Not exactly pocket sized, but fits in a bag and sits nicely on my desk in the office, on the couch, in bed on the train.
At the bottom of the pack is a 10000mAh USB battery which should give about 5 hours of playback. Next in the stack is a WD PiDrive containing my entire music collection encoded as 320kps mp3’s. At the top is a RPi 3 with the headphone jack desoldered and a IQAudio Pi-DAC+ hat with the superfluous headers and phono connectors desoldered. This is more than capable of driving my Mitchell & Johnson electrostatic headphones.
The components are all mounted on transparent PVC boards which were laser cut by RazerLAB.co.uk from a design I made in Illustrator. The top plate featuring the Volumio and RPi logos (I should have also included the IQAudio logo, but didn’t think at the time). The boards are separated by black nylon spacers.
This is running the latest version of Volumio 2.
Works well, there are some bugs in the software, but nothing too bad, and given this is an early release is very good. Control is via my Android tablet which connects directly to the unit via wifi when away from the home network, and when at home the unit can be connected to the network via an ethernet cable and controlled either by my tablet or laptop.