Moog Guitar pickup - how does it work?

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Moog Guitar pickup - how does it work?

Post by Fianemoti » Fri Nov 15, 2019 5:16 am

The Moog Guitar is (at least on paper) by far the coolest guitar ever. But I cannot afford one, so I'd like to reverse engineer it. I think I have a good idea of what it does, but I'd like to start some discussion so I can find out how off-base I am.

What we know: Moog says their system is "not a sustainer", "listen[s] and control[s] each individual string at exactly the same point", and is a "single coil design". They describe how each pickup can independently reinforce or cancel the strings vibrations at its own point to generate complex harmonics, so I think it is improbable that the piezo pickup is an integral part of the system.

What I think this means is that each string has its own coil which fundamentally works like a regular single coil in the way it senses - but it also works like an electromagnetic generator at the same time with the control signal being driven from one end and the output taken from the other end. The control signal and the output are fed into a differential amplifier, and since the control signal is common to both signals but the signal generated from the strings is not, the control signal is canceled. The only missing piece from that which I can think of offhand is that the series inductance of the coil would shape the control signal which is mixed with the output signal, so the cancellation might not be perfect ("perfect" relative to the CMRR of the diff amp, that is) - there is probably a workaround for that.

The control signal itself is a variable gain amplifier whose output can be configured between inverting and noninverting for vibration reinforcement/cancelation (respectively?). The input signal to this amplifier is the output of the pickup.

The pickups are a diamond/parallelogram shape overall, and rather wide - so I think the polepiece is a blade and the coils are oblong and offset from the parallel of the strings by about 20 degrees or so to allow larger coils and a wider string sensing area for each string.

That's my hypothesis on how it works, anyway. Maybe I'll get a chance to try this out over winter break - I can build a test rig with a couple of nails on a 2x4 with a .010 string tied on.
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