Shocks to the lips from the mic

Boskins

New member
Hi, I'm Boskins and I am a noob!

I am setting up my first home studio and am getting mild electric shocks from my dynamic mic when I touch my guitar strings. The shocks are tingling like if you put a pp3 battery on your lips, not sharp shocks like static.

I have checked, replaced, removed, re-ordered and reintroduced practically every part of the signal chain.

With guitars attached to their amps and the mic attached alone to the mixer and speakers there is never a shock. Once I introduce a piece of equipment running on AC power to the mixer, the tingle returns. This happens when I attach a keyboard on AC or introduce an effects loop where the effects are running on AC.

With the keyboard and the effects running on battery power there is no tingle so my assumption is that AC power is leaking through my signal chain

I have checked the guitar amps, the mixer and the power strip are all correctly grounded, everything is running from the same strip and I have checked that my mains ring is correctly wired to ground. I have tried two separate mixers, switched out or updated many cables and tried introducing an external ground connection from the mixer and from the speaker casing.

I haven't tried ground loop isolators yet but since these are designed to remove hum and I don't have any hum, I didn't want to buy more stuff I don't need. I realise that a foam shield on the mic could help but I don't want to just mask the problem. I want to get to the bottom of it.

I am running out of things to try and would appreciate any suggestions as I am very keen to not electrocute my children or their friends.

Many thanks, Boskins
 
No, some piece of your equipment is NOT grounded correctly. I would suspect the guitar amp as it happens no matter what other AC-connected device you add to the system.. Is it a 3-prong plug on it? The ground and negative may be tied together. This is a dangerous set up and I would advise you to not keep 'experimenting'.

What 'mixer' are you using (it sounds like it may not be powered, or is USB or battery powered?) What amps, please provide all models/names of all your gewar.
 
As [MENTION=39487]mjbphotos[/MENTION] suggests, the amp would be the first thing to look at. If it's not got a 3-prong plug it should be converted, but it should also have a ground switch that can be toggled, so try that. I'd also try a different guitar, mic and cords for both just to chase the problem from the mic/guitar ends back to the next piece of gear. Switch in a different amp, etc.

And, buy an inexpensive AC line tester tool that can confirm your outlets are wired properly. Don't mess around with this stuff. If you find something wrong, get an electrician.
 
Thanks MJB and thanks for the safety warning. The two guitar amps have three pronged plugs, we call these kettle leads in the UK. They are a Fender Mustang 2 and an Orange crush 35b. The speakers attached to the mixer are powered nearfield studio monitors Roland MA15 which has a three pronged plug from the power outlet and a two terminal polarised power cord at the powered speaker end. The mixer is a behringer 1202FX which is powered through a type G three pin plug, the mic is a behringer MX8500, the keyboard is a Casio CTX700 and the external effects unit is a Boss RV6 reverb pedal.

When you say the ground and the negative may be tied together, do you mean the power cord or inside the amp? The shocks persist whether I use both amps, one of them or the other so I thought it unlikely (although not impossible) that they were at fault.
 
Thanks MJB and thanks for the safety warning. The two guitar amps have three pronged plugs, we call these kettle leads in the UK. They are a Fender Mustang 2 and an Orange crush 35b. The speakers attached to the mixer are powered nearfield studio monitors Roland MA15 which has a three pronged plug from the power outlet and a two terminal polarised power cord at the powered speaker end. The mixer is a behringer 1202FX which is powered through a type G three pin plug, the mic is a behringer MX8500, the keyboard is a Casio CTX700 and the external effects unit is a Boss RV6 reverb pedal.

When you say the ground and the negative may be tied together, do you mean the power cord or inside the amp? The shocks persist whether I use both amps, one of them or the other so I thought it unlikely (although not impossible) that they were at fault.

Hi Boskins.
Do you own a multimeter?
If you do, with all equipment safely unplugged, I'd ensure continuity between the mains earth pin at the plug, and the chassis of the amp, of your guitar amplifiers.
Any exposed nut/bolt/metal on the amp faceplate should be fine as a test point.

It's reasonably common for 'smart' people to disconnect the mains pin, often just cutting the wire inside the plug, and it's not a good idea.

It might not be the solution to your problem, but it's something I always check after seeing a few horror-story amps.
 
