A perhaps slightly-odd guitar project

[dmlandrum]

This is a pretty large project that I've been thinking about for a long time. I want to build my own tap guitar, modeled on the idea of the and the . One thing that doesn't get across in these videos is that the treble and bass sides of the strings are actually on separate channels so they can be processed separately. They do this via custom pickup designs, and given that this is an electronics forum, it's the electronics that will be of interest here, of course.

The other interesting thing that came out in the last year is the . Aside from including the ubiquitous Moog 4-pole ladder filter (yawn) in the guitar itself (more on that later), they also use custom pickups. Not to split the strings up into regions, though, but instead, to include an active magnetic resonant coil per string per pickup, based on the eBow idea. The basic idea of the is that there is a small pickup coil which feeds through an op-amp circuit and feeds out through another coil which resonates a magnetic field in sympathy with the string. Of course, a little thinking shows a few things you can do with this idea, like flipping the output coil various degrees out of phase for different effects. Built into a pickup, you can use the main pickup coil as the signal to feed the circuit for the output coil under each string. The support circuitry can be kept "off to the side", ie, elsewhere in the guitar, to keep the pickup complexity down to a minimum.

What I want to do is to combine these two ideas, and make a tap guitar, with two regions, and with the "infinite sustain" system integrated into each pickup. Instead of putting all the electronics in the guitar, though, and then controlling it all via CV (internal or external). I would rather keep all the electronics external, except what is required for the eBow-like functionality, which would probably be best to stay in the guitar, except for the controls for it, which I think would be best kept in an external pedal.

So I guess my first task is to nail down the pick-up design. Now, coils aren't magic to me. Neither are op-amp circuits. The interesting part that I can't find much on is a way to continuously vary the phase of the signal through the amp. I'm guessing I could do this with some kind of all-pass filter, but I really don't know where to start.

The other thing the Moog guitar can do is to use the output coils in the pickups to mute strings that aren't being played. I'm guessing they detect which strings aren't being fretted by electrically connecting all of the frets and then checking which strings are going to ground. At least, that's the first method I can think of. That sounds like it might not be completely reliable, though. For example, if you energize each string (with a very minimal current, of course) through the bridge and then check which ones go to ground, it seems to me that just touching them with your fingers would ground them. I'm not sure the best approach to take here.

Anyway, this is the brain dump of my more interesting dream project. I belong to another music-related electronics board, but they always do a good job of discouraging large projects like this for some reason. Of course, it's also all analog, which means most here might not be interested. I have nothing against digital solutions, if they should present themselves, though.

[dmlandrum]

Heh. Feel free to disregard this brain dump. I guess I was bored last night. If I ever get around to a project like this, I'll definitely work out the electronics part first, and probably test it by retrofitting an existing guitar. Still, I am a physics major after all, and ideas like feeding a signal to a solenoid coil to vibrate a string are more interesting to me than more practical digital projects.