Jazzmaster Dial-a-Tap Wiring

Q: What is Dial-a-Tap Wiring?

To understand dial-a-tap wiring, start with the idea of a coil splitting switch (between single coil and double/humbucking pickups). A humbucking pickup is simply two pickups wired in reverse, or out-of-phase. When two coils are wired out of phase, any hum present in both coils will be cancelled, and any signal that is unique to each coil will be let through. A coil splitting switch simply grounds one coil, leaving the other coil in the signal chain–voila, you have a single coil pickup now.

A dial-a-tap simply adds one simple idea to a coil-splitting switch: instead of grounding one coil by a switch, we ground it with a variable resistor/potentiometer–now we can VARY the relative amplitude of one of the coils. With this wiring we can dial up, through that potentiometer, varying degrees between single coil and double coil.

Brilliant!

Understanding the Humbucker

Here is the diagram from Seth Lover’s original patent. There are two coils, with the polarity reversed, and note that they come together at the point labeled “19”, that’s our Center Tap.

Q: What Can You Do with a Dial-a-tap Setup?

Well, you can focus in on a range of sounds. Here is just one use case: say you want a single coil Stratocaster sound but want just a little more beef, a little more thickness and bass that a double-coil pickup will give, you can simply dial up the amount of fatness you want.

Q: Is a Jazzmaster Suited to Dial-a-tap Modification?

Yes and no, well, mostly yes. Jazzmaster default pickups are single coil, so you can’t tap a single coil; remember you need those 2 coils with opposing windings to even BE a humbucker. So, you’ll need humbucking pickups like Curtis Novak JM-HC (the non-humbucker is Curtis’ single coil JM-v). Revel pickups also makes a humbucker, but I haven’t tried them.

What the Jazzmaster does have going for it–and this is a big one–is the rhythm section built in to the guitar: no routing, no drilling, space and bracket for pots are already there….again: Brilliant!

Here is a video of me demonstrating the dial-a-tap wiring:

Here are the basic steps to follow:

You can always order a pre-wired kit from Rothstein Guitars. In fact, I made my kit from a Rothstein kit that I modified. He ships his kits with EVERYTHING you need. Now, if you don’t do the Rothstein kit, or want to mod it, here are some notes/instructions:
You’ll need to source some double coil pickups that have a coil tap. The coil tap means that there is an electrical connection between the two coils of the humbucker. Some humbuckers only have 2 wires, some have 3 wires, and some have 4 wires. The 3 wire or 4 wire humbuckers have a tap.
Now, the Curtis Novak JM-HCs that I used were advertised as “Can add a tap”, although as of 2024, I believe these pickups are sold with the center tap already wired. When I got my pickups in 2020, they had two wires, but a single center solder point between them, but no wire attached. I added the red wire shown here:
An electrical meter is your friend here. I set my meter to Ohms and tested red wire to white, about 5600 ohms, and red wire to black, about 5600 ohms, and white to black about 11000 ohms. Bingo! the red is a working center tap.
There is a schematic which shows the wiring at the bottom of this post.
I tried this wiring first with 500k linear mini pots in the Jazzmaster rhythm section and I got the full range of single-to-double coil between 0 and 1 on the volume knobs. Remember what is happening electrically here…the rhythm section mini-pots, as you rotate, send signal to ground–basically grounding out one of the coils (because you are grounding from the center tap) leaving one of the coils to send signal out the jack. Because it takes very little signal to ground out a humbucker, I found that 100k Audio taper pots worked better than 500k and gave me nearly a full range of variability between single and double coil.
While you’ve got your Jazzmaster apart, why not wrap the entire wiring cavity in copper foil?

Here is the Dial a Tap Schematic I Came Up With

Some notes on this schematic and what is going on here. For a moment, ignore the rhythm section of the wiring (the red and black wires). Without the rhythm section, the wiring is a standard humbucker wiring setup with a 3-way switch and a volume and tone knob that controls both pickups. The rythmn section–all it’s doing is adding a ground in the middle of the two coils of each pickup–that’s it. That grounding removes one of the coils of each pickup leaving one pickup hot to send a signal.