Hi Boskins.
Do you own a multimeter?
If you do, with all equipment safely unplugged, I'd ensure continuity between the mains earth pin at the plug, and the chassis of the amp, of your guitar amplifiers.
Any exposed nut/bolt/metal on the amp faceplate should be fine as a test point.

Hi Steenamaroo, I have now tested between the mains earth pin and the chassis' of the two guitar amps and both are showing continuity. I have also discounted the powered nearfield monitors attached to the mixer by replacing them with headphones and the issue is still there.
 
Well, that's something. :) Safety first.
I'm not an electrician or trained in the field, just to be clear,
but I'm thinking maybe the Behringer power supply isolates from mains earth so its chassis is floating?
It's nothing more than a guess but I've seen a lot of laptop power supplies do this, and your mic (and grill) would be getting their path to ground via the mixer.

If I'm right I'm not sure what the proper, safe, remedy is. Thinking out loud more than anything.
 
Try this as an earth check.

If you have a guitar lead handy with a jack one end and bare wires on the other plug the jack into any unused socket on the mixer. Connect the shield end of the bare cable to any chassis screw on the guitar amp. Do you still get a shock?

Alan.
 
These things can be a real devil to trace. Grounds /earths serve of course, two functions. The most important is to provide the absolute best path for a fault current to travel down when something goes wrong - the function that saves your life. The other function is the one the sound and music people like - it helps remove hum and noise. The real issue for the tingly shock syndrome is that earths/grounds are not all equal.

I won't bore you with the electrical theory, but in most UK homes, the ground is derived locally, and the odd thing (for non-electrical bods) is that all that happens is that the neutral connection is physically joined to the earth in the place it comes into the building. By the time it gets to your studio space, or worse, your outside studio space, the Neutral and earth have drifted apart. In larger buildings - theatres and cinema type places, there can be a few volts difference between N and E. The upshot is this few volt difference can be where the hum gets into your sound system, or worse, where your guitar earth is not quite the same as the PA earth. Transformers in guitar amps can add to the problem, and in tube amps, the higher voltages can also leak. Amps (as in electrical Amps) kill. In fact, milliamps can kill, but you can feel very low levels of current on your lips, cheek, ears, back of your hand - places where skin is thin and nerves a plenty. Sometimes you can even generate sparks - tiny ones if you have a steady hand.

I have a Strat that is very sensitive to me not touching the strings. When I take hands off, on one of my amps, it buzzes. My body mass is enough to sink the tiny current flowing.

The snag of course is determining how much current actually flows through you, rather than down the earth cable. A normal meter cannot measure it - connecting it provides the path to get rid of it. If a normal meter does indicate current flow, I'd be very wary of touching the thing that is 'live'.

A useful tip for tracking these things down is a short piece of cable with a couple of crocodile clips - you can dab it around your equipment touching cases to other cases, or guitars etc - and when the culprit is found you might hear or see a tiny spark. It's rare to find a spark that sustains, because that would be a serious fault worth a real electrician looking at for safety reasons - but if the tiny spark is a single one that doesn't come back for a second discharge after say a second - but does after a minute, the clue is there - Capacitors. Somewhere, and often again in the guitar amp are some capacitors that are charging from tiny current from the electronics - maybe leakage from a transformer, or other daft sources - even iffy phantom power supplies. touching your lips gives a good path to escape - and the familiar tingle.

Do NOT expect a typical electrician to be able to find any of this stuff - not remotely what they trained to do. Electronics folk are the ones to find it, if you can't.

I kept getting a shock on stage - I was too close to an FX light being used to project ripples onto a background and every time my right bare forearm touched it, it made me jump. A shock - a sharp tingle. It had a transformer and there was capacitor to ground - quite common in switch mode power supplies - often called a Y capacitor. Intended to reduce RF interference. just a rubbish design, not a real fault. swapping to a different power supply cured it.

Proper systematic swapping and the little bit of cable with croc clips can point to the dodgy device - but if you're not completely happy with how this works, common sense says don't do it. Hum problems and shock problems are often similar ends of a different issue.
 
