[RE: VCDO]

[David Halliday (Volt Computer)]

Been discussed a bit here - problem is that the loop doesn't track the
incoming frequency exactly and there is a bit of "portamento" as it settles
down.

Probably useful as an "effect" but not as a precision oscillator.



-----Original Message-----
From: Gene Zumchak [mailto:zumchak at cerg.com]
Sent: Thursday, April 08, 1999 6:06 AM
To: Karl Helmer Torvmark
Cc: Harry Bissell; Dave.Peachey at natwest.com; synth-diy at mailhost.bpa.nl
Subject: Re: [RE: VCDO]


Guys,

    I have another idea, and there is probably somebody that can implement
it.  Use
a simple voltage controlled high frequency oscillator and divide it down by
the
number of samples you want to have per waveform, say 64.  Use a phase-locked
loop to
lock the 64 times oscillator to the audio frequency you want to create.  The
audio
frequency is taken from an audio exponential front-end VCO.  The result will
have
the same accuracy and stability of the your audio VCO.  The audio VCO is not
intended to generate tones, just a square wave for phase locking and can be
consequently as simple as possible.  Any comments?

Gene Z (the other Gene)



Karl Helmer Torvmark wrote:

> On 7 Apr 1999, Harry Bissell wrote:
>
> > Gentlemen; Check out Linear Technology App note 14:
> > Designs for high performance V-F converters (by Jim Williams) How about
a 1 Hz
> > to 1MHZ V-F converter, .06% linearity, 25ppm/Deg C. gain, 50nV/Deg C
zero
> > shift, 0-10V input range. You have to add your "Expo converter Du Jour".
Other
> > designs impressive. Expensive. And probably need a really professional
job at
> > circuit layout to get even close to that performance. But it's probably
a
> > better deal than trying to overdrive and audio VCO. No, I haven't tried
it
> > myself. (Jim Williams is in a league with Bob Pease, thet're just on
different
> > teams...)  Harry
>
> I've been looking into this myself. Unfortunatly, the Linear parts
> specified are hard to get (at least here in Norway). But, I've managed to
> scrape together what I need, and I'm planning to make a PCB and test it
> when I get the time (I'm swamped with school work just now, so this will
> take a while). Nontheless, I think this design looks like just what is
> needed for wavetable synthesis and other projects which need a high-speed
> oscillator.
>
> --------------
> Karl H.