I've been having one or two problesm with this amp.
One of the LEDs became a bit flickery and went on and off as I moved the tube. Turns out the positive wire had snapped where it was soldered to the PCB. Worst still, I had real difficulty clearing the hole. I tried Trevor's red hot needle trick....it didn't work. I almost lost it a one point. I ended up damaging the PCB and am now unable to solder the LED wire to it. Damn! Anyway, I managed to solder the positive wire directly to the LED resistor so it does still work although it's a bit of a bodge.
The other issue's a little more of a problem. The balance between the headphones isn't right. Things sound louder in one phone than the other. I've taken a number of readings around the circuit as suggested by the designer and it would appear to point to the volume pot not applying the same resistance to each channel. It is especially evident at low listening levels. The solution is to add some additional resistance to the louder channel or buy another pot.
Hmmmm. Where'd I put that Novo?