The beast has been tamed. It sounds good too, although my headphones are cheap Sennheisers. The headamp is enclosed in a Hammond enclosure, using the aluminium casing as heat sink, it gets hot. It makes for a nice way to keep the coffee warm by placing the cup on top of the amplifier.

Q6, Q8, Q15, and Q17 are the output transistors, and needs heat sinks, I have not calculated the exact size needed, but the bigger the better. I use the aluminium chassis of a Hammond 1455N2202 with the transistors mounted on the bottom, and it gets warmer than I like. Never test the amp without proper heat sinking in place, as the output section will most certainly release the precious blue smoke.

Power supplyI have used a 2X12V toroid, a rectifier bridge, and 4700uf on each supply rail. Each channel draws about 200mA. 

GroundingSome attention is advised when wiring the ground, my first ground layout resulted in a nasty saw-ish 50Hz hum from the amplifier. I now connect the separate grounds from the input RCA connectors to their respective ground pads, next to the input pads. The power ground are connected to a star ground between the 4700uf power supply capacitors, as well as the ground wire from the headphone jack.

Files: SE Class A headamp schematic and PCB SE Class A headamp schematic and PCB (Cadsoft Eagle)

Generated on 2018-05-03 01:14:21.909535