[sdiy] New Vco

[René Schmitz]

Hi Jürgen and all,

>Nice little oscillator, René !

Thanks!

>How's the tracking for higher octaves ?
>The discharge current from the 4069 cannot be very large,
>but then again the output resistance of the "integrator"
>inverter may do some compensation ...

The ought to be high frequency compensation if you really 
need the higher octaves. Reset time is about 1us. The 
oscillator goes flat. I don't think the output resistance 
does compensate, the reset thresholds of the schmitt aren't 
affected by that. A small Franco resistor could help. Rbe is 
not that much of a contributor IMO, these BC5xx transistors 
have pretty low Rbe.

>I've once designed a little EMS-style variable Sine shaper
>around a 4069 - maybe some time we'll have a CMOS-only
>little synth ! I'll take a look if I still have the drawing.

That should be possible, I have another little project up the 
sleeve, a state variable + VCA where the OTAs have been replaced by 
linearized mosfets. Opamp integrators though.

I noticed the compression in the summing stage for the pulse. There 
is also some squashing. (Hmmm, you can modulate with triangles, and 
get a sort of sine action...)

Cheers,
 René


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