[sdiy] Smith's Evolver Desktop's spikey VCO waveforms

David G Dixon dixon at mail.ubc.ca
Thu Jun 6 19:01:24 CEST 2013

> > > but the 'normal' notches on triangles I know are right on 
> the tip of the wave and (IIRC!) symmetric on both halves.
> > 
> > The ordinary simple way of constructing the triangle from a 
> rectified sawtooth gives this glitch (if nothing more is done 
> to prevent it). It's just on the tops OR the bottoms though!

Yeah, but unless the saw-tri shaper is built of old duct tape by hamsters,
the glitch shouldn't be that prevalant or ragged looking (given that it is
just a slew-rate issue in the rectifying/inverting opamps, it should just be
an elegant little spike), and it should be right at the apex of the
triangle, not several degrees prior.  Plus, this glitch seems to infect all
of the waveforms, and not just the triangle.  Why would a tri-shaping glitch
show up on the pulse wave, for example?  It looks like some kind of clock
noise infecting the PSU to me.  Plus, the pulse looks very dodgy.  (I must
say I'm not terribly impressed with the quality of the waveforms in those
scope shots.  I would offer a VCO with waveforms like that for sale.)

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