[sdiy] Ovens for oscillators?

[Magnus Danielson]

From: Glen <mclilith at ezwv.com>
Subject: [sdiy] Ovens for oscillators?
Date: Tue, 06 Mar 2001 17:17:48 -0500

> Hi everyone,

Hi Glen,

> I know that some precision quartz crystal oscillators use ovens to keep the
> circuitry's temperature elevated above room temperature by several degrees.
> The exact temperature of the oven is closely regulated, to prevent
> temperature drift affecting the components. 
> 
> Now I know that this sounds like an extreme measure to suggest for
> home-built synth oscillators, but has anyone tried it?

Yeap. Old trick. The Fairchild uA726 was used in many exponential
converters. It has a builtin heatertransistor with regulator, so you
basically just apply power and it's a done deal. Sadly enought, these
are no longer made and availability is, eh, tought ;)

You could cook up a similar thing over a CA3046 transistor setup, with
heater transistor and sense.

> Would it eliminate the need for special tempco resistors?

It would reduce. Like in the quartz crystal case, you use temperature
compensation first, and then you _add_ temperature stabilization.

You could do without, unless you are haunting obscene stability.

> I realize that if the oven's power failed, the oscillator might
> indeed need recalibration afterward, or at least a long warm up time
> before use.

Well, you don't really have the same trouble as with crystal
oscillators where you have an aging mechanism which depends on
temperature. You do have the actual temperature problem, so the speed
by which you get back to the stable temperature is an issue. Warmup
times does not have to be that long for acceptable musical use.

This is not like high frequency precision measuring.

> Unless special mobile power sources were employed, it would make the
> synth less mobile, and probably not suited for taking to a live
> gig. However, for an experimental synth that always stayed in one
> location, and always supplied power to the ovens, might it be useful?

Maybe, maybe... my frequency counter is turned off, but the red light
is on for the standby of keeping its reference oscillator heated.

I wonder if you are not taking the measures a bit overboard, but then,
if you do you are in good company with fellas like myself ;)

Cheers,
Magnus