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Permalink Reply by TruckDrivingFool on February 17, 2013 at 5:50pm

My SWAG - Since it seems to hit roughly every 15 sec for 5 sec, I'd wonder if it's noise being picked up from something in the amp or just in the room where you are. Have you tried different amps and locales?

I'll add that on the few I've done I notice a difference out in the open vs. being somewhat shielded in a box so once it's installed that might help.

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Permalink Reply by t-belly johnson on February 17, 2013 at 10:03pm

Doesn`t sound like regular feedback and Ross is right,it may be the location.I`ve had that sort of noise when I`ve been plugged in and sat at my computer.As you were only testing it,and hooked it straight to a jack I take it it`s not been earthed yet or shielded? If you can,try it on another amp just in case.

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Permalink Reply by Scott aka Farmer Ted on February 18, 2013 at 1:13am

Ross & T-belly make great points regarding shielding. Single pole pickups, even when wax potted, attract all sorts of electronic disruptions (i.e. florescent lights, cell phones, local radio/cell towers, etc.)

Shielding the cavity where the pickup will rest in/on box will help to reduce/eliminate this noise. If there will be a volume/tone pot too, its imperative to shield that cavity too. Copper shield tape is great. Just remember to solder a wire to the shield and connect that to ground (either the back of one of the pots or to the jack ground (negative).

Since your sound test was done without the above mentioned scenario, it is the likely reason for the amplified "disturbance in the force".

Good luck

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Permalink Reply by Mark on February 18, 2013 at 1:30am

I'm pretty sure that's not feedback. It sounds more like noise from some poorly-screened electrical device in the general vicinity. There's nothing wrong with your pickup. Any pickup will act as a receiving antenna for stray electromagnetic signals that are an annoying but unavoidable part of modern life (although "humbucking" pickups cleverly manage to cancel a lot of it out).

Given that it comes in pulses like that it looks like something which operates intermittently. Maybe something with a motor that switches on and off (like a fridge or an automatic door), or maybe something else that operates intermittently and which has a noisy power supply. I suppose it could be something like a door buzzer or a radio control.

It's also possible that there's noise getting through on your house mains supply if the offending source is in your home.

A few questions might help us narrow it down. Does the noise happen if the amp is just left switched on with no pickup or guitar plugged in? (in which case it might be something inside the amp or the amp itself might have poor screening against external noise) Does it happen any time you switch the amp on or was it just that one occasion? (If it's all the time then look at stuff which runs all the time, such as fridges or air conditioning, if it's only occasional then think more about stuff like door buzzers or remote controls which are only used intermittently)

I did some quick analysis.

The following pic shows what the waveform looks like.

And the next one is a frequency spectrum

It looks like there's a basic waveform somewhere in the 3kHz to 5kHz range, which has some modulation on top of it (amplitude modulation and frequency modulation). Looking at the wave form I can see amplitude modulation at frequencies around 6Hz and 12Hz.

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Permalink Reply by Craig Mayhem on February 18, 2013 at 3:44am

2nd vote for cell phone. they scan networks on regular intervals. 

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Permalink Reply by Mark on February 18, 2013 at 4:18am

It doesn't sound like a cellphone to me. Phone interference is quite distinctive - you tend to hear groups of short pulses when it affects audio equipment (maybe you have weird cellphones over there).

Whatever the source might be, the best solution will probably be shielding (unless it's coming through the mains line into the amp rather than via the pickup). Its a good idea to shield anywhere inside a guitar where you have wiring.

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Permalink Reply by hocuspocus on February 18, 2013 at 10:04am

Thanks guys, all your inputs are extremely welcomed. Actually, the noise is not there with the amp turned ON, and the cable connected. But when I connect the pickup, then it starts after, say, 10-20 seconds. The wavelenght from 3 to 5 Khz respects the 4.8 kHz of the pickup, but whatever it tells, I'll make some more tests tonight. I'll place the setup at different places in the house, and maybe outside.

It is also true that the pickup itself is not shielded, but that will be my next series of tests, if I don't find anything else before. But again, many thanks for your help.

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Permalink Reply by hocuspocus on February 18, 2013 at 10:44am

What was I saying, refering to 4.8 Khz of the pickup. Is that confused or what ?  Anyway, I'll come back with tests results.

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Permalink Reply by Mark on February 18, 2013 at 11:44am

Yeah, I think you're getting confused there. The 3kHz to 5kHz is a reference to a frequency within the sound you're hearing. I think what you're referring to when you mention 4.8k is the resistance of your pickup, ie. 4.8k ohms - a different thing entirely. No connection between the two.

Most important thing is, don't worry about the pickup. It sounds as if that's fine and dandy. So go on ahead and finish fitting it in the guitar.

Sorry if I've confused things at all. I was just hoping I might help you track down the source of the noise - because I've had experience of these types of things getting really annoying.

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Permalink Reply by hocuspocus on February 19, 2013 at 12:54pm

Mark, don't worry. I get everything you mentioned and its very helpful. I just got confused alone. Your analysis is exactly what I was hoping for, since that is usually the right way to approach this kind of problem. Looking at the frequency and trying to match something in the environment that induces this. Many thanks again for your help.

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Permalink Reply by hocuspocus on February 18, 2013 at 11:44am

So far, I'm progressing. I moved the amp in the basement and the louder hissing coming every once in a while is not there. Before I was in the living room, right next to the TV set. Who knows. I did not have this problem before with my electric guitar so I didn't know.

Its fun learning, right ?  Anyway, I still have a continuous hissing, much lower (high frequence, but less audible), that may be surrounding static waves picked up by the pickup. (that why we call it a pickup, right ?). Just the amp, with the guitar extension cord, I hear nothing. As soon as I place the pickup at the end of the jack, holding the wires manually, then I hear the hissing. I even tried without the pickup, but just holding the 2 feet long cable I was using with a female jack that I am supposed to install in the cigar box, and it picks up the noise also !  So it looks like I am in for a shielding job on the pickup and also on all the wires that will be installed in the Cigar Box.

Does any of you know if all those shields must be connected to the negative side of the jack ?

Thanks guys.

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Permalink Reply by The Phrygian Kid on February 18, 2013 at 11:54am

Yes. Ground it to the sleeve on the jack. I often use the foil that frozen apple pie or Danish comes in for shielding, works great

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