AW: [sdiy] ICL8038

[patchell]

    My experience with both chips (8038 and XR2206 as well as the XR2207), is
that the XR chips were much easier to apply than the 8038.  If you can locate
the XR chips, I would go with them.  But personally, I would not bother with
either.  I would stick with the OTA type oscialators for triangle cores and the
ASM-1 type oscilators for sawtooth cores.

Czech Martin wrote:

> I have the feeling that this IC has some problem
> with wide range sweeps. And AFAIR you need a PNP expo pair, because current
> has to come from the power rail. But I may be wrong.
>
> When I was young (16) I built a nice VCO using a XR2206 and CA3046 expo
> pair. I remember that it worked
> imediately with a very wide sweep range, more then 1:10000. Of course, you
> can't have sine and tri at the same time with this design, but the sine is
> much cleaner than what I got out of the 8038.
>
> No saw also, but sqa. A tri to saw converter is a no-magic, and the sine can
> be fed into that, too.
>
> I remember that some pll projects in my favourite mags always used the
> XR2206 chip, never 8038.
>
> So, perhaps you would like to have a look into the data sheet as well.
>
> m.c.
>
> > -----Ursprüngliche Nachricht-----
> > Von: Tavys Ashcroft [mailto:bigtex at cwnet.com]
> > Gesendet: Samstag, 9. Juni 2001 10:45
> > An: Synth-DIY list
> > Betreff: [sdiy] ICL8038
> >
> >
> > I've been pretty interested in using the ICL8038 as a VCO for
> > non-precision stuff.  Right now I'm just getting started with the
> > whole synth-making thing, so I'm not too worried about perfection.
> > This chip looks really good, though, because I could use all three
> > waveforms, have a large frequency sweep range, and adjust duty cycle
> > all very easily.
> >
> > Now I was just on the music machines page and a brief .txt file
> > mentioned an electronotes circuit which gives a much larger frequency
> > range and is much more useable as a VCO.  Does anyone here know where
> > or how I could find such a schematic, or where I would start out to
> > design something like this from scratch?
> >
> > The description was as follows:
> >
> > In typical Electronotes fashion there follows a "cheater" circuit for
> >       the 8038 which bypasses the current-to-voltage problem
> > altogether and
> >       injects exponential current directly into what would
> > normally be pins
> >       for timing resistors, making the VCO exponential with a 30,000:1
> >       voltage/frequency sweep. The outputs are Sine,
> > Triangle, Sawtooth,
> >       Square, and Pulse (with PWM). This circuit uses an NPN matched
> >       transistor pair, followed by a PNP matched transistor
> > pair, along with
> >       5 op-amps and a FET.
> >
> >       While this sounds attractive, if the performance of this VCO is
> >       expected to be as good as possible, then the two
> > matched transistor
> >       pairs will add up to about twenty bucks. This combined
> > with the cost
> >       of the 8038 itself makes this design less attractive
> > than say one of
> >       the later Electronotes designs which use only one
> > matched pair or even
> >       a 3046 transistor array, plus a few op-amps, with
> > performance specs as
> >       good as anything ever available commercially (and
> > better than most).
> >
> >
> > If passing out electronotes articles is a no-no here (I seem to get
> > that drift), then where do I find electronotes articles?  I'm getting
> > much more interested in finding such a circuit as my plans-on-paper
> > are starting to want to become a real machine, and soon.
> >
> > -Tavys
> >

--
 -Jim
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