[sdiy] monolithic VCO chips for FM??

[Scott Stites]

> 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?

That's what I'm referring to.

> 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.

He would not publish anything he wasn't 100% sure of.  That would be best
way to commit suicide in this highly lucrative market (=-D).

> 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.

That would be very interesting for me!

> 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.

He's got it in the book that's coming out.

> 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?

Nope, this is more of an electronotes type of app.

I've been referring to a manuscript that he sent me - this is for a new VCO
chip book that should be appearing shortly.  I feel bad about discussing
these things and then not giving details.  I can't give details for the same
reason that I wouldn't distribute a Blacet, Oakley or MOTM schematic - it's
their bread and butter, and I'd have to respect that.  Plus, then Thomas
wouldn't send me any more of these juicy designs to try out =0).

But, at the same time, I am not acting as a shill.  I love a good design,
and I'll recommend anything I think works well.  If  it was crap, then I
would say it was crap, or, more likely, wouldn't mention it at all.

> 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.

That's the point of this book.

BTW, I find the XR2206 a much more interesting chip than the 8038.  Look at
the balanced modulator that's built into it.  As a multiplier, it's spec's
are (as Thomas puts it) 'punk'.  But, think about waveshaping possibilities
built right into the chip.....and there's a *great* linear design for it as
well as the expo design.

Cheers,
Scott