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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]

Unless your name is Les Paul. Read on.....

http://www2.gibson.com/News-Lifestyle/Features/en-us/les-paul-the-recording-model-1113-2012.aspx

http://www.youtube.com/watch?v=n2zitOYZqnU

[Mike Sokol]

Unless your name is Les Paul. Read on.....

http://www2.gibson.com/News-Lifestyle/Features/en-us/les-paul-the-recording-model-1113-2012.aspx

http://www.youtube.com/watch?v=n2zitOYZqnU

You can hear it start buzzing around 1:45 when he takes his hands off the strings.

And now we know why... Hah

[Craig Hauber]

We sound technicians have done too little to protect our stage musicians.

Maybe because we've been beaten over the head with the "always have a licensed electrician do things for us or fear liability" concept that we no longer wish to open our mouths!

Sure would hate to recommend a proper fix only to have someone electrocuted shortly afterwards due to some other totally unrelated backline issue that you now get the blame for.




(-don't get me wrong, I always try to fix any safety problems no matter who's fault it really is, but the current litigious nature of american society does make me concerned)

[John Roberts {JR}]

Maybe because we've been beaten over the head with the "always have a licensed electrician do things for us or fear liability" concept that we no longer wish to open our mouths!

In these times liability is a valid concern. If you are uncertain about a remedy, DO NOT DO IT. That said common sense and self preservation suggests not ignoring an obviously hazardous situation.

Sure would hate to recommend a proper fix only to have someone electrocuted shortly afterwards due to some other totally unrelated backline issue that you now get the blame for.

me too... Peavey was sued because a player was killed by properly designed and built guitar amps. When push comes to shove, it helps to follow safety agency standards.

(-don't get me wrong, I always try to fix any safety problems no matter who's fault it really is, but the current litigious nature of american society does make me concerned)

There is a difference between rewiring a venue's outlet(s) that could open you up for liability, and taping over a dangerous outlet so it can't be used.

I can't imagine anyone incurring personal liability from adding a GFCI in series with their portable mains power distribution. These are available in power strips or other configurations. If I was a performing musician I'd be tempted to buy my own as cheap shock insurance.

When in doubt do what's right.

JR

[edit] Regarding the safety implications of grounds in the context of a guitar, I am of the strong opinion that a ground there that provides a low impedance path to mains ground puts the musician at higher risk of harm. Grounded chassis provide human safety when internal mains power faults get loose inside the chassis. The grounded chassis, shorts out the power fault to first protect the human from high voltage, and secondly to trip the mains breaker and remove the fault. In a guitar there is no such human safety benefit from a low impedance ground path, just noise abatement.

Ironically the old stinger cap if sized properly is arguably less dangerous to the player, than the low impedance ground path if the fault is an energized microphone ground (or hot ground in back line distro). However if a power fault occur inside a floor pedal that energizes the ground lead the hard grounded guitar amp input will be more protective. 

In my judgement adding a cap in series with the ground lead "at the guitar" is prophylactic against energized microphone, energized floor boxes, or energized amp grounds. If the cap is sized to deliver less than lethal current while still adequate for shielding, why not?   [/edit]

[Mike Sokol]

[edit] Regarding the safety implications of grounds in the context of a guitar, I am of the strong opinion that a ground there that provides a low impedance path to mains ground puts the musician at higher risk of harm. Grounded chassis provide human safety when internal mains power faults get loose inside the chassis. The grounded chassis, shorts out the power fault to first protect the human from high voltage, and secondly to trip the mains breaker and remove the fault. In a guitar there is no such human safety benefit from a low impedance ground path, just noise abatement.

That's probably correct, but it's really a legacy issues as there must be millions of guitar with "grounded" strings in existence.  I doubt that's going to change quickly.

Ironically the old stinger cap if sized properly is arguably less dangerous to the player, than the low impedance ground path if the fault is an energized microphone ground (or hot ground in back line distro). However if a power fault occur inside a floor pedal that energizes the ground lead the hard grounded guitar amp input will be more protective. 

