This is a headphone amplifier that came with the Stereo Sound Bessatsu DigiFi No. 22. As those familiar with it know, this is a complete board that operates as a headphone amplifier when powered via microUSB. It uses the standard Burr-Brown 2134 op-amp. (You should be able to read it if you zoom in on the photo.) Since it's socketed, you can enjoy changes in sound by swapping the op-amp. You can also add two more op-amps to the empty sockets to enable balanced output. It will be shipped via Yu-Packet Post. Thank you.