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Your body is grounding the guitar

14 (43.8%)

The guitar is grounding your body

5 (15.6%)

Touching the strings creates a ground loop

0 (0%)

The strings are acting like an antenna

9 (28.1%)

You've got an electric personality

4 (12.5%)

Total Members Voted: 32

Voting closed: September 26, 2013, 09:44:26 AM

[Bob Leonard]

Heard of those fuses but tend to think that by the time the fuse blows the damage will have been done.

The picture showing the guitar electronics is from a 75' - 85' Gibson SG. Note the full brass shield / ground plate the pots, selector switch, and 1/4" jack are mounted to. This was a Norlin mod which has since been dropped by Gibson. Other clues to the age are the ceramic caps, and non Switchcraft jack. The ground wire is the single wire attached to the bridge pickup volume pot (lower left pot in picture), which is routed through the pickup cavities to the tail piece.

[Bob Leonard]

Here is the R0 (1960 historic) wiring. Note the location of the ground wire and the use of "bumble bee" caps. All of the Gibson historics are accurate including the Switchcraft switches, jacks, and capacitor type.

[Bob Leonard]

1957 historic. Note the "Black Beauty" caps.

[Bob Leonard]

1954 historic. Note the green caps.

[John Roberts {JR}]

Heard of those fuses but tend to think that by the time the fuse blows the damage will have been done.

Perhaps... My experience with fuses in the context of design is that they are not precision wrt trip current, also the current that causes the fuse to open is not a sharp knee at exactly the trip current, but soft and could blow slightly lower after a long time, and to make it blow quickly depends on how much overload above the trip current for how long.

10mA fuses are expensive because they are not widely used like higher value fuses to prevent fires from overheating, but seem uniquely about human safety. If I was a fuse maker I would be apprehensive about selling such fuses but I guess they have experience and liability insurance.

My recollection was that human safety standards were set down around 3 mA, but apparently GFCI target 5 mA so that is in the same ball park.  I did find a few 5mA fuses on google but they probably make the 10mA fuses look cheap, and only one was in a normal fuse package. I am not even sure how to make a reliable 5-10mA trip current mechanical fuse, but apparently they have. 

OK enough about fuses, would a 10mA fuse protect the talent? Probably yes. From multiple sources, it appears that 10mA is the threshold of painful shock, 50-100mA ventricular fibrillation can occur (disturbed heartbeat that can lead to death), 100-200 fibrillation definitely occurs. So he would definitely feel the shock. !0mA is 1/5th the current where fibrillation "can" occur and 1/10 the current where it "does" occur, so a fair overload margin for fuse action, while there could be a momentary stress. 

One last factor is how does the actual current travel through our body? Our core or innards have significant water content so a pretty good conductor of electricity (say around 100 ohms). While our skin resistance is orders of magnitude larger, up to tens of K or higher for dry skin. The wetter the skin (with salt from sweat) the lower the resistance.  Since electricity follows the path of least resistance, it is highly unlikely that current will harmlessly travel across your skin, but will quickly sink down into your core. The old warning for tube gear technicians to keep one hand in your pocket when poking around a hot chassis has validity since the current path between two hands is likely right through your chest and heart.

FWIW Amp makers could include the equivalent of GFCI built into the preamp input to open up that ground when it detects a few mA of current flowing there but this seems to contradict most conventions about safety ground practice, that want labelled grounds to sink amps long enough to trip a breaker. Such a feature, would only protect if no pedals are involved, and would make a faulty pedal even more dangerous.

JR 

[Kevin Maxwell]

If you were talking about hum than the answer is very simple.

It hums because it doesn’t know the words. ;-)
 

[Bob Leonard]

Mike Sokol,

So what is the answer in your book?

[Mike Sokol]

Mike Sokol,

So what is the answer in your book?

I have a diagram to post later, but according to my logic the answer is The Strings Are Grounding You. When you're holding the guitar but not touching the strings (or anything else grounded) then your own body is ungrounded and picking up all sorts of noise from the environment. This is the same buzzing noise you'll hear if you touch the tip of a 1/4" phone plug that's connected to the input of your guitar amp. Since your belly is close to the back of the guitar, this noise voltage is coupled into the unshielded, high-impedance circuity of the guitar (including the pickups). The reason it's a high-frequency "buzz" and not a low frequency "hum" is that there's high-pass filter circuit formed by the capacitor formed by distance of your "belly" to the internal guitar wiring.

When you touch the guitar strings with your hand, that provides a low-impedance earth-ground path from your body, through the strings/bridge/tailpiece of your guitar, via the shield of your phone plug, to the chassis of the stage amp, then finally through the power cord to the (hopefully) grounded wall outlet. So any of the ambient electrical noise your body was picking up via a capacitive coupling to the wiring in the walls (and more) has now been shorted to ground, and the noise stops.

If you ask guitar players and sound engineers how this works, I would guess that 99% of them think the opposite, that your body is grounding the strings. But being that the strings are always grounded (should be), then that can't be what's happening.

However, I do like the discussion on decoupling caps and 10 mA fuses which could probably stop musicians from being electrocuted. But very few guitars have these features, with the vast majority being wired with strings and all metal pieces being "grounded" to the sleeve of the 1/4" phone jack. I'm sure it's 99.999% that way in the guitar world unless someone knows something I don't know.

What do you think? This all makes perfect sense to me, though I've not personally measured inter-belly/guitar capacitance and calculated the high-pass filter effect. Would be easy enough to do as an experiment and run the calculations though...

[John Roberts {JR}]

A simple observation that reinforces this, we all know the loud hum that occurs if we touch just the tip of a guitar cord plugged into an amp. while if we touch the tip and sleeve at the same time we are far less noisy.

Unless you are standing barefoot on a conductive surface.

JR

PS: I still prefer cap coupling the ground at the guitar, VS a fuse, but either seems like an improvement wrt safety. This could easily be built into a cable end so the guitar doesn't need to be messed with. Wireless mics also reduce the risk of exposing the meat to a hard ground (or hot) via the wired mic.

[Mike Sokol]

PS: I still prefer cap coupling the ground at the guitar, VS a fuse, but either seems like an improvement wrt safety. This could easily be built into a cable end so the guitar doesn't need to be messed with. Wireless mics also reduce the risk of exposing the meat to a hard ground (or hot) via the wired mic.

I agree there could be safer ways to "ground" a guitar without exposing the musician to shock treatment. Also in reference your wireless comment, I've run into a few guitar players who use a belt-pack RF transmitter for just that very reason. They won't play through a standard guitar cord for fear of getting shocked. And you know, I really don't blame them for the paranoia. We sound technicians have done too little to protect our stage musicians. I believe that discussions like this are a great way to educate everyone as to the importance of proper grounding and the dangers of electrical shock on stage. 

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