SV: [sdiy] Active VCO temp compensation

[karl dalen]

Hi George!

The CEM 3374 concept, yes, Xpander, Polaris and OBMx etc.

Mat04 are waste of money in analog polys, all
scaling should be done by the MCU, the simplest
would be to sense the -Vbe point of the expo
then create a scaler routine that takes that
voltage wich are directly temp dependant of the
expo into a tuning offset, lets say at the rate
pitch/temp change. However that would ruin the
Lin FM.
Or just sense one of the trannys in the LM3046
and maintain the Lin FM possibility!
Or place a Tempco on each array and sense that!
Or use Rene S multiplier solution, i.e CEm3340,
but that eats two arrays, one for each VCO!
Or just heat upp the expos!

What about the questions i had for you earlier on George? ;-)

Reg
KD


--- Den sön 2008-12-21 skrev George Hearn <georgehearn at btinternet.com>:

> Från: George Hearn <georgehearn at btinternet.com>
> Ämne: [sdiy] Active VCO temp compensation
> Till: synth-diy at dropmix.xs4all.nl
> Datum: söndag 21 december 2008 19.37
> I'd like to modify my polysynth design to use active
> temperature
> compensation by making the VCO's output a temperature
> reference voltage that
> has a TC of 3300ppm/c.  This would then be used to derive
> the DAC reference
> voltage in order to compensate for the VCO exponential
> converter temperature
> drift.  I would like to do this by using a MAT04 quad
> matched pair or
> LM3046, using two transistors to make the exponential
> converter and somehow
> use the others to generate a voltage proportional to Vt. 
> Does anyone have
> any ideas?  The CEM3374 had this arrangement and it was
> successfully
> employed in the Oberheim XPander and Matrix 12.  Regards,
> George
> 
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