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Problem with 60Hz Hum in Guitar pickups.

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LAN_403

GODSFUSION

Mon Apr 24 2006, 04:23PM

Registered Member #157 Joined: Sun Feb 12 2006, 08:00PM
Location:
Posts: 76

No the amp plugs into the wall. Would it be worthwhile to line the electronics cavity with copper foil tape?

- wayne -

Steve Conner

Mon Apr 24 2006, 04:45PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Dang, I wish I had thought of Bjoern's idea, it's so much more elite.

I really do think screening the cavity would help. I've had cheap guitars in the past that buzzed like crazy, but my current axe hardly picks up anything. I just opened the electronics cavity to have a look, and it's screened with black conductive paint, although the lid is plain plastic. Do make sure that the tape makes contact with ground, or it could make the problem worse.

Hazmatt's point about grounding the pickup pole pieces is probably a good one too, although it could be a tricky job, you might end up taking the guitar almost completely to pieces. My guitar has metal covers on its pickups which probably help.

The buzz never bothered me too much, since I hardly ever play the instrument without touching the strings

Hazmatt_(The Underdog)

Mon Apr 24 2006, 07:00PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

In practice, its what the manufacturer's try to do. Just touch the poles without touching the strings and you'll get the point immediately!

I really don't think you need a processor to get rid of hum. Ground strap comes to mind. And if you don't like it being passive, fine, have a ground strap connected to a comparator that subtracts the signal picked up from your body out of the signal that goes to your amp.

Some amps are shielded inside. They don't bother with using a full enclosure, usually just a C shape chassis and a large sheet of metallized paper or foiled internals. What reduces noise more then shielding alone is sunbber caps on the HT supply, and especially for the op amps.
A lot of the small solid states have noise on their op amp supplies. They're just using a zener and a 5W resistor to drop the 40-65V power supply to about 18 for the op amps. This is a really crummy way of doing things I think. The op amp supplies could use some good filter caps, and ideally would be on a seperate supply all together!

Anyways, you have options. I used RG174U because I didn't want to paint my guitar innards.

Carbon_Rod

Tue Apr 25 2006, 03:53AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

"I really don't think you need a processor to get rid of hum."
True, for instrumentation or instruments it is usually recommended to keep analog and digital as physically and electronically separate for as long as possible. I remember a project that used to be rather sensitive. It could pick up the digital noise from pocket calculators and wristwatches a few metres away.

A simple 60Hz/50Hz narrow tuned â€œNotch Filterâ€ is a classic solution. With good op-amps the quality loss is negligible.

I doubt grounding and possibly electrocuting musicians is a good solution (insert GFI extension cord joke here.) AC has a way of doing funny things to large conductive objects: depending on where you live the white LEDs will dimly light up if one lead is grounded and you touch the other terminal.

DSPs and SOCs have their place too â€“ mostly in consumer items. Those new all-in-one stomp boxes can do just about anything a person could ever want. I guess itâ€™s rather a personal preference when it comes to what type of sound is acceptable.

Steve Conner

Tue Apr 25 2006, 11:59AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I think... I hope... Bjoern was being ironic with his proposal for a digital hum destructor :P

I tried the pole piece touching experiment on both my guitars. On the good one it doesn't produce any hum at all. My cheaper axe gives a loud hum when you touch the pole pieces on the humbucking bridge pickup, but nothing on the single coil neck pickup.

Personally, I don't like stomp boxes much. I have two tube amps, a high gain one that I built from scratch when I was into metal and wanted those dual rectifier type sounds, and a more vintage sounding one that I bought cheap second hand (it was an off brand and faulty) and modified. The high gain amp has all of its power supplies regulated by solid-state regulators, even the 475V plate supply, which should make hazmatt happy :P

The tubes were all removed in this picture.

[Edit: Go here

to learn how to post pictures.]

Dr. Slack

Tue Apr 25 2006, 05:51PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

You might find you have a problem with the guitar lead, rather than the pickups or amp. My son trashed his lead a while back, so quietly went out and bought a new one, the cheapest he could find. Then he asked me why his guitar was humming. A few experiments showed it was electrical pickup to the inner of the new lead through the pathetic attempt at screening on the el cheapo cable. Sorted with a decent lead.

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