Electric Shock from guitar?

D

dgaeremie

New member
I feel your pain, I get that when I plug a line in from my computer to my POD.
I gave up on looking for loose wires, cause there were none...

Do you have anything else plugged in?
MP3, computer line-in, but looking at your gear there are no line ins...

The lazy fix for me was to play guitar on a carpet. (`ヘ´)
 
oops, yeah i mean my amp.

Oh, how do i check the grounding?
the amp is about 1year old though so shouldn't be too bad eh/

Hmm, maybe i'll try putting a carpet there

Also, at the back of the guitar, the part where you string your strings in...i get a shock there as well. So i'm kinda thinking every part that connects to the amp will give me a shock =/
 
Your guitar strings are grounded,
imo to say that there is a grounding cable that links to your bridge/string claw.

This is why you get zapped when you touch anything that is connected to the strings.

I do not know how this works as I am not too much into circuits,
but without this string grounding, there will be much noise.
(perhaps some pro from this forum will be able to enlighten us on string grounding...)

This acts as a link between your strings to your amp.
If there is a current passing through it from the amp...
ZAP! and you have become grounding for the amp. =_=

I do not think that opening up your amp will help, but it is worth a try.
Just chk for any loose cables dangling about in your amp.
(Chances there are none, if not it will not work... or it would have short circuited first)

And lastly there shd be a connection that leads to the metal case of the amp.
This is usually terminated using a screw/or maybe soldered?.
This is the cable that leads back to the ground plug.
Check that it is not loose and tighten it if needed.

Likely, this is a case of bad electronics/circuit design.
You may need to use the carpet treatment. (´～`)
Or get a new amp... oh well.
 
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Awesome, thanks all for the suggestions! (:
Should go get my amp checked too...will keep you guys updated (:

But just wondering, what does the carpet do to the amp?
 
maybe is your pedal. users of Boss GT 10 comfirm kena shock also. I kena Addy also kena shock
 
Hey Guys, this is a very confusing subject. Very hard to explain in words, easier with pictures...

"Potential Difference" - All electrical charges want to to go Earth (yep, the stuff we're standing on). If we consider Earth to be absolute zero, then any conductor that may have electrons flowing through it, will have a "potential" to earth, meaning the electrons carried within the conductor would love to jump to earth. If the charge is so great, it will ionize the air and hit the ground (e.g. Lightning). Better yet, any conductor that comes along (more copper, your body etc.) that has a low resistive path to earth, will cause a flow of electrons to Earth.

Furthermore, any two conductors may have a potential difference to earth and if they are different charges, a potential difference between them.

So what does this all have to do with guitars?

As Zeruel pointed out, your strings are grounded - but to what? The audio path's shield conductor... Ok, so the purpose of this conductive path is to shield the 'hot' signal from extraneous noise. RF interferences should be induced into this path and shunted away. it's not just the cable, your guitar, your amp and your effects can also pick up noise, and therefore the preferred practice is to make most of these chassis out of metal, or to shield the internals and make all input and output shields common (connected together).

It also provides a 'virtual' zero voltage for equipment designers. They may or may not decide to treat the shield as 0Vdc. This is important as the 'hot' signal will be floating above this reference voltage point.

So, a couple of huge problems... What if you connect your gear to various power supplies, or worse yet, to different wall outlets which might be on a separate phase (electricity is transmitted to you from SP Services on three phases, 120deg apart)? What if one piece of equipment buffers the signal internally and uses a different reference ground? (i.e. has a different potential difference to Earth).

Tube amps can be nasty too. They are always in a metal chassis with all grounds common. If a tube starts to go terminal, it can start leaking current to ground. You WANT this, because it will blow a fuse and protect you (hopefully) before 600v+ starts heading your way.

The manifestation of these scenarios will be that the potential difference to Earth of your strings, will be different to other electrical appliances around you (including your stomps, your rack, your amp, the PA system...). Where there is a Potential Difference, and then a path (YOU!) electrons will flow and you will feel it. (I used to be an electrical engineer/mechanic/fitter.. oh yeah, I've felt the electrons baby! Big time...)

