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

[Tim Ressel]

I also used the AN299 design, with a slight change. I
used a MAT04 instead of a CA3046. The specs are much
better for the MAT04. You have to replace one
transistor with an external device; the MAT04 only has
4 transistors. Also the max current is lower for the
MAT04 (30mA). THis was all worth it; the results were
quite good indeed.

--TR

--- "Oren B. Leavitt" <oleavitt at ix.netcom.com> wrote:
> 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
> 
> 


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