Moog Guitar pickup - how does it work?

[uvacom]

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.

[Mark Hammer]

I would say a better place to start is to go to a place that has one and actually use it. The problem is that what people write for ad copy or even for product reviews is not necessarily the most descriptive or accurate.

[uvacom]

I would say a better place to start is to go to a place that has one and actually use it. The problem is that what people write for ad copy or even for product reviews is not necessarily the most descriptive or accurate.

Nobody in my city has one that I know of. Besides, unless they let me tear the thing apart (highly, highly doubtful) I'm not sure what I'd gain from the experience that I couldn't get from audio demos, in terms of understanding the inner workings of the device.

I think I found the patent, anyway - Activity indication, external source, and processing loop provisions for driven vibrating-element environments - Patent 6610917

It looks like they might actually use separate coils for generating and sensing (although it doesn't actually *say* that, they are just different functional blocks on the provided diagram), but otherwise the concept is pretty much what I imagined. It does mention a piezo as the drive transducer and a hall effect sensor as the vibration sensing transducer, but also mentions that as only a possible implementation. Guitar pickups are also mentioned as possible drive and sensing transducers. Since the piezo output is simultaneously available, I don't think the actual moog guitar uses the piezos as drive transducers.

[David Schwab]

Are you sure that's the patent? The Moog guitar was designed by Paul Vo, and that patent is issued to Lester F. Ludwig.

My guess is the Moog guitar uses the piezos as the string signal to run to the string driving coils. This way they eliminate the feedback loop if one of the pickups is sensing the strings, as with regular sustainor circuits.

The shape of the pickups seems to indicate that they are split coil humbuckers, or they use an active dummy coil system.

I've been wanting to try one out. It seems very cool. The fact that the system can dampen the vibration of the strings is really freaky.

[uvacom]

Are you sure that's the patent? The Moog guitar was designed by Paul Vo, and that patent is issued to Lester F. Ludwig.

My guess is the Moog guitar uses the piezos as the string signal to run to the string driving coils. This way they eliminate the feedback loop if one of the pickups is sensing the strings, as with regular sustainor circuits.

The shape of the pickups seems to indicate that they are split coil humbuckers, or they use an active dummy coil system.

I've been wanting to try one out. It seems very cool. The fact that the system can dampen the vibration of the strings is really freaky.

Paul Vo designed it, but whose to say what the product development looked like? Maybe Moog was like, "Hey Paul, one of our engineers just had the mother of all wet dreams and the U.S. patent office just granted us this incredibly broad patent for everything from an electromagnetic sensor-driver arrangement to a chemical chaos interface, see what you can do with it!".

Anyway, there's creative marketing, and then there is blatant lying, and if they say the pickup is a single coil design and it drives the string at the same point it senses it, but they use a humbucker and use the piezo pickup as a sensor, well they are lying. Personally, I don't think they're lying. Moog has a track record of producing forward-thinking instruments.

At any rate, I think controlled feedback of some kind is really at the heart of what makes the system work.

[Mark Hammer]

Looking at the patent, it is a MUCH more expansive all-encompassing thing than the final Moog guitar incorporates....and I thought the Moog was "busy".

[uvacom]

Yeah, the patent is pretty broad, but the *primary* invention at least appears to be a system to sense and control vibrations from e.g. a string. That's what makes me think it has to do with the Moog guitar. But even at that, it's vague.

[David Schwab]

Looking at the patent, it is a MUCH more expansive all-encompassing thing than the final Moog guitar incorporates....and I thought the Moog was "busy".

Plus they say the pickup is patented, and I don't see a pickup design in there. That's also a 10 year old patent. I doubt they would have waited so long to market the guitar... the patent will expire too soon.

I think they applied, and they might have the details hidden to stop people from copying the patent until it is issued.