Well....for what it's worth - I used split my signal and run two amps (an Ampeg B50R and B100R). I'd run direct to the B100R and thru a Sovtek Big Muff (regular, not bass) to the B50R. I'd keep the level lower on the B50R and crank the volume on the Big Muff.....so, clean, the majority of the volume was from the B100R, but both were running clean. Then when stepping on the pedal, the fuzz would kick in nice & loud, but the same volume level of clean bass was coming from the B100R. I used these 2 amps eventually because they're fairley inexpensive, light, have a small footprint and you can stack 'em. To begin with, I used the same idea only used an Ampeg V4B thru a 2 15" Kustom cab for the clean and a Marshall 100 watt Lead thru a 4 12" cab for the fuzz.......sounded fucking great, but too much shit to haul around. Anyway, that's how I got the "screwdriver thru the skull" sound.