In my judgement adding a cap in series with the ground lead "at the guitar" is prophylactic against energized microphone, energized floor boxes, or energized amp grounds. If the cap is sized to deliver less than lethal current while still adequate for shielding, why not?   [/edit]

I think a cap in series between the strings and the guitar output jack shield would be reasonable and safe. But if the cap is in series with only the cable shield, that could inject 120-volts AC into the input stage of the guitar amp itself. While a tube amp might be able to withstand this fault, I'm pretty sure your average transistor guitar amp would have its input stage destroyed. You would probably need to add series caps in both the shield and signal paths of the unbalanced guitar cable, and providing clamping diodes across the input of the amp. All sorts of tonal issues could be involved if not designed carefully, but I'm sure that problem could be overcome.

I can't imagine anyone incurring personal liability from adding a GFCI in series with their portable mains power distribution. These are available in power strips or other configurations. If I was a performing musician I'd be tempted to buy my own as cheap shock insurance

Interestingly, a backline power fed from RPBG (Reverse Polarity Bootleg Ground) wiring will stop plug-in GFCI's from working. What will happen is that while the GFCI may "trip" due to the current imbalance, since the GFCI can't' disconnect the safety ground, the backline amps plugged into it won't have their chassis disconnected from the "hot ground" outlet condition. The amp chassis (and guitar strings) will be connected directly to the 120-volt line with a low-impedance path, the most dangerous of all shock conditions.

As I've noted here, this RPBG wiring condition most likely occurs in houses of worship originally built before 1970. Since old wiring didn't have safety grounds, and modern performance stages need safety grounds, many of these buildings have been "upgraded" to grounded receptacles by church volunteers who sometimes perform bootleg grounds instead of running all new grounded wiring back to the service panel.

With that in mind, perhaps the e-guitar industry needs to revisit the idea of guitar string grounding and come up with a solution (such as in-line caps) that will protect musicians from electrocution while not interfering with the tone. Much more to think about. 
 

[John Roberts {JR}]

That's probably correct, but it's really a legacy issues as there must be millions of guitar with "grounded" strings in existence.  I doubt that's going to change quickly.

Yup, but a guitar cable maker could actually do something useful. 

I think a cap in series between the strings and the guitar output jack shield would be reasonable and safe. But if the cap is in series with only the cable shield, that could inject 120-volts AC into the input stage of the guitar amp itself. While a tube amp might be able to withstand this fault, I'm pretty sure your average transistor guitar amp would have its input stage destroyed. You would probably need to add series caps in both the shield and signal paths of the unbalanced guitar cable, and providing clamping diodes across the input of the amp. All sorts of tonal issues could be involved if not designed carefully, but I'm sure that problem could be overcome.

Equipment failure IM0 is a secondary concern if the shock is being delivered through a human's body. Clamping the guitar input depending on how it is done, could return us to the low impedance path scenario where human safety is at risk. FWIW The guitar amp input is probably already cap coupled and many solid state products have input clamps already to protect against static damage, and any current delivered through the pickup has the pickup impedance in series with it which "may" (?) be enough to limit it to sub lethal range. 

Interestingly, a backline power fed from RPBG (Reverse Polarity Bootleg Ground) wiring will stop plug-in GFCI's from working. What will happen is that while the GFCI may "trip" due to the current imbalance, since the GFCI can't' disconnect the safety ground, the backline amps plugged into it won't have their chassis disconnected from the "hot ground" outlet condition. The amp chassis (and guitar strings) will be connected directly to the 120-volt line with a low-impedance path, the most dangerous of all shock conditions.

There should be a special room in hell for electricians who do that. Bootleg ground is dangerous enough, reverse bootleg is a killer.

As I've noted here, this RPBG wiring condition most likely occurs in houses of worship originally built before 1970. Since old wiring didn't have safety grounds, and modern performance stages need safety grounds, many of these buildings have been "upgraded" to grounded receptacles by church volunteers who sometimes perform bootleg grounds instead of running all new grounded wiring back to the service panel.

+1 and any place where DIY electricians are involved. The case I am aware of was in a residence.

With that in mind, perhaps the e-guitar industry needs to revisit the idea of guitar string grounding and come up with a solution (such as in-line caps) that will protect musicians from electrocution while not interfering with the tone. Much more to think about. 
 

I suspect there just aren't enough deaths from this to cause manufacturers to mess with working guitar designs. From my experience talking with guys who design and manufacture guitars, they are far more concerned about tone, and probably consider potential shock issues as somebody else's problem.  I am pleasantly surprised that one added a fuse. I can't imagine the safety agency ever condoning lifting a safety ground, despite my personal opinion, while UL does not approve guitars.

