Seriously? The switch is on the back right next to all the jacks on the B2. Maybe the input jack switches it on and off? Or just unplug you wall wart when you're not playing, I always do so they wont heat up and burn my house down while I'm at work.
wall wart
just unplugging it would turn it off
but i just looked online and the B2/2.1 are the only ones out of the bass ones that actually have on/off switches