This headphone amp was built back when, Head-Fi infamous and longtime reclusive, NwAvGuy was still posting on his blog from parts listed on the site sourced from Mouser, digikey and others. I was a Mechanical engineer that had access to an EE lab to solder this up with professional equipment.
Originally this amp was built as the rechargeable battery version. A little later NwAvGuy wanted to provide a DAC for this amp that could also be a DIY project but ran into licensing issues as well as difficult to DIY solder components so it was offered assembled and retrofittable into the original enclosure footprint. This unit includes that add-on.
Up for sale is an enthusiast built Objective2 Headphone amp with O2 DAC, AC power supply and a mini USB cable.