[sdiy] 4069 VCO again

[jbv]

Hi René,
Thanks for your detailed reply.

>
> > - I didn't found anything about stability & calibration...
> > any clue ?
>
> Well, I have not made any serious tests with regard to the stability.
> But my guess is that you could improve it with a expo which employs a
> monolithic dual, instead of the glued-together transistors.

Any recommandation for an easy-to-get dual transistor ?

>
>
> > - I was wondering how this little thing would behave
> > in a polyphonic context (several such VCOs in parallel)...
> > any risk to see them lock together ? decoupling issues ?
>
> I would recommend to use seperate supply regulators to keep soft sync to
> a minimum. The CMOS has large current drain when transitioning, so there
> is some chance for syncing. (As with any circuit with a non constant
> current drain.)

do you mean 1 real supply regulator for each VCO ?
or could a 2.2 ohms resistor (between Vcc of each ic and positive supply)
with a 100 nF decoupling cap be enough ?
I've successfully used that technique with some LM3915 driving bargraph
LEDs for instance...

>
>
> > - how to modify it to accept 1V/oct VC from a uC + DAC
> > + SH expo converter ? I guess it'll make the circuit even
> > simpler...
>
> That depends on how you want to implement it of course. Beware though,
> that the integrator current is sunk into Ub/2 and not GND, which makes
> this a somewhat challenging.
>

which means it isn't for me, as my analog sdesign skills are pretty
limited...
the purpose was to make the design simpler, while increasing performance
by digital control of the expo converter...
I guess I'll stick with a dual transistor, and generate regular 1V/oct with

the uC & DAC...

Best,
JB