[sdiy] Building an Ondes Martinot or French Connection style controller?

[Mike Beauchamp]

I've built a few simple portamento controllers, and I want to build a
sort of Ondes Martinot controller (Sort of like the Analogue systems
"French connection" controller -
http://www.analoguesystems.co.uk/Reviews/fconnection_review.htm). I
mean JUST the portamento string-ring interface, not the keyboard
interface. If nobody's seen one before, here's a nice video explaining
one.. http://youtube.com/watch?v=ybYIhomm5KM

I've never actually seen the inside of any of these controllers and
I'm sort of curious as to how they might work. I'm wondering if anyone
has seen inside, or know exactly how they might work mechanically?

My first guess would be to have the string wrap a few times around a
pulley wheel attached to a 10-turn potentiometer (or a geared down
single turn pot, to avoid having a pulley wheel with a circumference
as long as the actual playing field area). I'm wondering if maybe
either of these controllers came up with a way of avoiding the string
from "slipping" on the pulley over the course of time, or if just
wrapping a string around a pulley multiple times would cause enough
friction to avoid this (I'm reminded of old FM tuners, which I THINK
slip over time). Also, if there's something to deal with tension on
the string.. and what kind of string it might be?

The second thing (and this one is a lot more complicated in my mind)
is how the "button" style volume controller works. The best solution I
came up with brainstorming last night would be to have the button a
miniature version of a cry-baby wah-wah pedal, but with a spring so it
returns to it's top position. The lever would be attached to a geared
shaft which would ride against the gear of a potentiometer (just like
in the wah wah pedal).

Mike