Head Box RS is a reference quality headphone amplifier with fully balanced tube input stage (double triode tube 6922) and single ended, class A „FET (Field Effect Transistor)“ output stage. It offers balanced and unbalanced input as well as balanced and unbalanced bypass connectors for using the pass-through input signal with other components. Volume control consists of a precise volume regulator with matched resistance between left and right channel. A special output impedance selector allows to adjust output impedance in three steps 5, 20 and 50 ohms to achieve better im-pedance matching between amplifier and headphones. Some experiments with different positions of output impedance selector are highly recommended to get the ultimate sound experience for your headphone. An advanced multi-stage power supply with four different output voltages is used to achieve the best possible S/N ratio for out-standing reproduction of detail, dynamics and imaging with any dynamic headphone! Features Fully balanced double mono design Tube input stage Class-A FET output stage Switchable output impedance for ultimate performance Superior low distortion Low noise components for ultimate dynamic & detail Output: 6.3mm socket Full metal casing in silver or black Optional Upgrade: Linear power supply Power Box RS Uni 1 (or 4) for further improved sound quality   Technical Specifications Power output 350 mW at 32 ohms / 60 mW at 300 ohms Crosstalk - 58 dB Frequency response 30 Hz - 20 kHz /(+0,2 dB; -0,05 dB) THD+N 0.17% (XLR in, output impedance setting 5 ohm, load 32 ohm Gain 9 dB S/N ratio 99 dBA Headphone jack 3-pole ¼“ (6.3 mm ) co-axial jack Line-level input 1 pair RCA + 1 pair XLR Line-level output 1 pair RCA + 1 pair XLR Outboard power supply 20 V/3 A DC, suitable for your country's mains supply Power consumption 1,3 A DC Dimensions W x H x D 206 x 72 x 200 (209) mm Weight 2150 g without power supply