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When I point my guitar pickups towards my desktop computer from several feet (2 1/2 - 3) away, I can hear a lot of buzzing/clicking, depending on what the computer is doing (idling vs, say, playing video). Are the pickups picking up radio interference from the computer which is being demodulated by the amplifier, or are they inductively coupled to the computer, despite the lack of coils & distance?

I have trouble believing that it's radio interference that they're detecting (I've never gotten an AM signal through my amp, for example), but given the distance, I also have trouble believing that inductance is generating the noise. Can anyone shed some light on this?

Thanks

EDIT: To clarify, I'm talking about a single coil pickup, not a humbucker. I'm not really interested in reducing noise, it's not an issue for me. I'm just curious about what mechanism is involved.

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    \$\begingroup\$ Gibson or fender - humbucker pup or normal pup? This can make a vast difference. \$\endgroup\$ – Andy aka Jan 19 '15 at 13:48
  • \$\begingroup\$ Sorry - I'm talking about single coil, not humbucker. I'm not actually asking about reducing noise, I'm just trying to understand the source of it. \$\endgroup\$ – Joel Jan 20 '15 at 0:19
  • \$\begingroup\$ I'm not suggesting how to reduce noise but it can be helpful to know what you are using in order to diagnose what it is you are receiving. \$\endgroup\$ – Andy aka Jan 20 '15 at 8:13
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You can shed a little bit of light on this by playing with the guitar (i.e. pickup) orientation. If some orientations are much noisier than others, then almost certainly it's the inductive coupling.

As to whether the interference is in the RF region and your amp is rectifying it, my guess would be no, but if you really want to be sure, try adding a small cap in parallel to the input of your amp, something like 100 pF (which will slightly affect the tone). If that gets rid of most of the noise, then it was indeed RF.

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  • \$\begingroup\$ Orientation is definitely a factor. \$\endgroup\$ – Joel Jan 20 '15 at 4:05
  • \$\begingroup\$ Also, forgot to mention: in a way, radio interference is inductive coupling. \$\endgroup\$ – biggvsdiccvs Jan 20 '15 at 5:22
  • \$\begingroup\$ This stuff is fairly new to me, but isn't it possible to have inductive coupling without causing radio interference? I get that they're similar, but my understanding was inductive coupling had more to do with the magnetic field than anything else. \$\endgroup\$ – Joel Jan 20 '15 at 12:36
  • \$\begingroup\$ Well, the field is electromagnetic. If the magnetic field is changing, you get radio waves. For the low end of the RF spectrum (longwave, around 100 kHz), the receiver antenna is a actually a coil on a ferrite core. \$\endgroup\$ – biggvsdiccvs Jan 21 '15 at 8:02
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There is probably some of both going on. A vibrating guitar string causes only a small voltage to be produced in a pickup coil, so the output of these have to amplified quite a lot. Due to the high gain, small amounts of noise that would otherwise go unnoticed become audible.

One way to tell the difference between magnetic and capacitive pickup of the noise is to shield the pickup electrically but not magnetically (or vice versa, but that's harder to do). If the pickup is already in a metal case, ground that case to the ground of the amplifier the pickup is connected to. That should significantly reduce capacitive pickup but not change inductive pickup. If the noise is still there, then it's not from capacitive pickup at the coil. That doesn't necessarily mean it's due inductive pickup by the coil since there are various other paths of noise into the system, but you've eliminated one possibility.

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  • \$\begingroup\$ Is there an alternative ground I could use? The entire signal is running through a DC-powered effects-pedal chain, and I'm not sure where I would start with that (okay, by unplugging all but one of the pedals. After that, I'm a bit lost). \$\endgroup\$ – Joel Jan 19 '15 at 13:22
  • \$\begingroup\$ Use the ground from whatever box the pickup is directly connected to. \$\endgroup\$ – Olin Lathrop Jan 19 '15 at 13:34
  • \$\begingroup\$ I think the answer is much easier - with single coil pickups, you'll have interference from outside sources, humbuckers are dual coil and reduce hum. I've actually tested that with my own guitar and computer. \$\endgroup\$ – Femaref Jan 19 '15 at 15:58

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