Hi guys, I recently built a sabertooth, my problem is this, I have a bass active and when I connect it to my pedal and then to the amp i hear a very weak sound, but when I connect to a passive bass I listen very well. What will be the problem ? I hope you can help me thanks in advance.
The Sabertooth is a transistor-based effect like a Fuzz Face, and as such it much prefers seeing the impedance of a typical passive guitar or bass driving it. An active bass has a built in preamp that changes the impedance (and probably the current) that the Sabertooth is seeing on its input. Google around for "Fuzz Face and buffer" and you'll probably find better explanations.
Also you can install the impedence control pot ala the "Mastotron". Look in the mods section and you should be able to find it.
Better yet, google "active bass" and "woolly mammoth", since that's your exact issue. There appears to be about a gazillion results.