Aguilar OBP1SKSET 2-Band Boost Onboard Bass PreampActive electronics and preamps give you bands of EQ to shape your bass's tone. Using these active EQs lets you find your signature sound directly from your bass. Aguilar sets the standard for aftermarket onboard preamps. The Aguilar OBP 1 runs at either 9V or 18V and gives you the benefits of active electronics while keeping the natural tone of your bass intact. You get two bands of 18dB boost at 40Hz and 4kHz via the OBP 1's discrete all FET