Il y a une procédure pour calibrer la pédale d'expression.
comme le site de behringer semble avoir quelques soucis de traducteur je te file la version anglaise...
Citation : It may be necessary to recalibrate the pedal.
This can be done as follows :
Remove the power supply plug from the X-V-Amp, and make sure that the X-V-Amp is placed on a stable surface.
Look underneath the ends of the pedal to check that the rubber pads are seated properly.
Start the calibration with the pedal fully open.
Press and hold the keys "Delay" and "Reverb" together.
Keep these two keys held down and reconnect the power supply plug.
On start up, the display will show "PU" - which means "Pedal upper"
Gently move the pedal fully forward (closed) until it reaches the end of its travel. The display will now read "PL".
Caution - there is no need to apply too much pressure !!
Gently move the pedal backwards (open) until the rubber pad rests against the casing.
The display will now show "PU" (pedal upper).
To confirm the calibration and return to the normal operating menu, either
(a) Press and hold the keys "Delay" and "Reverb" together, or (if this has no effect)
(b) activate the pedal switch (press down hard on the end of the pedal).
The unit will re-initialise itself, but the original settings will not be overwritten.