[sdiy] 1v/oct expo converter front end for SSM2164 quad pole vcf..

[blacet at blacet.com]

Seems like a lot of filter designs do not worry about the tempco. In a VCO
it is mandatory but not so much in a filter. Of course, if you wanted to
use a high Q setting as an oscillator, then it might be nice to have more
accuracy temp wise.


>> Here is a cv summer suitable for a 2164 filter. Based on 10V
>> cv range, it will provide 0-2V to the control pins of the
>> 2164, with 2V being minimum filter freq.
>>
>> http://www.blacet.com/2164cvsum.jpg
>
> Yeah, that looks about right.  If you want tempco, you can put a voltage
> follower after this with a divider on the non-inverting input, and put the
> tempco resistor on the grounded leg of the divider.  I've got a
> spreadsheet
> model for predicting the correct resistor values for the various tempco
> options to minimize tempco errors based on size and tempco coefficient (it
> isn't perfect tempco, but it comes close) if you're interested.  In that
> case, I actually put a fixed feedback resistor on the CV summer and do the
> tuning with a small trimmer on the upper leg of the follower's input
> divider.
>
> I don't use tempco in my own filter builds, but I leave the option on the
> board for others.
>
>