Some words about Power...and how it's wielded!O.K. folks! We have to be on the same page with the arithmetic needs of Power (in Watts) and how the physical laws applies.
To achieve and maintain an output waveform at (1) Watt with no clipping of the signal waveform we need (10) Watts on tap. To run at (10) Watts continuous with no clipping of the output waveform we need (100) Watts. See the Logarithmic (and Allegory) progression? Likewise a 100 Watt waveform would need 1000 Watts to back it up (and yes I'm keeping it elemental for a teaching aid).
And yes, the 10 milliwatt would need a hundred milliwatt etc......
And these steady-state loads, for progression examples, are ideals! The real world is more brutal.
I smiled at the reaction of a member that exclaimed "that's ridiculous" after he had read that member Thinker had tried the HE-5 from Krell Mono's. 300 Watts O.M.G.!!
Power has never really been an issue with the broad spectrum of headphones. Holding a 1/4 in. plug in your teeth and rubbing your sockie-feet on the carpet is enough in most instances. Even the hard to drive Senn 6XX is relatively easy in comparison.
Member Zanth wrote that the EAR HP-4 has one watt output and called it plenty for the HD800...not really. He knew this but has forgotten!
Headphone amps have a lot more in common with Pre-Amps than Speaker amps, noise being the qualifying issue. Brute force wasn't, till now wanted, needed, or cared about. Times change! And we have to change with them!
And I almost forgot about damping factor and back EMF and the Hazards it causes for Headphone amps that weren't structured for the by-product of current demand of Planars...a whole nuther' can-o-worms folks!