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Why does a guitar amp buzz stop when you're touching the strings?

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


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Author Topic: Guitar stops buzzing when I touch the strings  (Read 89078 times)

Helmut Gragger

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Re: Posting Rules
« Reply #130 on: February 02, 2015, 04:55:23 AM »

Please note. Important.

The aforementioned ground bracelet will be an elegant solution at least for recording situations, when the optics does not hurt.

Note that this device has a 1MOhm resistor to ground. It is meant to discharge electrostatic voltages to ground (earth), where no noteworthy currents are involved. I have verified the function thereof for quietening the human body as an antenna in the proximity of a guitar.

Although touching real ground does the same, one should resist to ground the body by a direct hard connection (without a resistor), because the vicinity of an amplifier with potentially malfunctioning earth connection would create a beautiful, potentially lethal current path through the body as displayed on the video earlier up this thread.

The solution is to maintain contact to the guitar ground with such a bracelet, which most conveniently is accomplished by attaching the alligator clip to one of the strings. Any which way the bracelet is applied, the 1MOhm resistor will limit all currents to a safe level.

-helmut

« Last Edit: February 02, 2015, 10:48:21 AM by Helmut Gragger »
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Kevin Graf

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Re: Posting Rules
« Reply #131 on: February 02, 2015, 10:49:42 AM »

This too goes away with earthing, so this supports the theory that the human body is the cause of the problem, not the guitar.
The body seems to act as an antenna for all sorts of electromagnetic junk. Huh, were you aware of that?
-helmut
The human body acts as a capacitor connected to Mother Earth.  The capacitor value can range from about 100 pF to 700 pF depending on a number of factors.  A Non Contact Voltage Probe needs this capacitance to work as do portable radios (at some frequencies). 
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #132 on: February 02, 2015, 11:28:42 AM »

Welcome to this very old thread.

You mention that cap coupled ground was somehow problematic at 470 nF but a 1 Meg ohm via wrist strap connection was adequate.

First 470 nF seems large, IIRC 47 nF is more reasonable to keep current from a mains connection down to human safe levels.

I can imagine any cap being problematic in series with the guitar pick-up but that is not the intended connection, it is only between the exposed metal parts and the guitar amp input ground.

I had to google Suhr air coil and that appears to patented guitar pickup technology? This may be familiar to some of the guitar players here (not me, but google is my friend).

I am interested in human safety aspects of guitar players exposed to dangerous voltages from faulty guitar amps or improper stage wiring that presents a dangerous voltage potential between guitar and microphone. A performer was just killed down in Argentina from such an accident.

Your 1M wrist strap is surely not a shock path hazard, but I wouldn't hold my breath for getting musicians to wear one, or even one of the less invasive factory static management methods (like anti-static carpets and grounding foot straps) etc..

JR 
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Helmut Gragger

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Re: Guitar stops buzzing when I touch the strings
« Reply #133 on: February 02, 2015, 03:15:28 PM »

Welcome to this very old thread.

I was warned that the last post was more than three months ago. Who cares, nobody found the solution yet.

You mention that cap coupled ground was somehow problematic at 470 nF but a 1 Meg ohm via wrist strap connection was adequate.
First 470 nF seems large, IIRC 47 nF is more reasonable to keep current from a mains connection down to human safe levels.

The 470nF was recommended by the guitarnuts site.
And yes, a 1MOhm between me and the earth contact did the job.

I can imagine any cap being problematic in series with the guitar pick-up but that is not the intended connection, it is only between the exposed metal parts and the guitar amp input ground.

That┤s the way it is used.

I had to google Suhr air coil and that appears to patented guitar pickup technology? This may be familiar to some of the guitar players here (not me, but google is my friend).

Just for the records: it is explained here.
I just mentioned this to make clear that it is not mains hum I am talking about. The Suhr coil is a big, core-less air-coil that functions akin to the second coil of a humbucker.

Your 1M wrist strap is surely not a shock path hazard, but I wouldn't hold my breath for getting musicians to wear one,

Yes, it would be detrimental to somebody┤s macho image of a long-haired axe-wielder, but nobody would see it if they were desperate in a recording session ;D, sssh!

or even one of the less invasive factory static management methods (like anti-static carpets and grounding foot straps) etc..

This works?

Well, the outcome of this experiment was, there is currently no non-invasive solution. The cap made funny problems, maybe I should try a smaller one as you here suggested.

-helmut
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #134 on: February 02, 2015, 03:44:37 PM »

I was warned that the last post was more than three months ago. Who cares, nobody found the solution yet.
I guess that depends on what problem you are trying to solve. My focus (and this forum) is generally on trying to prevent electrocution deaths, not single coil pickup hum.
Quote

The 470nF was recommended by the guitarnuts site.
And they were trying to block DC voltage from a rogue guitar amp, not AC current from miswired mains.

470 nF is 6.7k @ 50Hz. 230VAC is 34mA and enough current to disturb heart rhythm if traveling through the musician's core.

Quote

And yes, a 1MOhm between me and the earth contact did the job.

