[sdiy] Newbie question regarding the 4069 VCO

[Harry Bissell Jr]

My application was a switch... but its food for
thought

I didn't notice the shorting jacks... I suppose if I
had the right switch contacts, I could achieve the
same goal. Eliminating the opamp would have been a 
good thing for me, oh well too late now

Thanks

H^) harry


--- René Schmitz <uzs159 at uni-bonn.de> wrote:

> 
> Hi Harry and all,
> 
> harrybissell wrote:
> > One caveat of the summing design... (which I
> mentioned to James offlist) ...
> > is that it is
> > "almost" a current source (as Rene says) .   If
> you change the input impedance
> > of one of the nodes (such as by changing it from
> an open circuit, to lets say
> > an opamp feeding from an LFO with zero volts...
> > you will change the pitch noticably !   In a
> modular this might not be a
> > problem, in a stand-alone
> > synth this must be designed around.   If you hold
> the modulation inputs at all
> > times (with voltage
> > follower opamp outputs) you will not have an
> issue.
> 
> Thats true, and the reason why there are switching
> jacks shown on the 
> layout. The unused input is switched to GND to keep
> its input impedance 
> more or less constant. (One of the design goals was
> "no opamps"...)
> 
> Cheers,
>   René
> 
> -- 
> uzs159 at uni-bonn.de
> http://www.uni-bonn.de/~uzs159
> 
> 
>