The motor speed control circuit is a mess of incomprehensible resistor networks, but it all boils down to the diagram on page 4 of this datasheet - http://www.rcscomponents.kiev.ua/datasheets/upc1470ed3iuf.pdf- "RT" controls the torque and "RS" controls the speed.
RS is selected by the 33/45/78 switch, and RT is controlled by the pitch knob. So when you're varying the pitch you're actually varying the torque, dunno why it's set up like that. I'll rip it all out and experiment with different values of RT and RS when I get a chance - maybe we can get more torque at low speeds.
Yeah man I'd love for other people to have a go at building this thing, hit me up if you have any problems with it. Here's an updated version of the schematic that should be a bit more flexible as it has input signal biasing (will work on devices other than the PT-01) :
Yeah man, will have a few of these made up and see if anyone wants to buy them.
If you wanted to put them as a standalone faderbox you'd probably want to add input and output buffering, which is simple enough but would have added another 6 opamps to the design (so at least another 2 chips).
Yeah man that's me, hit me up on facebook. I'm nearly finished the PCB design, here's what I've got so far :