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 circuit board that operates as a headphone amplifier when powered via microUSB. It uses the classic Burr-Brown OPA2134 op-amp. (You should be able to read it if you zoom in on the photo.) Because it's socketed, you can enjoy changes in sound by swapping out the op-amp. You can also add two more op-amps to the empty sockets to enable balanced output. Replacing the capacitors is also relatively easy, making it easy to modify and fun to play with. It will be shipped via Yu-Packet Post. Thank you.