This is a USB stereo DAC with an onboard headphone amplifier. It’s based around the PCM2702 chip from Burr-Brown. It uses default HID drivers, so it’s plug and play. An Analog Devices AD8066 opamp is used to amplify the line level signal from the DAC. Designed for a Hammond 1593K case (2.6″x2.6″). My understanding of PCB layout was not great at this time (2006, 2nd year university), so while the board worked fine, there’s a lot I would change.