Here is an easy home made Headphone amp with 2-gain settings (10x & 6x) with small footprint for portability. Powered with an onboard 9 Volts battery and external supply option also.
Four screws will secure the battery between main PCB and another top blank PCB. .
I am planning a denim stiched pocket cover for this one. .
(There was an error in routing around volume control which is corrected in the PCB schematic as shown).