouth touching the mic" singers), what could be causing this?

For context, it has happened at two separate gigs, with plenty of absolutely shock-free gigs inbetween.

After the first set last night, I tried a different XLR cable, which did not remedy the problem.

Here are my current (sorry!) lines of troubleshooting thought:

• Dodgy mic - will try a different mic next time...but would a dodgy mic do this?
• Dodgy mains block - I am just using your common-or-garden white mains extension strips.
• Fault with the desk. Unlikely as it only happens on rare occasions, rather than at every gig.
• Dodgy grounding within the venues.

Other variables which may or may not have any bearing:

I am a singing guitarist, who does not use a wireless, so I am wired to my amp, via a pedal board into the front end, with another into the FX loop. Both use cheap Stagg mains power into a daisy chain.
I am also wired to the desk for in-ears, via the 1/4 jack AUX output into which, via a 1/4 to mini-jack adaptor, I plug in a long mini-jack extension lead, into which I pug my earbuds.

Danny1969

You get a shock because the ground on the mic (grounded by the XLR cable ) is above real ground or visa versa. Basically the guitar is grounded on the strings and the mic is grounded ... if there's a voltage difference between grounds you will let current flow when you touch the mic and that is what you are feeling. 

Check all kettle leads and extension leads have a solid ground. Then check PA and guitar amp as well. 

springhead

^^^ this, plus it could be the mains wiring at the venue.  Do you plug your desk into same outlet as your guitar amp?  If not there could be a potential difference between the earths on the outlets, i.e. ultimately between your strings and the mic.

RnRD

Danny1969 said:

You get a shock because the ground on the mic (grounded by the XLR cable ) is above real ground or visa versa. Basically the guitar is grounded on the strings and the mic is grounded ... if there's a voltage difference between grounds you will let current flow when you touch the mic and that is what you are feeling. 

Check all kettle leads and extension leads have a solid ground. Then check PA and guitar amp as well. 

Thank you, I shall check all of that.

springhead said:

^^^ this, plus it could be the mains wiring at the venue.  Do you plug your desk into same outlet as your guitar amp?  If not there could be a potential difference between the earths on the outlets, i.e. ultimately between your strings and the mic.

Thank you. 

Last night, my amp was in a different outlet. Often, they would be in the same outlet - just happened that there was a separate mains socket right behind where my amp was situated last night, so it didn't need to be plugged into the same extension as the desk.
Excuse my electrical ignorance, but from what you are saying would I be right to think that plugging them into the SAME outlet might help to mitigate the problem?

poopot

Had this once before…

everything was plugged into the same ring/outlets etc… but… the earth had come out of its connection in the extension cable I was using for my amp…

check the earth connections in all of your power leads also check the earth connection inside the amp and the pa…

and when you’ve made sure everything is fine and dandy with your gear… go and buy a socket tester from screw fix, use it at the next gig!

Danny1969

You can certainly have ground difference between sockets around the room ... especially if they are on different ring mains. In most circumstances though you will hear this as there will be a buzz from the PA and amp. 

Plugging everything into one socket by daisy chaining all the extensions can solve the buzz issue but bear in mind the total current draw ability will be limited by the lowed rated lead. If there's a 5 amp extension reel  in the chain then that's the max current you can draw after that reel in the chain even if all the rest are rated at 13A.

Plugging all the gear into one bad outlet isn't a good idea though so for safety reasons it's not a bad idea to carry a basic socket tester. That will tell you if the socket is correctly earthed and whether it's reversed on the live and neutral. It's also a good idea to give your own gear a basic PAT test. Just give it a good visual now and then and make sure there's only around 0.5 Ohms or less between the chassis and the earth pin of the plug. 

springhead

RnRD said:

Danny1969 said:

You get a shock because the ground on the mic (grounded by the XLR cable ) is above real ground or visa versa. Basically the guitar is grounded on the strings and the mic is grounded ... if there's a voltage difference between grounds you will let current flow when you touch the mic and that is what you are feeling. 

Check all kettle leads and extension leads have a solid ground. Then check PA and guitar amp as well. 

Thank you, I shall check all of that.

springhead said:

^^^ this, plus it could be the mains wiring at the venue.  Do you plug your desk into same outlet as your guitar amp?  If not there could be a potential difference between the earths on the outlets, i.e. ultimately between your strings and the mic.

Thank you. 

