Ground Topology inside a Guitar

[rjb]

P.S. I understand how a low ohm coil in series with the pickup makes the sound transparent, but isn't it a given that most dummy coils will have low inductance since there is no magnets or ferrous pole pieces?

The voltage induced in an antenna is proportional to the area enclosed by the coil, and to the number of turns (I think).
The inductance is proportional to the area enclosed by the coil, and to the square of the number of turns (I think).
I'm ignoring the coils' lengths, whose effects are insignificant in this discussion (I think).

A large round dummy coil requires many fewer turns to detect the same voltage as a dummy coil that is the same size and shape as a pickup's coil.
Thus, the large round dummy coil with few turns will have significantly lower inductance than the little elongated dummy coil with many turns.

I didn't explain that very well, but it's just a matter of geometry and some physics.
I'm just saying that a big round dummy coil will have even lower inductance than a "traditionally-shaped" dummy coil.

In the example given in the patent, the pickup's inductance was about 2 Henrie, and the dummy coil's inductance was about .02 Henrie- a factor of 100:1. The patent didn't say what the inductance of an air coil with the same shape and turns count as the pickup's coil would have been- but it certainly would have been higher than .02 Henrie.

I hope I answered your question.
-rb

[Ward]

I just put one in my triple P-90 strat and it didn't work at all
Do I need to make another coil with more wire? Say 500ohms?

[frus]

In hand-waving terms: The foil shield blocks high-frequency electrical noise; the coil picks up low-frequency magnetic hum.

ah, ok I get it
so no chance for trying to buck the high frequency noise as well?

[rjb]

so no chance for trying to buck the high frequency noise as well?

Short answer: No, no chance.

[frus]

so pot and shield it is
thanks!

[epis]

Hi guys, here is my final impression :

Like everything in the life, it's about compromises. I have the coil installed in an old Samick, alnico pickups , middle RWRP.
Coil definitely works, I do agree with 80% noise reduction, but it made noise in positions 2,3,4 a bit higher. It is still acceptable, but noisier than without the coil
I didn't hear any difference in tone quality, pickups sound same as before.
I'll try one more time with around 350 turns as rjb suggested, and adjusting circuitry.
That's it for now, thanks again to all of you.

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[Ward]

Hi guys, here is my final impression :
Like everything in the life, it's about compromises. I have the coil installed in an old Samick, alnico pickups , middle RWRP.
Coil definitely works, I do agree with 80% noise reduction, but it made noise in positions 2,3,4 a bit higher. It is still acceptable, but noisier than without the coil
I didn't hear any difference in tone quality, pickups sound same as before.
I'll try one more time with around 350 turns as rjb suggested, and adjusting circuitry.

If you swap the leads on the middle pickup AND reverse the mag polarity you'll be laughing. You really want the middle wound the same direction so the start wire is still the ground like the br and neck but for the time being swap the wires and reverse the mag pol.
What's this about NOT bucking the high frequency noise? with the shield mine's got no upper noise, just a real little 60hz hum but real low. I've now gotta experiment to quiet down the P-90s, seems I'm on my own there.

[Steve A.]

I have the coil installed in an old Samick, alnico pickups , middle RWRP.
Coil definitely works, I do agree with 80% noise reduction, but it made noise in positions 2,3,4 a bit higher. It is still acceptable, but noisier than without the coil I didn't hear any difference in tone quality, pickups sound same as before.
I'll try one more time with around 350 turns as rjb suggested, and adjusting circuitry.
That's it for now, thanks again to all of you.

I would suggest getting a 4 pole 5 position super switch and wiring it up so that the dummy coil is used ONLY in positions 1 & 5. With a RWRP middle pickup positions 2 & 4 are already humcancelling so you don't need the dummy coil there. For position #3 you could swap the leads from the dummy coil to make it humcancelling with the RWRP pickup.

Good luck!

Steve Ahola

P.S. I don't have time right now to figure out the wiring scheme but I can get to later. (I'll probably want to use it myself.) I forget- what was the diameter of your dummy coil. I think that you said it was 200 turns of 35AWG wire.

[rjb]

I would suggest getting a 4 pole 5 position super switch and wiring it up so that the dummy coil is used ONLY in positions 1 & 5. With a RWRP middle pickup positions 2 & 4 are already humcancelling so you don't need the dummy coil there. For position #3 you could swap the leads from the dummy coil to make it humcancelling with the RWRP pickup.

If I had a Strat, that's what I'd do. Oh yea, I do have a mini-Strat set up as a 5-string tenor guitar... I guess that counts.

