Audeze says 1-4W for all their lineup, even the very efficient XC. Don’t fall in to the marketing trap of paying for more (unused) power vs quality (implementation). Make sure there is enough with some headroom (ie., 80% max volume).
You can calculate the power needs for your headphone at different listening levels here:
http://www.digizoid.com/headphones-power.html
Insert the impedance and the sensitivity. For planar dynamic headphones you typically don’t need to worry about the headphone’s impedance curve changing over the frequency band because, as a purely resistive load, it will be flat. For dynamic headphones it’s good to know if the impedance curve changes over the frequency band. For example, the Audioquest Nighthawk has a very flat impedance curve, but the Utopia’s impedance curve peaks just over 300 Ohm at 50Hz but then levels off to around 80 Ohm at 1kHz.
Back to the LCD-3 this is the power required for SPL peaks using the above calculator:
As you can see it doesn’t need megawatts to make you deaf, despite what the marketing would say. For reference here is the power specs for the Mojo and Hugo2:
Mojo
70mW - 300 Ohms
600mW - 32 Ohms
720mW - 8 Ohms
Hugo2
94mW - 300 Ohms
740mW - 33 Ohms
1050mW - 8 Ohms
Hugo2 has about 25% more power available and both devices have a max of 500mA of Current delivery (more than enough) for the LCD-3. There are devices like the iFi iDSD BL that output 4W max (peak@16 Ohms) and 1.56W (continuous@ 64 Ohms). That kind of power output will be unused by most headphones but there are a few that need that kind of power, like the Hifiman Susvara, depending on how loud the music is played.