So, you maybe thinking you don't have your bare feet buried in wet salty muddy earth, why am I conducting? Well, it doesn't have to be a perfect path to earth to feel much...

Ever put a 9v battery teminals on your tongue? Tickles.. Hurts a little too, right? If you hold a 1.5v battery between your fingertips you don't feel a thing, do you? (Wet slimey tongues conduct pretty well!)

Voltage is the pressure that pushes electrons through you. Current is the flow of those electrons. Guitars have very very low voltages eminating from them, and don't drive much current. Mind you, it takes less than 30mA to stop your heart... Under ideal conditions, you wouldn't need too high a voltage to push 30mA through the resistance of your body.

Current is what you are feeling. Your body, your shoes, the carpet, the air - they will all conduct electricity to varying degrees, but these are all highly resistive paths.

in your case, you are getting just a little tickle right? (must be otherwise we'd be at your funeral...) It may be that you are near something that is causing that potential difference. If you plug guitar-to-amp, nothing in between, do you get a tickle? How about WITH the Zoom back in the path? Can the zoom run on batteries instead? Same issue with batteries or no?

There is one solution - ok maybe two, but the second would be more expensive and possibly not work in all cases. You can get an isolation transformer in the signal path. My favorite for this stuff is the Jensen JT-11P (Google it...). I bought some via the internet direct from Jensen (no reliable disty here) for about US$70 each. Build it into a metal box but ensure one side's 1/4 jack is isolated from the chassis (Neutrik make great jacks for this). You know, there's probably a cheap Chinese transformer of the same specs for a fraction of that, but if you sacrifice quality, the results may displease you. Basically all you'd need is a 600ohm:600ohm (1:1)transformer, no extra taps, but make sure it's potted and shielded in a can - you don't want this picking up noise. Jensen's site has diagrams, but the whole thing is so simple. This effectively preserves the shielding, but isolates your rig into two discrete paths.

Clear as mud? PM me if you need any help.
 
garbagetruckdriver: That was some very in-depth explanation there. Very sweet! You could start a thread on grounding alone, since you have both the experience and theory as an electrician.

dgaeremie: As garbagetruckdriver explained, standing on a carpet increases resistance to the grd. So it shd stop the electrons which loves passing though your fingers.

My case was that my computer's line out had quite a bit of current passing though it, nearly phantom power lvl. Using an Optical line out to a DAC solved it(I had a combo headphone amp lying around).

Actually now that garbagetruckdriver has mentioned, you may want to try to isolate the problem, it may not be your amp. :)
 
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Guys,

Got a few mins at the moment so I thought I'd throw up some further comments and suggestions...

There is a test you can do - you'll need a multimeter/voltmeter and possibly an extension cord or extension outlet.

Set your meter to AC range. The three pin outlet used in Singapore is often referred to as a G type - an earth pin receptacle, an Active (aka Line) and a Neutral. If I recall correctly (forgive me, I'm overseas today and don't have one in front of me), if you look at an OUTLET and orient the earth pin to the top, the lower right pin socket is the Active/Line.

Plug your meter's test probes into the LINE NEUTRAL sockets - you should see 230v to 240v. Now plug into the LINE and EARTH sockets. Your meter should read the SAME (230v to 240v). If it doesn't and is off by more than a few volts, your building has an Earthing problem and you should consider contacting me for the next tests, or go straight to an authorised Singaporean electrician for help resolving this.

Okay if all is as expected, remove the probe in the LINE socket and keep the probe in the EARTH socket. You now have in your hands a properly grounded test probe.

