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Poll

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 80628 times)

Mike Sokol

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Guitar stops buzzing when I touch the strings
« on: September 19, 2013, 09:44:26 am »

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.  8)

Thanks to Al Keltz for telling me about this.  ;)
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Mike Sokol
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Steve M Smith

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Re: Guitar stops buzzing when I touch the strings
« Reply #1 on: September 19, 2013, 01:30:58 pm »

Can we post our own answers here to see how they compare to the 'official' answer?


Steve.
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #2 on: September 19, 2013, 01:35:12 pm »

You mean like none of the above? Or a little of this and a little of that?



JR
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #3 on: September 19, 2013, 01:35:54 pm »

Can we post our own answers here to see how they compare to the 'official' answer?

Steve.
Yes, please do....
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Mike Sokol
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #4 on: September 19, 2013, 01:41:33 pm »

You mean like none of the above? Or a little of this and a little of that?

JR

There's one primary reason for this effect, and certainly a few smaller ones. So please, post whatever mix of this and that you like. Nobody here's going to judge you for a crazy answer. In fact, a lot of my fundamental ideas on power and sound systems seemed a little crazy at first read (RPBG's for instance) but have since been validated by peer review.

No little green Martians, though.... as I'm pretty sure they have nothing to do with guitar buzz. 
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Mike Sokol
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Steve M Smith

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Re: Guitar stops buzzing when I touch the strings
« Reply #5 on: September 19, 2013, 01:55:13 pm »

My thoughts on the subject.

The input to the amplifier consists of the centre core of the lead in series with the pick up which is then in series with the outer shield of the lead.

Any mains hum picked up by any of these will present itself as an input signal to the amplifier.  The central (hot) core is obviously shielded so shouldn't cause a problem.  The pickups might add a bit but are generally o.k.

However,  the outer core of the cable will pick up any noise in the area.  The higher it's resistance (relative to the pickup) ,the worse the problem.

When you touch the strings you are grounding the guitar end.  Hopefully the amp end is already grounded. By grounding the guitar end, you are putting both ends of the shield at the same potential so it no longer forms part of the input signal.

With a good lead this isn't usually a problem as the noise picked up by the shield is generally of a much lower level than the guitar signal but if there is a fault with the ground shield or a high resistance part somewhere e.g. dry joint or oxidisation on a plug to socket contact, its relative level will increase.


Steve.
« Last Edit: September 20, 2013, 01:42:21 am by Steve M Smith »
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #6 on: September 19, 2013, 02:34:49 pm »

There's one primary reason for this effect, and certainly a few smaller ones. So please, post whatever mix of this and that you like. Nobody here's going to judge you for a crazy answer. In fact, a lot of my fundamental ideas on power and sound systems seemed a little crazy at first read (RPBG's for instance) but have since been validated by peer review.

No little green Martians, though.... as I'm pretty sure they have nothing to do with guitar buzz.
You don't know me if you think I worry about how my answers look.

I see this as a combination of grounding and damping an antenna, but neither is literally precise as we technically define grounds or antennas. The human body appears "ground-like" or loosely coupled to ground just enough, when the noise source is very high impedance. It's all relative so the effective path to ground can be weak and still work to suppress even weaker noise.

Several years ago there was an interesting discussion about using a capacitor to couple the guitar's metal parts to the guitar cable ground (amp's input ground-to chassis-to wall), so that the hum would be suppressed. However if the now "capacitor coupled to ground" musician is exposed to mains voltage, that current must also be small enough that it doesn't disrupt his heart's electrical system.   

I don't recall the magic cap value, but there was a range of values that satisfied both human safety and noise shielding constraints (100-240V, 50-60Hz).

JR

« Last Edit: September 19, 2013, 03:17:31 pm by Mike Sokol »
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Scott Helmke

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Re: Guitar stops buzzing when I touch the strings
« Reply #7 on: September 19, 2013, 02:55:45 pm »

What JR said - grounding/damping the human body so that it doesn't act as an antenna. When grounded to the guitar the body starts acting more like a shield instead.
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #8 on: September 19, 2013, 04:57:34 pm »

I'm going to stay out of this until we get some more answers to the poll. But somebody is getting very warm... 8)
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Mike Sokol
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Jonathan Johnson

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Re: Guitar stops buzzing when I touch the strings
« Reply #9 on: September 20, 2013, 01:30:53 am »

Since I have nearly no experience with guitar amps, and I've never inspected an electric guitar to see how it's made, I'll throw out a wild guess.

Why does a guitar amp buzz? There is current flowing through the pickups, which causes the strings to vibrate.

Why does it stop when you touch the strings? You stop the strings from vibrating, which creates a damping effect on the pickups.

(Maybe not. I really don't know.)
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Stop confusing the issue with facts and logic!

ProSoundWeb Community

Re: Guitar stops buzzing when I touch the strings
« Reply #9 on: September 20, 2013, 01:30:53 am »


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