2-3 Weeks. 45 Day Lowest Price - 100% Satisfaction Guarantee. The ONERR Boosted Line Selector BL-1 was designed to give usicians three very useful options: A/B box: Connect either two instruments to a single amplifier (with control of Level and Treble of one of the instruments) or one instrument to two amplifiers. Booster: Boost your guitar level and “push” a tube amp, warming your tone. Effect Loop: Create an external effect loop that can be bypassed when necessary.