is a buffer/boost with adjustable tone color and slight saturation. The DRIVE knob takes you from a warm, slightly dark boost at the lowest setting, to a full-range clean boost around the middle settings, to a bright saturated boost when maxed out. BB can serve as a buffer, a booster, a tone control, and can add more break up to whatever is before or after it. It can also serve as a great clean buffer for your pedal board.
BB as a buffer
If you set up BB as just a buffer, you'll enjoy added clarity when comparing the buffered signal to the bypassed signal. It's amazing how much signal loss there is in even short amounts of cable. To run as a buffer, you turn the volume up to max and leave the drive down. Then, increase the drive to where you like it.
BB as a volume boost/cut
You might want to set up a ZIM channel for a volume boost or cut. For this, install BB in Ch A and use the patching jacks to swap the order of effects - go into B first, and then into A.
BB as an EQ / Notch filter
You can use BB to change the color of whatever sound you already have. For this, install BB in Ch B and use B's Voice and Depth controls to alter the sound. This is best when after any ovedrive/dist/fuzz effects, but you can also get some neat sounds by doing it the other way around.
BB as a gain boost or overdrive
Not recommended. There are other ZIMcards that are much better for this kind of thing. VT is probably the place to start for a nice gain boost, and H9 will take you to the edge of OD, delving into distortion territory.