PWM - expression pedal goof

[Strategy]

Got a hefty John Lyons PCB shipment (thanks John!!) and promptly built the amazing PWM by Tim Escobedo. I know that several layouts implement LFO or envelope control over pulse width, but I thought expression pedal would be ideal for a wah like approach to pulse width.

I successfully added an expression pedal input with relatively little effort - a eureka moment of sorts which could be signs of emerging from noob-hood into relative competence 

The goof on my part was that I failed to ponder the value of my expression pedal (I only have one, the common Roland EV-5, which has an adjustable sweep range as well). As a result, I get only a hint of the expressiveness possible: it doesn't sweep enough through the pulse width to really be very nice sounding. 

The Width pot on PWM is a mighty 500K. I have no clue what the resistance range is of the EV-5, what is typical of expression pedals, or whether one even exists in my needed range!

Options:
- Identify an appropriate existing expression pedal (Moog/Roland/Korg/other) in my range - any suggestions?

- Modify an existing expression pedal to sweep 500K - how? what's inside one of these things, anyways?

- Make an expression pedal from scratch (any links to useful previous forum threads or wiki's greatly appreciated, if known)

Many thanks to you all for the help...
- Strategy

[John Lyons]

An expression pedal is usually just a variable resistor (pot) connected to some sort of treadle like a wah.
I would think that most are 10Kish.
You could get a 500K linear pot and put it in an old wah shell easily. Ideally you would need a long shaft pot
though so you may need to look around. You could probably find one with not too much looking though.

You need to long shaft to connect the pinion (gear) in order to use it with a wah treadle.
You could also look for a 1M pot and parallel a 1M resistor across the outer lugs and get a rough reverse log taper
but it may be easier to find a 1M long shaft pot...

JOhn

[Strategy]

Thanks John! That is awesome info.

a long type 500K pot shouldn't be too hard to find, and it also should be relatively easy to find another Roland EV-5 in the used bin at the guitar shop I go to here and see if I can crack it open and modify it.

I highly recommend the expression pedal mod for this pedal to anyone who is interested. Sweeping pulse width is expressive in a similar way to filtering, but it's different, hard to describe.

- Strategy

[Strategy]

Well I have my Roland EV-5 pedal opened up. It takes a 17mm-ish pot with a long stem. The trouble is, it's really NOT apparent how to remove the pot!! This is obviously designed to discourage such dissassembly!  Damn you roland!

I looked at the DIY expression/wah supplies on Small Bear http://www.smallbearelec.com/Detail.bok?no=548

It seems like you are required to have the "wah style" pot which has the gear edge so it can interface with the treadle. These only go up to 200K, which would work, but, to have maximum sweep I think modding an existing expression pedal might still be my best bet.

- Strategy

[Top Top]

This may not be the route you want to go, but I built a very simple expression pedal by Taking a 3/4" thick piece of wood and drilling a hole through the middle. I put a piece of metal rod through each side of the wood (you could also put one length all the way through), and a support on either side, essentially forming an axel and a support for the axel.

THEN, there is a short length of dowel, also with holes on each side. The metal rod goes snugly into the hole on one side of the dowel, and in the other side, there is a pot held up by an aluminum bracket wired to a jack. The shaft of the pot slides into and fits snugly in the dowel.

The pedal turns the dowel which in turn turns the pot. I have a wood stop under the back of the expression pedal, so that it stops at the maximum resistance that I need it for, so that I don't have pedal travel that is further than what actually does anything.

[Strategy]

This may not be the route you want to go, but

I applaud your raw approach to crafting a home-brew WOODEN expression pedal, this is fantastic! Unfortunately I don't have the tools for wood working. One option I am noticing is to obtain an inexpensive 500K volume pedal and use an insert cable to make it function as an expression pedal!

- Strategy

[John Lyons]

Any Long shaft (1/4" shaft) pot will work.
The gear (called a pinion) comes off and
attaches to the pot shaft. I wouldn't mess with th
Roland cheapie plastic expression pedals for anything
you'll use outside the bedroom.
Worse case you can reuse the shell for a wah.

[Strategy]

Oh- great! Thanks John. This makes things a lot easier! The Alpha 16/17mm pot series have long shafts, I think those may do the trick.

- Strategy

[John Lyons]

Use a full size pot with a 2" shaft (or so).
You can cut of the shaft excess with a hack saw.
You want to use a full size pot as it will last
longer and be more sturdy.