Sennheiser HDVA 600 Headphone Amplifier Symmetrical signal processing from input to output insures superb resolution, dynamics and musicality. Short signal paths featuring premium components are connected to a custom designed APLS four-pole potentiometer for precise volume control. Simultaneous operation with up to four dynamic, high-impedance headphones, two via four pin XLR input and two via high-quality 6.35 mm (1/4) jacks Chassis crafted from extruded and machined Aluminum minimize vibrations to help insure sonic integrity. High gain amplifier drives difficult low-impedance headphones with ease