You can now use this probe to measure the Potential Difference (to Earth) of various stages of your equipment's chain. Start with your guitar strings. Turn everything on, put the guitar on a chair face up. Touch the probe to the strings. You should see some minor deflection of the needle (or a small number if you have a digital meter). you'd expect to see millivolts (you may have to adjust the range to see an accurate measure of exactly how many volts.) I wouldn't be surprised to see a volt or two, but this is a major caution flag, and more than a few is a sign of danger.

Also test ANY exposed metal surfaces. I'd go as far as pushing the probe into the paintwork on the back (or if necessary) front of your amp, though you could also plug a cable into the input jack and just measure off the SLEEVE of the plug. Obviously, don't screw up the look of your amp. Again, test ANY exposed metal that you could come into contact with. (don't touch speaker terminals). Yes, even the strap fixing brackets (I've found some that conduct!).

Measure your stomp boxes and rack gear. everything.

Again, millivolts is to be expected, ~one volts = bad, many volts = danger. The danger is because one day you will set up your gear somewhere, on a hot humid day, you're dehydrated, standing on a invisibly conductive surface or near other gear... and you will get a big zap while your body is highly conductive. Remember, One hand is fretting your conductive strings, the other hand touches something else, and you get a massive charge across your chest, and your Heart. 30mA can STOP YOUR HEART, or send it into fibrillation... (hope someone nearby has a defibrillator!).

Ok, so now take that test probe and check EVERYTHING in your room or wherever you set up your gear. I bet you get some lminor eakage from your laptop or your computer....your stereo gear... a bedside lamp maybe.

So now you will know WHERE those potential differences are in your regular environment. We can't cure all of them, but damn, it's better you know where they are, and remember that with one hand grounded on your instrument, you're exposed to any potential difference nearby.

I'd also recommend you do this exercise wherever you set up. When I played in a touring band back in Australia, my road crew once connected the PA system to one electric outlet, the stage gear running off outlets on another circuit, and the lights on a 3 phase supply. Yep, the mics were on one phase, our guitars on another and a third of the lights on another phase. Do you know what that means? 240v supplies, phase to phase, are 415v AC difference. Touch your guitar and put you lips to the vocal mic and BANG, you get a huge shock, potentially fatal...

So guys, this stuff is really worth knowing. Please try my extension cord technique. learn it. use it. You can't see or smell electricity - it's a silent killer. Believe me, I've been to enough funerals...
 
Haha really gotta thank you all again for all the effort! :D

fgl: I'm not sure, i got my guitar repaired recently because of some problem with the volume knobs connection (the guitar made muddy or no sound when i played) ...watcha suggest?

garbagetruckdriver: Wow that's alot of explanation! :P
...I don't think it's that my house has some electrical problem, should be fine or it'll be tripping very often eh
...however, my amp's connected to this multi-plug thingy and there are other appliances (e.g. broadband modem, speakers, zoom pedal, FRIDGE) so maybe i connect it to the wall socket individually?
...Yeah my zoom can work with batteries, never tried it before though, also, i still do get a shock without the zoom connected (rarely)

zeruel: how do i check for the problem? Do i go check the p.d. of everything?

Thanks:D
 
Thanks alot Mr garbagetruckdriver! I learnt alot from your posts!

In my case, I had a guitar, a set of pedal effects (powered by an adapter with 2 pin plug) and a solid state amp with 3 pin plug. It is correct to say that all there is potential difference between me, the pedals and the amp, but the current "prefers" to go ground through the wall socket back instead of my body? (This case, no shocks)

That was HAD. Now I HAVE the same guitar, same pedals, same adapter BUT a tube amp with 2 pin plug (no ground). So, without the ground wire of the amp, the current has no choice but to go ground with my body? (This case, have shocks)

Is it right to say that if the previous SS amp I had did have a ground wire connected, I would have received the same shocks?

I assume that the pedals and amp have different potential difference, but since the currents are flowing through the same cable, does the PDiff of the amp and pedals settle between themselves already in the cable, by the time it reaches the guitar? If so, the shocks I get are the PDiff of the gears and the earth only?

Would the grounding wire solve the problem, fully or not?

