Rolls HA540 MK2 Tube-Powered Headphone AmpThe Rolls Bellari HA540 MK2 is a headphone amp intended to work with a wide array of cans, from consumer to audiophile grade. The amp utilizes a 12AX7 tube running at 150V. As such, the HA540 MK2 produces a clear, powerful sound when paired with CD players, computers, or DACs. On the front of the unit you'll find 1 4" and 3. 5mm stereo headphone jacks, as well as a prominent volume knob. The rear gives you RCA and 3. 5mm inputs on channel one and RCA