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There seems to be a lot of disagreement/confusion out there regarding which type of pot to use for volume and which for tone control. I was under the impression that audio worked best for volume and linear for tone but I've been told the opposite also. I've always bought into the argument that the human ear perceives volume changes on a logarithmic scale thus the need for audio type pots.
Any thoughts?
Nelson

Nelson,
I've always used audio for both Volume and Tone. Here is a copied description from a google search on the topic. "westhost" or something...can't recall...but it's not mine:

Potentiometer Tapers
The taper (also called "law") of a pot is important. We need not worry with trimpots, since they are almost always linear, and I do not know of a supplier of anything other than linear trimpots. For all panel pots, we must be aware of the use the pot will have, and select the correct type accordingly.

The most common use of a pot in audio is as a volume control. Since our hearing has a logarithmic response to sound pressure, it is important that the volume control should provide a smooth variation from soft to loud, such that a given change in position of the pot causes the same sensation of volume change at all levels.


Figure 4 - Potentiometer Tapers

First, the term "taper" needs some explanation. In the early days, when an audio taper (logarithmic, or just log) was needed, the resistance element was indeed tapered, so that it provided a different resistivity at different settings. By changing the physical taper, it was possible to make a pot provide the exact gradient of resistance needed. By definition, a linear pot has no taper as such (the resistance element is parallel sided), but the term has stuck, so we might as well get used to it.




The violet curve in Figure 4 shows an antilog or reverse audio taper pot. These are quite uncommon, but used to be used for balance controls using a log/antilog dual section (commonly called dual gang) pot. It is shown on the graph mainly for its interest value, but they are generally an historical component now.

All this tapering proved a rather expensive exercise, so manufacturers economised ("they" won't notice the difference!), and worked out a method of using two resistance elements of differing resistivity, and joining them to create what I referred to as the "Commercial log" taper. In short, it doesn't work (not properly, anyway), and the discontinuity where the two sections join is almost always audible with cheap "log" pots.

Project 01 showed how this can be fixed, and I will explain the logic and maths a little more as we progress. In the meantime, I suggest that you get an old pot and dismantle it so that you can see exactly what is inside. I could show you some photos, but there is nothing like doing it yourself to really get to know the subject.

Pot Markings
Now, this should be dead easy - a simple code to indicate the resistance and law of a pot should cause no grief to anyone, right? Wrong! It wouldn't have been so bad if someone hadn't decided to change it, and even then, it wouldn't have been so bad if there was no overlap between the "old" and "new" "standards" ... I think you can see where this is headed by now.
Taper Old Code New Code Alternate
Linear A B LIN
Log (Audio) C A LOG
Antilog F N/A N/A


Wasn't that a nice thing to do? It is obviously important to check before you make assumptions, or you can easily get the wrong type - especially if working on older equipment.

At least the resistance marking is usually sensible, so a 100k pot will be marked as 100K - but not always. The coding system used for capacitors is sometimes used as well (especially on small trimpots), so a 100k pot could also be marked as 104 - 10, followed by 4 zeros, or 100000 (100k) ohms.

Because they are variable, there is a much smaller range of potentiometer values, almost always in a 1, 2.5, 5 sequence. Common values for panel pots are 1k, 5k, 10k, 25k, 50k, 100k, 500k and 1M - 2.5k and 250k went missing along the way, and these are not stocked by very many distributors. 25k pots are becoming harder to get as well. Not all values are available in log and linear, and in some cases you may even find that for a particular type, you can get them in any value you want, as long as it's 100k (for example).


Dave-SKG38907.5480671296

_________________
Dave Bland

remember...

"If it doesn't play in tune...it's just pretty wood"

This topic comes up quite often in forums, and a lot of the confusion
seems to be reinforced by much misinformation both in books and from
suppliers. Here is a copy of an email which I recently sent to answer this
question from from a member of a different forum.

"The exclusivity of audio pots for guitar volume is an very popular myth
that is unfortunately perpetuated by books and suppliers across the
board. While loudness perception of the human ear is certainly
logarithmic, the way a typical guitar volume is wired makes the actual
taper of the loudness not match the taper of the pot. The pot is not only
increasing the output/pickup resistance as you fade out, but also
decreasing the output/ground resistance. The sum of the two ends up
not equaling an audio taper even if that is the taper of the pot.

By my own personal observations, audio pots tend to fade rather quickly
from about 10-7, very little from 7-3ish, then quickly from 3-0 (heavy
fade on the ends and moderate in the middle). This works great for
players in overdrive who want a quick "clean up" in the first third of the
turn. Then you still have some volume control in the middle, with a fairly
smooth "swell" at the bottom. This still seems to be the preferred pot for
a majority of players.

Linear pots have a much more even pan from 10-2ish, then a rather
sudden drop in the last 15%. I personally prefer these, but I tend to play
rather clean, and with only modest overdrive when any. These also don't
have the same need for the treble bleed cap/resistor setup that many
people use with audio pots. I'm not entirely sure why it works this way,
but they don't seem to loose thier trebles as much as you turn down.
Another advantage of linear pots is that in a two pickup / two volume
setting in which either volume will act as a master (e.g., Les Paul, middle
position) you can fade out one pickup with little effect to the overall
volume until you get down around 2ish. I assume this is why Gibson uses
300k linear volume pots. This is another fine myth perpetuated by books
and suppliers, that Gibsons should have 500k audio pots all around,
when they have been using 300k linear since the early 70's.

So in short, linear and audio act a little differently, but both work fine
for volume. Audio may give a little more liberty to set the overall value
of the pot, as when you try to nudge above 500k for a linear I think the
fade may start to differ but I'm really not sure. Tone pots on the other
hand will NOT work with linear pots in a passive tone control circuit. You
essentially end up with an on/off switch between 1 & 0 [It drives me nuts
that suppliers such as allparts list linear pots intended for tone - I really
have to doubt that anyone there has ever actually tried one]."

I'm not an electronics engineer, but I have spent quite a rediculous
amount of time on this particular issue. Out of disbelief when I first
learned that Gibson hasn't used 500k audio volume pots since the early
70's, I checked pots on a few hundred guitars to try to understand what
was going on, and also to see who was using what. I found almost all
imports use linear volume pots, and a few domestic manufacturers. The
only linear pots I found for tone were by mistake. Several of the Korean
PRS SE series had the volume and tone pots switched, after which they
seem to have switched to all audio pots in that factory to keep this from
happening again.

So there's my spiel on pot tapers and the myths surrounding them. sorry
to be long winded, but this is just one of those things I guess I let get
under my
skin.David Collins38907.6394560185

_________________
Eschew obfuscation, espouse elucidation.

Wow, I need to get out of this thread before my head explodes! Good to know guys around the OLF have the knowledge to discuss these kinds of subjects. By me!

Mike
White Oak, Texas

Is no one else going to touch this pot with a 10 ft. pole?
Nelson

I myself always used audio taper pot for both. This is just the way I learned. No real theory behind my use. But on my personal instruments I disable the tone. I only use a volume because I personaly don't like using a tone on solid bodies. Ifeel it just muddies the sound. I prefer to adjust my tone through the amp and pedalboard I use.