Creek - OBH-21mk2 - Headphone Amplifier Creek - OBH-21mk2 - Headphone Amplifier The OBH-21mk2 is essentially a very high quality miniature integrated amplifier OBH-21mk2 has three pairs of stereo RCA sockets on the rear panel for Line level input, looped Line level output, and a variable pre-amp output Weight: 22 ounces Dimensions: 7" x 3.75" x 2.25