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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

[Mike Sokol]

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.

Hey, I just report the news. Here's how an ungrounded, GFCI protected receptacle is supposed to be marked, according to the NEC (diagram courtesy Mike Holt Enterprises).



I think that verbiage should be sufficient to make a stinger cap floated ground GFCI legal according to the NEC. But something like "Current Limited Safety Ground" or "Instrument Noise Ground" would be more descriptive. I'm going to draw up a schematic and send it to my code monkeys to see what they think. Then it's build/test time.

[Mike Sokol]

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

Yes, a great video. This is exactly what I demonstrate in my NoShockZone seminar, except I use a B&K Variable AC supply to bias the guitar amp's ground from zero to 120 volts AC.

Way cool... 

[Mike Sokol]

Here's the basic diagram of my SafeGround for guitars.



Now, don't go building this yet as I still have to double-check all the fault paths, build a demo, gather empirical data as to peak and sustained fault currents, check the code legality, and see if it operates safety without making a guitar amp buzz. But it seems like a possibility.   

[Stan Sakamoto]

Why does a guitar amp buzz when you're not touching the strings, and why does it stop when you touch the strings or anything metal on the guitar? I'll provide the answer and explanation next week. 

Thanks to Al Keltz for telling me about this. 

I've come across this many times working with musicians. The hum and buzz problems can come from several issues such as a grounding problem from the amp to the guitar. First make sure that your amp has a good ground. When you connect your cable from the guitar to the amp that has no good grounding the cable becomes like an antenna picking up the noise transients from the guitar to the amp which amplifies the noise. Sometimes just by changing the cable from the guitar to the amp with a balanced shielded cable may fix the problem. Another issue is that the pick ups on the guitar is not grounded correctly and your strings and cable are looking for a good ground and stops humming when you touch the strings since your body is grounded. A hum in low frequency at 60Hz usually means that you have a ground loop.

[Bob Leonard]

Here's the basic diagram of my SafeGround for guitars.



Now, don't go building this yet as I still have to double-check all the fault paths, build a demo, gather empirical data as to peak and sustained fault currents, check the code legality, and see if it operates safety without making a guitar amp buzz. But it seems like a possibility.

Are you showing this as a separate device between the wall outlet and amplifier plug?

[John Roberts {JR}]

I won't speak for Mike, but my understanding is that this could be built into a GFCI outlet strip.

This could actually protect against reverse bootleg ground, while I don't like lifting the equipment safety ground from properly wired outlets.

This is like the stinger cap inside a two wire line cord guitar amp but chassis is cap connected to ground instead of neutral.

I might suggest a slide switch for each outlet that could selectively lift the ground.

I am still working on a late night beer-soaked design project to combine a non contact voltage sensor to detect for even reverse bootleg grounds and not even connect if it senses the hot ground present. it could even sense for and correct reversed hot-neutral, if I drink enough I may be able to tell ground from neutral and identify a floated ground. 

JR

[Jerome Malsack]

Are you showing this as a separate device between the wall outlet and amplifier plug?

What the question has been mostly is if the guitar player is not touching the strings or a metal part on the guitar, why does it buzz. 
If you approach a guitar it will buzz also as you get close enough until you touch the strings. 

[Mike Sokol]

I won't speak for Mike, but my understanding is that this could be built into a GFCI outlet strip.

This could actually protect against reverse bootleg ground, while I don't like lifting the equipment safety ground from properly wired outlets.

This is like the stinger cap inside a two wire line cord guitar amp but chassis is cap connected to ground instead of neutral.

I might suggest a slide switch for each outlet that could selectively lift the ground.

JR

Yup, the idea is to build a GFCI outlet strip with a few of the receptacles set up with a floated "SafeGround" for guitar players. I don't think the NEC or UL will allow any kind of switches on the individual safety ground paths, even if there's a GFCI involved. But I think they might allow a few receptacles on the end of the strip (or the entire strip) to be permanently ground lifted with a stinger cap and bleeder resistor, but only as long as there's a GFCI in that circuit. The idea is to eliminate hard-grounding the meat puppets in the first place, but protecting them from a hot-chassis to earth-ground hand-to-hand fault. And yes, this circuit should protect the musician (puppet) from an RPBG outlet induced shock between the mic and the guitar, even if the mic OR the guitar was the source of the hot-ground voltage.

