Close the switch to activate.
It has about 1-2mV of second harmonic distortion at full power (measured at 317-318Hz), and much less distortion with other harmonics. This means that it has a THD (Total Harmonic Distortion) of around 0.003%. This is not THD+N (Total Harmonic Distortion + Noise), and therefore does not include any thermal noise or any other kind of noise.
Note: I changed the amp by pushing it further into class-A mode, so the distortion might be a bit lower than what's said above. I also measured the efficiency to be 41% in its current version.
