Keyboard circuit (was Stretch tuning a resistor string)

[harrybissell at prodigy.net]

If this is the one I'm thinking of... it was a compensated reference voltage output that you use as the DAC REF IN. This way changing temperature will automatically compensate the DAC outputs. A good solution for Monosynth... but if there are multiple VCO which one do you use... or do you add a mux to keep the REF from the same VCO you are "writing" to ???

:^) Harry


 ---- On Jan 20 Haible Juergen <Juergen.Haible at nbgm.siemens.de> wrote: 
> 	>A temperature stable constant current source can be made with an op
> amp and
> 	>3 resistors, such a circuit was used in  the Moog 952 keyboard.  
> 
> I wonder, has anybody built a synth that had a temperature *tracking*
> current source
> to compensate for the expo converter error ? There was a Curtis chip that
> had a 
> temperature sensor on chip to track the reference voltage of a DAC. Should
> be possible
> to do the same thing for the reference of a keyboard resistor string,
> footage switch voltages
> and so on. Not for external CV, of course, which severly limits the
> usefulness.
> But just out of curiousity - has anybody done this ?
> 
> JH.