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Tech: Quelling pickup noise - ideas?

Will Fly 04 Jan 12 - 08:35 AM
Richard Bridge 04 Jan 12 - 08:48 AM
GUEST,Ray 04 Jan 12 - 01:10 PM
JohnDun 04 Jan 12 - 06:42 PM
Richard Bridge 04 Jan 12 - 06:48 PM
JohnDun 04 Jan 12 - 07:11 PM
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Subject: Tech: Quelling pickup noise - ideas?
From: Will Fly
Date: 04 Jan 12 - 08:35 AM

I've just had a solid, electric 5-string 'mandotenor' made for me (cross between a tenor guitar and a mandolin) which is in the process of being tweaked and finished by its maker.

There's an unusual amount of noise/hum from the pickup - more than in other instruments he's made - and though it sounds as though it's not earthed, the earthing is definitely there in the wiring.

It's odd, because when I touch the string or pickup with my hand as I'm playing, the hum stops. To me, this definitely sounds like a lack of earth. His solution will be to line the backplate (where we can get at the electrics) with silver foil, and use foil-type paint in the cavities - a technique which he's used to reduce hum before. He's an excellent luthier, but also slightly disconcerted by the unusual hum level. It's been tested on different amps and with different leads - all with a similar result.

I'm just curious as to whether there's a wiring solution to this - if my body can earth the instrument, can anything be soldered in to have the same effect? I've come across this in other, much older instruments and I'm sure it must have been tackled by other people. Ideas and suggestions welcomed.


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Subject: RE: Tech: Quelling pickup noise - ideas?
From: Richard Bridge
Date: 04 Jan 12 - 08:48 AM

I have done something similar with a mandoplank - a purely electric solid body mandolin. Removed pickup plate and pickups, glued tinfoil into the cavity, connected that to the earth side of the jack socket (it's tricky getting a good connection to tinfoil 'cos it's aluminium which does not take solder well) and hum gone.

Another way to reduce the hum is to use hot rails humbuckers in stead of single pole pickups but beware the frequency response is not what a custom winder of coils for something that was not a guitar would want.

Oh - teach my grandmother to suck eggs - use screened lead not twisted pair wiring!


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Subject: RE: Tech: Quelling pickup noise - ideas?
From: GUEST,Ray
Date: 04 Jan 12 - 01:10 PM

Hmmmm... (No pun intended!) I have a very similar but even more complicated problem.

I have a 5 string fretless bass. I bought it off fleabay a couple of years ago, at a bargain price, as know the luthier who made it back in the 80s and who reckons it's, more or less, unique.

The pickup it came with , to cut a long story short, was knackered and my luthier friend told me he'd stopped using that brand as they always failed. He fitted an LR Baggs but when I got it home - you've guessed it - Hummmm. I tried all the usual things - check the earth, take it off, put it back but it made no difference. Back to his workshop - no hummm.

By bass amp (small poxy cheapo - I'm really no bass player) doesn't hum with my other (straight electric) bass plugged in and the fretless doesn't hum when plugged into a headphone amp. Touch the plug socket and the hum goes away. The hum gets worse when I go near to any form of digital equipment so I'm convinced its some form of peculiar induction between the electrics and myself.

I too would appreciate any ideas.


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Subject: RE: Tech: Quelling pickup noise - ideas?
From: JohnDun
Date: 04 Jan 12 - 06:42 PM

You've probably already tried a different pick-up...   Sorry, had to mention it.

Way back, in my electronics apprenticeship days my old tutor used to talk of the times before wiring looms and multilayer circuit boards in radio sets.

Wiring layouts were routed in a similar way but not exactly the same in each set.   Sets that 'hummed' during production were sent to a lady with a big crochet hook thing who moved the wires away from any potential RF radiation and then tied them back to stop it recurring.

Any bespoke electronics sometimes needs tweaking and it will be a trial and error thing.   Richard is right , try screening, re-routing and shortening (sometimes lengthening) any leads/wiring.   Tin foil should be adequate but sheets of screening material are readily available from radio suppliers and may be more effective to shield areas.

Good Luck


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Subject: RE: Tech: Quelling pickup noise - ideas?
From: Richard Bridge
Date: 04 Jan 12 - 06:48 PM

Copper based adhesive screening sheet is expensive - but you can solder to it!


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Subject: RE: Tech: Quelling pickup noise - ideas?
From: JohnDun
Date: 04 Jan 12 - 07:11 PM

Ray

'I'm convinced its some form of peculiar induction between the electrics and myself.'

Rule yourself out of the equation and play it naked.....    alone!!!

Mismatches between instruments and amps usually reduce volume and doesn't create hum but if your fretless works on other amps and not yours then it may be something to do with mismatch.   Your headphone amp may 'match' your fretless better or its relatively low gain may not reproduce the hum.

Good Luck to you too.


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