This is my build of the O2 amplifier designed by NwAvGuy. All the details can be found on his site http://nwavguy.blogspot.com/
I stuck to the recommended components, and so long as you pay attention to the notes on construction in the details page it is a straight forward build. The custom front panel was ordered from Front Panel Express and surpassed expectations.
Anyone considering a headphone amplifier should really look into the O2, it ticks all the right boxes and sounds superb.
With its low output impedance it complements my 32ohm Grados and 80ohm Beyerdynamics very nicely.