Difference between Expression and Volume pedals??

Discussion in 'Effects, Pedals, Strings & Things' started by frizbplaya, May 16, 2008.

  1. frizbplaya

    frizbplaya Member

    Messages:
    392
    Joined:
    May 8, 2008
    Location:
    Minneapolis, MN
    I don't know the difference and it's been bugging me for a while now. I think the term "expression pedal" is thrown around loosely and that's what's confusing me. Can I get a technical description of what an expression pedal is supposed to do? Does a pedal like the DL4 send a voltage and get a different voltage back?

    I'm extra confused because my Memory Lane can take an expression pedal, but it's just sending an FX loop so what really needs is a volume pedal to lower the gain of the return, causing the feedback to be lowered. Rocktron makes an expression AND volume pedal http://www.musiciansfriend.com/product/Rocktron-Hex-Expression-Volume-Pedal-?sku=150144 that can take either an in and out TS or one TRS for MIDI stuff. Is that TRS just getting a lowered gain signal back like a volume pedal would do? Or is it a separate pot that give back a voltage or somethign? Can I send a TRS cable from the Memory Lane to the Rocktron? Am I making any sense?!?!?
     
  2. crazychu

    crazychu Member

    Messages:
    14
    Joined:
    Apr 8, 2008
    yeah i dont know either, i thought expression pedals were like wah wah pedals, but i dont think they are anymore.
     
  3. tone4days

    tone4days Member

    Messages:
    6,234
    Joined:
    Mar 2, 2005
    Location:
    central maryland
    i think of it this way .. cant vouch for the deep technical accuracy of this way of thinking, but it hasnt gotten me in trouble yet ...

    a volume pedal controls the amplitude of an fairly low voltage AC signal with an (approximately) audio bandwidth .. the signal contains the 'information' that is being manipulated ...

    an expression pedal controls a DC voltage level that can range up to a handful of volts or so ... the unit that the expression pedal is connected to 'reads' that DC level and uses it to control some other parameter (which, perhaps confusingly, can be the volume, but might just as easily be something like delay time, or number of repeats, etc) .. but the signal going to/from the experssion pedal is not the information itself ..
     
  4. mike@nortoncable.com

    mike@nortoncable.com Member

    Messages:
    3,286
    Joined:
    May 16, 2007
    Location:
    Bucks County, PA
    An expression pedal is an external control for a value on a pedal, another knob almost.

    lets say in the case of a Mooger fooger, you put the expression pedal into the rate, it will control the rate. On some delays an expression pedal might modulate the time.

    :)
     
  5. TweedBassman

    TweedBassman Member

    Messages:
    310
    Joined:
    Sep 19, 2007
    Location:
    Milford, CT
    put simply:

    a volume pedal takes the signal put into it, and sends a portion of it to 'ground'... just like the volume on your guitar. this is achieved by decreasing the resistance between the signal and ground as you press it towards the heel. it also has an output to go to the next pedal.

    an expression pedal works similarly, but usually uses a TRS (tip, ring, sleeve) jack. instead of decreasing or increasing the amount of resistance to ground, it simply increases or decreases resistance between the tip and the ring. in effect, this makes the pedal work more like the tone control on your guitar; instead of raising and lowering total level, it raises and lowers the amount of signal between two points (in the guitar's tone control, it's the amount of signal sent to a simple low pass filter).

    if i understand the memory lane's function correctly, the feedback of the pedal is sent to the tip and ring of the Expression jack. if you split the signal with a TRS to dual 1/4" cable (insert cable), you can place another effect between the tip and ring, giving the repeats their own effects loop. if you place a volume pedal in the loop, you have control over the feedback level. if you use a TRS cable into an expression pedal, it will act similar to the volume pedal by controlling the feedback level.
     

Share This Page