Dual Wire Wind? (Alternative to tapping/splitting)

[mcgruff]

Cunning plan: begin winding a coil with two strands of wire. After (say) 1/3 of the total number of turns, end one strand of wire and finish the coil with a single wire, as normal.

You now have two interleaved coils which you can connect in series for full power or "split" to 3/4 power (technically also 1/4 power although that option will likely sound horribly thin).

Anyone tried this? Maybe there are good, technical reasons not to which I'm not aware of.

[Helmholtz]

What would be the expected benefit compared to a tapped coil?

When you connect 2 coupled coils having same turns in parallel, nothing changes.
That's different from paralleling 2 independent coils, where inductance would be halved.

[mcgruff]

A better split sound with low-wind humbuckers.. maybe? A single coil on its own is usually too weak. This would let you set up a split sound which doesn't depend on the humbucker's coil size. Cut any number of turns of wire you like from each coil in the humbucker. And it would be fully humbucking.

[Helmholtz]

Please elaborate.
What configuration are you thinking of which wouldn't be possible with tapped coils?
A drawing would help.

[mcgruff]

This is what I was thinking of. Two coils on the right on one bobbin, two on the left on the other.

But I've over-complicated things. You don't need to run two strands of wire to achieve this. Just tap both coils. Doh!

Thanks for being patient. It helped me to clarify my thoughts.



Or this:

[Helmholtz]

Whenever you short many turns on a PU (as in your first pic), you're more or less killing the output.
Reason is the magnetic coupling like with a transformer

[mcgruff]

Thanks. The second schematic then, if I do this. That would mean either 6 wires to take to the control cavity from each pickup (!) or build switches into the pickup rings.

[Helmholtz]

But the second pic would give you the same results as with a humbucker having tapped coils.

[John_H]

Roland, do you think there could be significant capacitive coupling with two coils on the same bobbin?

[Helmholtz]

Roland, do you think there could be significant capacitive coupling with two coils on the same bobbin?

Hi John,
there will be some direct capacitive coupling between the coils but the major additional capacitive load would be due to reflected capacitance from the magnetic (or transformer) coupling.
The latter means that the sheer existence of a second coil on the same bobbin will increase the effective capacitance across the first coil even if the second coil is not used/connected.

[John_H]

Thanks Roland, and Hello back The capacitive coupling was the first though I had. That capacitance in concert with the reflected capacitance would create a high Q scenario. Any thoughts?

[Antigua]

This is what I was thinking of. Two coils on the right on one bobbin, two on the left on the other.

But I've over-complicated things. You don't need to run two strands of wire to achieve this. Just tap both coils. Doh!

Thanks for being patient. It helped me to clarify my thoughts.



Or this:

The second diagram is much better, because you don't want the unused coil to have electrical continuity. If it has continuity, then it becomes like an eddy current load and sucks up output and lowers the Q factor. If it doesn't have continuity, its still in circuit, but as a capacitance with respect to the primary. That will lower the resonant peak, but not the Q factor.

It's interesting to ponder whether the damping of the unused part of the coil would look different having the second coil laid beside the primary coil turn for turn, rather than having the unused coil entirely inside or outside of the primary coil, which is what happens with an ordinary tapped coil. I would guess your method would mean more capacitance, because the average and overall proximity between the primary and secondary is closer than if the secondary was entirely inside or outside of the primary coil.

[Zorshelter]

I tried winding with two wires at the same time on one bobbin, then connected in series, I put it in a humbucker with a 'normal coil I had laying around, this first attempt is strange sounding, I started doing a bode plot (and stopped it midway)for the pickup and it had kind of a plateau till maybe 800hz then big decrease and up again, kind of a U shape bode plot, sorry for not being precise, I had to leave sson after finishing the pickup and didn't run the tests I usually do,

The strange thing is that when I mesured the coil by itself (no screws, not assembled in the pickup), it had normal Resistance reading but the inductance was really low and the capacitance extremely low (a few nf if I remember correctly), don't know if this helps...

[Helmholtz]

The strange thing is that when I mesured the coil by itself (no screws, not assembled in the pickup), it had normal Resistance reading but the inductance was really low and the capacitance extremely low (a few nf if I remember correctly), don't know if this helps...

Not really surprising.
Low inductance is the result of the 2 coils being electrically out-of-phase. Reverse the ends of one coil.
Low capacitance - certainly no.
A nF capacitance is very large, as 1 nF equals 1000pF.
This large capacitance is due to the close proximity of the 2 bifilar coils.
Excessive capacitance is the main reason why bifilar winding is no good idea with PUs

[Helmholtz]

Thanks Roland, and Hello back The capacitive coupling was the first though I had. That capacitance in concert with the reflected capacitance would create a high Q scenario. Any thoughts?

Sorry for the delay, John. I had to think about your question.
With a series resonant circuit like a PU the Q (and thus the height of the resonant peak) depends on the square root of L/C:
https://en.wikipedia.org/wiki/Q_factor (scroll down to RCL circuits).
Means that a higher C lowers the Q-factor.

But more important than Q is that a large C means a low resonant frequency and thus poor HF response.