beyerdynamic A20 Headphone Amplifier - Silver ALPS potentiometer for variable volume control, Internal wide-range switching power supply for worldwide use 170 mW / 250 , high-gain RCA input, input signal can be looped through, entirely free from signal-loss thanks to the hard-wired RCA output T.H.D = 0.01 % at 170 mW / 250 , Elegant, wrapped screwless solid all-metal housing Audiophile grade, suitable for all headphones up to 600 Ohms Made in Germany with 2 year Warranty