[sdiy] Thought experiment...

[James Patchell]

Well, here is the solution I came up with for eliminating the 
Tempco...(Scott Bernardi worked on this with me)...

http://www.oldcrows.net/~patchell/synthmodulesII/200-1007.pdf

This methode of compensation work extremely well.  I used the second pair 
of transistors along with the expo converter to make a simple band gap 
reference and use the PAT voltage to control the gain of a very linear VCA....

At 08:08 PM 3/21/2005 -0500, D A F wrote:
>Hi all,
>
>I was taking a look at the schematic for the music from outer space VCO 
>board, when I got an idea concerning a possible way to elliminate tempcos 
>from VCO's.  I'm sure someone has probably thought of this (like 40 years 
>ago) but in any case, here goes...   If you had a quad of matched 
>transistors on a single substrate (such as in the new THAT 300 series), or 
>at least two thermally coupled pairs, couldn't you send one pair a 
>positive-going CV and the other pair a negative-going CV and then send the 
>two outputs to a differential amplifier, such that only the difference 
>signal would be amplified.  This would elliminate the change in current 
>with temperature from the final output, because it would be equal in both 
>pairs, assuming perfectly matched and thermally-coupled devices, and the 
>diff amp would 'ignore' it.  Any thoughts?
>
>
>Dave

         -Jim
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