Dummy coil for p90 (not effective)

[cakewalker]

A customer wants a dummy coil for his noisy p90s. I have made 2 alternatives with 41 awg. One is a typical p90 plastic bobbin, the other was around the same dimensions like a tremolo backplate.


But both of the results are not effective. When i connect them in parallel the tone drops hugely. Series wiring is better for tone but the noise reduce just %20.

Now i am thing of a bigger air coil like the ilitch system.

I think the magnetic field of p90s are different so i am missing something. Any suggestions?

[mozz]

Not experienced in that but have you tried both directions of the coil? Also maybe you need to try 42 gauge and wind a full bobbin, maybe 10k.

[Mark Hammer]

Hum comes from external sources. When two coils, whether they be a PAF-type humbucker, a pair of RWRP pickups combined in a Strat, a single coil paired up with a dummy coil, or something else, are used to cancel hum, they are operating like radio antennas, tuning in the all-rock-all-day station at 60hz on your dial. Like any radio antenna, reception will vary by orientation of the antenna. Getting hum cancellation depends on the two coils sensing the same amount of EMI. If one coil senses more, OR less, than the other, you may get hum reduction, but not cancellation. In the case of PAF-type humbuckers or dual-rail types, the two coils are close together and oriented the same way, such that they will both likely pick up the same amount of hum. A dummy coil CAN reduce hum, even if located somewhere other than right beside or underneath the functional pickup. But how much reduction will depend on many things one may not be able to control. Bt if one has the latitude to try different location on the guitar, one should experiment in order to find the best location.

[Helmholtz]

I'd think the dummy coil needs at least the same number of turns as the P-90, i.e. 10000+.
As this means a lot of inductance, series wiring will result in significant treble loss.
Parallel wiring might work better, but will lower output by up to 6dB.

[the great waldo]

The illitch system for a Les Paul works well and does'nt kill the tone.
Cheers
Andrew

[Helmholtz]

The big advantage of the ilitch system is the large coil area.
This means that e.g. 700 turns may have the same hum cancelling effect as 10,000 turns on a P-90 bobbin.
Less turns means much less inductance and thus less treble loss with series wiring.

[cakewalker]

Today i tried the same (uneffective) p90 dummy bobbin with polepieces, magnets and baseplate. The noise was less but the tone was darker as i expected.

Then i tried with just steel bars instead of two alnico magnets and the tone was better.

I would like to wound something like the ilitch system but i havent tried it before.

My new plan is to wind a very low resistance coil but also putting polepieces and baseplate to have the same geometry with the p90 bobbin.

[cakewalker]

The illitch system for a Les Paul works well and does'nt kill the tone.
Cheers
Andrew

Andrew
Did you tried it with p90s? Does the system has just copper windings or also steel polepieces or something like it?

[freefrog]

Today i tried the same (uneffective) p90 dummy bobbin with polepieces, magnets and baseplate. The noise was less but the tone was darker as i expected.

Then i tried with just steel bars instead of two alnico magnets and the tone was better.

I would like to wound something like the ilitch system but i havent tried it before.

My new plan is to wind a very low resistance coil but also putting polepieces and baseplate to have the same geometry with the p90 bobbin.

If I can share a slice of my own experience: I've got mixed results personally with the Ilitch recipe applied to P90's. More turns were necessary than for Fender style PU's and it altered the tone accordingly in my case. A way to solve that would be to make an air coil with a much bigger area,in which case it should be noisier with less turns but where to mount it? TBH, I've contemplated the idea of a wood or plastic baseplate following the shape of a body in order to mount the biggest possible dummy coil on the back of a guitar. Time is lacking for me to do such things now but I can at least share the idea here.

Let's also share what came to my mind while reading the other sentences.

Two P90's in series = roughly twice more inductance, shifting down drastically the resonant frequency. Hence a dark tone, logically (P90's have already a relatively low pitched resonance because of their high inductance, "naturally").

Pulling off the magnets of the pickup used as a dummy coil diminishes its inductance and therefore the inductive value of the two PU's in series. The tone regains some brightness... Again, seems logical to me.

I don't see a baseplate as necessary except to keep parts altogether but i'd certainly keep the most possible magnetically permeable material in the core of the dummy coil, since it should make it noisier (while increasing its inductance too, of course).

in his P90Hx models, Chris Kinman uses a low resistance noise sensor coil with a laminated core avoiding Eddy currents, BTW. But the thin slices of laminated steel are also what helps his noise sensor... to sense the noise. :-P

Patent here, FWIW: https://patents.google.com/patent/US7189916B2/en

Footnote: with a dummy coil having way lower DCR / inductance than the signal coil, a secondary peak should appear beyond the main resonant peak of the pickup. This secondary resonance can generate unpleasing sibilant harmonics if it's in the audio range and some HF noise if located beyond the bandwidth of the cab used... reason why the Ilitch recipe involves a dedicated tone circuit for the dummy coil (it doesn't alter the sound of the signal coil thx to the location of this circuit).

