[sdiy] VCO and expo converter question

[René Schmitz]

Hi Roman and List,

> Rene's idea of 4069 (I think) was to make it small and cheap. 

Yes, you got me right. Small, cheap and easy to construct.

Yet for such a simple circuit it has a pretty decent tuning range, and 
tuning curve.

The main drawback of that expo converter is that it uses passive 
summing, and so the inputs might interact due to changing drive impedances.
(When carefully examining my drawings you can see that I used the switch 
contacts of the jacks to ground the unused inputs. Which diminishes that 
problem.)

> If you
> modify it by adding precision opamp and even more precision
> transistor pair (in human language precision=expensive), then why
> bother using 4069 as integrator and schmit trigger. CMOS can't give
> you the stability that your new expo converter provides. I'd change
> it into standard opamp integrator and comparator. But anyway it's
> only my sick opinion. 

What makes you think that it wouldn't be stable?

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159