Zapco ST-104D SQ III Amp 4-Channel Class D Compact Amplifier 4x100w RMSST 104D SQ III 4 Ch. Class D Compact Amplifier The ST III amps were the first to get the new Studio brushed aluminum finned chassis 4 Channel, Full Range, Class D RCA and Speaker Level inputs Variable input gain control Variable electronic crossover Variable bass boost control Power @ 4: 4 x 100 watts RMS THD @ Rated Power < 0. 5%THD Power @ 2: 4 x 150 watts RMS Power Bridged @ 4: 2 x 300 W RMS Signal to Noise Ratio > 90dB THD + Noise < 0. 1%