VCOs for home-built modulars - update
jocke at netcontrol.fi
Fri Sep 1 09:13:04 CEST 1995
> 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.
I've had similar experiences with my home-built Chroma VCOs - no problems
at low frequencies. If I remember correctly, the sawtooth stops at around
5 Hz with the 1000pF integrating cap. I did, however, try to make the
integrator input/charge pump output trace as short as possible.
At high frequencies, the 20us blanking period becomes visible on a scope,
and the ramp less steep since the exp generator 'steals' an increasing
amount of current from the charge pump. This is the cost for having good
control current <-> frequency linearity.
But as mentioned before, the obscurities with this design are mainly
visible, rather than audible.
> I can't back this up but I think that human perception goes beyond
> 20Khz. Maybe it's just a tingle at the back of the neck or something
> that bypasses the ears but I swear there's something up there.
That's why d*g*t*l synths are what they are.... :)
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