Uncoupling HB coils

[Mark Hammer]

A buddy picked up a one-humbucker Squier Bullet Strat and asked about sticking one or more additional pickups on that were something a little different. He doesn't mind routing, and has no particular need to achieve some specific classic tone. So we're blue-skying it.

I got to thinking that traditional approaches to flipping between single-coil and dual coil sound have involved cancellation (bypassing, actually) of one coil on a side-by-side HB. The sensing area is still between the tops of the polepieces (screws/slugs),though.

It occurred to me that one could make a pickup in which alnico polepieces are used for one coil, and slugs for the other, with a magnetically conductive plate/keeper coupling them, insteasd of the traditional alnico bar as the coupling element.

So, let's say that my buddy and I come up with a means to flick a lever and lift the coupling element away from the alnico polepieces, such that that coil could be used as a true single coil (we have not done so yet; this is just a "what if..."). The second coil with the slugs would go unmagnetized. The overall pickup could be used with both coils in series for hum-rejection, though the second coil would function largely as a dummy with some iron in the middle for inductance.

How far away would the coupling element underneath need to be moved from the end of the alnico polepieces to make the alnico coil a "true" single coil? Or is the ideal distance so great that the remaining active coil could never really be a true single coil, but merely "different" by virtue of reduced coupling?

[Mike Sulzer]

Am I correct in thinking that the alnico pole pieces in coil one provides the magnetization of the parts of the strings over coil two through a coupling piece of steel? If so, I think that you are going to lose too much on the way. A pickup is not a closed magnetic circuit.

[frankfalbo]

Seems to me the "dummy" coil would do much more harm to the sound than a bottom coil. The current method of "besting both worlds" is to put an Alnico stack next to an HB coil that is magnetized with a small ceramic.

I also think the Alnico poles would charge the second coil a little solely based on proximity. In other words, there is no distance that is "enough" within the confines of a humbucker. So your dummy coil would contain some signal. The coupling element would also not charge the second coil to the level of a "normal" coil anyway. I imagine when all is said and done you'd experience about 20% of the difference you're used to hearing with an electronic coil cut.

Forget the lever and just prototype it in such a way that you can slack the strings and physically pull the coupler out. Make a recording of both sounds. If that's not "enough" difference then the moving coupler could never accomplish your goal.

[Mike Sulzer]

S

I also think the Alnico poles would charge the second coil a little solely based on proximity. In other words, there is no distance that is "enough" within the confines of a humbucker. So your dummy coil would contain some signal. The coupling element would also not charge the second coil to the level of a "normal" coil anyway.

Forget the lever and just prototype it in such a way that you can slack the strings and physically pull the coupler out. Make a recording of both sounds. If that's not "enough" difference then the moving coupler could never accomplish your goal.

Easy enough to measure:

3/32" above alnico rod: -365 Gauss
3/32" above slug coupled with 3/16" thick Xformer steel: 102 Gauss
Steel removed: 48 Gauss
slug coil removed, same location: 35 Gauss

All measurements are the vertical component.

[Mark Hammer]

First, thanks for your replies, guys. Much appreciated.

Yes, Mike, you are correct. The intent was that the second coil is charged by the alnico polepieces in the first one conducting through the coupling bar/plate, and by moving the plate I would be magnetically decoupling the 2nd coil and set of slugs.

Frank, I'm not entirely opposed to the notion of simply taking the 2nd coil right out of the picture. Using it as dummy coil is simply an option, but is not a requirement. I think it might be just as interesting to have some means to just push/retract the bottom coupling plate out of the way, and flick a switch so that only the alnico coil is engaged. I guess what I wonder is whether it would "behave" as a traditional Fender single coil, with the sensing area effectively above the top of the polepieces (with some side sensitivity thrown in) or would it continue to be between the top of the polepieces and the slugs.

Or, as I'm sort of taking from your comment, it would be some sort of bizarre amalgam of the two with an emphasis on the area over the polepieces and juuuuussst a bit within the gap between the polepieces and slugs. If so, then the extent to which it did that would depend on how far out of the way I could displace the coupling plate/bar.

Here's a tentative drawing. bring the coupling bar up, connect the slug coil, and it's a regular humbucker. Retract the coupling bar and disconnect the slug coil, and it's something more in the SC zone. Or at least that's the theory

[Mark Hammer]

Sonuvabitch!! How'd you do that?