50k Wah pot

[Legendin]

Hey all, new guy here. My name is Ariel, and I'm Studying electronics in senior high at the moment, building a few pedals in my spare time. Anyway, enough about me!

I've done some nasty stuff to my guitar, so to go along with the two circuits it now has, I decided to build a Bblender. The (slightly modified) schematic can be found here: Clickie Now to the problem. I really want the blender to be controlled by an EXP-pedal, but I have not succeeded in finding a 50k pedal (or a pot that can be installed in a wah enclosure from SB). So basically what I'm wondering is if any one here knows of a pedal or pot that might suffice, or have any other tips on what I might do. I've heard that some exp-pedals that were used with the old Yamaha synths were 50k, but I haven't been able to find any.

Hope someone can help me solve this little problem! 
Thanks

[Phorhas]

You can take a regular 100K Wah Pot. and parallel a 100K resistor to it (solder to lugs 1 & 3).

[Legendin]

Hmm... you sure that would work? Anyway, I'll test it out later when I get back home.

[smnm]

Hi - and welcome.

My experience may or may not be useful to you.
I recently transferred a circuit into a wah shell.
In stompbox form it had a 500K pot, but I found that in the wah shell, because the action of the treadle in my shell only turned the pot a little over a quarter of it's rotation, I needed a pot value about 4 times the original, so that a quarter of a turn (the rotation available to the pedal) would take me from 0 to a little over 500K.
I got a linear 2.2M pot and it works fine.  
It takes a bit of adjusting so that the zero resistance point matches up to the 'toe fully down' position,.

Measure the rotation of the pot in your shell, then you can work out what pot you need - a wider angle on the foot pedal = more rotation of the pot, so wider angle = more control. Most pots have a rotation of 270 degrees.

[phantom lord]

You can take a regular 100K Wah Pot. and parallel a 100K resistor to it (solder to lugs 1 & 3).

NEWBIE ALERT!!

so if I had a 100k pot, and used a 200k resistor, would that make it a 25k pot??? is there any way to make a 100k pot higher, like say 1m? like if I wanted to put an effect in a wah shell, and needed a higher resistance, how would I do that? could I take the insides of another pot and use it with the wah pot? (the part that has a sprocket shape to it, connected to the treadle)

[Phorhas]

When paralleling resistors the equation to use is the following:
(R1*R2)/(R1+R2)

So 100K || 100k is 10,000/200 = 50K

If we put 100K || 200K = 20,000/300 = 66.666666...K

[phantom lord]

When paralleling resistors the equation to use is the following:
(R1*R2)/(R1+R2)

So 100K || 100k is 10,000/200 = 50K

If we put 100K || 200K = 20,000/300 = 66.666666...K

thanks for the amazingly fast response!!! that was unexpected! so I figured out that a 34k res would take a 100k pot down to 25.3xxxxx. that equation alone will help me alot in the long run, so thank you for that!

[Legendin]

Sure, if I paralell a 100k resistor with a normal 100k wah-pot, I get a 50k resistance total between OPA1 and OPA2, but the thing here is that the middle lug on the pot is the one going to the input of OPA3, and thus just adding a 100k regular resistor in paralell probably wouldn't work with the blending effect. And btw, the pot needs to rotate all the way in both directions, as one of the extremes is OPA1's "full effect"-point, while the other is OPA2's. Take a look at the schematic..

Another thing, though, is there no way to adapt this circuit to accept a greater (100k) or lesser (25k) resistance in the pedal? That way I could just use a regular pedal for this..

thanks for your help.

[smnm]

Maybe a 47K pot would work? Easier to find -
but I don't think you'll be able to use it in an expression pedal if you need the full rotation. How about using an extra large knob that you can twist with your foot, or a tall thin knob mounted on the side so you can roll it w/ your foot - not very precise, but I've used it on a ring mod type effect with good results.