pot's linear/audio

[tcoil]

How can you tell if a pot is an audio or linear if it is not marked. I have a box of vintage pots. I can measure the impedance but not sure if they're an audio or linear taper. Is there some kind of test?

[Shrapnel]

One thing you can do is adjust the pots where the wipers are at half their full rotation and measure them. If it looks to be about half the resistance of the full pot, then it is probably linear, if you get a reading that is either 25% or 75% you probably have an audio taper or reverse audio taper (respectively, IIRC) pot.

[eleventeen]

I'm not so sure putting the pot in the middle of its rotation would be that conclusive. Unless the pot shaft had a notch in it, judging "half rotation" would be pretty inaccurate, I would think. I guess one could mark the thing with a Sharpie to get a better estimate of "half".

I think you'll have to get clip-leads for your ohmmeter. Measure the full resistance of the pot, then move one of the outer leads to the center terminal and rotate the shaft. Here's an situation where an analog ohmmeter would be a lot better than a DVM (used on its ohms setting) unless the DVM updated very quickly. The giveaway is when the outer-terminal to center-terminal resistance goes to maybe 70% of the outer-to-outer resistance at roughly half rotation or even less. That implies that the first suggestion you got, of measuring halfway would work, but older pots can be phenomenally inaccurate in terms of their total end-to-end resistance.

[tonewood]

One thing you can do is adjust the pots where the wipers are at half their full rotation and measure them. If it looks to be about half the resistance of the full pot, then it is probably linear, if you get a reading that is either 25% or 75% you probably have an audio taper or reverse audio taper (respectively, IIRC) pot.

I think this is correct. Putting the pot near the middle of its rotation is quite easy & an audio taper won't be anywhere near half way.

[stratele52]

Shrapnel is right. In the middle = about the same ohms = linear
                        In the middle = big difference = audio