skar audio rp amplifier series replacement bass knob control package skar audio this replacement bass knob for the rp series amplifiers makes for an ideal choice when you want to have quick access for adjusting the level of one or multiple amplifiers configured far away from your reach. compatible with the rp-350.1d, rp-800.1d, rp-800.1dm, rp-1200.1d, rp-1500.1d, rp-1500.1dm, and rp-2000.1d.