Rocket;390605 Wrote: 
> How would you say this output impedance would affect the headphone sound
> (apart form the gain issue)?

I hate to answer a question with a question, but...
What's the impedance of the  headphone being used?  

If the headphone's impedance is flat across the audio range, then the
output impedance of the source will have little or no effect.  If the
headphones impedance varies a lot, then, depending on the range of
variation, and the impedance of the source, there will be frequency
response variations.  One way to ensure this isn't an issue, is to
build a headphone amp with a low output impedance, so that it acts as a
true voltage source.  This is the approach used by amplifier/speaker
designers, and the one I generally prefer for headphones.

Having said that, I must acknowledge that there is an alternative
design philosophy, one which isn't used much for speakers, but has some
potential advantages.  Build the amplifier as a current source.  A cheap
and easy way to do this, is to build an amplifier with a high output
impedance, relative to the headphone.  IF the headphone/speaker has
been designed with this intent, then presumably, it won't suffer
frequency response issues.  And because it's driven by a constant
current source, it won't suffer from dynamic compression as the voice
coils heat up.  This makes it an interesting approach for the two
extremes, stadium rock concerts with thousands of watts cooking big
voice coils, and headphones with pico watts cooking ultra tiny
coils....

Cheers,   Dave


-- 
DCtoDaylight

Audiophile wish list: Zero Distortion, Infinite Signal to Noise Ratio,
and a Bandwidth from DC to Daylight
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