Hey guys, I have been in contact with Zach Vex about the Woolly Mammoth and active basses. Here is what he said: Hi Brandon, I think you can effectively use the Woolly with a passive bass using a moderately high pot wired as a volume control to reduce the volume and increase impedance. Or, you can put a series resistor in line with the signal. Either of these could be soldered into the enclosure at the input to the circuit board. I can forward your email to Chuck Zwicky and if he has time he might write to you with suggestions. I also have some mods I can do as well. Just so everyone knows.