Two coils, one bobbin

[Chris Turner]

So, I was thinking of trying this for the giggles:

Picture a simple J bass single-coil pickup... now what I wanna do is wind another coil on top of the single coil that's already there. The coil would be wound directly on top of the existing coil, and would be wound in the same direction, around the same pole pieces/magnets. Kinda like 2 coils in parallel, I guess you could say.

What are the drawbacks, if any, of doing this? I'm gonna do it regardless, but I'm just curious to hear anyone's thoughts on this.

[bbsailor]

So, I was thinking of trying this for the giggles:

Picture a simple J bass single-coil pickup... now what I wanna do is wind another coil on top of the single coil that's already there. The coil would be wound directly on top of the existing coil, and would be wound in the same direction, around the same pole pieces/magnets. Kinda like 2 coils in parallel, I guess you could say.

What are the drawbacks, if any, of doing this? I'm gonna do it regardless, but I'm just curious to hear anyone's thoughts on this.

Chris,

As a learning experience here are the issues that you may observe.


1. The space available for the new outer coil may be limited. Assume that you put the same number of turns of AWG 42 or 43 over the inner coil, and wired it in parallel, you would reduce the impedance by about half.

2. The added capacitance of the outer coil would reduce the resonance point.

3. The output of the outer coil, because it is farther from the core magnets, would be about 30 percent less than the inner coil.

4. If you wound about 10 ohms of AWG 28 to 30 magnet wire over the inner coil and connected it to about a 100 ohm (even up to about 500 ohms) to 20K ohm (even up to 200K ohms) step up transformer you would increase the output voltage by about 44 times (for the 100 ohm to 20K transformer) and could do the following:
4.1 Wire and switch the transformer output in series and parallel with the inner coil for tonal changes.
4.2 Switch between the inner coil and the outer coil (connected through the transformer) for a sound with less capacitance and a higher resonant point
4.3 Try a variety of audio transformers to learn about optimum matching for a better understanding of low impedance pickups.
4.4 Try putting a variety of tone circuits (high cut with capacitor or band pass with a coil and inductor) on the outer coil/transformer to shift the resonance point to emphasize or attenuate various frequency bands.

Your best learning will occur if you have an Extech LCR meter and a USB oscilloscope to observe and measure the output. Keep good notes and share your results.

Joseph Rogowski