Questyle M15C 3.5mm / 4.4mm Dual Output Jacks Adjustable Gain I have kept this unopened since I purchased it. I am selling it because I bought a DAP (Digital Audio Player) and have no opportunity to use it. The M15C is equipped with four SiP current mode amplifier modules and supports both 3.5mm single-ended output and 4.4mm balanced output. Furthermore, it newly adopts a gain switch. Users can freely switch the gain mode according to their preferences and the characteristics of their earphones/audio systems. Thank you for looking.