I am having a problem with my LPB 2ube stereo preamp pedal. The right channel drive pot seems to have no effect on the signal, and also when I tap lightly on the case while playing a note I get a crackling sound. I swapped out the the tube but this did’nt solve the problem. I’m tempted to open it up and have a look at the connections to the drive pot but I am concerned about the high voltage warnings in the manual. So any advice or ideas would be appreciated !! Thanks, Johnny Banjo