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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 102455 times)

Jerome Malsack

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Re: Guitar stops buzzing when I touch the strings
« Reply #80 on: January 03, 2014, 09:36:36 AM »

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.

So has this been approved for use? 
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #81 on: January 03, 2014, 10:35:35 AM »

So has this been approved for use?

Nope, it's just an experiment on my part. If I get some time I'll build one in the next few weeks and measure all the worse case fault currents. I'm pretty sure it's safe, but getting it code approved could be an issue, but who knows...

Christian Güssmer

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Re: Guitar stops buzzing when I touch the strings
« Reply #82 on: January 03, 2014, 05:15:23 PM »

There's quite a few different types of buzzes you can hear during a sound check.

Hi Mike,

I've been in situations like this during the last years quite often and do have some "tricks" at hand, but unfortunately exactly this kind of buzz is hard to eliminate. Also I confess that I would have ticked the wrong answer in the poll, so thanks again for discussing it. At the moment I just wanted to know if I maybe missed a point in this quite large text.

Moreover there are often bands touring Europe with their backline on US power and those transformers, powerstrips and different wiring schemas add another layer of complexity - up to dangerous issues.
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #83 on: January 03, 2014, 06:38:58 PM »

I've been in situations like this during the last years quite often and do have some "tricks" at hand, but unfortunately exactly this kind of buzz is hard to eliminate.

The trick is to learn what causes these various unwanted noises so we can come up with quick fixes. And sadly, a standard electric guitar with high-impedance single-coil passive pickups is an antenna waiting to pick up interference. I would always build a Faraday cage from copper foil for my own guitar players which helped a lot in the crappy clubs full of neon beer signs buzzing. But that's not something you can do during a sound check.

At a gig last week I found than when the guitar player leaned against the concrete block wall behind him, his strat copy hummed (not buzzed) like crazy. When he stepped a foot or two away the hum went away. I looked on the other side of the wall and saw a big circuit breaker panel. I'm sure there was enough magnetic coupling to the pickups that no amount of shielding would have stopped it. I told him to stay away from the wall and his guitar wouldn't hum, which he hadn't figured out for himself.

Quote
Moreover there are often bands touring Europe with their backline on US power and those transformers, powerstrips and different wiring schemas add another layer of complexity - up to dangerous issues.

I had the reverse happen when Chumbawumba (Tub Thumppin') did their first show in the US on the roof of a garage in Washington DC. I have the dubious distinction of running sound for that gig. The funny thing is that I was using the MHA Audio M6 British rig (the original AC/DC Hells Bells system) which used Cameleon power amps and processing on 230-volts. We had a huge transformer that stepped up a 100-amp 120-volt feeder to 230-volts with all UK wiring and distro. We also had a second American distro split for the standard Edison 120-volt back line.

When Chumbawumba's manager called me from the hotel to advance the show, he insisted I needed to provide 120-to-230 volt transformers for the band's UK gear. But I told him I was running the only sound system in the USA with British plugboard 230-volt power running around stage, and the lads would feel right at home plugging in without any transformers or adapters. 

The rest is history with helicopters circling the building and nearly everybody in the band getting arrested except for my sound crew (their plan from the beginning).

Mac Kerr

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Re: Guitar stops buzzing when I touch the strings
« Reply #84 on: January 03, 2014, 07:43:31 PM »

The trick is to learn what causes these various unwanted noises so we can come up with quick fixes. And sadly, a standard electric guitar with high-impedance single-coil passive pickups is an antenna waiting to pick up interference. I would always build a Faraday cage from copper foil for my own guitar players which helped a lot in the crappy clubs full of neon beer signs buzzing. But that's not something you can do during a sound check.

At a gig last week I found than when the guitar player leaned against the concrete block wall behind him, his strat copy hummed (not buzzed) like crazy. When he stepped a foot or two away the hum went away. I looked on the other side of the wall and saw a big circuit breaker panel. I'm sure there was enough magnetic coupling to the pickups that no amount of shielding would have stopped it. I told him to stay away from the wall and his guitar wouldn't hum, which he hadn't figured out for himself.

Bill Whitlock tells a story of a stage with the same problem, and it turned out to be caused by a current loop in the building plumbing that was connected between 2 buildings with different electrical service. Putting in an isolating section in the pipe fixed the problem.

