A quick question re pots...

[Now they tell me]

I've always been a little uncomfortable with misleading abbreviations.  For instance, when Madbean says to use a 100kA pot, does that mean 100k Audio Taper, or does that mean 100k "A Taper" which if you look it up on a pot data sheet might mean something completely different?

What does it mean really?

Thank you kindly.
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[kgull]

There definitely is contradictory info out there on potentiometer abbreviations (eg, sometimes B means linear and sometimes means audio) but when it comes to hobbyist guitar pedals, everything I've seen is pretty consistently as follows:

A = Audio or Log Taper
B = Linear Taper
C = Reverse Audio or Anti-Log Taper
W or S = Log/Anti-Log Taper (used mostly in Tubescreamers)

[BrianS]

You can also refer to the schematic which normally identifies the pot (50A, 100B, etc...) if you're not sure about the build doc. 

[Now they tell me]

Well yeah, the schematic is what I'm looking at.  I know what it says.  I just don't know what it means.  If they just said "audio" or "linear" that would mean something.
.

[Zigcat]

Is there a particular schematic you have questions about?

[somnif]

Well yeah, the schematic is what I'm looking at.  I know what it says.  I just don't know what it means.  If they just said "audio" or "linear" that would mean something.

Most of the time in hobbyist pedal work, audio/log = A, linear = B. (There are rare exceptions if you're using European schematic from the 60s, but this rule will suit you 99% of the time)

It can also sometimes help to think of what the pot is doing, for example Volume knobs are almost always log pots ("A" type).

A Log type pot has a logarithmic rate of resistance increase. So for a 100k "A" pot - fully counterclockwise its 0k, at 50% knob turn  its 10k, at fully clockwise its 100k
For a linear type, its a linear increase, so at 50% knob turn its 50k
For antilog/rev. audio at 50% its 90k.

[davent]

[Now they tell me]

Is there a particular schematic you have questions about?

It's the Afterlife, the effect control pot in the path that provides current to the LED in the optoisolator.  It's not real obvious what this should be.  For instance I like linear volume controls and log tone controls in guitars for the way that they respond.  But this is a more mysterious application.

And complicating that, if the top half of the knob rotation gives me extreme compression, I'm going to want to decrease the percentage of that series resistance that is controllable, so the pot's whole range will be a useful range for me.  So what is half of a log pot?  And is half of a log pot still log? 

Guitar techs have real trouble understanding that if you want to eliminate wasted rotation on a tone pot, the pot value that you end up with is extremely politically incorrect.
.

[Zigcat]

I know, it can be confusing. I this caae, Brian is refering to 100k audio taper pots. What kgull mentioned is fully correct. Apparently, older terminology used all sorts of goofy letters, but I think for the DIY community, most of that stuff has been standardised.