[sdiy] Expo-Con

[René Schmitz]

Hi Busby,

this is only a principal schematic, in practice you would have to have 
extra circuitry to make it work.

I0 would be your reference current, which is assumed here to be 
constant. I is your current output, and Vb is the voltage input to the 
exponentiator.

In order to really keep I0 constant, one often uses an opamp. Keeping 
the collector potential constant and closing the loop on the emitters.

Maybe the NPN/PNP arp style exponentiator is more what you want.
Have a look at the vco4069 at my pages for an example.

Cheers,
  René

Am 03.02.2015 um 06:11 schrieb Busby Bergson:
> Hi There -
> I'm a new user to the group and a new(ish) builder of synthesizers.
> I've been trying to understand exponential conversion.
>
> I looked at Rene Schmitz's explanation at:
> http://schmitzbits.de/expo_tutorial/index.html
>
>>From that, I know that I'm not necessarily interested in heat
> compensation or accurate tracking. So the double-transistor on Ian
> Fritz's site makes the most sense to use:
> http://home.comcast.net/~ijfritz/trans1.gif
>
> But I'm not sure how to use it. There are three unspecified
> connections here. I'm a little confused about what goes where.
>
> Can anyone help?
>
> Thanks,
> BB
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