4-channel 2U digital power amplifier is designed for multi-zone distributed speaker systems and professional sound applications. It engineered with class D technology and operates at 85 percent efficiency. It consumes almost one-third less power than conventional analog amplifiers. It has compact and lightweight single or dual rack-space design and ultra-low heat dissipation. It is comprised of high and low impedance, each equipped with an independent power supply for each channel to assure continuous operation and unmatched reliability and performance. Other features include recessed stepped attenuators for precise gain calibration, removable dust filters for easy maintenance, and optional isolation transformer.