Whenever I use my F1-X (always in conjuction w/ my SF-2 superfilter and my Markbass- amp) I get these annoying & damaging electric, loud pops that overloads my amp. these sounds are independent of bass-choice(elan & epic), cables and grounding, &c. could the choice of voltage cause this problem? on the F1-X you can choose between 220V and 240V. we have 230V in sweden...what would you choose? best regards from sweden/ kristjan aunver

What voltage is the F-1X currently set for?

If you haven't already found it, here are the settings.

hi, davehouck, and thanx for your promt reply. I talked to my tech-wiz and we agreed that these pops might orign from a defect 12AX7-tube. because this annoying effect doesn?t come until the amp is warmed up. I?m gonna try this theory with a spare. changing voltage was no remedy. I?m stuck on 240V. thanx from sweden/ k aunver

I checked with dad, and he says he would use the 240V for Sweden.  
 
Let me know what you find after you change the tube.