My HD660s sounds the same...

[IXOYE]

I have an IMac 24 and the headphone out is more than enough to drive easy to drive headphones, I'm really impressed with the quality of the audio outputs on the newer Mac's

 

[bigshot]

I don’t think there are published specs on that. It would be nice if there was. I find that old school receivers have beefy headphone outs too.

 

[71 dB]

It is not only the power with headphones. It is also the output impedance:

Voltage divider: If you drive 32 Ω headphones with an amp with 100 Ω output impedance, only about 24 % of the amp voltage is driving the headphone, but if you instead use 300 Ω headphones, 75 % of the voltage is driving the headphones. The difference due to voltage divide is 9.8 dB! However, if the amp output impedance was only 2 Ω, the difference would be only 0.3 dB.

Frequency frequency issue: If the impedance curve of the headphone isn't flat (constant or near constant on all frequencies), there will be frequency response errors due to amp voltage dividing between amp and headphone differently on different frequencies. The lower output impedance, the smaller this problem is.

Distortion and damping: The amp creates an electro-mechanical system with the headphones. That's why the amp output impedance can affect the distortion level and damping of the headphone. Lower amp output impedance means lower distortion and stronger damping. Increasing* output impedance one can shape the sound of the headphones rounder/more relaxed/less precise if that is what someone prefers.

So, the output impedance of a headphone amp is an important aspect of how headphones sound, but a bit overlooked while people seem t concentrate a lot on the raw amp power available. Since the voltage sensitivity and impedance curves of different headphones vary drastically from each other, this is an complex issue. Every headphone model is a separate case.

* The easiest way to do that is to make an extension cable with serial resistors to increase the impedance seen by the headphones in series.

 

[The Jester]

It is not only the power with headphones. It is also the output impedance:

Voltage divider: If you drive 32 Ω headphones with an amp with 100 Ω output impedance, only about 24 % of the amp voltage is driving the headphone, but if you instead use 300 Ω headphones, 75 % of the voltage is driving the headphones. The difference due to voltage divide is 9.8 dB! However, if the amp output impedance was only 2 Ω, the difference would be only 0.3 dB.

Frequency frequency issue: If the impedance curve of the headphone isn't flat (constant or near constant on all frequencies), there will be frequency response errors due to amp voltage dividing between amp and headphone differently on different frequencies. The lower output impedance, the smaller this problem is.

Distortion and damping: The amp creates an electro-mechanical system with the headphones. That's why the amp output impedance can affect the distortion level and damping of the headphone. Lower amp output impedance means lower distortion and stronger damping. Increasing* output impedance one can shape the sound of the headphones rounder/more relaxed/less precise if that is what someone prefers.

So, the output impedance of a headphone amp is an important aspect of how headphones sound, but a bit overlooked while people seem t concentrate a lot on the raw amp power available. Since the voltage sensitivity and impedance curves of different headphones vary drastically from each other, this is an complex issue. Every headphone model is a separate case.

* The easiest way to do that is to make an extension cable with serial resistors to increase the impedance seen by the headphones in series.

Easy to hear all of the above using headphones with a wide impedance difference and a valve headphone amp with a switchable multi tapped output transformer …

 

[Svperstar]

My HD660s sounds exactly the same (to me) when I plug it in to my laptop 3.5mm output, and when I connect it through the entry level desktop stack (one of the highly regarded ones in the internet, I won't say the company name.)

I prefered my HD580 and HD6XX out of my old Dragonfly over my Modi Multibit -> Asgard 2. Turns out I am not a big fan of the Modi Multibit so it gathers dust.