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

Michael Zacherl sdiy-mz01 at blauwurf.info
Thu Jun 6 21:31:31 CEST 2013


On 6.6.2013, at 19:01 , David G Dixon wrote:

>>>> 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.

hear, hear! 

>  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?

that's what I tried to point out, also by saying it's on both VCOs and looks similar.

>  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.  

neither am I. Then again, also as Tom (indirectly) pointed out, it's the ears which decide.
And the Evolver's 'character' is ... errm ... gritty.  ;-)

thanks for making the point! 

> I would never offer a VCO with waveforms like that for sale.)


Where's your shop? ;-)

m.

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