The throw required for wah and volume pedals?

[sean k]

I'm just starting building a row of four teadle operated effects. Two treadles for the feedback and speed of the echobase, one volume pedal (using the anderton mod at Tonepad) and a wah pedal of the inductor variety.

Designing it up on paper I think I have to get the maximum use of the rack and pinion for each pedal so from up to down I use up all of the pedal rotation but now I'm not so certian as I remember a fellow saying that the way to tune a wah pedal was about how the pot was set in relation to the rack... and this is whats got me thinking.

If this is indeed true then the rack and pinion on a wah aren't set for complete use of the "throw" but for some percentage of that throw so the pot can be tuned in. Is this true?

If it is better to just tune into maybe 60% of a pots rotation then at this stage it's just a matter of me moving the rack and pinion closer to the treadle axis, and adjusting the pot, and this would be much easier to live with than building the whole thing then finding only a percentage of the treadle movement does what I want it to.

[jacobyjd]

I don't think the PURPOSE of the lack of use of the whole pot rotation is 'tuning'--I think it's a shortcoming of the mechanical design.

[sean k]

Therefore the optimum mechanical design uses the whole of the pots rotation?

I can live with that... after all, it's the easiest way to design something... well, not easiest, but the most thorough I suppose.

I'm just thinking now that having the ability to turn the pot and a system of different positions for the rack, being able to move the rack mount axis away from the bottom of the pedal, could give you the ability to tune in your most comfortable foot position for the greatest wah effect.

Excuse me, I always over think things at the beginning of a build.

Neat box eh?, just right for building four treadle pedals into. Friend of mine picked it up at the dump and when I saw it at his place I thought it was too useful to ask for but a few months later I was back at his and saw it was still unused so I asked and he said yes and that it was on its way back to the tip anyways.

[pazuzu]

was that a spoiler from the top of a pickup truck?

[sean k]

Sure would'a spoiled my pickup truck if I had one 

Not sure actually but I think it's a test project done by a student in shop class to illustrate all the skills he's aquired.

[pazuzu]

would have been cooler tig welded.

that's a sweet enclosure though. i just spent an hour ripping apart the furnace that was replaced from my house. it's from the 50's. about 150 lbs. of sheet metal goodness.

[petemoore]

  It basically has to be less than the full throw, otherwise the pot would bottom out, either breaking the rack, pot, gear or something.
 If the wah is set up right, that's enough range and allows treble adjustment.
 Could be it was thought of as a compromise that could be made to not matter.
 I had enough trouble with pedals seeming broken by way of volume pot turned all the way down to make all volume pots with a stop resistor to Gnd. so they can never go all the way down to no output.
 I built a couple ''springs 'n string'' [ernie ball volume pedals have this] type treadle pedals, probably not as reliable as the rack & pinion but seems to be holding up just fine. A little treadle jab only moves the pot CW a slight amount [because of the shaft resistance and softness of the long spring, quicker on the turn down [short spring stretches a little when treadle toe goes up], operates 100% potshaft range...took a few to find and make a workable, right sized pulley for matching the ratio of the potshaft range to the treadle travel.

 
 
 

[jacobyjd]

Sean--pete is right--you need to be careful that you don't max out the pot.

On my Crybaby, I removed the rubber stops from the pedal. I replaced the ones on the heel with really thin foam bumpers, and I left the ones on the toe off. Basically just enough stoppage to keep metal from clacking. It gave me a little extra pot travel without getting dangerous.

[aziltz]

I'm curious.  I know you didn't design the box, and it looks like a great find, but to me it looks like toe down is already elevated at a decent angle.  Could pose a comfort problem, no?

[petemoore]

  Ok...since I'm not going into production, and it'd take some distribution to make it worth machining up to make 'em outta plastic or whatever.
  A "Barberpole" 45 degree angle threaded pot-turner, kinda like the old time 'push down to turn screw CW' screwdriver.
  Take a tube of say metal, machine a twist-slot up each side, stick your shank in, install the shank pin [it goes through the shank and the twist-slots]...push/pull of the shank = CW/CCW twist of the tube.
  See, then it'd be so easy to make an up/down and side/side pedal, 2 separate controls with 1 pedal [like the old Foxx phase?/I forget what the other side/side controlled...a dual springs/strings treadle control method...funny insides, pulleys and strings strewn this way and that.

[pazuzu]

I'm curious.  I know you didn't design the box, and it looks like a great find, but to me it looks like toe down is already elevated at a decent angle.  Could pose a comfort problem, no?

i wouldn't think so. looks like you would just stand back farther with your leg at a greater angle to compensate.

[aziltz]

i wouldn't think so. looks like you would just stand back farther with your leg at a greater angle to compensate.

I tend to fall over a lot while getting on and off a wah pedal that's a far reach.  but I'm also a 6'3" klutz.

