The Minibox Amplifier add on card for the HiFiMan HM-901 Audiophile High Resolution Digital Portable Music Player. The HiFiMan HM-901 MiniBox amplifier module was designed by the famous portable amplifier designer Three Stone. This is incorporated with the two OPA627 op-amp and four BUF634 buffer chips in DIP packing instead of SMT packing. So buy this Head Direct HifiMan HM-901 Minibox Amplifier Card Was £159.00 Now £139.92.