[sdiy] Tempco vs. "Substrate Oven" in VCO and VCF

[Roman Sowa]

Controlled oven obviously takes more power to heat it, so that's 
probably the reason for not so widespread solution. You need to heat it 
up to the temperature that is not likely to happen in regular 
conditions, at least 40 deg. C. About 40-100mA to waste just on heating.

I made some measurements of ovenized transistors VCO a while back, in 
particular it was Polivoks VCO which is not famous for its stability. It 
reaches more or less proper tuning within one minute and then slowly 
decays. In firs hour it drops about 6 cents, and another 4 cents during 
next 3 hours, although the test wasn't performed in a room with 
stabilized temperature so it's rather a curiousity than science.
Graph attached, if it doesn't get thru, I can send 3 different graphs to 
whoever is interested (3 min, 10min, 4h).

Roman



W dniu 2016-02-29 o 01:33, sleepy_dog at gmx.de pisze:
> Hey there,
>
> first a question about thermistors (this is what "tempco" are, correct?)
> In circuits for voltage control of a VCO or VCF which use a tempco, how
> much could one deviate with the coefficient, say for instance in Thomay
> Henry's newest VCO based on the TLC555 timer? I think it was spec'd at
> 3500 - what if I could get one with 3470 or 3600 more easily?
>
> Also, I find Rick Jansen's Moog VCF schematic interesting, which uses 3
> remaining transistors in a 3046 transistor array as a controlled "oven"
> for the NPN matched pair, to get rid of temperature sensitivity.
> How come I don't see this kind of solution more often? Is the tempco
> solution "better"?
> How much current will the "oven" draw, and does this reduce the lifetime
> of the IC?
>
>
> Regards,
> Steve
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