Lurking and Tempcos

[Harry Bissell]

I think that Synthesis Technologies (Paul Schrieber) has them.
(no I'm not a stockholder...) as may some others... TomG had some but
I don't know if he sold out of them or not...

I've played with the heater option... The passive heater on the VCO4 does
not work much better than the unheated chip. If you check out National
Semiconductor AN-299 you will find a active heater... one that regulates
its temperature. I have a schematic for a version of this which I'll post here.

TomG also has an alternate "active" heater which uses an external transistor
as the heat control element... It is a little simpler than my version (which was

intended to be a temp controlled differential pair for 'any' use). I haven't
built
that version but It looks OK too...

Air drafts are probably the biggest problem with any of these circuits... a tiny

puff of air sends them hunting for a corrected temperature...

Regards: Tempco Resistors... these have to sense the chip temperature very
well, so some thermal mass (like epoxy potting) or at least styrofoam insulation

is a good idea.

Good Luck (I'm using tempcos BTW...)

:^) Harry

Scott Chicoine wrote:

> Hello all,
>
> Since I actually have a question, I suppose it's time I step out of the
> shadows that I've been lurking in for over a year.
>
> I've taken the plunge and built my very first VCO.  After much
> hemming-and-hawing, I decided to build TomG's VCO4d.  I played around with
> it on the breadboard for a bit using the heater option, hoping I could get
> away without using a tempco, but I found that it was still somewhat
> sensitive to temperature changes.  So, I'm considering using a tempco
> resistor instead.
>
> I *know* this has been answered at least once, so forgive me, but:  where
> can I get a small quantity of these 1K +3500ppm/C tempco resistors?  I think
> someone on this list mentioned once that they had some for sale... who was
> it?  I've also got a query into Micro-Ohm, but they've got a $50 minimum.
> Speaking of which: has anyone used any of their devices for tempco, and
> which device did you use?
>
> This list has been a great inspiration and has renewed my childhood dream of
> building my own wall o' synth.  Also, many thanks to TomG for the EFM page
> and making all his hard work available to those of us who are "design
> challenged".  :)
>
> -ScottC
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