what is an expression pedal ?

[petemoore]

http://www.sweetwater.com/store/detail/EXP2Pedal/

  I have a Korg Triton Extreme, and just bought a 10k pot in a new volume pedal, but am again interested to know what's inside an expression pedal, the one in the link goes to the 'assignable pedal' jack in the back of my keyboard, used for expression/volume/etc...assignable.

[artifus]

http://www.strymon.net/tag/expression-pedal/

[Mark Hammer]

There's two general types.  One involves a pot used as a voltage divider, and involving a TRS stereo plug/jack.  That subdivides into two forms.  In one (the more common of the two), the device under control provides a voltage which the pot divides down.  The pedal essentially substitutes for an onboard voltage-control knob.  The less common form will involve something like a 9v battery in the pedal itself, straddling the two outside lugs of the pedal pot, which divides down that voltage and feeds it to the device under control.

The other type of expression pedal simply involves a variable resistance, usually to ground, and a mono plug/jack.  In this instance, the pot is usually controlling only one parameter, rather than providing anything generic that can be used/decoded to control some assignable parameter.  In my old blue MXR digital delay, there is a control-pedal jack that assumes a 50k variable resistance to ground, for controlling delay time only.  On the other hand, in my Line 6 M5 unit (as well as the M9 and M13), the expression input is simply a variable 10k resistance, not a voltage divider, and can be used to control any of a variety of parameters.  I rigged up a photocell, stuck it on the guitar top between the bridge and controls, and used it to control a Whammy program with my pinky.

[petemoore]

   I have a dual ganged 10k pot, sleeve to the 'right hand' lugs of each wafer, then tip goes to the top pot center, ring to the bottom pot center, essentially a 2x 10k divider assigned to TRS jack.
   I tried a wire between the center and outside lug of the top pot, making the controller = a 10k variable resistor between sleeve and tip [ring and sleeve connected].
   I don't get any control using what I have as a variable resistance and then variable resistive divider...but it just seeems counterintuitive to have 9v in a control pedal if it can be done any other way...making me think the 9v method isn't used for the Korg control pedal which probable/purportedly somehow controls paranmeters in the the Korg Triton Extreme when plugged into [and patched correctly] the Triton assignable pedal jack.
   I'm still curious about the 'somehow' of
  ...what is in the Korg controller pedal?         ...or...
  How many lugs does the assignable pedal jack in the Triton have, and what do these connections see whcih would make for parameter chage/control?

[artifus]

from: http://www.strymon.net/tag/expression-pedal/

also:

http://www.soundonsound.com/forum/showflat.php?Number=322584

and:

I now too have discovered the secret to making an expression (volume) pedal work on the Korg Triton Extreme  . For the expression pedal to work you need a STEREO cable. So simple but i never knew this and the technical guys at the music shops here didn't seem to think it would make a differrence. With my stereo cable in hand I am able to get the following:- Boss FV 50 L, a cheapy little Zoom pedal, Ernie Ball Jnr all to work perfectly. Simply connect the expression pedal to the keyboard using the stereo cable, go to the global mode screen and select the input device, select volume and there she goes. To control only selected timbres of a combi, you need to go to the Midi screen, MIDI4 screen allows you to select which timbers are effected by the pedal. So now you can swell in strings, pad, motion at your leisure. I am now also using a switch to tap in arpegiator tempo's.

[petemoore]

  Works but 'glitches', I have to go all the way back 'again' to bring the speed up sometimes. Reducing the speed works every time, but increasing the speed 'misses' and I have to go to slow...then not too quickly pan to fast to get the leslie speed control to go fast again.
   Works pretty good anyway since I'm getting used to it.
  Marc's discount store had these 'volume pedals' for 50 cents apiece, so I went back and got another for volume control [rewired it and added a jack to feed signal through the 10k pot...can't beat the price, both pedals for a buck ! !

[Mark Hammer]

Car racing games often come with a pair of spring-loaded foot treadles, often with a 50k pot under each foot.  Unlike cast-metal foot controllers, you can't just leave these in a position.  They always get pushed by the internal spring back to upright (heel down) position.  Still, within those limitations they can be adapted for use in a guitar context, and you can often find them cheap at 2nd hand stores or yard sales. 

[artifus]

i have one of those pedals i picked up for pennies ages ago i've been trying to think of a project for, the pots are 10k i think, but are quite hard to control smoothly.

@pete - i would check the manual and/or explore the midi screen mentioned in the above quote, i'm pretty sure you would  be able to alter the behaviour of the pedal from there.

*also* the quote mentions selecting an input device in the global mode screen and to choose volume pedal, which would be wired differently to an expression pedal - see what other options are available and try expression, if available, depending on how you've wired your pot.