digital control of analog component question...

[Rob]

Well, one nifty thing I have seen is that ANY capacitive element in a
circuit can usually be replaced by a trigger spike.
So, for example, if you were to take the cap out of a VCO and replace it
with a periodic trigger spike, the standard VCO circuit should just become a
sort of waveshaper with the trigger determining the frequency. Then you dont
even NEED a stinking D/A..

Now THIS is some food for thought. Imagine the possibilities of a perfectly
in tune VCO, with the same harmonics but without the pesky drift.
I have been meaning to try this for some time, as I saw this very example in
a project at my work and it worked well. Really intriguing, I about yelled
outloud when I came across it in the circuit I was troubleshooting.

Rob

----- Original Message -----
From: Harry Bissell <harrybissell at prodigy.net>
To: The Proteus <proteus at xmission.com>
Cc: <synth-diy at mailhost.bpa.nl>
Sent: Wednesday, January 12, 2000 9:44 PM
Subject: Re: digital control of analog component question...


> I believe that the major difference between the DCO and the VCO is that
most DCO's
> produce a waveform that starts over from the beginning of the wave with
each change
> in frequency...  sort of an unintended reset function. Most samplers work
this way.
>
> VCO's respond with a continuous waveform... even a jump between octaves is
a smooth
> transition... and glide etc is always smooth, not a series of steps...
>
> And some circuits are halfway inbetween... but few... very few...
>
> VCO's... because I can taste the difference....
>
> :^) Harry
>
> The Proteus wrote:
>
> > Gents,
> >
> >         This opens up a whole new topic of discussion on how to
interface
> > the D/A to the analogue circuit. I was grilled on a question about the
> > difference between VCO's and DCO's in an interview for my current
> > employer, and the only difference I could think of is that a DCO is a
VCO
> > with D/A on all the CV inputs. Then it got me to thinking, how many
> > current output DACs there are out there, and even some of them having
> > logarithmic current output. Why have an I->V converter on the output of
a
> > DAC, then go trhough another V->I converter on the input of the VCO?
Since
> > most VCO's I've worked with and built have an OTA current-control gain
> > cell at its core, this could prove to be an advantage both in noise and
> > parts cost. Anyone care to followup on this thread? Any other
differences
> > between a VCO and a DCO that people have noted over the years?
> >
> > The Proteus - Morphing the convergence of technology and passion.
> > -- Musician - Producer - Engineer  -  UNIX Admin Extrordinaire --
> > "...the best workaround for a bug in a UNIX utility is to install
> >  the GNU version" - Kragen Sitaker
> >
> > On Wed, 12 Jan 2000, Magnus Danielson wrote:
> >
> > >
> > > Yes, this is one of many popular ways of doing it.
> > >
> > > Then there are more ways to control curcuits by digital meants, like
CMOS
> > > switches and such. There are also all kind of hybrid solutions by
which the
> > > frequency generation is done digitally but waveshaping is done by
analog etc.
> > >
> > > Cheers,
> > > Magnus
> > >
>
>