[pazuzu]

i'm 6'4 and my last name is Klotz.

but i rarely use a wah pedal, never really been my thing.

[aziltz]

i'm 6'4 and my last name is Klotz.

but i rarely use a wah pedal, never really been my thing.

not to hijack a thread, but the best guitar for clumsies is the telecaster.  the thing takes a beating.  My put a good dent in the drywall via the head stock this week when i lost my balance and then tried not to kick the knobs off my liquid sunshine.  built like a tank.

[Gus]

For a Wha.  The throw required is what is needed to sweep the wha.   I mean this in a good way.  The standard wha pot(two transistor inductor like wha) is more or less just a volume control after the first gain stage that then "feeds" the EF (emitter follower) after it.  People need to think about the wha first gain stage  The gain it is set by the collector resistor and emitter(or lack of emitter) resistor if the hfe is high enough and the series input resistor.  Then the wha pot is used to divide down the amplified signal at the output of the first gain stage to drive the EF, SO if you adjust the gain you can get the sweep you want with more or less of the pots rotation.

IMO there is no one value resistor(s),inductor,transistor(s) etc in a wha that makes it sound good ,understanding how you can adjust the first gain stage to work with the pot and sweep cap makes it much easier to adjust a wha to what you want.

[sean k]

I left my camera plugged into the PC so the batteries have gone dead, so I haven't got photos yet, but I spent last night getting one treadle set up complete and it works from end to end of the pots rotation, and feels quite easy under the foot, so I can easily have the amount of movement on the treadle adjustable by where I put the stops, or if need be, put resistors on either end of the pots

There really is a whole bunch of work ahead of me to get this right and after just one treadle finished I hope I have the endurance to get through the other three.

Incidentally, I kinda looked into finding the types of rivets used on this enclosure, the type where you have a die on either side and hammer them up, and they were about $3.00 each  ,which seems ridiculous, but I suppose when everybody uses blind type pot rivets then it stands to reason that the older ways of acheiving something get more expensive. I'll keep looking though because I do like the little round heads and the somewhat hidden nature of the amount of work involved.

Ad thanks Gus, for that info, I'll keep it in mind when I build the Wah board for this.

[R.G.]

Here's the background info.

Pots have a maximum mechanical turn angle, obviously. This is usually 270 degrees to 300 degrees, varies by the pot mechanical design, for insight of which, see "The Secret Life of Pots" at GEO. They have a different and smaller electrical turn angle, as some of the rotation at each end is taken up by the slider being on the end-metalization. There do exist pots with no mechanical stop, which will rotate continuously. They have an almost continuous resistive band, only a small dead zone, and are mostly used for servo applications.

The mechanical rotation limits are mechanical stops. If you force it beyond the stop, you break something inside.

So the best you can ever do is have a mechanical setup which is ... exactly... equal to the mechanical travel. That will produce small dead zones at the end, but not break the pot. You can have a mechanical setup which rotates the pot the electrical travel, exactly, but is prevented from hitting the mechanical stops. This is perfect electrically. But you have to then align the mechanical and electrical travels between the mechanical rotation mechanism and the pot itself.

Most wah pedals, the Vox style in particular, have less mechanical travel than the pot will rotate, so there is some adjustment of the electrical travel within the mechanical travel; you can make it more bass or more travel by pulling back the plastic rack and rotating the gear a bit forward or back. But you don't get the full electrical travel when you do this kind of thing.

Making the mechanical travel match the electrical travel and not break the mechanical stops in a pot is a non-trivial mechanical design problem for us junior MEs.  

That completely leaves aside the issue of foot comfort. My approach to user interface has always been that if it was hard to design, it ought to be hard to use.

[pazuzu]

i'm 6'4 and my last name is Klotz.

but i rarely use a wah pedal, never really been my thing.

not to hijack a thread, but the best guitar for clumsies is the telecaster.  the thing takes a beating.  My put a good dent in the drywall via the head stock this week when i lost my balance and then tried not to kick the knobs off my liquid sunshine.  built like a tank.

no man, i'm not clumsy, my last name really is Klotz. like the racing oil company.

[sean k]

Well this thing didn't take very long at all to design, after all it's just a few arcs on paper, but it's takin' a while to build simply because I'm deciding to drill and tap just about everything and little 3mm taps clog fast in aluminium.

One treadle complete, three to go.

This is the main shaft so you can see that two treadles share each supported part of half of the shaft though I might add a little brace inbetween each pedal if it needs it.

Here you can see pretty much how each treadle is mounted to the shaft... or the basics of it.

A bit blurry but heres the business end of things. I kinda took it for granted that if the travel on the rack and pinion equaling the rotation of the pot is what I want to use and it's available. The spring is part of an old lawnmower starter spring. Thats my favourite bit.