Patent here: https://patents.google.com/patent/US7259318B2/en

FWIW. HTH. If I've done some mistake or ambiguous statement, MEF members will correct my post and I thank them for that.


EDIT - BTW, I've mounted once a series P90 coil with magnetically permeable core as a noise sensor in a guitar with P90's. To correct its darkening effect, I've added in parallel with the whole assembly a RL circuit (resistor + highly inductive tiny coil, not really noisy in itself since it was small). Once tuned, the whole had "realistic" measured specs (right inductance, right resistance) compared to a noisy P90 alone... but without noise. The only downside was a weaker output level, requiring to set the pickups closer to the strings.

[Helmholtz]

As adding ferromagnetic parts to a PU-shaped dummy coil can improve hum cancelling, one might think the reason is increased inductance.
This is not true, even though inductance increases.
From Faraday's law of induction it follows that the induced (noise) voltage depends on B*A*N, where B is the average magnetic noise field (more exactly the flux density) penetrating the coil, A is the area enclosed by each wire loop and N is the turns number.
(Furthermore induced voltage increases with frequency.)
Induced voltage does not depend on coil inductance.

The added parts don't change A or N, but rather increase the B field through the coil due their high magnetic conductivity (permeability).

Generally for series wiring the impedance and inductance of the dummy coil should be as low as possible to not unnecessarily alter the PU sound.
This is best achieved using a large area, low inductance air coil a la Ilitch.

[freefrog]

+1 from the start about higher inductance as an annoying side effect when one tries to make a small dummy coil noisier (and therefore more able to counteract the noise of the signal coil)...

That said and to complete my previous testimonial: if it's necessary to use a dummy coil of the same size than a pickup and with the related downsides, it might be interesting to mount it in series on the hot side of the pickup rather than on the ground side... It might appear as counter-intuitive and that's not a strategy that I'd apply to a wide air coil but with pickup sized dummy coils, putting them on the hot side changes how they reshape the resonant peak and has less effect on the perceived tone. IME at least. YMMV. FWIW.

[cakewalker]

I added a video. The cable is going directly to the amp. This time i wired all of them parallel to see which one is the best for noise cancel.

First dummy is a p90 coil and you can hear that the noise is lowered good.

Second one is a 41 awg and 2.5k air coil. And my question is about that. Was it supposed to cancel noise better because the are is larger?

No matter i connect it series or parallel there is no significant change. I thought that i was connecting it wrong or reverse but i changed the wires and the result was the same.

Third one is a strat pickup around 6k and you can hear that the noise was much lower.

https://youtu.be/pIWm37wlrX8?si=G9bRTmcgjF5faJrt

[freefrog]

Yes, a larger area* should make an air coil noisier and more efficient to counteract the noise of pickups once wired properly.

Reason why (and as supposed by my first testimonial) if an air coil works better with a Strat pickup than with a P90, it needs either a larger area*, either the same area with more turns - I'd try AWG 38 or even 36 rather than 41 BTW: it will be less resistive and therefore more "transparent" tonally.

*Ilitch sells a "rhomboid" coil supposed to fit in the cavity of a Les Paul and to cancel the noise of P90's. It's not of a larger area but it's shaped like a ribbon (rather than a cylindrical or tubular coil), whose flat width helps to regain the sensitivity to noise not permitted by the relatively reduced area.

https://www.ilitchelectronics.com/pr...ncs-in-lp-sdc/

But as I said, the Ilitch recipe works better IME with Fender style single coils and with any pickup, it is more or less efficient anyway according to the location/position of the air coil (relatively to pickups and noise sources).

FWIW.HTH.

[Helmholtz]

No matter i connect it series or parallel there is no significant change. I thought that i was connecting it wrong or reverse but i changed the wires and the result was the same

There should be a significant difference.
Maybe your air coil has shorted turns.

Also a dummy coil can only reduce magnetic hum.
It will not mitigate electric field (aka electrostatic) noise.
The latter requires grounded shielding.

[Jazz P Bass]

Not to derail the thread but this subject got me to thinking about my Fender Jazz Bass Special.
The neck pickups are humbucking while the bridge pickup is a single coil.
I have always had annoying issues with noise on that bridge pickup.
Being a single coil, it makes sense.
So., I Googled it and found that Nordstrom makes a dual humbucking pickup for the bridge.
I purchased the NJ4SV, and it is amazing.
Full sound and absolutely no noise.