Cancelling Single Coil Hum Using A Capped Out Coil

[LarsXI]

Would it be possible to run a strat 2/4 position and put a cap on the middle pickup that bleeds off all audible tone except for stuff around the 60 cycle? Thus obtaining the neck/bridge pickup alone but still with hum-canceling benefits?

It seems that this would have been done before if it was possible.

[GregP]

People have used dummy coils, but I don't fully understand how one is constructed. Somehow it's picking up the hum but not the signal (I guess it's not using polepieces to pick up vibrations and create current?)... so no cap necessary, just the dummy coil itself.

[LarsXI]

Hmm, thanks for the lead, I'll put some research into the dummy coils.

For my project specifically, I'll have a single coil neck and humbucker bridge. I was hoping to work some switching that would use one of the two humbucker coils in this method. I'll have to do some experimentation.

[SwedishLuthier]

Dummy coils are essentialy a single coil pickup without pole pieces. Usually they are don with a much larger diameter (not nessesarily round) and with fewer turns. There exist ready made systems were you buy a special pickguard with a dummy coil more or less attached to the underside perimeter. Very expensice stuff IMO. If you can find a cheap MIM fender strat pickup with a solid plastic core and magnets that are possible to push out of the coil it is perfect.Jam it into a pocket you rout under the pick guard (sorry if I'm stuck in the strat thinking right now...) and connect it electrikal out of phase with the neck single coil and it will be more or less quite.

[LarsXI]

yeah, I was beginning to think of doing it that way. I should have an extra p90 to experiment with, so in the end, it may be similiar to the blueshawk.

Thanks for your help

[Mattia]

Dummy coils don't have magnets, but hum can still be induced in a coil of wire without magnets wrapped around them. Wire that out of phase with the rest, and you get rid of some of the hum. That's how I understand it, anyway.

[psw]

I think the original suggestion may have a lot of merit...

I found a way of splitting HB pickups for instance in which there are a few variations and I am about to put in my next project. Instead of splitting the pickup by canceling one of the coils, you use a tone control to bleed off the treble which leaves the full treble of the other...if you follow.

So, with the Hum canceling 2/4 positions, you could use a cap to remove a lot of the treble on the middle leaving the bridge or neck giving the full treble response and a little bit fatter middle pickup in the background fattening things up a little in the bass...a little bit different to what you were suggesting, but would still be noise cancelling.

It wouldn't sound like the neck or bridge alone, but it may sound better/warmer/fuller/etc. Unlike a humbucker, the middle pickup and it's pair though are a fair distance apart which creates that hollowed sound of the 2/4 positions unlike an HB with close coils and so the cancellation effects and hence the sound will be "different"...

To manage it though, you may need a super switch and some experimentation and clever wiring. On a conventional switch, if you have a cap rolling of the middle pickup highs, the mid alone will be muffled and potentially all pickups will sound like they are muffled...you need to separate the pickups at the switch to affect each independent of the other...

Bear in mind though, that single coils can be made relatively quiet with shielding and or sheilded cables and such...often remarkably so. Noiseless single coils have improved dramatically in recent times of course and it is likely that your suggestion, though has merit and may well be quiet, could not compete with these or a dummy coil solution.

Still...it would be an interesting experiment. Targeting a particular frequency with passive components may be a little tricky, to be that specific you may need active filtering anyway and a more complex switching would still apply...

pete

[LarsXI]

I wonder what a very large capacitor would do for us. Such that the cutoff point would effectively kill all audible tone. I have no idea if this would cut off the hum as well, but if something like a dummy coil works, who knows?

[Geo]

I wonder what a very large capacitor would do for us. Such that the cutoff point would effectively kill all audible tone. I have no idea if this would cut off the hum as well, but if something like a dummy coil works, who knows?

60hz is lower than the lowest guitar pitch (80 hz) so you should be able to use a large cap (0.1?) to dump all guitar frequencies while still passing 60hz... if that's what you're asking.

This will kill the fundamental hum (60 hz) but NOT its overtones, which you hear as buzz. So, probably not effective.

Edited May 16, 2008 by Geo

[SwedishLuthier]

Have you guys ever though about how steep (I think it is called that) a first order filter (that is essential what a capacitor is in this case) is. IIRC it is 6 db per octave, meaning that if it would be possible to cut 100% at 60 Hz, it would cut everything BUT 6 db at 120Hz, letting only 12 db through at 240 Hz and only 18 db at 490 Hz. 18 db is really more or less nothing.

This solution needs at least a third order filter that IIRC have 24 db of attenuation per octave, but even that would probably be very audible in the range of a guitar.

Now feel free to chip in with better knowledge of filter construction and teach me a lesson on filter technology as I have most likely messed everything up...

Once again, a dummy coil in parallel with the neck SC will do nothing to degrade the sound, will kill the hum and is a tested solution. BTW, SRV had one in his NO1 and it certainly didn't make him sound bad...

[LarsXI]

Yeah, I'm thinking dummy coil at this point as well. The coil would be only slightly more difficult to obtain and install than a cap.

[ansil]

look at hackaday.com there are some princeton guys who made a really effective 60hz filter with overtone filters.

ed

[GregP]

Can't seem able to find it. Their search engine is a bit wonky.

[ansil]

something to try but its still active. using an inverting input on a opamp with a steep set of filters on it. try it its interesting.

[Paul Marossy]

I just put Fender "Hot Noiseless" pickups in my guitar. They act like a humbucker but sound like a single coil. To me, that's the easiest, most direct way to eliminate that pesky 60-cycle hum. I'm glad I did it!