REFERENCE series RA50 is a 5-channel amplifier rated at 4 x 50 + 1 x 250 Watts. The amplifier is 2 ohm stable on all channels. Built-in variable 40-125 Hz switchable low-pass filter as well as subsonic filter for subwoofers. Built-in filters that allows active crossover to a 2-way system or a mid bass speaker in a 3-way system. Grand bass 0-18 dB and Phase shift control. High level input with automatic start.