Anyone willing to help a 1st timer out?

[BurncardXI]

Hi All -

Can someone answer for me what the difference in pots are in relation to the millimeters?  (i.e. 16mm, 12mm, 24mm)?

Thanks!

[Minion]

MMM....I think the differance is size? there should also be specs for shaft length and thickness...Smaller pots are good for pedals as they are smaller and can be more easilly fit inside an enclosure ,Bigger pots seems to have better tracking and seem to last longer before getting scratchy......

[Mark Hammer]

Though you may be too young to remember it, vinyl discs would always oblige the record company to think long and hard about what songs would be first and last on each side.  The reason was that, although the album turned at the same speed for all songs, the distance travelled on each rotation of the disc (i.e., the perimeter) would depend on where you were - closer to the inside or closer to the outside.  Songs placed closer to the outside were afforded more bandwidth because the same content was stretched out over a much longer perimeter.

In a sort of analogous way, pots where the resistive strip is distributed across a wider radius oblige the wiper to travel a longer perimeter.  Now it would probably be a mistake to equate a longer perimeter with a necessarily more precise and predictable change in resistance (taper), but it would not be unreasonable to suggest that the circumstances are more favourable for producing a more precise pot when each degree of rotation moves the wiper over a longer distance.  It's still up to the manufacturer to take advantage of that.  You can get small pots that vary widely and others the same size that have decently tight tolerances.

Life of the pot is another matter.  It is possible to design a bad wiper that scrapes the resistive strip harshly and shortens the lifespan, or a wiper whose tension (and quality of contact with the resistive strip) is not well-maintained, whether the pot is small-radius or as big as your hand.

A lot of boutique manufacturers make extensive use of the 16mm Alpha pots with generally favourable results.  The 12mm pots are the ones that tend to be found on things like Boss pedals.  Keep in mind that: a) you can space smaller pots more closely, but need to have the appropriate knobs to do so, and b) most pots come in different formats, such as right-angle PC-mount, chassis mount, and so on.  My experience is that the smaller pots tend to be designed around automated installation (i.e., PC-mount) more often, or at least you run into them more often.

Beginning builders often have a difficult time judging where things need to go in a box/chassis.  For that reason alone, I would suggest using 16mm pots for early builds, so that you have a little more latitude in where you drill holes.

[BurncardXI]

Mark - thanks for the perfectly detailed answer.  I understood it perfectly, and it makes sense.  The unfortunate thing is, I already have the 24mm pots from Smallbear...  So, in heeding your advice, I'll reorder the pots and save the 24mm's for another project.

Time to get my hands dirty.

Wish me luck!!!!