Humbucker coil tap with passive shunt, or Shuntbucker.

I have been fitting the pickups to my guitar build and they came with five wires. A shield wire and green ground wire combined. The coil tap connection red and white together and black for hot. It occurred to me whilst wiring it all in that simply shorting out the bottom coil to ground to coil tap whilst giving a good single coil sound, was a bit simplistic and short sighted. There has to be some use for the output of the now shorted coil other then dropping it to ground.

The easiest mod would be to short it to ground with a capacitor. This way I should get the brightness from the top coil but with some added bottom end and a small amount of hum-bucking from the bottom coil. If you plot the impedance (AC resistance) of say a 47nF (0.047uF) and 100nF capacitor you will get the following impedance values.

If  I presume that the _average_ impedance of each coil would be say 3k then you can see that with the 100nF capacitor (red plot) half of the output of the shunted coil will be lost via the capacitor at 500Hz.  Without some complicated measuring I can't be sure exactly what the impedance of the coil will be at a particular frequency. I do know how the capacitor works though and it had to be worth a go. I went with 47nF (blue plot) in the end and am very happy with the effect on the bridge humbucker. Below is the diagram showing the two coils from a humbucker and how the capacitor shunts the bottom coil.

Shuntbucker with frequency dependent shorting of unused coil.

It has a distinct change when tapped as you would expect but the pickup has a lot more balls, more P90 than strat sort of sound. For the bridge pickup this is ideal for me as I never found a use for a single coil bridge position. After trawling the net I did find that this is not a new idea, coil cut was a term I found amongs some others. Considering the simplicity of the modification, and the potential in using more complicated passive networks I am a little lost as to why the vast majority of sites will just short out the one coil and concentrate on additional phase and series parallel switching.

I think the major pickup manufacturers have also not actively brought to the fore this simple modification or even re-voiced there own pickups with a passive shunt so that when taped you get something better sounding. Combining a capacitor, inductor and resistor network across the lower coil could tailor curves into the pickup and tailor the response beyond wire gauge, turns and ad-hoc parasitics. It seems a vastly unexplored path, maybe it needs a name people can identify with, so maybe coining the term Shuntbucker would help it stick in the conscience.

EDIT:

I have found that as per the follow on article “Pickup Frequency Response Measurement.  Humbucker, Single coil and Shuntbucker” this really needs a series resistor with the capacitor to make this work. The issue is that the capacitor and coil inductance are too resonant and the transition results in the mid-range being swamped.  I have found that a 47nF and 3k3 resistor across the bottom coil works well for me.