Single ended about 11 oclock. The BHA-1 runs pure Class A so even at full rotation of the volume control would not be an issue.
james
For what it is worth, by comparison, I run my Schiit Lyr amp, which has 6 watts of power, at 9:00 o'clock and the headphone jack of my BP26 at 10, using my LCD-2 headphones. In each case, higher volumes would be close to being dangerously high.
LCD-2s are 50 ohms, and HE500s are 38 ohms. So my guess is that the BHA-1 power might be closer to that of my preamp jack than to my Lyr.
Dave