[hackerspaces] Musical Instrument Magnetic Pickup Coil Design Questions

Hank The Curmudgeon hkrishman at gmail.com
Tue Jan 19 18:23:01 CET 2010

I have several questions regarding magnetic musical instruments pickup
coils. I am beginning to think about designing a tuned resonance rod
instrument where the oscillations of the rod’s free end are converted
into an electrical signal.

Question Number 1: Conventional design places a magnet on the rear end
of the coil’s core. Would there be any difference in voltage (signal)
generation if the magnet were mounted on the tip of the resonance rod
verses the back of the coil core?

Question Number 2: What is the standard impedance input value of a
typical guitar practice amplifier, which is what I am going to be
using during initial testing, for audio reinforcement? I'm
anticipating a total of five pickup coils in my instrument. For sake
of argument let's say the needed impedance input was 100 ohms. Should
each of the coils be wound to an impedance of 20 ohms and wired in
series? Or should the pickup coils be wired in parallel? If wired in
parallel would I need to use diodes to isolate the coils for total
signal out at that point?

A few design details to throw into the mix:

- The resonance rod and the coil core are in axial alignment when the
resonance rod is at rest. Initially the rods will be sent into
resonance by the impact of a drumming mallet.

- The air gap between the tip of the resonance rod in the end of the
coil core will be relatively substantial (1”) if I can mount the
neodymium magnet on the end of the resonance rod.

- The number of windings and wire gauge on the coil are currently open
to change as needed/desired.

- The coil’s output will be fed into an analog synthesizer for

Thanks in advance for the assist in this matter!

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