What's the Best Pick-up Shield Material?

This question I think might lead to an interesting thread.

I have just installed a Fralin humbucking P bass pickup for my upright bass that is acting like a single coil. We came to the conclusion that the hum was happening because the coils are not on the same plane. Bummer.

So to fix it, I want to shield the P/U 100% with a metal that passes the magnetic field but not the hum. Copper is ugly. He suggested a Nickel Silver alloy which even McMaster Carr doesn't have. Could Sterling be good? Straight Nickel?

Does anyone have a source for the alloy Fralin talks about?

It sounds wicked, I just need to shut it up. I would order it as 2 humbuckers next time.

Is it a 4-wire pickup? Are you sure it's not just wired incorrectly?

[quote author="kafka"] Are you sure it's not just wired incorrectly?[/quote]

We went through that and then we realized the situation. The coils are about 20 deg to each other so they will never truly humbuck. Ooops. :roll:

Maybe get some copper shaped/beaten nicely then get it silver plated........ or get some silver leaf ...... maybe from a jewellers supply.... you could try aluminium foil...... maybe a heavier grade than the cooking variety, similar to the seal on some powder tins.........get some expensive nickel spray, seal the pickup first and spray the whole thing, then wire the spray to earth.......just thoughts....... :roll:

for electrostatic shielding, anything conductive will do, thickness dosen't matter. For magnetic shielding, you need ferromagnetic material - iron, nickel or mu-metal - and here thickness counts.

Jakob E.

Did you

twist the wires?

run the wires in braid?

how did you ground?

Take a picture or draw the wiring (not a schematic, how the wires are run)

Details details details in wiring pickups.

BEESWAX!


Did you try Potting the Pick up..

I have some original Fender 60's Jaguar Pickups (with the crazy metal Claw) .. WOw they were noisy -- buzz hum you name it - they were loud....

then I potted them in Beeswax ... and absolutely NO buzz hum. Even when next to a Computer Monitor...

http://www.guitarnuts.com/technical/electrical/index.php

Are you sure you haven't mounted one of the halves upside down?
This would make the pickup work as a single coil.

Either that or Lindy has installed all magnetic pole pieces in the same direction. If this is true you may be able slide one half of the pickup's pole pieces through so that it can be mounted upside down.

This is easy to check. Just flip one half of the pickup upside down and see if it isn't quieter. Also check the rest of the wiring to be sure the hum isn't coming from somewhere else.

If you still have a problem send the pickup back to Lindy for a new one. A properly working humbucker should not hum very loud at all. A 20 degree difference shouldn't account for a lot of noise.

I have read don't use only beeswax

but to use 20% beeswax and 80% paraffin. This was from a Stew mac L.F. article. I use a temp control electric cooking pot with a water bath the 20/80 mix is in a coffee can with a temp probe in the water. Cool thing Michaels sells 4 oz of beeswax then you need to find a store for the 16 oz canning block of paraffin

I believe the 20/80 is so not to break the wires as the pickup goes from cold to hot or hot to cold.

Interesting. I didn't pot the wires just the actual pick itself.. good to know :thumb:

I'm with Tim, something doesn't sound right. Can you put the two pickups on the same plane and see if the hum goes away? My bet is that it wouldn't.

If electrostatic shielding is related to the problem, conductive, EMI/RFI shielding paint is available from McMaster, but only in larger sizes (1 pint+). Perhaps there is another source that will sell smaller quantities. You could also mix some silver flake with clear nail polish to make a basic conductive paint. PM me if you are interested and I can get you some more info on where to get the flake.

I have an ulterior motive for this too. I also have an upright, and the (very expensive) transducer system that I have for it now sounds like doo doo. The PBass pickup is on my to-do list.

-Chris

I meant I potted the pickups. The wire is the wire used on the coil(s) Most stuff is around #42, heating and cooling will sometimes break fine wires if the potting materal does match the rate of change of the magnet wire.

Babyhead,
Try running a piece of copper adhesive tape down the middle of the back of the neck so that when you're playing your hand is always touching it. Connect it to ground at the jack. You could also try grounding out your strings. This may be the source of your noise. All guitars have their strings run to ground so that when you're playing your body becomes a huge shield.

Chris,

What's wrong with your transducer? Usually the shielding on them fails and can be repaired with a little copper tape or some delicate soldering.

I have made an upright bass pickup from a Precision pickup and it worked fine. Schaller used to make a similar magnetic pickup for uprights.

Gus,

For potting pickups I've always used pure parafin in a double boiler with no problems.

There are some things I think I can do to help. There is 2 conductor shielded cable to the output jack with the shield carrying ground to the backplate of the pickup. I think I need to cut that ground and run a solid ground to the backplate and additional shielding as well as the strings.

I cannot arrange the 2 halves on the same plane because they are fixed between 2 plates that form a V at about 120 deg. or whatever the curve of my fingerboard is.

I would also assume Fralin would have potted the p/u.

I like the idea of silver flake and nail polish. Maybe a hobby supply has it locally.

Maybe mu metal for the backing, but not for the front as we would shield the p/u from the strings!

I like the idea of silver flake and nail polish. Maybe a hobby supply has it locally.

TK- I have a Barcus Barry bridge transducer that sounded horrible until I found the right preamp. This venture is not a quest for tone, it is about being able to be loud before feedback!

What kind of field are we dealing with when get hum from a single coil?

Thanks all...

[quote author="babyhead"]I cannot arrange the 2 halves on the same plane because they are fixed between 2 plates that form a V at about 120 deg. or whatever the curve of my fingerboard is.[/quote]
I just meant temporarily, for troubleshooting. It might not act the same without the plate though?

[quote author="Tim Campbell"]What's wrong with your transducer?[/quote]
It works fine, I just hate the tone I get from it. I've tried various positions, shims, etc.... No joy. I seem to hate the contact piezo sound in general though. I use magnetic pickups for my acoustic guitars when playing live and never record with transducers.

This is the bad boy I use:

K&K Bass Master

-Chris

OK Chris,
Now I understand. All piezio's distort on the initial attack of a note and there seems to be no way around this. It's what accounts for this percussive sound of a piezio.

I've had some ideas about a condeser pickup and that's certainly what Fishman tries to emulate with their thin film approach.

Another aproach would be to use 2 Pecision pickups wired as 2 mini humbuckers beside each other.

[quote author="Emperor-TK"][quote author="babyhead"]I cannot arrange the 2 halves on the same plane because they are fixed between 2 plates that form a V at about 120 deg. or whatever the curve of my fingerboard is.[/quote]
I just meant temporarily, for troubleshooting. It might not act the same without the plate though?

[/quote]

It is pretty permanent.

I'm going to work on it later today.

Have you definately tried reversing the two wires coming from the second 'block' of the P-Bass pickup? If you get them the wrong way round, the pickup acts like a single-coil.

I know you said you 'went through that' but you didn't actually say that you reversed ONE "Block-Pair" ONLY...

I apologise if you did in fact do exactly this, but since you didn't specifically say that this is what you tried, I wanted to run it by you. -It'd be terrible if it hadn't been tried, because it really does make a P-bass pickup into a buzz-generator if you reverse one block!

:wink:

Keith

I'm with SSLtech on this,

just want to add a little thing, it happened to me that the colours of the PU wires were not the same as on the schematic. This can make you believe it is well connected but in fact it's not. It took me a whole afternoon to find it. Just 4 stupid little wires...

My apologies if you have verified this, or already tried to 'mis'-connect something for the sake of experimenting.

Good luck debugging!

Re: Alfoil thickness..... that was so it didn't look like a chicken leg.... :green: