What part of the coil to tap?

[Mark Hammer]

Okay, let's say you wanted to make an overwound pickup and tap the coil at some portion of the total number of turns. Where would you prefer to have the effective portion of the coil be, the inner or the outer portion? That is, if you wanted to have a choice between 7000 and 9000 turns, would you make the 2000-turn difference be the first 2000 turns starting from the inside closest to the polepieces, or the last 2000 turns on the outside and furthest away from the polepieces?

And why would you coose that option?

Related to this, let's say you had a humbucker with, oh I dunno, 4500 turns on each bobbin, and wanted to tap that sucker so that each coil was reduced to 3500 turns. Would there be any virtue or added value to tapping one coil closer to the outside and the other closer to the inside?

[David Schwab]

I say inner. You are closer to the core/magnets that way. The "extra" (hotter) windings go on top of that.

[Spence]

Yes I agree. Once tapped you still need the inner coil to be in circuit.

[Zhangliqun]

Another vote for inner turns here. Never seen it done any other way at least.

[Mark Hammer]

Based on your replies, I feel compelled to ask: If my coil consisted of, say, 2500 "unused" turns close to the polepieces, and another 5 thousand "used" turns from that point to the outside of the coil, what should I expect to hear?

My sense is that surely the inductance of that 5000 turns would be different when the circumference of those turns is greater, and that the DC resistance would certainly be greater than if I was using the inner 5000 turns and adding 2500 more around it.

But should I expect less output when those outer 5000 are a little more distant from the polepieces?

Could I help things out, if I decided to use the inner turns as the add-on, by using a thinner gauge for the inner turns, so as to minimize the polepiece-to-coil distance and overall outside circumference?

[Scott S.]

What about doing the tap vertically, which is I guess is similar to a stacked humbucker that is not wired out of phase

[Mark Hammer]

I think the problem there is keeping the upper and lower windings separate. Feasible, though.

[Zhangliqun]

It's not a problem, just a matter of determining which lead will be ground and which will be tap. If you had a 10k single coil and tapped it at 5k, you could wire it for either 5k inner or 5k outer, just swap hot and ground.

For a more realistic scenario on the specs, if you decided you wanted your tapped portion to be the outer turns, and say it was 7k tapped and 10k full, if the 7k is on the outside, it would probably sound a bit fuller, more bass response than if the 7k was on the inside because an outer tapped portion would be wider overall and see the longer bass wavelengths better.

[David Schwab]

Originally Posted by Mark Hammer

I think the problem there is keeping the upper and lower windings separate. Feasible, though.

Not hard at all.

[Rosewood]

I'm no mental wizard but it seems like inside next to the poles would be the most sensitive so you would want that main part of the coil close to the poles. With a single coil pickup (no bar magnets), the further the windings are from the poles the less they contribute to output, am I right?

[GlennW]

Those bobbins look a little...noodley. j/k

[Zhangliqun]

Originally Posted by Rosewood

I'm no mental wizard but it seems like inside next to the poles would be the most sensitive so you would want that main part of the coil close to the poles. With a single coil pickup (no bar magnets), the further the windings are from the poles the less they contribute to output, am I right?

You're probably right in theory, but I've never tried it so I can't verify. That said, the greater width of the coil might compensate some for the reduced sensitivity in terms of overall output. But again, just theorizing...

[Dave Kerr]

Steve Kersting's page has some nice FEMM simulations

[David Schwab]

Originally Posted by GlennW

Those bobbins look a little...noodley. j/k

Perfboard...

[David Schwab]

Originally Posted by Zhangliqun

You're probably right in theory, but I've never tried it so I can't verify. That said, the greater width of the coil might compensate some for the reduced sensitivity in terms of overall output. But again, just theorizing...

Two things seem to happen... as the coil gets wider, the outer wraps are less sensitive than the inner wraps, and the top of the coil is more sensitive than the bottom.

I made a stacked Tele pickup similar to the Jazz pickup in the photo, when listening to each coil separately, the top is bright and twangy, and the bottom coil is dark and mellow.

[GlennW]

Originally Posted by David Schwab

Perfboard...

Thought Sam might have offered some magic stuff.

[Mark Hammer]

I wind by hand so YMMV, but it strikes me that the inside turns are generally wound more snugly, most likely because they are abutting a solid surface rather than the spongy mass of a coil such as outside turns would encounter. So, while moving the turns away from the polepieces (by having an "inside layer" of turns that is removed from the active coil when the tap is selected) should have the expected effect in terms of output, I can't imagine the inside turns provide that much of a distance between the polepieces and the principle portion of the total coil.

I suppose part of the confusion might also stem from different visions of what a "tap" might be. Personally, I'm talking about the difference between a reasonable number of turns for an acceptable output level, and additional turns reflecting a "heated up" total coil, as opposed to a 50/50 split or something like that. So, say I have 1500 turns of #43 wire on the inside, next to the polepieces, and throw another 6000-6500 of #42 on top of that. Realizing that the square of the distance from the polepiece plays a role, how much real distance is created by that first 1500 turns of #43? Hard to imagine it is a greater distance than what the plastic bobbin around HB polepieces provides, and we certainly seem to be comfortable with that.

The other thing is that the same 1500 additional turns added to the outside will change the DCR more appreciably than when they are the shorter circumference format on the inside of the coil. If I have understood things correctly, a tap on the inside (using my proposed 6500+1500 hypothetical scenario) would result in less tonal change from the basic coil than would a tap closer to the outside. Is that logical?

And thanks for the pickup pix, Dave. Suitable flatwork materials are always a problem for me. If YOU can use perfboard, then I don't feel quite to bad about using copper-clad board. I can etch a set of pads on the underside of the lower flatwork piece that will accommodate taps. Not as robust as brass rivets, of course, but serviceable enough.

[David Schwab]

Originally Posted by Mark Hammer

And thanks for the pickup pix, Dave. Suitable flatwork materials are always a problem for me. If YOU can use perfboard, then I don't feel quite to bad about using copper-clad board. I can etch a set of pads on the underside of the lower flatwork piece that will accommodate taps. Not as robust as brass rivets, of course, but serviceable enough.

Alembic uses copper clad board.

I made this stacked Tele pickup with copper clad board.

I left crude solder pads on the bottom, but never used them.

[Peter Naglitsch]

the top of the coil is more sensitive than the bottom.

I have actually measured those things in a real life test set up. I did a test with a single A5 rod, and "half a coil", meaning I did a standard SC coil but only 1/2 of the height, leaving the rod to stick out at one end. Then I could easily flip it around and measure the output AND the frequency response. This was done to learn how much the upper part of the coil contributed vs the lower part.

I could also repeat the experiment with and w/o a steel base plate like on a Tele bridge pup.

Without a steel base plate the overall output of the “bottom half” was 50% of that of the upper half (1/3 of the total out coming from the bottom part and 2/3 coming from the upper part). The frequency response was pretty similar between the two cases. With the base plate the bottom half had a tiny bit more output, but not as much as I expected it to have.

[GlennW]

Maybe that partially explains this?