Pots.....which do you like best?

[mth5044]

Mounting options aside, any preferences based on the actual electronic performance of the pots?  It would seem that the longer wiper in a larger diameter pot would allow for more precision in setting the value of the pot. 

If you were controling the wiper from the other end it would, but since they are all operating from the middle spindle thing, it won't make a difference. You can find pots with more degrees of turn. I think we use 270? Maybe 300? I think there are 315 or something too.

[armdnrdy]

The Alpha pots that we normally use (depicted in post 1) are 300 degrees.

[Keppy]

Mounting options aside, any preferences based on the actual electronic performance of the pots?

Not the ones discussed in this thread. Wah/swell pots have some more consideration, though. The larger considerations for normal pots are durability and longevity. Other things being equal, I think larger pots are supposed to be more long-lasting due to the wider area of contact between the wiper and the resistive track. As far as standing up to abuse, the way the pot is mounted to the PCB can be as important as the construction, or more so.

[alanp]

Mounting options aside, any preferences based on the actual electronic performance of the pots?  It would seem that the longer wiper in a larger diameter pot would allow for more precision in setting the value of the pot. 

Not quite, it's the larger knob that lets you do a smaller turn.

If you want true precision, get a multi-turn pot and be done with it.

[KazooMan]

I know about multi turn pots.  I still think that a larger diameter pot can be set more precisely.  The wiper has a finite footprint that makes contact with the  resistive material. The size of the knob has nothing to do with it.    The longer the resistive strip the finer you can adjust.  

Here's a thought experiment, taken to an absurd limit (that is often the way to see through a problem).   Think about stretching the circular resistance material out in a straight line.  Let's say that the resistor from a small pot is 1/2" long.  Now we compare to a really large diameter pot where the strip is 6" long.  It is easy to see that the large pot can be adjusted more precisely.  Make the small pot even smaller and eventually the width of the wiper and the length of the resistor are so close you have no room for adjustment at all.

Or another thought.  Think of the pot as being made with a wire wound resistor.  If the resistor wire is the same diameter for the two pots, the larger one will be made with a wire that has less resistance per inch.  The larger pot will have more turns of wire.  With the small pot as the wiper goes from one turn to the next there is a change is resistance equal to that of the length of one turn.  Same for the larger pot, but the resistance increment is smaller and there are more of them.  The same holds true for a continuous band of resistive material.  The larger pot has a longer path with a lower resistance per distance material.  Yes, a comparable turn of a given number of degrees will give you the same resistance change, but the larger pot will give you a smoother transition and it will be easier to set to a specific value.  

Actually, the knob can make a difference.  As was mentioned, a larger knob will give you more control.  Still, as the size of the pot decreases you are limited by the precision of the internal components. 

[Havaden]

I prefer the tayda pots. they are dirt cheap and got over decent quality in my opinion

[Keppy]

I know about multi turn pots.  I still think that a larger diameter pot can be set more precisely.  The wiper has a finite footprint that makes contact with the  resistive material. The size of the knob has nothing to do with it.    The longer the resistive strip the finer you can adjust.  

This is only true if the pot has some amount of "stick" to it and can only be turned in finite increments. If the action is smooth and the pot turns continuously with no sticking/stepping, then the function is exactly the same whatever the internal size. The knob is important, because it scales the distance traveled by the indicator into a distance traveled by the wiper, and that scaling is missing from your analogy.

[armdnrdy]

I still think that a larger diameter pot can be set more precisely.

Okay...Let's take two 10K linear pots. One is 24mm and the other is 9mm.

They both have 1/4" shafts. They both measure 5K at 50% rotation but....the 24mm has a longer resistive track.
Now how does that work? 

The 24mm resistive track is made up of a lower resistance material.

[KazooMan]

Keppy:  Note I did correct the knob size issue in my post.  Yes, a larger diameter knob gives you more control over the position of the wiper.

These are real world components, not something with a wiper contact area the size of a quantum dot.  You cannot continuously reduce the size of the pot and expect it to perform as well as the larger model.  There will be "sticking and stepping" as you called it for both pots.  The effect of this is greater for the smaller pot.    Give it a try, I just did.  A 9mm and a 24mm B10K pot.  No knobs, just identical sized shafts.  Pick a target resistance value and see how well you can dial it in.  The larger pot was easier for me.  The 9mm pot ( a good quality one I purchased when I was building a Dig-Dug) is touchier and moves in larger steps no matter how hard I try. It can be dialed in, but it is not as easy.

