[sdiy] DCO theory

harry harrybissell at prodigy.net
Wed Jun 19 04:39:38 CEST 2002


The Roland charges the cap with an 'almost correct' constant current
source... so the amplitude varies only slightly

H^) harry

mark verbos wrote:

> wouldn't this make the amplitude change with frequency? does the micro
> control some kind of VCA? Is there an AGC circuit?
>
> mark
>
> phillip m gallo wrote:
>
> >I havent thrown one of my Rolands on a scope yet ( may do that tonight ) but
> >wouldnt this make a choppy malformed sawtooth?  Wait. You said Sawtooth not
> >triangle.  I'd still think that you couldnt get a clean waveform this way
> >or maybe I'm just not groking this yet.
> >
> >-->No. The Timer output pulse just saturates a transistor to "short" across
> >the integrator cap to restart the ramp.  In a analog VCO a comparitor's
> >output performs this function.  This is a hybrid  digital modulated/analog
> >oscillator.
> >
> >regards,
> >p
> >
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