[sdiy] CV inputs with bipolar "amount" knobs

[David G. Dixon]

> >> But if you want the curve to be less steep around the center you want
> >> an exponential or even better an nth power response such as x^3.
 
> Regarding the x^n response: you can also just use x^2. It'll be better
> (the central dead zone will still be significant while not taking up
> as much range of the knob).

You cannot achieve x^n responses with parallel resistors as I've described.
In fact, you can't really describe the response you get with any common
curve fit.  Also, putting a trimmer of the same size in parallel gives a
significant degree of flattening, and smaller trimmers don't flatten that
much more.  The additional flattening is the most modest near the centre,
where one would actually want more.

The problem with this technique is that the first derivative of the response
at the centre does not approach zero, so the response is not flat in the
centre.  The slope is decreased significantly from the original linear
response, but does not approach true flatness.

The advantage is that it doesn't add significant current load to the
circuit, and it does allow one to fine-tune the centre of the pot.