AW: CA3046 exponential converter

[BJ]

jhaible wrote:
> I've seen this on some Moog synth (maybe the Rogue), too.
> You don't really need an extra transistor for temperature sensing, if you
> monitor the voltage across the transistor of the expo pair with the
> reference
> current (the one inside the opamp feedback loop). This works perfectly
> if you tie its base to GND and use the base of the "output" transistor for
> the CV input. The only drawback of this method is that you will need a very
> low impedance resistor divider for the CV in that case (best would be an
> active divider, i.e. inverting omamp with gain << 1). That's because the
> accuracy of the exponential function is very sensitive to a resistance in
> the
> base of the "output" transistor, while it's not so critical on the
> reference
> transistor (which operates at a fixed current anyway).
> 
> The good thing is that you can really build three tracking expo converters
> from a single 3046: One reference transistor, 3 output transistors (with
> individual CV's on their bases), and one heater transistor.
> 
> One Moog synth (The Rogue or the Micro ?) has a very well tracking VCF
> built with this method, so it can serve as an additional, tuned VCO.
> 
> JH.

Hmm, are you refering to my design around the shemo i sent
to you OR have you seen this app in a other machines?Where one
would use the reamining two transistors as an oven as i did.
If so ,where is it done ,besides the Rouge and the Micro?

Regarding to the Rouge, is int the Rouge using a 100ohm tempco
resistors on the base of the expo transistors as temp comp!

This oven thing is nice, the Moog Source uses this scheme
but with a over designed oven and sensing circuit, but the VCOs
are rock solid stable, i vas fooling around with one of these
machines back in the mid 80 and was impressed with the stability
and since then i only do Oven VCO's.

BJ