[sdiy] Henry Walmsley's page

[David G. Dixon]

Yes, Ian, I hadn't really thought about it (indeed, I spent all of about
three minutes looking at the schematic), but it would be very difficult to
get this VCO to track even above about 1.5 kHz.  I'd only just read
something about V-F chips in H&H recently, but didn't really make the
connection, as I have no prior experience with them.  .

This thing is basically an analog wavetable oscillator, isn't it?  Is this
similar to how DCOs are driven? 


> Since the VCO core is just used as a clock, it seems to me that it would
> make *much* more sense to use a F-V chip (charge balance oscillator)
> rather than a switched integrator.  I used the LM331 for my DoubleDeka
> VCO, and it has phenomenal tracking up to well over 100kHz, and rock
> steady temperature compensation using the Pease scheme.
> 
> For the OTA-based VCO it will be difficult to get the core frequency over
> about 40kHz with decent tracking -- and even that will take quite a bit of
> effort. That will leave you with a max frequency of ~2.5kHz.
> 
> As far as needing an interpolator, well I guess that's a matter of
> taste.  I actually like the steps -- it gives the sound its own special
> character, and it's easy enough to filter down to a smoother waveform.  (A
> single pole filter changes a step into a ramp, no?)
> 
>    Ian