Alesis RA 500 Professional Reference Power Amplifier Rated output, per channel 4 ohms @ 1kHz, .02% THD+N 250 watts RMS per channel 8 ohms @ 1kHz, .05% THD+N 150 watts RMS per channel 8 ohms, bridged mono mode 500 watts RMS Signal to Noise Ratio 105dB, 22Hz-22kHz bandwidth referenced to rated output Frequency Response 10Hz  70kHz +0, -3dB Input impedance 20k , balanced, 10 k unbalanced Size " 18.9" W x 5.63" H x 10.71" DRack Units: 3RU Height Weight: 28.5lbs Provides a crisp, clean signal for outstanding performance and extended speaker life Designed for studio use with advanced convection cooling for heat dissipation Stable operation for extended sessions, unaffected by heat-related complications, without the distraction and annoyance of fan cooling Bridgeable to Mono for Monoblock or single channel use Height - 2 RU ( Rack Units )