More to experiment with, but I think this simple grounding system would eliminate electrocution hazards for the guitar player from his amp, while stopping ground loop hum, high-freq buzz, and even providing shock/electrocution protection from a "hot" microphone. And there would even be protection from shock due to Reverse Polarity Bootleg Grounds. I might even have a better filter design than the stinger cap and bleed resistor, but if that works and envisioned I'm keeping it proprietary for a potential patent.

I'm heading out to Texas for 12 days to teach a bunch of seminars, but I'll build one of these when I get back and test it for guitar-to-mic fault currents and buzz abatement. In the meantime, unless you're qualified to work on live voltages and measure them safely, then PLEASE don't go building one of these and wade into the kiddie pool holding your guitar. This is all still highly experimental.

[Christian Güssmer]

1st: sorry for bringing up this old topic
2nd: thanks for that discussion, really interesting stuff in here
3rd: is there any recommendation about what to do to stop that buzzing? From what I understood, the discussion about fuses and caps is about human protection... I mean standing on a stage in the middle of a soundcheck and there is exactly that buzz that shouldn't be there.

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.
(...)

[Mike Sokol]

1st: sorry for bringing up this old topic
2nd: thanks for that discussion, really interesting stuff in here
3rd: is there any recommendation about what to do to stop that buzzing? From what I understood, the discussion about fuses and caps is about human protection... I mean standing on a stage in the middle of a soundcheck and there is exactly that buzz that shouldn't be there.

There's quite a few different types of buzzes you can hear during a sound check. The one referenced in this thread is caused internally by electric guitars with high-impedance electronics. It occurs when a human is standing very close to the back of the guitar (within a few inches) but not touching the guitar strings. The body acts like an antenna booster, collecting harmonics of the 60 Hz hum all around us, and coupling it into the guitar electronics as buzz. If you turn the volume knob(s) down on the guitar or move away from the back of the guitar, this type of buzz should stop. If it doesn't stop, then there's a different reason for the buzz. For instance, if the guitar player is using an unshielded speaker cable instead of a shielded instrument cable to plug into his amp, then the amp will probably be nearly quiet with the guitar volume turned down, but buzz like a swarm of angry bees with the guitar volume turned up, even if your body is far away from the guitar body. If the amp buzzes or hums even with it's volume control turned down, then the amp itself likely has an open capacitor in its power supply. Also, I've been on stages with a lot of big electrical conduits and wiring underneath, and the guitar or bass would buzz/hum depending on where the musician stood or oriented the neck of the guitar.

During a sound check you can only do quick fixes, so if the guitar/amp is buzzing, get the musician to move around a bit and see if it changes. Have them try a different instrument cable and see if it changes. If the backline amp buzzes just sitting there with the volumes turned down, then tell them to get a backup amp.

Also, I found a Yamaha bass guitar a few months back during a sound check that had double pickups and a balance knob to set the relative volume. It hummed/buzzed when the bass player turned this balance knob all the way to the left or right, but was hum/buzz free in the middle. I'm guessing it was some sort of split humbucker pickup arrangement, but once we got his bass hum/buzz free during sound check, I was good to go for the gig and didn't do more research.

Oh yes, remember that many XLR outputs on GK bass amps are neither balanced nor does their ground lift switch actually lift the ground. You'll want to add your own external DI box to fix this buzz/hum.

The key to this sort of troubleshooting is to have a quick bag of tricks you can quickly try. If it's really the instrument doing it, then all you can really do is put a gate on that channel. But I like being able to help a musician figure out what's really wrong with their rig which helps the next sound guy to work with him or her.   Pay it forward...

[ProSoundWeb Community]