volume pot impedance for an expression pedal?

[pinkjimiphoton]

hi guys,
just curious.. i swapped out my venerable morley pwb from my live board and used it last nite, but noticed i was getting like, a low mid "howl" kinda feedback from my les paul i usually don't have issues with...was wondering if maybe it was the impedance of the pot in the volume pedal?

it's a 250k pot, and designed for "hi z"... but i was thinking, since it's at the end of my dirt and stuff, should it be a low z? maybe more like 10k cuz it's in between pedals?

is it worth swapping out and playing with it a little, or do ya think i'm barking up the wrong tree? for all intents, it's full up most of the time anyways. sounds great, other than that howl sometimes.

or could it be cuz i ran out of good coax and used a shit plastic jumper?

advice and opinion gratefully sought, thanks peeps!

[anotherjim]

I think you're right. If it's like when you turn down the guitar volume with a noisy input and the noise gets worse? Then a 10k pot ought to cure it. You could temporarily tack a 10k resistor from the pedal pot wiper to ground. It would change the taper but it would give a clue that it's worth changing the pot.

[pinkjimiphoton]

yeah jim, it's exactly what's happening. it's between my dunlop univibe and my venerable pearl flanger, so i think it's buffered on both sides.
when i turn my guitar down some, is when the problem happens the most which seemed weird.. i have passive high and lo cut filters built into most of my guitars, so right now to nuke it i have to roll off most of the bass.
i will try your suggestion out over the weekend. i am thinking it's gotta be an impedance issue, as the pedal was designed for being first in line (doesn't work with a fuzzface as i would want it to ) thanks my friend!

[anotherjim]

Having thunk a bit more, you may lose some bass out of the preceding pedal with a 10k pot. A schematic I found for the Dunlop vibe has 680R + 470nF out from an op-amp with a 10k pull down after the cap. Adding 10k pot on that will raise LF cut to about 60Hz. You shouldn't notice that with normal 6 string but you may have octave down stuff?

[pinkjimiphoton]

hmmmmmm,  after the volume pedal it goes to my "pink's clipper", a pearl flanger and a boss super phase then my a/b/y box for the talkbox... a is a nux time force delay, b is an EH 44mag to drive the talkbox.
the volume pedal is plastic with a metal base. starting to think maybe i should open it up, make sure all the wiring is shielded and put some kinda faraday shield around the passives that's connected to ground, cuz it is around a 60  cycle hum issue i'm having, which is kinda weird with a les paul with humbuckers, especially since i'm rolling off bass from the guitar.
i gotta get thru some repairs today.... adapting a dano fab echo so it will fit in a crybaby shell and sweep the delay time with the treadle for the classic tom scholz "spaceship" effect for a friend (likley take all day) and then a gig tomorrow....

but it could be proximity thinking about it too... my thursday nite gig i am just about AGAINST my amp.

[anotherjim]

I'd definitely look into getting that pedal screened.

[pinkjimiphoton]

thats what i'm thinking too jim, i was thinking buffer, but there's already plenty of buffers i think. i didn't wanna go with metal for the pedal cuz bernice (my pedal board is so damn heavy it has it's own name and gravity) is around 80 lbs already.

shielding it should hopefully do the trick.

thanks for working with me with great advice bro