BTW, I never resolved the ticking issue with the Dig-Dug.  That has been an issue for many.

[armdnrdy]

And you performed this test by hand and without bias? 

[Jdansti]

But how many fairies can sit on the wiper of a pot???

[italianguy63]

But how many fairies can sit on the wiper of a pot???

Depends on if they are wearing boots or not.

MC

[KazooMan]

I at least tried the experiment that confirmed my prior experience, rather than throw some anonymous internet barbs at another poster.   Smaller pots do not perform as well as larger pots.  Sorry, size does matter.   You have obviously never tried it.  In an ideal world, all things would be linear and they would all scale with size.  We do not live in an ideal world.  There is a price to be paid for smaller scale.  It may not be relevant for most effects pedals, but it is real.

Just curious.......  Anything in your background that would suggest specific knowledge about this subject?  Anything in your background that would suggest any knowledge about any subject?  Oops, another anonymous internet barb.  Ouch!

It is easy to anonymously throw arrows at anyone posting on the net.  I have found, through experience, that I get better performance in many builds with larger diameter pots.  Small diameter pots are really "twitchy".  They have a tendency to jump,from just a bit too little to way too much.  You can use any pots that you like, but I will continue to use at least 16 mm and hopefully 24 mm pots where I can.

[armdnrdy]

If you were offended by my humor...I apologize but...there was no malice intended.

After you posted your results, I did try it...the same un-scientific method that you did...by hand and with a meter.

The two pots I tested were what I had on hand at the time. An Alpha RD901F-40-15R1-B100K (9mm 100KB) and an
Alpha RV16AF-10-15R1-B100K (16mm 100KB)

I have to be honest....I did not get the same results that you did. I did not see a difference in resistance during rotation.

I guess the real way to do this would be to connect the shaft to a servo motor and record the resistance along the whole path of the wiper.

Maybe I'm not seeing something here but....I really do not see the need to dial in any parameter on any effect to an exact amount.

That was not an internet barb...that was strictly my opinion.  

[mth5044]

I don't quite understand the bigger pot being more precise. If you have the same knob on the pot, wouldn't you be able to turn them to the same exact position, get the same exact resistance because you are going the same exact amount of degrees? Assuming the pots ideal pots with a perfect spread of resistance material. In the real world, we know they have a somewhat large tolerance.

I could understand that you'd have better precision if you were tracking along the outside of the pot as you have the resistive material spread out over a larger area, but in both cases to are controlling from the origin. Would both the 24mm and 9mm pot read 50k on a 100kB pot when the knob is set to 180 degrees (idea pots)? Would nudging that knob up just a hair the same amount result in the same resistance? I don't see why it wouldn't.

I think testing between two pots isn't a great way to do it since there is so much variance. You'd have to have a large sample size, or find the perfect pots.

[bluebunny]

I don't quite understand the bigger knob being more precise.

If you used a 12" vinyl record as the knob, turning it 1^o would be like moving it a quarter of a centimetre at the edge - quite doable.  If you leave it without a knob and just turn the 6mm pot shaft, to move it the same 1^o you have to move it about 0.05mm around its edge - quite tricky.

[mth5044]

^sorry, meant pot. Knob size makes sense.

[MrStab]

i usually go with the Alpha 16mm long-pins with 6.35mm shafts. much less soldering, more knob options, more support for my boards. i've recently had to go with obscure 9mm pots with 6mm knurled shafts for a parametric EQ though - 9mm because it's easier to wire up 3 modular boards than it is to wire 10 pots coming off of one, and knurled because i had no other practical choice for 100k dual-gang reverse-log pots besides China.

so whatever's practical.

[duck_arse]

being a current pot thread, I have a pot question. if a pot, alpha, 16mm, A100k, straight outta the bag, let's say, is installed with a fawlty millenium circuit putting maybe 2.5 volts between wiper and ground, will the DC do any permanent damage to the pot? I ask because the brand new pot now crackles when swept up to near max volume in the repaired (fetzer) circuit, not something I'd expect from a new pot.

there was no smoke.

[Canucker]

I don't know the answer to that one.....but my comment is......I've Never never never had a pot smoke. HA! That didn't sound weird until I typed it....but seriously I've had a cap in an amp smoke....a resistor in an amp burnup...but only ever had a pot get scratchy, or crackle....what would cause a pot to smoke?