The Portaphile 627 uses three Burr Brown OPA627′s, one each for the Right-Left-Ground channels. Each opamp is then buffered with two Burr Brown BUF634s per channel for a total of 6 buffers. This allows the opamp to work efficiently at powering your headphones regardless of being large high impedance headphones or small low impedance current hungry earphones. The OPA627 is widely considered to be the best opamp for audio applications and is the reason I built the new Portaphile around this high end opamp.
Three Channel Design, Isolated Output Ground, Four Layer PCB, 3 x OPA627 , 6xBUF634′s, Jung Multiloop Topology, Powered by Single 3.7V Lithium Ion (Included, Rated for 500 Charges), Power Adaptor/Charger Included (5V), Runs 4 Hours on a full charge, Battery charges in 2.5 Hours when Ampliifer is charged while off, External Hi/Low Gain Switch (7/2), Small Size (2.824′x3.19″x.748″), Elna Cerafine