[sdiy] Temperature stable lin-exp converter with a CA3086 or CA3046

[Oren B. Leavitt]

Hello all,

Yes, this has been used widely.
IIRC, the earlier MiniMoogs used the CA3046 in this manner in the VCOs, before
the ua726 was used.
A very simple 20Hz to 15kHz VCO that uses the LM3046 (akaCA3046) this way is
outlined in National Semiconductor's application notes AN-299.
About 12 years ago I built a few VCOs that use heated CA3046's for the expo
converter and they have worked very well.

Oren

Rob Mantel wrote:

> Hi all,
>
> In this book I have here, they use a CA3086 (or CA3046) to build a lin-exp
> convertor for a VCO. Two of the transistors inside do the real lin-exp
> conversion, two others are used to control the temperature, one as 'sensor',
> one as 'heater'. From what I understand of it this should lead to a constant
> temperature of the ca3086 (kind of like the old ua726 got its constant
> temperature from its oven), so no external temperature compensation is
> needed anymore.
>
> Is this a well known thing to do? If so, why doesn't everyone do it this
> way, it is a very cheap solution, no expensive parts involved at all. Does
> anyone have any experience with the temperature stability of VCO's built
> this way?
>
> Rob (who floods the list with questions today, sorry)

--
Oren Leavitt
oleavitt at ix.netcom.com