Tempco-less VCO -- What is it worth?

[françois]

I've come across this app-note from National Semi, I guess many of you were already aware of it:
http://www.national.com/an/AN/AN-299.pdf
(AN-299 Audio Applications of Linear Integrated Circuits)
They describe an exponential (V/oct) VCO built around a CA3046 transistor array, which they claim achieves 0.25% linearity without any tempco element. In fact they use one transistor as the exponential element, and the others as a servo loop (temp sensor + heater). Reminds me of the (defunct) uA726.
Since I have no lab, not even breadboard, at hand, I would like to know if anyone of you has tested this circuit, and how it actually performs.
Thank you for any advice.

[andrewF]

some EFM VCOs had the 3046 `chip heater` option. I cannot give any opinion on them tho, I have only built tempco versions.

[Peake]

I believe that the Moog Prodigy uses the CA3046 for a heated trannie pair.

Doesn't Oakleysound offer a Prodigy VCO board? Someone does.

[françois]

Thank you.
I've come across a few VCO schematics that make use of a similar technique for chip heating. I think I'll give it a try as soon as possible.
I have to admit I don't like using a tempco resistor, the thermal paste and all that... I prefer having a chip at a given stable temperature. Of course, it can only be as good as the matching of the trannies on the chip, which can vary quite a lot. But the 3046 is (much) cheaper than the µA726 was...

[françois]

I could check that the Moog Prodigy does make use of a 3046 array for temperature regulation via chip heating. The circuit is very well explained in the Service Manual, which I checked out at
http://www.freeinfosociety.com/electronics/schempage.php?cat=1
Maybe you already know this site? It is full of schematics & service manuals for plenty of audio equipment, not only synthesisers, but also effects, amplifiers...

[Peake]

Yes, that's a great site!