That┤s the way it is used.

Just for the records: it is explained here.
I just mentioned this to make clear that it is not mains hum I am talking about. The Suhr coil is a big, core-less air-coil that functions akin to the second coil of a humbucker.

Yes, it would be detrimental to somebody┤s macho image of a long-haired axe-wielder, but nobody would see it if they were desperate in a recording session ;D, sssh!

This works?
In a recording studio the threat from bad mains wiring is much less, and extraordinary shielding has been used inside some studios (up to and including a faraday cage). I wonder if a wide open single coil pickup would sound natural with no hum at all, not unlike the fake feedback they add to movie soundtracks whenever an actor uses a microphone in front of a PA.  8)
Quote

Well, the outcome of this experiment was, there is currently no non-invasive solution. The cap made funny problems, maybe I should try a smaller one as you here suggested.

-helmut

I can not guess what you mean by "funny" problems. A smaller cap is likely to be even funnier if wired in series with the guitar pickup. Like i tied to explain the cap is supposed to be wired only between the ground coming from the guitar amp, and the exposed metal parts on the guitar (not in series with the audio circuity).  The premise is that the reactance of a 47nF cap,  which is lower impedance than your 1M wrist strap, should be adequate to quiet down the player's self noise when he touches that exposed metal on the guitar. The rationale for the smaller value cap is to keep current from a mains wiring (or faulty amp dumping AC like from a bad stinger cap) below safe levels. (single digit mA).   

JR

PS: Reportedly the cap in series with exposed guitar metal does not make it quieter or noisier, just safer. 
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Helmut Gragger

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Re: Guitar stops buzzing when I touch the strings
« Reply #135 on: February 03, 2015, 01:40:20 PM »

I guess that depends on what problem you are trying to solve. My focus (and this forum) is generally on trying to prevent electrocution deaths, not single coil pickup hum.

I understand that. Yet the initial subject of this thread was the question where the noise comes from. That┤s how I stumbled over it.

And they were trying to block DC voltage from a rogue guitar amp, not AC current from miswired mains.

Thats a point. I agree on a smaller cap.

I can not guess what you mean by "funny" problems.

I cannot remember why I finally removed it again on the Strat, this was months ago. There was some problem. However, on the LP it made the problems described earlier, like some hum in certain positions of the volume pot, which came and went with the proximity of the body and disappared totally when I made direct contact. I cannot explain that.

A smaller cap is likely to be even funnier if wired in series with the guitar pickup.

Looks like my two attempts to make that clear were a failure. The cap was never in the tone path, always the way you describe.


PS: Reportedly the cap in series with exposed guitar metal does not make it quieter or noisier, just safer.

I┤d be happy if it would not make the guitar louder, but it does (BTW, I am not talking about single coils). However the discussion here turned my focus to the practical tests and insight that (and here we are back to the original subject of this thread...)  there is nothing on the guitar that can be done to remedy that buzz.

-helmut
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #136 on: February 03, 2015, 03:22:07 PM »

FWIW I understand the guitar players are picky about their sound so any safety approach must not interfere with best sound.

One guitar maker uses something like a 7mA fuse inside their guitars but those are pretty expensive and 7mA is on the higher limit of what I would like to see (clearly better than nothing). Simple fuses down at low single digit mA do not appear to be practical and/or cost effective.

In another thread I am looking at two different hypothetical solutions for leaving the guitar fully grounded and still protecting the human.

The more expensive approach involves a 3 pole relay that disconnects power and ground when it detects a shock hazard. My less expensive approach that is barely at the schematic stage now, is to fabricate an electronic fuse with a pair of power mosfets in series, that when turned off provide 400V of isolation. I propose using a 100 ohms resistor in series with this solid state fuse to sense for current, but a smaller R with more precise detection could be used if really needed. I suspect 100 ohms is adequate for shielding.

Good luck with your mission and thanks for the clarification.. I wonder if guitar controls (like pots) might benefit from having their metal case hard grounded, but floated from the guitar's external metal shielding that is cap coupled?

Ideally providing my safety precautions external to the guitar is probably more acceptable to the guitar players than messing around inside their axe. 

JR
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Helmut Gragger

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Re: Guitar stops buzzing when I touch the strings
« Reply #137 on: February 04, 2015, 03:55:51 PM »

FWIW I understand the guitar players are picky about their sound so any safety approach must not interfere with best sound.

 ;D You nailed it my friend. View it that way: good tone saves their day, so rather die if the tone is bad.

In another thread I am looking at two different hypothetical solutions for leaving the guitar fully grounded and still protecting the human.

That is very interesting. Could you point me to this thread? Please understand, I find this forum is not one of the usual guitar modding places I am hanging around, just the title of the thread was suggesting so. I cannot imagine where this would be buried under. Thanks.
I yesterday tried to find this thread starting from the top of the forum - no chance. I had no idea where this would be dug under. Had to resort to the search function.

I wonder if guitar controls (like pots) might benefit from having their metal case hard grounded, but floated from the guitar's external metal shielding that is cap coupled?

