Robert Murphy wrote:Yes, expression pedal equals volume pedal.
With respect, a "Volume" Pedal contains a pot (or equivalent variable-resistor-type of component) in series with the output of the instrument, and governs the strength of the signal that is ultimately delivered to the Amplifier through the 'output' jack of the Pedal. The Volume Pedal therefore has an Input Jack and an Output Jack in order to be placed in series between the instrument and the amplifier.
An "Expression" Pedal (in the true sense of the terminology) usually also contains a pot, but in this instance the variable resistance of the pot is used to produce a variable Control Voltage from the 'static' voltage that is transmitted TO the Pedal FROM the Amplifier (or Effects Unit).
This variable Control Voltage is then transmitted BACK to the Amplifier (or Effects Unit) where it is then analysed as a percentage against the known static voltage and the resultant ratio used to then trigger the modification of a condition or parameter in a circuit within the Amplifier or Effects Unit.
This backwards-and-forwards of voltage transmission is usually accomplished via the ONE SINGLE (stereo) cable or jack that is attached to the Expression Pedal.
At NO point is the cable from the instrument actually plugged into the Expression Pedal.
Under certain (programmable) conditions, yes, one could use the variable Control Voltage output from the Expression Pedal to be assigned to the output VOLUME of the Amplifier or Effects Unit, but certainly NOT in the way that most pedal steelers traditionally use and set up a true Volume Pedal....
Just a small (?) pedantic rant about correct terminology before someone buys an Expression Pedal and tries to use it as a series-connected Volume Pedal for their Steel Guitar. ....It WON'T work....
Respectfully,
Peter