VCOs for home-built modulars - update

SuperBAD MoFo mr808 at
Thu Aug 31 20:23:26 CEST 1995

gstopp wrote:
> >     THE CHROMA VCOs:
>      I got the Exar 4151's in the mail (thanks Ric!) and made a dual
>      sawtooth VCO per the Chroma schematic. This dude has a sweep range
>      from around 60 hertz (try to go lower and oscillation stops) to
>      just above 30 khz. Waveshape ranges from a very jittery
>      rounded-off rising saw at the low end, to a fairly normal-looking
>      saw in mid-frequencies, to a half-sawtooth half-square-wave mutant
>      thing around 15 khz, to a train of narrow pulses around 25-30 khz
>      before they dwindle away into thin spikes.

Sounds like you have a problem w/ either your construction techniques or 
your substitutions - my Chroma has no problem oscillating at low 
frequencies.  I think the sawtooth does flatten out on the bottom a 
little bit at high frequencies, but this doesn't really have an audible 
impact on the harmonic content.  Not sure what happens in the ultrasonic, 
but what are you doing that requires an ultrasonic oscillator anyway?


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