-----
 
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dgaeremie - interestingly, yeah, refrigerators are notorious for leaking current. Big current flows through the ac motor that drives the compressor, and a fair amount is induced into all the surrounding metal, which is earthed. Also when the compressor kicks in, the motor temporarily draws a startup current around 6x nominal max current to get the motor started. Ever get any clicks or pops in your sound? In any case, yeah, it wouldn't be a bad idea to get your gear off that power board with the fridge...

Quick note here too - this kind of leak will not blow a breaker or fuse.
*fuses blow fast on a short, but will tolerate current well over their rated value. (you could draw 22 A continuously over 20A fuse wire until it eventually got hot enough to melt, months later...).
*circuit breakers operate magnetically and are more sensitive to tripping on even the slightest over-current, but are slower than fuse wire on a short.
* there is a different kind of breaker sometimes called a "safety switch" or as we call them in Oz, and ELCB (Earth Leakage Circuit breaker). This is a special breaker that compares the difference between the current flowing through the active and neutral. if there is more than 20 or 30 mA, it trips.

theunknown - something that jumped out at me when I read your post - you have a tube amp with NO EARTH? This is not good. Tubes can fail catastrophically - meaning the anode, cathode, heaters or grid can melt and bend, and possibly cause a short. this short could put hundreds of volts onto the metal chassis of your amp. As we discussed before, your hands are touching metal strings connected to that amp!!! What is the model of this amp? I'm curious to know. PM me if you like.

Next important note - the Role of the Earth wire!
I talked about the existence of potential differences... Now we can't always eliminate them, so we need to be able to shunt them away from us. The Earth wire provides a LOW RESISTANCE PATH to the earth. Just like lightning, current will flow through the lowest resistance path it can find to the dirt outside. Your body is actually a highly resistive path, compared to copper wire.

Kirchhoff's law - states that the current entering a junction equals the current leaving junction. Your equipment is the source of the current flow, your body is one path, the earth wire is another. Hopefully that earth wire is no more than 0.1ohms resistance to earth. Your body is hopefully in the megaohms. So, the law says that most of the current will take the earth wire, but even then, some will flow through you, if there is a path THROUGH you. If your building earth system is bad (rusted or loose connections, smashed, removed, or just in really dry soil that doesn't conduct well) you are not so well protected and the current will divide between what can flow to earth and the rest goes to you!

Why are there power cords with only two pins? Well, I know the Australian wiring rules intimately, and I can only assume the Singapore code would be very similar (both derived from European standards, not American). There is the concept of "Double Insulated". If an appliance has two layers of adequate insulation from the active components within it to outside it, it does not require earthing. usually things encased in plastic with no external metal parts comply with this rule. But then again, there are countries with very lax regulations and if that gear is imported without compliance to local regulations, you are exposed to danger!

So guys, try to pull all your audio rig off the same power strip. A guitar amp and some effects are going to draw only a few amps from your 20A protected circuit - no problem. Try not to touch anything else that might be electrical or structural metals (window frames!) when you are playing.

sorry I didn't directly answer all your questions guys - some of this would be much easier with diagrams to show you were the flows could be and the things that would normally cause them. I really don't have the time to do that right now. Perhaps in a couple of weeks when I get back to Singapore...
 
*_* what's those electircal things oh my I think music is so much easier than those stuff, I see stars *_*
 
dgaeremie said:
fgl: I'm not sure, i got my guitar repaired recently because of some problem with the volume knobs connection (the guitar made muddy or no sound when i played) ...watcha suggest?
Click to expand...

did it have the same shock problem before the mods?

bring back to the shop that wired it up for you ... bring along your amp and effects to to check ...

dont mess with these kinda "shorts" .... you dont want a painful reminder later on .. trust me. ...
 
I vote for sticky!

Kudos to garbagetruckdriver!
I would need a week to digest and read up on those stuff.

And I am sure this clears up a lot of haze in regards to grounding.
 
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