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Author Topic: Noisy guitar: a head-scratcher  (Read 4265 times)

Ryan McLeod

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Noisy guitar: a head-scratcher
« on: May 27, 2015, 08:27:38 PM »

This one is hurting my head - nothing to do with a show, but it bothers me that I couldn't easily figure it out.

Imagine a house with 10 rooms. In 9 of the 10 rooms, a hi-end electric guitar plugged into a hi-end, hi-gain amplifier sounds great and has pretty minimal noise & buzz for the amount of volume coming out -as expected.

In ONE room, the amp is noisy as hell - upon powering up, the noise level itself is louder than the sound of the guitar - a solid buzz, that wavered with where the guitar is facing. If I face north or south it's much worse than east or west - and east or west is still much worse than the other 9 rooms in the house.

It sounds like 60hz with loads of harmonics, and gets louder as the amp turns up.

The only difference is the plug in the wall, and a quick check with a DVM says it's wired correctly.


So..... Any guesses?



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Mark Cadwallader

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Re: Noisy guitar: a head-scratcher
« Reply #1 on: May 28, 2015, 12:32:17 AM »

A DVM will not show a swapped neutral-ground. I belive that a no-load test might not reveal a loose neutral connection. Whether either of those conditions can cause the noise issue you have described is something I don't know enough to answer.  You might post this question in the AC power and grounding sub-forum and see what real electricians have to say ....


Edit: fix typos
« Last Edit: May 28, 2015, 12:55:15 AM by Mark Cadwallader »
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Michael Lascuola

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Re: Noisy guitar: a head-scratcher
« Reply #2 on: May 28, 2015, 12:43:46 AM »

I might try an extension cord to one of the other 9 rooms, to rule out the outlet in the "bad" room.
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Stephen Swaffer

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Re: Noisy guitar: a head-scratcher
« Reply #3 on: May 28, 2015, 01:15:44 AM »

A DVM will not show a swapped neutral-ground.


Edit: fix typos

Nor will it show a reverse polarity bootleg ground.  Run an extension cord from another room and use its ground pin as a reference to check the receptacle for a more definitive test.
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Steve Swaffer

Bob Leonard

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Re: Noisy guitar: a head-scratcher
« Reply #4 on: May 28, 2015, 07:55:50 AM »

What constitutes a high end amplifier?

A swapped neutral/ground won't cause 60 cycle hum, in the end both the neutral and the ground run to the same ground point in the box. A swapped neutral and hot leg will cause this hum. Pull the outlet and check the wiring. Hot wire to brass screw, neutral to silver colored screw, ground to green screw. Then check back to the panel and look at any junction boxes to see if there is a swap at that point.
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Bill McIntosh

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Re: Noisy guitar: a head-scratcher
« Reply #5 on: May 28, 2015, 08:01:15 AM »

...
So..... Any guesses?

Is the guitar player using a wireless feed to the amp?
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Mac Kerr

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Re: Noisy guitar: a head-scratcher
« Reply #6 on: May 28, 2015, 08:37:09 AM »

This one is hurting my head - nothing to do with a show, but it bothers me that I couldn't easily figure it out.

Imagine a house with 10 rooms. In 9 of the 10 rooms, a hi-end electric guitar plugged into a hi-end, hi-gain amplifier sounds great and has pretty minimal noise & buzz for the amount of volume coming out -as expected.

In ONE room, the amp is noisy as hell - upon powering up, the noise level itself is louder than the sound of the guitar - a solid buzz, that wavered with where the guitar is facing. If I face north or south it's much worse than east or west - and east or west is still much worse than the other 9 rooms in the house.

It sounds like 60hz with loads of harmonics, and gets louder as the amp turns up.

The only difference is the plug in the wall, and a quick check with a DVM says it's wired correctly.


So..... Any guesses?

What kind of pickup is on the guitar? I don't see how it can be anything but sensitivity to a local magnetic field if the noise changes as you move the instrument. If the room with the noise is near the electrical source, or plumbing that may be carrying ground leakage current there could be a local magnetic field created.

Mac
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John Roberts {JR}

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Re: Noisy guitar: a head-scratcher
« Reply #7 on: May 28, 2015, 10:30:18 AM »

+1 to the extension cord test... See if the problem is the outlet or the room.

JR
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Brian Bolly

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Re: Noisy guitar: a head-scratcher
« Reply #8 on: May 28, 2015, 10:36:46 AM »

Waiting to see if the extension cord idea pans out, but I'll throw this into the ring:

Completely off the wall, but what are the odds that 9/10 of the rooms are plaster backed with metal lath, room #10 has been redone with sheetrock, and there's some external interference-generating object nearby?
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Ryan McLeod

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Re: Noisy guitar: a head-scratcher
« Reply #9 on: May 29, 2015, 11:20:49 PM »

Quick update:

The extension cord test identified that it's the room, not the electrical.

Guitar is a Suhr Strat or fender Strat, both with Humbuckers in the bridge positions, amp is a Suhr Badger.

If  amp is connected to electrical in them questionable room, I get noise.
If I move the amp to another room and get electrical from that other room, it's nice & quiet.
If I keep the amp in the questinable room and run an extension cord to the known 'quiet room', I still get the noise.

Keeping the amp plugged in the 'bad room' and walking out the room with the guitar and amp live, the noise quickly reduces as I move away from the room.

SOMETHING is throwing a magnetic field in that direction - no plumbing closely that I'm aware of. I think I'll just shutdown everything breaker-by-breaker and see what makes it go away!   




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Re: Noisy guitar: a head-scratcher
« Reply #9 on: May 29, 2015, 11:20:49 PM »


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