Ground Topology inside a Guitar

[Steve A.]

Hi guys, I did make this dummy coil, just as an experiment, 6" diameter, 600 turns, 41AWG, 1.4 kOhm, I connected it to single coil pickup, straight to the amp.
I expected at least a bit of regular single coil hum reduction, but it didn't work for me. No changes in hum level at all. What do you think, where did I make mistake ?

I agree with rjb's analysis but wanted to add some details from the Chiliachki patent application which suggests the following specs:
1. "signal picking coil" (AKA "sensing coil") 7,000 turns of 42AWG wire; ~7.00K DCR, 2.0H inductance.
2. "noise picking coil" (not to be confused with the "nose picking coil" so I prefer to call it the "dummy coil" ) One example would be: 8" diameter, 200 turns of 36AWG wire, 250R DCR, 0.02H inductance

The patent also shows that the nose, er, noise picking coil is shielded. One way to shield it would be to wrap the dummy coil with electrical tape and then wrap 1" width copper foil tape around that (be sure that it is in the desired shape when you do that.)

The patent mentions that heavier gauge wire could be used but it does not suggest the diameter, number of turns and DCR for the heavier wire. It also has a suggested schematic with two controls, one to reduce the amount of noise reduction and the other to brighten the sound a bit if desired.

The new paradigm of dummy coils introduced by the Chiliachki is not merely noise reduction for single coil pickups, but that the noise reduction is very transparent- it changes the sound of the pickup itself as little as possible.

Steve Ahola

P.S. Here is a link to the Chiliachki patent:

http://www.blueguitar.org/new/misc/p...chiliachki.pdf

[rjb]

The patent mentions that heavier gauge wire could be used but it does not suggest the diameter, number of turns and DCR for the heavier wire.

IIR, the patent mentions a range of wire gauges & suggests the "noise picking coil" use a gauge "at least 2 steps heavier" than the "signal picking coil". (Sorry, but I'm being lazy & didn't double-check the patent).

...two controls, one to reduce the amount of noise reduction and the other to brighten the sound a bit if desired.

...not merely noise reduction for single coil pickups, but that the noise reduction is very transparent- it changes the sound of the pickup itself as little as possible.

I really don't get the purpose of that "tone control". However, I haven't yet built & experimented with a dummy coil.
Have you tried it? Is it beneficial?

Beating a dead horse, stating the obvious: The reason the noise reduction is transparent is because the dummy coil's R & L are insignificant compared to the pickup coil's R & L - so the dummy coil barely changes the overall circuit's Q.

[epis]

Thanks to both of you guys, I'll try with ticker wire and different number of turns. Just one more question, i feel a little bit confused.Main purpose of the coil, is it to reduce electric noise in general, or 60Hz hum, I expected it to work as humbucker?

[rjb]

Thanks to both of you guys, I'll try with ticker wire and different number of turns. Just one more question, i feel a little bit confused.Main purpose of the coil, is it to reduce electric noise in general, or 60Hz hum, I expected it to work as humbucker?

The purpose of the dummy coil is to reduce 60Hz hum, like a humbucker.
The purpose of the foil shield around the dummy coil is to block electric noise.

[epis]

Sorry guys, this didn't work for me. I made second coil, 6" diameter,200 turns, AWG35,122Ohm. I got same result as first time.
I do understand that additional circuitry could affect efficiency of the coil,number of turns is very important, but my coils didn't reduce the hum of 7.14KOhm single coil pickup at all.Just to make it clear, I did try everything, I have a lot of experience, so it wasn't about some beginner's mistake.
I'll fallow this thread, I would like to hear from other builders about it. Cheers from Ottawa

[Ward]

Well my coil is wound with 36 wire to 350ohms, it's 16" in circumference and does work well. Try lowering your ohms? Have you reversed the wires on the coil, maybe you have it wires ass about? or just flip it over as RB said. My coil isn't shielded either.

[epis]

Thanks for your input Ward. I'll try to connect it directly into my strat. I did try reversing the wires, changing relative position of the coil toward pickup and the amp.

