[sdiy] monolithic VCO chips for FM??

[Scott Gravenhorst]

James Patchell <patchell at cox.net> wrote:
>This I find very amazing...(i.e. BS)....If you look at the data sheet for 
>the XR2206, sweep linearity is only 8%....this is no where close to 
>flat....the ASM-1 oscillator is somewhere around 0.01%....
>
>At 12:44 AM 8/22/2004 -0700, Scott Stites wrote:
>>According to Thomas  the XR2206 is performing *better* than the 8038 - he's
>>gotten nine flat octaves out of it, but has gotten only seven out of the
>>8038.

When referring to an 8038, are we referring to the datasheet suggested
circuits which I think we all agree are crap or are we referring to the
Thomas Henry method which is claimed to have a quite wide, flat response and
none of the heat issues normally associated with it?  

I just hate to see the chip trashed when it _can_ be used in a circuit which
does not have the stereotypical drawbacks.  Thomas Henry is no slouch and I
seriously doubt he would have published that his results showed that the 8038
_can_ be very linear if it were, in fact, not so.

Granted, it is not an expo VCO, and it may not be cost effective to add an
expo converter, but for those few of us who do use linear control voltages,
it seems to be quite a nice VCO, having sine, tri and square (saw easily
derived from tri) from only 2 IC packages.

I still must try it, and I will post my results when I do.

Maybe someone can come up with a simple, clever and inexpensive expo
converter for the Thomas Henry version so that it can be used for those folks
too.

Also, regarding the XR2206, where can I find the Thomas Henry circuit for
this one?  Did he do the stick-it-in-the-feedback-loop-of-an-opamp thing with
that one too?

We must remember that any part can be used poorly or used well, the greatest
transistor can be used to make a really crappy amplifier.  Implementation is
everything.

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