What part of the coil to tap?

[GlennW]

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]

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?