What all is required of a secondary coil in order to allow it to humbuck effectively?

[John Kolbeck]

I know that on a typical humbucker, both coils are essentially identical, but that in stacked humbuckers, the humbucking coil often uses a different gauge of wire, and is therefore different in some electrical respect from the primary coil, but somehow still manages to cancel out noise fairly completely.

In order for that second coil to humbuck, in addition to being opposite phase of the primary coil, is it necessary for it to produce the same voltage as the primary, or the same amount of current, or both?

[David King]

It needs to have the same orientation and the same turns*area of the sensing coil. It need not sense the string movement at all but it needs to cancel out the noise signal with an equal and opposite voltage I would think. I'm not sure how current plays into this exactly. Then again I'm just a dabbler here and others will be happy to argue whatever it is that they know.

[Richard]

There's another thread here about DiMarzios and their "dual resonance" patent. Anyway, according to their patent, if there are the same number of wraps, even with a different gauge of wire, the hum is cancelled. I don't know how this applies to stacked single coils but I guess that there can be some variation between the coils and still cancel hum.

[LtKojak]

I know that on a typical humbucker, both coils are essentially identical, but that in stacked humbuckers, the humbucking coil often uses a different gauge of wire, and is therefore different in some electrical respect from the primary coil, but somehow still manages to cancel out noise fairly completely.

In order for that second coil to humbuck, in addition to being opposite phase of the primary coil, is it necessary for it to produce the same voltage as the primary, or the same amount of current, or both?

John, search for the patents. It's all explained there.

HTH,

[Mike Sulzer]

I know that on a typical humbucker, both coils are essentially identical, but that in stacked humbuckers, the humbucking coil often uses a different gauge of wire, and is therefore different in some electrical respect from the primary coil, but somehow still manages to cancel out noise fairly completely.

In order for that second coil to humbuck, in addition to being opposite phase of the primary coil, is it necessary for it to produce the same voltage as the primary, or the same amount of current, or both?

This is not necessarily simple because in some designs the permeability of the material in the two coils is not the same. Also the magnetic material outside the coils has some influence and might affect the flux through the two coils differently. The idea is to produce opposite voltages from distance magnetic fields (that is, farther away than the strings). Since the two cols are in series the currents will be the same (except at very high frequencies where different coil capacitances could have an influence) and a function of the external circuit.

Some designs attempt to keep the magnetic circuit of the top coil isolated from that of the bottom coil to keep the flux from the strings out of the bottom coil, thus reducing cancellation of the signal.

[J M Fahey]

Agree on the same voltage, opposite phase rule for hum cancellation; if in series current will be the same on both, by definition.

Now to do it on purely passive pickup system it's difficult (not impossible), specially while developing it, because for full cancellation both pickups must prodce exactly the same hum signal; fine tuning may involve winding more or less turns.

Of course, once found, you can make thousands more or less easily.

The only humbucking system I had in my hands was an Alembic Bass, long ago, and as far as I remember it had a hidden third coil between the two visible ones, but the system was active, so a trimpot could fine tune to perfect cancellation.