uA726 replacement, CEM 3340, etc.

[Harry Bissell]

The higher the temperature you run the substrate at... the higher the ambient temp
you can perform with... This is why the 726 runs so hot...

I don't expect to use my synth much above 50 celsius... or below 15C... so I can
live with a lot less compensation range. The 726 is (well, was) available as a
Military part... My temp ranges might be different if I was (for example) a Polaris
Missile...

The 726 is in a tiny TO-5 high thermal isolated case (the opposite of normal
construction)... The 3046 is in a normal case where the designers expect you want
to get rid of heat.  So the 726 only needs 5-10 mA where the 3046 will need 50-100
to get similar performance...

The trade off is to run the chip as hot as you are comfortable with... there will
be a best spot for the servo loop type control, as you can add heat but can't
"remove" heat actively.

Here's the performance of a heated 3046 vs an unheated. Its the Nat Semi AN299
design...  :^) Harry

"Paul R. Higgins" wrote:

> Thanks to everyone who sent info on the CEM 3340.  I'm going to download the
> datasheet.  I can't believe I threw mine away years ago.
>
> I still have one question, though: does anyone know what the deal is about the
> 3340 running so warm?  That is probably why I was told (erroneously) that the
> 3340 had a substrate heater.  I have heard anecdotal reports that thermal
> dissipation is an issue with this IC (see previous posts).
>
> I would also be interested in hearing about people's experiences with substrate
> heaters (e.g. heated 3046s) vs. tempcos.  Someone also mentioned the high
> temperature that the 726 ran at; surely you don't have to abuse a 3046 that way
> (or a 726 for that matter) to get the benefit of a thermally stabilized expo.
> Barry Klein has a good example of a thermostatically controlled heater in his
> book ("Electronic Music Circuits").  And of course, Tom G has used heated 3046s
> in his VCOs.  (I'm building a modified version of his Mad Mouse right now, and
> I'm considering adding a heater to the VCOs).
>
> Regards,
> PRH
>
> Paul Higgins
> email: higg0008 at tc.umn.edu
> University College, University of Minnesota
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