I made a simple pickup to fit my modified baritone guitar (tuned it in fifths, and adjusted it accordingly).
My wife made me promise that it would be a "non-destructive" pickup, so no drilling allowed.
I came up with this:
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I sandwiched two 25x5x3mm strong magnets between two popsicle sticks. I made a single loop around the magnets using some electric wire which I had lying around, keeping it in place with two tie wraps. I coupled the single loop with a 1:500 current transformer (Talema AS-104). Finally I soldered a microphone cable to the transformer.
The result is a low Z pickup with a balanced output suitable for a microphone input.
The distance between the two sticks is just a bit wider than the thickness of the top, with the use of two screws the pickup is clamped in the soundhole.
I've made two short soundclips, one with only a wee bit of reverb,
Merry Christmas!
Hans