POTS: Custom tapers

Don't ask me why, but I randomly thought of doing a quick post on custom pot tapers.  Maybe it's because occasionally I have a gain or fuzz pot that isn't behaving how I would like it to, and I find this very annoying.  I'm sure it's happened to everyone at some stage.  However, adding an extra resistor to a linear pot, this can sometimes be addressed.

RG Keen has an excellent reference piece, which I'm sure you've probably read by now.  

But if you are anything like me - I'm slightly embarrassed to say that I lose interest pretty quickly when I see equations.  In retrospect, maybe playing with electronics wasn't the best hobby for me.

Below is a model of a standard 100k linear pot in LTspice fed 10 volts DC.  The simulation sweeps the pot from 0 to 100k in 10k intervals.   As you can see, the voltage on the output raises nicely in 1v intervals as it should.  

Pots are, after all, voltage dividers, with the total pot value always being the same when measured between the outer lugs 1 & 3.  So sweeping the pot in 10% intervals gives a nice, predictable linear sweep.  I'm not a pro at LTspice, so instead of a typical graph, I've done something a little different - hopefully, it's clear to the reader.

CUSTOM POTENTIOMETER TAPERS

But let's say you don't want a nice linear sweep, but you only have linear pots.  Well, in this case, you simply add another resistor between the lugs of the pot, and as you can see, the sweep has changed.  Instead of a nice even spread, the resistance varies across the sweep, resulting in a non-linear response.  The smaller the resistor value, the less linear the response will be.

But - the extra resistor is in parallel with the pot, reducing the value of the pot in the process of changing the taper. 

Flip it around, and now the sweep works in the opposite direction.

You can even do odd things with a wider range at either end.

Or a focused range at a particular point - why you'd want to do this, I'm not sure, but it's there if you want to try.