9mm pots Watt rating issues - Will they last in a muff with clipping switches

[Quazza666]

Hi there, Been building some pedals using 9mm Alpha pots from Smallbear of late and I have been advised that the voltage rating may not be up to scratch. One fellow builder expressed that he had a mate who had some fail. Only rated at 0.05W

I am using them for a Muff build where I am switching clipping diodes in both gain stages. I am using toggles to do this so they are non shorting switches. Been using them in muff without switching for a wile with no issues and also a Bazz Fuss style pedals with no issues.

The concern was that when lifting the diodes it could overload the 9mm pots and short/burn them out.

Is there anyone out there that can shed some light on this? Dont want to put a lot of work into building and designing, only to have the pots not last.

Any help would be great!

[gordo]

Good question on a first post!  Welcome aboard.  There's nothing we do in the voltages we work with in the pedal world (short of high voltage tube based stuff and even then...) that will stress any pots, down to the little trim pots you have to set with a screwdriver so experiment to your heart's content.

They're always subject to mechanical failure from dirt and oxidation but if you're using quality stuff (and Smallbear's stuff is) you're covered.  In fact the 9mm are nice because they're completely sealed.

If you figure out a way to fry a pot with a muff circuit I hope you'll share the schematic :-)

[culturejam]

If you figure out a way to fry a pot with a muff circuit I hope you'll share the schematic :-)

Haha, I was thinking the same thing. 

[Quazza666]

Fantastic guys. Thank you.

I have the schematic attached for reference.

So given that the rating for most 16mm pots is .25W and the 9mm is .05W I have nothing to worry about?

I believe all the stuff coming out of the Chinese manufactures in the small pedal footprint use 9mm, so they should be OK.

[somnif]

Fantastic guys. Thank you.

I have the schematic attached for reference.

So given that the rating for most 16mm pots is .25W and the 9mm is .05W I have nothing to worry about?

I believe all the stuff coming out of the Chinese manufactures in the small pedal footprint use 9mm, so they should be OK.

You're low balling the 16mm pots a bit, most Alpha and alpha clones I know are rated at half watt. As for the 9mm, they're a bit dinkier but still rated to 50V standard.

In any case, you'll be fine. The Muff is one of the lowest current draw pedals you'd commonly run into, most flavors won't pull 5mA total. Hell some are under 2mA. Assuming you were on the high end of that scale, even if the pot was seeing a full 9V (which its not), you'd only pull ~45mW.

In other words: You'd good to go. Have fun with it. Only time you'd really need to worry about toasting a pot is if you were using one as a voltage cut at the start of a circuit and shorted one end of it. If you had a typical wall wart powering the thing that could get a bit exciting (IE it would get a bit warm and smell funny).