[sdiy] VCA response - continously variable between linear and exponential

Donald Tillman don at till.com
Sun Mar 3 16:23:35 CET 2013

On Mar 1, 2013, at 6:58 PM, neil harper <metadata at gmx.com> wrote:

> i'm looking for some advice/pointers on how to get a VCA response curve
> to be continuously variable between linear and exponential. i can do
> switchable between the two, but is there any trick to getting everything
> in between?
> if it helps, my VCA is lm13700 based but i don't mind starting with
> something else.

The ARP2600 addressed this with separate linear and exponential control voltage inputs.  Each has an input pot, so it's a simple matter to pipe a control voltage into both inputs and adjust the contributions of each.  That should be easy to implement.

Another approach is for a pot to add some resistance in series with the emitter of the transistor doing the exponentiation.

It may be good to think about exactly what sort of transition between exponential and linear would be the most musically useful.

  -- Don

Don Tillman
Palo Alto, California
don at till.com

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