Keyboard circuit (was Stretch tuning a resistor string)

[Tim Daugard]

Does anyone know where I can find the schematic for this?

> On a related note, someone mentioned never having seen a temperature
> compensated constant current source in a commercial synth keyboard. The
> Arp 2600 ( If I remember correctly) had a diode as part of the constant
> current transistor's base bias divider. This was in there to help cancel
> the VBE drift of the transistor, and thus give greater stability under
> temperature swings.

I have been using an led to set the base bias point for the current source
(V+ to Led (V+ -1.6V)  to [base connection] to Gnd. The emitter is Vcc to a
resistor (fixed or variable) to emitter. Transistor is PNP which gives a
good current regulation. I haven't checked actual temp or load regulation of
this circuit yet. I was using the circuit to provide a constant current
source for a 555 to get a ramp voltage instead of a capacitor curve. If any
one has an interesting current source I'd be interested. I'm trying to build
a low cost synth with each module under $5 so far the only two modules that
have broke the budget is a power supply (transformers cost too much) and a
distortion effect/mixer (8 pots).

Tim