[sdiy] CA3086 and CA3046?

[Christian]

I'm making a VCO using the CA3086 at the moment.
Should I use the two transistors to the left of the chip which already
share a common emitter?

Also, Farnell Electonics supplier here in the UK has discontinued the
range of 1K Tempco resistors but they will supply a 1K Thermistor
(code 679331) in its place which I am going to try to use. Anyone any
thoughts or things to add?

Christian.

On Thu, 16 Aug 2001 01:05:04 +0200, you wrote:

>At 17:35 15.08.01 -0400, Dr Strangelove wrote:
>>Well, the 3086 is used in the Oberheim SEM.  Their advertisements from the 
>>time claim that tuning stability was better than ALL the competition.  Maybe 
>>people are not using the 3086 because they're just *too* good. (:-)
>
>Well, I think that is actually due to the circuit topology. Apart from
>using a tempco resistor for temperature compensation, its reference current
>is chosen so that the temperature dependancy is minimal. (Arround the
>reference current the impact of drift is lower than at very low or high
>frequencies.) Also the SEM has a Rbe correction, which renders the not too
>great transistors in an 3086 or 3046 in a respectably precise expo convertor.
>
>Cheers,
> René