MBQUART ONX1.2000D Onyx D-Class Mono Amplifier by MBQUART. $318.89. Sophisticated and stylish black onyx heat-sink, and illuminated MB Quart logo give the Onyx amplifier an incredible look. This amplifier is loaded with features and power (CEA-2006 compliant), offering superior quality and durability at an affordable price. The amp is 4/2/1 Ohm stable, feature variable low pass, subsonic filter, solid RCA inputs and outputs, and built-in system diagnostics.