volume pot power ratings

[lavastudios]

hey guys, i'm building my first pedal (an electra type distortion), and the instructions don't mention anything about what power rating is recommended for the pots. mouser has a100k pots with either a 40mW or 60mW rating, but not the 125mW and 250mW ones i normally hear people talking about. i've searched but haven't found much mention of the lower values, can anyone tell me if they are suitable for volume pots in pedal builds?

cheers!

simon

[PBE6]

Someone can correct me if I'm wrong, but 40mW should be more than enough power handling capacity for a pedal build.

P = I*V = V^2 / R

V = sqrt(P*R) = sqrt(0.040 W * 100,000 ohm)

V = 63.2 V

Considering that the maximum voltage a pot will ever experience in a pedal build is less than 30 V (and honestly closer to 9 V most of the time), a 40mW pot should do just fine.

BTW, who are these people talking about power handling with pots?? Never seen such a conversation here on DIYStompboxes.

[lavastudios]

oops, just realised i put this in the wrong section, i was doing it on my phone and couldn't see the site very well. thanks for the info though! not sure if it was on here, but i have seen people discussing whether 125mW vs 250mW makes an audible difference

[PBE6]

It shouldn't make any audible difference.

[GibsonGM]

Someone can correct me if I'm wrong, but 40mW should be more than enough power handling capacity for a pedal build.

P = I*V = V^2 / R

V = sqrt(P*R) = sqrt(0.040 W * 100,000 ohm)

V = 63.2 V

Considering that the maximum voltage a pot will ever experience in a pedal build is less than 30 V (and honestly closer to 9 V most of the time), a 40mW pot should do just fine.

BTW, who are these people talking about power handling with pots?? Never seen such a conversation here on DIYStompboxes.

There's no real *WRONG* answer...it depends on the application...  Typically there is a limiting resistance in series with the pot to protect it, among other things.   Now, instead of calculating using "100,000" for your resistance,  try it when the pot is turned down to 100 ohms...I DO hope you have a limiting resistor there, lol.   It's about current flow, not resisting it...if that makes sense.  I used to burn them up when I was new as I'd turn them down, ha ha....all the time...

Personally I use 1/4W ones as they are standard, and you kind pretty much bet that anyone designing for a 9V supply is using them. If Mouser doesn't have them, Small Bear sure does, as well as the forum store I bet!  Good lesson about something we all have to remember when messing with pots if we don't want the magic smoke to come out...

**Edit** It's not so much about voltage, it has much more to do with current!   And no, there should be no audible difference...