Great idea Alan! so the mixer is 'floating' and the ac current from my ac equipment needs somewhere to ground other than through me. In fact I think I replicated what you are suggesting without breaking open a lead by simply connecting the lineout from one of my guitar amps into one of the mixer channels. No shocks so far, I will do more testing and add the other elements back in but seem to be making progress here. Thanks everyone. Will mark the thread as solved after a few days testing
 
Doesn't that Behr Mixer use a wallwart power supply? If so, then there are only 2 wires to the mixer input, not 3. (no separate ground)
 
The power supply is unusual. It has a three pronged wall plug and connects to the mixer using a three pronged connector which is described in the specifications as supplying 2 x 14.8V at 2 x 500mA however I suspect that although the power supply is grounded, it isolates from the mains earth so that the mixer itself is 'floating' as suggested by Steenamaroo above. By connecting my grounded guitar amp to the mixer as suggested by Witzendos the issue appears to have been resolved and I hope that a safe route to ground has been established. The idea that the mixer is 'floating' appears to borne out by the fact that I cannot detect continuity between the ground pin of the plug and the chassis of the mixer using a multimeter.
 
Proper systematic swapping and the little bit of cable with croc clips can point to the dodgy device - but if you're not completely happy with how this works, common sense says don't do it. Hum problems and shock problems are often similar ends of a different issue.

Try this as an earth check.

If you have a guitar lead handy with a jack one end and bare wires on the other plug the jack into any unused socket on the mixer. Connect the shield end of the bare cable to any chassis screw on the guitar amp. Do you still get a shock?

Alan.


With the laptop PSU I mentioned, this is the road I went down.
Manually earthing the chassis solved the issues I was having so, in the end I made a permanent cable to to provide a solid earth path.

As I say, I don't know enough to call this 'correct' or 'safe', and I can't speculate as to why the mixer chassis wouldn't be connected through to proper earth,
but I ran the laptop with the diy earthing cable for a long time with no further issues.
 
I think the thing I learned years ago was that these leakage currents are often just bad design. The adding of earths works, and provides a route for fault currents to go to earth, and not through you. There is however, a BIG but. The strap you have made to earth solves the problem, but what happens if the problem actually was something breaking down, or seriously faulty and your strap is keeping you alive, not just 'un-tingled'. Something happens in your setup, so you pull a plug (the one with the strap) and suddenly the shortest path to earth is through you!!!

This actually happened to me on stage a few years back. UK band, the Barron Knights. Guitar player frantically waving and pointing and I see the mains plug and the jack have been pulled out of their sockets, unpowering a guitar processor. I crept on stage, leaned over the amp and grabbed the metal audio jack. The radio receiver with grounded metal cases touching my right arm where I was leaning over, and when I touched it it went up my arm and out through the thin skin on my underarm - I got a belt and a burn. The amp had a fault, and the earth wire was loose in the plug, but the ground was through the processor and jack cable. Once removed, the radio receiver earthed to the guitar amp was live! I wonder if I had used the other hand, and the current came in through my left hand and out through my right arm, my heart would have been right in the path. Scary thought.
 
Takes a story like that once in a while to reinforce the importance of hobbyist disclaimers!
Thanks for sharing (and for not using your left hand too! ;) )

Looks like the behrry suppy provies 2X18 VAC and 1X36 VAC.
Seems like a similar situation to the one described here?
 
I was at a live gig once and went to sing and get a shock, pretty heavy one. I always insist at shows that they plug in the bass DI to the PA, that way I am connected to the PA earth via the shield. Of course this does not matter if using a wireless system as long as the PA is earthed.

The jack lead eliminating the problem should not be the long time solution but has proven that the shock problem is between the amp and mixer, or something plugged into the mixer. Floating earths make it harder to solve these problems, in fact floating earths are supposed to eliminate these problems. Just to clarify, does any other item of gear plugged into the mixer have an earth to chassis mains plug on it? If so you may solve the problem by making the lead between that item and the mixer with a lifted shield?

Alan.

I should have pointed out that a lot of laptops now have the mains earth pin connected to the negative of the cable to the computer, some wag decided that it was safer for the user. This earthing caused all the computer noise problems with interfaces via the USB port. All the really old laptops did not have this and never had a problem.
 
Yes - totally crazy systems that makes so many systems buzzz like mad.

I also think it very important that we make it clear that breaking the connecting in the ground/earth AUDIO cable can be positive in terms of hum reduction when there are issues, but if anyone ever hears musicians (singling them out because it's stupidly still common practice) talking about removing the ground earth wire from 3 conductor mains plugs as a solution, it's your duty to tell them to not be so heart stompingly stupid!
 
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