Lin or Log?

[jorgenkjellgren]

I´ve been looking at some of the perfboard projects on http://www.aronnelson.com/gallery/ and I was wondering how you can tell if a pot, say for volume, tone and such is supposed to be linear och "log" (not even sure what that stands for) ?

Thanks, Jörgen

[Ge_Whiz]

You can always use either, but in some circumstances, one type will give a better 'spread' of control than another. Usually,

log (logarithmic) will be labelled 'log' or 'A' - usual for volume / gain / level controls
lin (linear) will be labelled 'lin', 'B', or not at all - usual for tone and blend controls

[Mark Hammer]

It's been gone over many many times, but since you are obviously new here (welcome! another mind to corrupt!! ), and since the topic was discussed under threads that may not be easy to search for, I'll go through it once more.  Do take a moment to check the FAQ, though.

1) Whenever a control is used for "more" of something (like more volume, more speed, more distortion), the human ear tends to prefer a log taper.  It is in the nature of hearing and perception generally, that logarithmic changes "feel" more linear to us. Odd, but that's the way the brain works.  In some cases, because of the nature of the circuit, reverse-log tapers may be required.  Happily, these instances, while absolutely annoying when they happen, are rare.

2) Whenever you need to know the "middle" of something, such as a cut/boost tone control, or a blend/mix/pan control, a linear taper is needed because the visible middle of the pot will be the electronic middle.  Here, the control is not only being used to get "more" of something, but "less" of something as well.

Those would be the two guiding principles that youcan rely on when building/replacing something without enough information to go on.

Having said that, taper is always, always, always, a question of your preference.  For example, the degree of distortion in many pedals is generally dialed in via a pot used as a variable resistor (two solder lugs out of 3).  Some folks are more interested in shades of greatest distortion, and some are more interested in shades of gentle distortion, while others don't particular care about one end of the spectrum vs the other.  Given that the taper simply dictates how much pot rotation is needed to make meaningful changes at different points in the pot's range, the "ideal" taper of such a pot might be different for each of these groups, and each would be absolutely correct in using it.

The same, incidentally, might be true of speed/rate pots for modulated effects.  Although a log pot is often preferred in these instances, some folks may be more interested in small differences at faster speeds, and others interested in small differences at slow speeds.

Perhaps the most important thing to keep in mind, however, is that taper mistakes will never ever stand in the way of whether the circuit **works**.  Merely whether it can be controlled in a manner that is pleasing and helpful to the user.  The rest of the circuit doesn't "know" the taper of a pot.  All it knows is that there is 10k, 100k or whatever in position X.

[jorgenkjellgren]

Wow, thanks a lot guys! Sorry to take up your time instead of searching the FAQ.
This was really helpful!
Jörgen

[6079smith]

mark hammer's post above is probably the best thing anyone could read if he (or she) should need an explanation of potentiometers. should copyright stuff like that...

anyhoo, my personal experience here is that "A" or "B" or whatever nomenclature is used to distinguish linear fron logarithmic is NOT standard. i once bought 10 pots; six were marked "1M B" and four were marked "1M A". they were all 1 megaohm linear; they all came from the same drawer. if possible, measure in the shop before buying, or if ordering online, make sure "log" or "lin" is mentioned somewhere. sorry if this seems elementary, but i have made a few mistakes. like the pot mistake.
regards,
a.