[sdiy] Potentiometer standards and the pot graph

[Ken Stone]

>To my dismay, I found if I use 300K pots I'll get a response closer to
exp(log?) than linear. Bummer.
It may be possible to use the "log conversion" trick to correct the curve.
Add a resistor from the wiper to one end - just do it in the opposite direction.

>Then I checked 100K pot into 100K input resistor and the response is in the
middle of log and linear response. Surprising. It seems the ideal attenuator
pot value for 100K impedence is a 10K pot. Shouldn't this value be the
standard as opposed to 100K or 50K pots for true linear response.

For a pure linear response, yes. You will note that a lot of synth stuff
just uses linear pots all the time. We don't need to go to log as we already
have a good enough curve. The second reason for using 100k pots is to keep
the input TO THE POT at 100k impedence too.

And yes, the higher the resistance, the greater the noise. That is why
sometimes you will find an op-amp circuit made using low value resistors,
particularly when being used with low-noise op-amps. Mostly this is an issue
with mike pre-amps and other high-gain circuits.

Ken
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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