P.S. I don't have time right now to figure out the wiring scheme but I can get to later.

I'm eager to see the wiring scheme.

I forget- what was the diameter of your dummy coil. I think that you said it was 200 turns of 35AWG wire.

The patent example was 200 turns at 8" diameter.
The OP built one 200 turns at 6" diameter and is going to try another with 350 turns.

Note that if you change the geometry of the coil from a circle, you decrease the sensitivity of the "noise picking coil" - because the area enclosed by the coil is reduced. Life is a compromise.

[epis]

Hello again, new update :

New coil same diameter 6", 310 turns, AWG 35, 175 Ohm , NO shield works great, noise reduction looks to me same as in humbucking positions 2 and 4.
I put switching PS one foot far away from the guitar and noise cancellation is great.
I'm not gonna use shielding in future, it's real PITA comparing to the rest of the work, and I didn't find benefits of using it.
Thank you Steve for the tip about super switch, great idea, it will eliminate the problems I mentioned earlier.
Thank you rjb, your calculations of number of turns depending of the size of the coil works well, I didn't go all the way to 356 as you suggested, I was kind of skeptical because of the experience with first coil.
All together, it works, it's worth it, there is no significant change in tone, at least to my ears.
Cheers from Ottawa, Damir

[Steve A.]

If I had a Strat, that's what I'd do. Oh yea, I do have a mini-Strat set up as a 5-string tenor guitar... I guess that counts.

I'm eager to see the wiring scheme.

I have it drawn out but no scanner or draw program working right now. Back in the old days (before on-line graphics!) we'd have to spell things out. So here it is...

A & B are the common terminals of poles 1 and 2 and are connected to the volume pot
C is the common terminal of pole 3 and is connected to the signal returns from all 3 pickups [B-,M-.N-]
D is the common terminal of pole 4 and is connected to ground [GND]
B+, M+ and N+ are the leads from the pickups which would normally be connected to the volume pot
DC+ is the dummy coil lead which would have been connected to the Neck and Bridge pickup signal return
DC- is the dummy coil lead which would have been connected to ground
NC means "not connected"

The switch positions are as follows:
A. 1 N+ and middle tone control
. . 2 [ditto]
. . 3 NC
. . 4 B+ and lower tone control
. . 5 [ditto]

B. 1 NC
. . 2 M+
. . 3 M+
. . 4 M+
. . 5 NC

C. 1 DC+
. . 2 GND
. . 3 DC-
. . 4 GND
. . 5 DC+

D. 1 DC-
. . 2 NC
. . 3 DC+
. . 4 NC
. . 5 DC-

Orientation of DC+ and DC- is very important- unless you can just flip the dummy coil over.

Steve Ahola

P.S. Error-checking is welcomed! BTW the middle pickup is not connected to a tone control. I think that works better than having the bridge pickup not connected to a tone control- unless you need to clean the wax out of your ears.

P.P.S. Shielding the dummy coil would be kinda like adding a metal cover to a humbucker, something that many or most people don't do. I think it would be necessary only if you were going to play in one of those Bars From Hell which were wired by Satan himself!

[rjb]

So here it is...

T'anks.

[Steve A.]

Well, I'm finally getting around to adding the Chiliachki circuit with a 4 pole 5 position megaswitch to one of my strats and looked up this thread to get an idea of how many winds to do.

I made a rig for winding the 18" circumference coil from a pair of the $1.99 Harbor Freight 12" bar clamp/spreaders. After punching out the drive pins I used two of the stationary pieces mounted in holes about 7 5/8" apart. I left the part with the squeeze handle off- it just got in the way. I'm up to 200 turns- I think I will go up to 330. I will post a picture of the rig tomorrow- what is great is that you can set it for whatever circumference you want by drilling out another hole on the bar.

When I'm done winding I'm going to use a few splotches of Minwax polyurethane to hold the wire together so I remove it from the rig without trashing it. When I have it shaped for the swimming pool route I will put a full coat of the Minwax on it. The pickup cavity is shielded and the pickguard has foil so that should handle the grounding (although I might trying wrapping copper foil tape around the coil to make sure.)

Steve Ahola

P.S. I see that the Ilitch site has added a wiring diagram for a RWRP middle pickup and a 4 pole 5 position selector switch:

http://www.ilitchelectronics.com/tes...01/hex013E.pdf

They also have wiring diagram for using a RWRP middle pickup with a REGULAR strat selector switch (hint: leave the black wire of the middle pickup connected to ground when you wire up the black wires of the bridge and neck pickups to the dummy coil.)

http://www.ilitchelectronics.com/tes...01/hex012E.pdf