Mac
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Jonathan Johnson

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Re: Guitar stops buzzing when I touch the strings
« Reply #85 on: January 03, 2014, 10:16:28 PM »

Bill Whitlock tells a story of a stage with the same problem, and it turned out to be caused by a current loop in the building plumbing that was connected between 2 buildings with different electrical service. Putting in an isolating section in the pipe fixed the problem.

That would be interesting to see on a rider: "Ground lift adapter for 1" FIP threaded water pipe"
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Stephen Swaffer

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Re: Guitar stops buzzing when I touch the strings
« Reply #86 on: January 04, 2014, 10:32:36 PM »

Heading off topic a bit, but for a current loop to exist there must be potential (voltage) difference leading to a possible hazardous situation at the isolating section, besides the NEC requiring any metal parts-plumbing, etc to be bonded to ground. Obviously fixed one problem (so does clipping a ground pin off a 3 prong plug sometimes) but maybe creating another??  Or am I thinking wrong?
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Mike Sokol

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Re: Guitar stops buzzing when I touch the strings
« Reply #87 on: January 04, 2014, 10:40:15 PM »

Heading off topic a bit, but for a current loop to exist there must be potential (voltage) difference leading to a possible hazardous situation at the isolating section, besides the NEC requiring any metal parts-plumbing, etc to be bonded to ground. Obviously fixed one problem (so does clipping a ground pin off a 3 prong plug sometimes) but maybe creating another??  Or am I thinking wrong?

Sometimes there will be a failed neutral in a building bus and a water pipe becomes the actual neutral return path through the neutral/ground in another panel. So while there might only be a volt or two difference between the remote ends of a water pipe, isolating it in the center could cause a 120-240 split-voltage problem in one of the buildings. I would be extremely careful to measure everything BEFORE cutting into any pipes you know are carrying current. However, it would be cool to put a clamp-on ammeter around a water pipe and read the current, which could considerable with up to hundreds of amperes. I would tread lightly in this instance.
« Last Edit: January 04, 2014, 11:31:51 PM by Mike Sokol »
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Mac Kerr

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Re: Guitar stops buzzing when I touch the strings
« Reply #88 on: January 04, 2014, 11:26:47 PM »

Heading off topic a bit, but for a current loop to exist there must be potential (voltage) difference leading to a possible hazardous situation at the isolating section, besides the NEC requiring any metal parts-plumbing, etc to be bonded to ground. Obviously fixed one problem (so does clipping a ground pin off a 3 prong plug sometimes) but maybe creating another??  Or am I thinking wrong?
Sometimes there will be a failed neutral in a building bus and a water pipe becomes the actual neutral return path through the neutral/ground in another panel. So while there might only be a volt or two difference between the remote ends of a water pipe, isolating it in the center could cause a 120-240 split-voltage problem in one of the buildings. I would be extremely careful to measure everything BEFORE cutting into any pipes you know are carrying current. However, it would be cool to put a clamp-on ammeter around a water pipe and read the current, which could considerable with up to hundreds of amperes. I would read lightly in this instance.

IIRC in this case there was a difference in ground potential in each of the attached buildings due to different location of the cold water pipe's connection to actual dirt, and the separate electrical service to each building. Isolating the 2 buildings so they each were grounded to dirt only at the CW pipe got rid of the current in the pipes. It was not a case of miswiring, but of multiple ground potentials because of location. Ground potential varies across distance because physical dirt is a high impedance path.

Mac
« Last Edit: January 04, 2014, 11:28:58 PM by Mac Kerr »
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John Roberts {JR}

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Re: Guitar stops buzzing when I touch the strings
« Reply #89 on: January 05, 2014, 10:32:54 AM »

Sometimes there will be a failed neutral in a building bus and a water pipe becomes the actual neutral return path through the neutral/ground in another panel. So while there might only be a volt or two difference between the remote ends of a water pipe, isolating it in the center could cause a 120-240 split-voltage problem in one of the buildings. I would be extremely careful to measure everything BEFORE cutting into any pipes you know are carrying current. However, it would be cool to put a clamp-on ammeter around a water pipe and read the current, which could considerable with up to hundreds of amperes. I would tread lightly in this instance.
Good point but if a water pipe is actually serving as a safety ground and carrying fault current, what better time to discover that then while sorting out the wiring.  :o

While the term ground loop is widely over used, plumbing could form a classic loop were major magnetic fields in the area generate loop currents and voltage.

JR
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Re: Guitar stops buzzing when I touch the strings
« Reply #89 on: January 05, 2014, 10:32:54 AM »


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