I have a spider lll 75 w/FBV pedal. I find the volume pedal does not raise the volume at a steady, even rate. The first 3/4 offers very little change. When it gets to the very end, the volume goes from good to really loud when I barely move the pedal. It's either barely on or wide open with very little movement. Can the pedal be recalibrated for a more even volume?  donald in louisiana