what pot for a basic volume pedal?

[armstrom]

A friend has asked me to build him a simple volume pedal to put at the front of his effects chain. My plan is to use the expression pedal shell sold at smallbear http://www.smallbearelec.com/Detail.bok?no=548 . However, I'm not sure what kind of pot to use. My design will be as follows:
In -> op amp buffer/gain stage -> volume pot -> op amp unity gain buffer -> Out.

So, the question is, what kind of pot should I use? I know I can use a linear pot if I don't care about how "natural" the range feels.. but if I want to maintain a proper audio taper do I need to use a reverse log pot? From looking at the picture of the enclosure it seems the gear system rotates the pot counter clockwise when the "toe" is down and clockwise when the "heel" is down.  That means  I will have to wire the pot backward from a normal volume pot (ground to lug 3, output on wiper and input on lug 1) Does this imply needing a reverse log taper? Also, is there an easy way to address the lack of "travel" (the pedal not fully rotating the pot from stop to stop)?

-Matt

[petemoore]

So, the question is, what kind of pot should I use?
  I'd use one with a "D" shaft so the gear fits.
  I know I can use a linear pot if I don't care about how "natural" the range feels.. but if I want to maintain a proper audio taper do I need to use a reverse log pot?
  Seems sensible, especially if you want toe down to be volume up.
  From looking at the picture of the enclosure it seems the gear system rotates the pot counter clockwise when the "toe" is down and clockwise when the "heel" is down.
  I'd go with fully CW when the toe is down, opposite of the common volume pot wiring/response: 'turns up when top of knob goes left' volume arrangement
  That means  I will have to wire the pot backward from a normal volume pot (ground to lug 3, output on wiper and input on lug 1) Does this imply needing a reverse log taper? Also, is there an easy way to address the lack of "travel" (the pedal not fully rotating the pot from stop to stop)? 
  The shaft travel is "X" Amount with wah treadle, some %age of potshaft rotation won't be used.
  Seems like reverse log'd be the one, that or heel down = volume up...
  I decided I didn't like my volume controls to ever be able to go to fully off, seems too much like broken that way [had some long debugs because of volume @ 0%], your needs / tastes may differ.
  Volume pedals can be 'fidget-ey', hard to precisely set, I'd prefer one that is able to go from 'normal' to 'boost', instead of all the way up to 0%, that way it'd be easier to fine tune "X" volume, it'd never shut off on me, and never go crazy loud volume.
 

[armstrom]

Thanks for the reply.

   I'd go with fully CW when the toe is down, opposite of the common volume pot wiring/response: 'turns up when top of knob goes left' volume arrangement   

As far as I can tell, the enclosure dictates the direction of rotation. It will rotate the pot counter-clockwise when the toe is pressed down. In order to change that you would have to modify the pedal enclosure itself to either place the gear on the other side of the pot or flip the pot so the shaft is point 180 degrees in the other direction. Neither sounds easy

[MikeH]

The problem I've run into in trying to make a volume pedal in a crybaby type shell, is that the mechanics of those shells and the rack and pinion gear setup, doesn't allow 100% pot travel, as pete already stated.  Either you have to live with your volume being down just a hare all of the time, or you have to deal with not being able to kill your volume all of the way.  Both are unacceptable to me 

[armstrom]

I'm considering adding a normally-on momentary switch in the heel that will cut the volume when the heel is pressed ALL the way down. Of course, this will only work if the volume gets fairly low before the switch is hit, otherwise the transition could be a bit jarring I have access to machine shops so I may try to make a custom gear/rack set with a smaller diameter so I can get more rotation out of the pot for the same linear travel but that will be a last resort.
-Matt

[Ben N]

The problem I've run into in trying to make a volume pedal in a crybaby type shell, is that the mechanics of those shells and the rack and pinion gear setup, doesn't allow 100% pot travel, as pete already stated.  Either you have to live with your volume being down just a hare all of the time, or you have to deal with not being able to kill your volume all of the way.  Both are unacceptable to me 

+1

[JKowalski]

The problem I've run into in trying to make a volume pedal in a crybaby type shell, is that the mechanics of those shells and the rack and pinion gear setup, doesn't allow 100% pot travel, as pete already stated.  Either you have to live with your volume being down just a hare all of the time, or you have to deal with not being able to kill your volume all of the way.  Both are unacceptable to me 

+1

Why dont you allow the pot to go to fully off, and make up for the lack of travel the other way by increasing the gain of the signal going into it.

So you have your gain stage, into a volume pot... The gain is set high enough to get unity at the limits of the pot travel. That would let you go from unity to fully off...

[armstrom]

Yeah, that's probably what I'll end up doing. Should be easy to determine exactly how much gain is required.
-Matt

[dan5150]

Once it all said and done, wouldn't it just be cheaper to buy a volume pedal?

After the cost of the shell, and the engineering & time you put into it....

[petemoore]

  I just did something similar.
  JFet Blaster driving Dist+, room for one panel mount.
  Not sure of how much drive I wanted, I used stuck a volume trimpot after the Stratoblaster, mounting the "Gain" control on the panel.
  Set it up, play it, adjust the volume accordingly...done !
  Being able to go above unity and just the idea of an active helping out in there makes sense.
  The volume control on the guitar of course would be a duplication [ignoring the value differences] of a passive volume pedal.