JR

PS: While this is a little odd, a special GFCI outlet strip with it's internal ground cap-coupled could protect the meat puppets from lethal shock in case of RPBG. I can not imagine UL ever blessing that, but perhaps a GFCI with only a two wire line cord? Again a rather odd duck, and no I am not seriously suggesting this. This 2-wire outlet strip could break out a terminal for ground that the user would have to tie into a ground (or float). This may have some merit for managing back-line noise, as long as the ground is connected to something safe. I can not imagine UL blessing this.

PPS: Perhaps a non-contact voltage sensor built into a GFCI outlet strip with a relay or Solid state switch  disconnect for all three connections, could sniff the ground and not connect if that ground is energized. (Sounds expensive). UL might actually bless this.

[Bob Leonard]

This is a very nice video from Taylor guitar describing the problem at hand.

http://www.taylorguitars.com/media/audio-noise-and-grounding-david-hosler

[Mike Sokol]

I can not imagine UL ever blessing that, but perhaps a GFCI with only a two wire line cord? Again a rather odd duck, and no I am not seriously suggesting this. This 2-wire outlet strip could break out a terminal for ground that the user would have to tie into a ground (or float). This may have some merit for managing back-line noise, as long as the ground is connected to something safe. I can not imagine UL blessing this.

Actually, according to code the proper way to install a "grounded" receptacle in ungrounded wiring is to install a GFCI outlet WITHOUT the ground screw connected to anything. However, the outlet is supposed to be marked as "No Ground" that's visible from the outside. I've never seen one marked this way, but that's how code describes it. GFCI receptacles don't need the safety ground wire to operate, so the "meat puppets" (my son's description) are still protected from shock.

I think you could probably take a standard $10 GFCI receptacle, disconnect the internal ground screw from the incoming Edison plug, and put a "stinger" capacitor in parallel with a high-ohm resistor between the incoming safety ground wire and the GFCI ground screw. That way your guitar's ground plane potential would be held close to earth ground voltage by the 100K resistor, the capacitor would shunt any RF frequencies to the backline safety ground (if it existed), and any fault currents between the guitar strings and external grounds or hot-ground mics would be limited to below 5 mA when the GFCI trips, and less than 2 mA after the GFCI trips, even if you were plugged into an RPBG mis-wired backline receptacle with a hot ground.

I know a couple of code monkeys who could probably tell us if this sort of gizmo would be a code violation or not, but I suspect it would pass all code requirements, as long as the proper label was affixed to the outside of the receptacle.

Seems like an interesting experiment, and something that could save lives WITHOUT affecting guitar tone. Plus it would be cheap to build from off-the-shelf components. Less than $20 even using new parts.

What do you think? Worth building and gathering some data? If you think it's worth a try, I'll draw up a pretty diagram and post it here tomorrow.

And no, I won't try this out on a meat puppet. I'll use meters instead...
   

[John Roberts {JR}]

If it is legal to wire grounded outlets without the ground as long as you identify and label them that sounds like a possible combination (with GFCI) that could protect muso's against hot grounds. As I mentioned it might be useful for noise abatement to break out a separate ground terminal.  Perhaps a ground lift switch, per outlet.

If I was smart I'd just do this instead of talking about it, but I like the idea of automatically sensing for a hot ground, and just saying no mas... The ground lifted GFCI outlet strip would allow the show to go on, which may not be the best thing in the big picture. Any killer outlets need to be condemned and fixed. Enabling them is just perpetuating the human risk.

   JR

[Jonathan Johnson]

However, the outlet is supposed to be marked as "No Ground" that's visible from the outside.

Design-conscious people (AKA "women") will balk at the presence of any label on an outlet, regardless of it's necessity for safety. If the coverplate had "NO EQUIPMENT GROUND" molded into the plastic, that would be more design-sensitive in that it would be the same color as the rest of the plate and blend in with the decor easier. But what big-box home improvement store is going to stock something that they'll never sell? The price would be significantly more than a standard coverplate (due to economy of scale), and Joe "Weekend" Warrior isn't going to buy such a coverplate because they have no idea why they need it. And besides, it won't be available in the style that his wife wants.

[ProSoundWeb Community]