I got a set of Senn HD600's a few months ago and have been testing different portable amps to pair with them. Being they are famously "hard to drive", I had limited my search higher power portables like the FiiO E12 and the Cayin C5. But due to some feature preferences I also picked up a FiiO E12A this week, even though it is clearly designed and marketed for use with low impedance cans and iem's. The E12A does rather easily reach the volumes I need (less than half way on the volume pot) but there does indeed seem to be something missing from the sound compared to the other two amps. It's kinda hard to put my finger on it, but overall it's flatter, less alive, less spacious and more confined, sorta like using the HO jack on my DAP (FiiO X3) compared to the LO into an amp. I am wondering if this has to do with the lack of power or just other differences in the circuits, or both.
 
So really my question is simple: with volumes matched, what does a higher powered amp do for hard to drive HP's that lowered powered amps can't?

So really my question is simple: with volumes matched, what does a higher powered amp do for hard to drive HP's that lowered powered amps can't?

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It should not sound different for the higher maximum power output alone, as long as the following conditions are met:
- you listen to the amplifiers at accurately matched levels (this requires measurements, preferably of the voltage on the headphone drivers while playing a tone at a constant level)
- the lower powered amplifier never clips or has otherwise excessively high distortion at that output level driving your headphones
One common reason why people often find higher powered amplifiers to sound better is that they tend listen to them at a higher SPL, because the gain is usually also higher, and that means higher output level at the same volume setting. Level matching by ear is not reliable. If the comparison is done sighted, then expecting the more expensive/powerful/etc. amplifier to sound better, even unintentionally and sub-consciously, is also a potential issue.

Power=volume mostly. If your source outputs the same power/volume any amp needs the same power to let it sound louder. Some amps reach that maximum amplifying output sooner because they have less power, so they might clip at the same volume and same power as a more powerful amp.

what about the power alavaible for louder parts, without clipping/?
 
not all music is dynamically compressed, and a powerfull amp is much better for dynamic range.

dobrescu george said:

  what about the power alavaible for louder parts, without clipping/?
 
not all music is dynamically compressed, and a powerfull amp is much better for dynamic range.

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If it doesn't clip or distort, then what's the issue? Available power that is never used has nothing to contribute.

An amp amplifies the whole signal, not only the softer parts. It does not do anything with the dynamic range, the DR is in the source. Softer parts will be louder, but the louder parts will become even louder than they were. So the range between soft and loud only moves from less soft to louder.

then why do they sound different?
 
even the amp in hugo was a little weak for hd800 no matter the volume in my experience..

Some amps add various processing to the sound, which is not present in original sources/records. Many headphones are also sensitive for impedance mismatches. Too high impedance = freq response swings, most notably in the lower freqs (so higher imp = warmer sound).
 
Also psychology has a great impact. Maybe the greatest.
Oh the Sansa clip is such a tiny player. *listening* - yes it sounds tiny. *Adding an amp*, yes now it sounds much fuller. 
Which may be not the case since the Sansa actually has quite some power to drive at least almost all IEMs and many headphones.

The biggest diffrence in the Amps between the e12 and the e12a is the battery supply voltage, apart from the obvious change of opamp's.
This has a direct relationship to the doubling of battery life in the e12a.
Because the e12a hasn't got as much voltage at the power supply (battery voltage) the result is a loss of power to drive the larger sized diaphragms, in the larger headphones. I think the dynamics are lost at this point. And we feel something missing in the audio.
Where tiny miniature balanced armatures have no need for larger voltage swings (the e12a). And other circuit designs are needed to get the most out of those tiny transducers.
This is why different amplifier designs are needed for different driver application's.

audioxxx said:

 I think the dynamics are lost at this point. And we feel something missing in the audio.

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Missing dynamics is the cause of the lower volume, which is cause of the lower power.
 
Because the music is too soft, it sort of seems to be lacking dynamics. But that is not completely true: the dynamics are right there in your FLAC file, but need more volume to be heard correctly. It is not true that at the same volume level at amp A you have less dynamics than on another amp B, if the volume is the same. They must sound the same if the amps are not clipping, the output imp is the same and your source is the same. Other differences inside the amps are, AFAIK, very difficult to hear and probably placebo.

whether it's placebo, power or other design differences in the two amp circuits, i don't know. but i do know that in unblind testing i like the sound of the E12 more than the E12A for the reasons i stated above. maybe i can get the help of my wife or a friend to do a blind test before i send back the E12A. though i think my wife is already pretty sick of all the headphone talk.
 
and just to be clear: i am running these both nowhere near clipping.
 
anyway thanks all for your input.

bzippy said:

  whether it's placebo, power or other design differences in the two amp circuits, i don't know. but i do know that in unblind testing i like the sound of the E12 more than the E12A for the reasons i stated above. maybe i can get the help of my wife or a friend to do a blind test before i send back the E12A. though i think my wife is already pretty sick of all the headphone talk.
 
and just to be clear: i am running these both nowhere near clipping.
 
anyway thanks all for your input.

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You must match volumes, exactly, in order to do a proper comparison. Do a Google search for "Equal Loudness Contour" as well as "Fletcher-Munson" and read up a drop. The louder you go the better it will sound.

Level matching by ear is not reliable.

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Yes it is - You fiddle around with the knob (!!) until both units sound the same and there you have it : Matched to within 0.2dB
If you can't achieve that - At least one of the units is not transparent .

bufferoverflow said:

...
If you can't achieve that - At least one of the units is not transparent .

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It's not as simple as that. The perceived difference can still be caused by bias. So all comparisons need to be done in a bias-controlled way - i.e. in a blind manner.

What differences ?
Unless one of the units is total crap - There IS no difference
(That's my bias - I expect to hear no difference at all - If I do hear a difference, something is wrong)