[Ward]

I did notice that if I was too close to the amp I would get more noise.

[rjb]

...I made second coil, 6" diameter,200 turns, AWG35,122Ohm.
...my coils didn't reduce the hum of 7.14KOhm single coil pickup at all.

Hmm, I would expect some effect. And the pickup & dummy coil are parallel? And the dummy coil is a circle (if you flatten it, its enclosed area is reduced)?

Someone should check me on this, but I'm pretty sure the induced voltage in a coil is supposed to be proportional to the area of the coil times the number of turns. So don't worry so much about the resistance of the "noise picking" coil- that's just a function of the wire thickness- fatter wire equals lower R; as long as R is relatively low compared to the "signal picking" coil's R, you should be fine.

In the patent, the example given is for a pickup with 7000 turns of #42, which happens to come out to ~7Kohm and ~2Henrie (I'm guessing this is on a Strat bobbin). For the dummy coil, they use 200 turns of #36 in a circle with 8" diameter, which happens to come out to ~250 ohms and ~.02Henrie.

It looks like your pickup is pretty similar to the one in the example. But your dummy coil is smaller. Area of a circle is proportional to radius squared, 3" vs 4"- so multiply 200 turns times 4 squared over 3 squared = 16/9. 200 turns x 16/9 = 356 turns. Try adding 156 turns to your dummy coil, take 2 aspirin, and call in the morning.

[frus]

The purpose of the foil shield around the dummy coil is to block electric noise.

how is the shielded coil supposed to pick up noise then (I understand that's its purpose)?

[epis]

Update

I removed partially pickguard from my strat and connected the coil. First coil didn't work,it just added extra noise. It was picking up a lot of noise from my laptop's switching PS.
Second one, 200 turns, AWG 35 worked VERY well. Just two things for future builders :
- I think it MUST be shielded, otherwise it would act as an antenna for high frequency noise
- it SHOULD be potted, it's very microphonic
Tone wise, I don't know yet, after I install it permanently, I'll post my impressions.
Only one thing bothers me, why it didn't work at first. Maybe because of the absence of real ground ?
Thank you guys for cool idea and useful tips. Best regards, Damir

[rjb]

how is the shielded coil supposed to pick up noise then (I understand that's its purpose)?

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

[Ward]

I'm gonna shield mine now n see what's what. Cheers.

[Ward]

Right then, I wrapped the copper tape around the coil, soldered on the ground wire then wrapped insulation tape around again in case of shorting. Plugged into the amp, now it doesn't work at all. I'd put the coil in upside down. So anyway, yep, shielding is a must for sure. I can let go of the guitar now with no great noise occurring and I'm not getting the high oscillations with treb and pres maxed like I was. Brilliant, f#*^ing brilliant.

[Steve A.]

I really don't get the purpose of that "tone control". However, I haven't yet built & experimented with a dummy coil.
Have you tried it? Is it beneficial?

No, I have not tried it yet. I ran into an unusual effect when I wired up a 6 pole switch on a 2HB guitar which allowed the two pickups (and their controls) connected in series. The tone control for the pickup connected to ground acted strange- I thought that I must have wired it up backwards because as you turned it down it made the signal brighter!. What was happening was that the "bottom" tone control allowed the high frequencies from the "top" pickup to go directly to ground rather than have them go through the bottom pickup which would have swallowed a lot of them up (typical of a series linkage of HB's.) The tone control in the Chiliachki circuit would likewise shunt some of the high frequencies from the sensing coil directly to ground rather than routed through the dummy coil, with the effect of having it make the sound brighter. Hmmm... with a low LCR coil the effect would not be that much. FWIW the Ilitch system does not use that tone pot but has two volume pots, one for two of the pickups, one for the other.

So I figure that the whole Chiliachki circuit is there to fine tune the dummy coil for your particular guitar, setting your own compromise between hum cancelling and tone. With the two controls there the author was fairly certain that the design would work with most typical single coil pickups.

Steve Ahola

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?