Hmm. That┤s easily tried. That would also make the shielding more solid (which is not accessible from outside). I use a smaller cap as you suggested (a Y-cap perhaps? I have tons of them lying around.) and let you know.

-helmut
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #138 on: February 04, 2015, 04:19:59 PM »

;D You nailed it my friend. View it that way: good tone saves their day, so rather die if the tone is bad.
Yup, they may use some unsafe legacy guitar amps for the tone, but science is our friend, and we may be able to protect them from themselves without stepping on the tone.
Quote
That is very interesting. Could you point me to this thread? Please understand, I find this forum is not one of the usual guitar modding places I am hanging around, just the title of the thread was suggesting so. I cannot imagine where this would be buried under. Thanks.
The parent forum is about live sound reinforcement, but the sub-forum where this discussion is located specializes in "AC power and grounding."  During live performances guitar players who also sing can find themselves bridging between two different power drops. As long as both power drop grounds are 0V no problem, but stuff happens, so a mic and guitar ground may have mains voltage between them.  :o   
http://forums.prosoundweb.com/index.php/topic,152668.msg1400186.html#msg1400186
Quote

I yesterday tried to find this thread starting from the top of the forum - no chance. I had no idea where this would be dug under. Had to resort to the search function.

Hmm. That┤s easily tried. That would also make the shielding more solid (which is not accessible from outside). I use a smaller cap as you suggested (a Y-cap perhaps? I have tons of them lying around.) and let you know.

-helmut
A Y cap (self healing) is best for worst case scenario.

JR
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #139 on: February 04, 2015, 04:59:23 PM »

;D You nailed it my friend. View it that way: good tone saves their day, so rather die if the tone is bad.

Yes, an oldie but goodie thread comes back to life. I just had an interesting install gig that's on topic for this thread. I'm installing a new digital console with a digital snake in a church with a rather large platform/stage. It's some 60 ft wide and 3 ft tall. They're putting a portable stage directly in front of the main stage for their new Saturday night youth service. And this B-stage has a drum kit, electric guitar, electric bass, multiple acoustic guitars, and a bunch of singers. Just what you would expect for this sort of service. Last week I was there to assist with the first load-in and sound check for this new stage, and the e-guitar player was complaining about her guitar buzzing "again" and that it must be ungrounded because if she touches the metal pickup guard or holds the strings the buzzing will stop. This was a single-coil Telecaster which as we all know is subject to RF induced buzz. A quick demonstration of me moving the guitar close to her body (buzz) and moving it away (no buzz) showed that she was the source of the noise. Then I grounded myself on another back line amplifier I had previously tested for grounding, and had her touch my hand while her guitar was hanging on the strap in front of her and buzzing like crazy. As we could predict from this thread, the buzzing stopped.

OK, that's old news that we all understand, but here's the next experiment. I had her spin in a circle slowly in buzz mode while standing on the stage and the buzz didn't change. But when she stepped away from the stage and stood in front of it, the buzzing was reduced significantly. It was like the stage itself was radiating the same kind of buzz we get from neon signs in a bar.

A week later I was climbing around under the stage to hook up a few speaker drops and saw that it's all metal studding. And there's many J-boxes connected to the studs for strength. And lots of the receptacles are the orange isolated ground types. So I started to wonder if the metal studs under the wooden stage were grounded/bonded to the electrical system. Then today the tech director drops the big bombshell, that they regularly cross connect some of the dimmers to power stage boxes and non-dimming fluorescent fixtures, and just set the lighting console so that the "dimmer" channel can be only 0% or 100%. I explained to her that Triac dimmers never really get to 100%, it's more like 99% on, and that plugging audio gear into a Triac patched receptacle was a VERY bad idea that could be causing her buzz. Especially since she now tells me that ANY electric instruments she puts up on the stage, including digital drums, buzz like crazy.

My hypothesis is that the metal stage structure may never have been bonded to the electrical service ground, and there could be a bunch of DIY installed electrical receptacles that are improperly bonded to stage metal. That's might causing this stage to re-radiate the dimmer hash from the 99% full-on Triacs. Or something like that.

I'm supposed to be doing some stage box rewiring at this church in the next week or so, and should have time to set up an experiment with buzzing guitars and drums. I'll begin by bonding the metal stage structure to the ground in the service panel. I'll also bring an o-scope for the AC power and look for the tell-tale spike caused by a Triac dimmer at "full-on". If I'm correct, then bonding the stage superstructure to the service panel ground and un-patching the dimmer racks from the stage receptacles should eliminate the buzz in the e-guitars and d-drums. But we shall see.

Sounds like another really good reason that metal stages should be properly bonded to ground. In this case an ungrounded stage really COULD mess up the sound of the guitar with a bunch of extra buzzing.
« Last Edit: February 04, 2015, 07:02:57 PM by Mike Sokol »
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Mike Sokol
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Re: Guitar stops buzzing when I touch the strings
┬ź Reply #139 on: February 04, 2015, 04:59:23 PM ┬╗


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