Last night, my amp was in a different outlet. Often, they would be in the same outlet - just happened that there was a separate mains socket right behind where my amp was situated last night, so it didn't need to be plugged into the same extension as the desk.
Excuse my electrical ignorance, but from what you are saying would I be right to think that plugging them into the SAME outlet might help to mitigate the problem?

Yes if they're in the same outlet then their grounds will be the same, no potential difference between them.  As has been said you also need to ensure that your mains cables and extension leads are in good health and their ground wires are secure. 

RnRD

Lovely, thanks all.

This kind of help is why I have returned from my self-imposed Fretboard exile.

Much appreciated.

ICBM

The biggest chance of this happening is when mics are plugged into a mixing desk which is at the back of a large venue and on a different ring main from the stage power. The real problem is that it doesn't matter if your own stage gear is in perfect order, and plugged into a properly-earthed mains supply on stage - if the mixer has an earth fault, then your earth wiring simply creates the best path to earth for the leakage, via you when you touch the mic while you're holding your guitar. Worse, an RCD on your own gear will not protect you since when they trip they don't lift the earth connection.

If you're using all your own gear, it's best if possible to run everything from one power socket - if you need to use 4-gang extensions, use a 'tree branch' arrangement rather than a 'daisy chain'. Ideally you need one fully 13A-rated extension (which can be quite short) which you can plug four others into (also preferably 13A), and four more on each of those (which can probably be 5A), giving 16 outlets. If that's still not enough, either for number of outlets or for total power draw, use the same again and plug them both into a double wall socket - that will give you a combined power availability of 6KW. This should guarantee that all the equipment earths are connected to each other and hence eliminate the possibility of a voltage between different pieces of equipment. It isn't a good idea for the whole thing to also not be earthed, but it's still safer than running from two separate supplies where one isn't earthed and the other is - that needs to be avoided at all costs.

In the old days when these problems were more common than they are now and there were no RCD distribution boxes etc, I also started removing the direct ground connection from the strings of all my guitars, and fitting a high-voltage cap in line. This preserves the noise suppression, but prevents a shock via the strings or bridge, trem arm etc. Other parts like pickup covers and metal control plates, and the output jack, are still a potential hazard but you're less likely to be holding those at the same time as touching a mic, and if you do you're less likely to be grasping them with your fingers wrapped around something you can't let go of. I still do this even today, just for extra peace of mind.

roberty

I've had this before in some dodgy venues back in the day, it's horrible. Is it dangerous at all because I was told at the time it could be

Supportact

On the bright side, the constant threat of electrocution can really inject a sense of tension into a performance. 

chickenbonejohn

I have experienced this, and had both 220volt mains shocks and 48 volt phantom power shocks. Neither is pleasant, and the former is potentially lethal - I've been lucky and got away with it to tell the tale. . First advice is if you get an electric shock from a mic. , stop playing and step away from the mic. immediately - I find that friends and family usually prefer it if I don't arrive home in a body bag after gig. Is the PA your own equipment? Get everything PAT tested (amps, powered speakers, desk, mains cables, extensions, adaptors etc - it's cheap to have done) and don't use any of it until you have had it tested and any faults attended to. I had this happen at a pub gig, and the guy running the PA simply said, "I'll put a foam windshield in the mic.". I told him that it was definitely not OK as a solution, and told him I would not carry on.  While he was arguing the toss about it and grumping, one of the powered speakers started putting put lots of blue smoke and it all had to be turned off. I packed away my guitars and amp, and walked out...the audience were absolutely fine about it. Don't compromise on this sort of thing - it's is a real risk if you are using someone else's gear and have no assurance that it has all been maintained and checked properly.

shufflebeat

I carry an ART pro split for several reasons, one of which is that it has a transformer isolated output which can be handy in situations like this.

The transformer isolated output won't allow phantom power through so condenser mics can't be used unless they have a battery power option.

https://artproaudio.com/product/prosplit-transformer-isolated-mic-splitter/

MikkiMcMurderer

Would playing with a guitar wireless  protect you from this situation @ICBM ?

ICBM

MikkiMcMurderer said:

Would playing with a guitar wireless  protect you from this situation @ICBM ?

Yes up to a point.

If there's a serious fault with the PA and the mic casing is properly live, you could still get a nasty shock, but even that is less likely to be fatal than if you're also holding a well-earthed guitar.