Originally Posted by plonter
anyway,just listening to the M50 out of the earmax and it sounds fine to me,can't notice anything suspicious that points on underamping, what exactly are the sings of underamped headphones? is it distortion of some kind...maybe the need to turn the volume pot all the way up to reach a normal volume level?
I don't think it's so easy to find out what exactly could be wrong without doing some measurements.
I'm sure the min. requirements were chosen with some headroom in mind. (it looks like that amp also has 35 ohm resistors in series with the hp jack, for protection)
Originally Posted by TheWuss
some other folks may be able to help more.
but, my general impression of underamped phone (i tried my 600 ohm dt990 out of an ipod just to be able to say for sure what "it" is) is that the sound will be flat, boring, not loud enough, and may even distort when certain big transients hit.
"flat, boring" is more likely a problem with mismatched output impedance. (see below)
Low gain and/or limited output can be the reason for "not loud enough".
However if you can really hear distortion with increasing volume, then it's pretty clear that the amp cannot handle the load.
Originally Posted by aimlink
For me it hasn't been an issue of sheer volume. I've heard headphones with a lot of volume and yet they aren't well amp'd. The first thing to suffer is usually the bass.
The Ed8's for example have a boomy bass and perhaps even more voluminous, when unamp'd. Once, amp'd, the bass tightens up and becomes more controlled and less intrusive. This is an even more marked phenomenon with the D5000's.
With the HD650/600's, there's a loss of dynamism and energy in the sound.
In the end, I don't think you can tell a can is underamp'd unless you've heard them well amp'd.
I have reason to believe that mismatched output impedance (Zout) commonly is misunderstood as "underamped" or "unamped" (stupid, misleading word imho).
Take the HD555 and plug it into the jack of a receiver with >120 ohm Zout and you'll be shocked by the amount and flabbiness of bass.
Plug the same 'phone into an amp with < 1 ohm and the huge amount of bass will disappear and mids will start to dominate.
The scale of such FR variations depends on the nominal impedance and impedance curve of the headphones, and can range from non-existent to huge.
This would also explain why the bass is "even more voluminous, when unamp'd".
"loss of dynamism and energy" is too vague for me to comment on.
If you wanted to do a listening test between the amp in question and another, probably more suitable, amp I'd suggest to match the output impedance just like volume.
Edited by xnor - 5/8/10 at 6:10pm