[sdiy] Hi / search? / programmable resistor for VCO?

[The Old Crow]

   Hi David,

   I am familiar with the circuit.  What you want is a programmable 
current sink.  Something like a DAC driving an exponential V/I 
converter.  I did this for range setting in my CS VCO module. Well, the 
DAC was external, but you get the idea. ;) --Crow

On 1/6/2014 10:24 PM, cs80 at therogoffs.com wrote:
> Hi all.
>
> Thought I was already subscribed here but I guess not…   I have an idea/questions about a digitally controlled resistor for a VCO.
> However, inspired by the weird Yamaha IG00153 VCOs in the CS80/60/50, I was looking at controlling the resistance.  In these synths, the keyboard/DAC generate exponential CVs for the VCO’s linear input.  However, this has a limited range and the octave switching is done by selecting different resistances to ground using FETs and some extra circuitry to clean up offsets.