normally everyone says that if you got easy to drive headphones, you don't need a amp. but my "easy to drive" Etymotic HF5 sound different in a amp then straight out of an ipod.
in fact, it's always better sounding, is the amp inside an iPod classic just that bad? do amps in any way change the sound output? or am i just loony and thinking I'm hearing a difference?
Technically speaking all an amp should do is apply gain, i.e. make it louder.
The majority of the dedicated amps available shouldn't effect the sound signature all that much, and in my experience they don't sound all that different from each other.
However when we're talking about an iPod the amp is not good enough to properly drive many headphones. When it can't deliver enough power, distortion increases by massive amount, high volumes can't be reached, and the device start clipping. This is what makes many full size headphones sound bad when driven straight out of an iPod. Hence the need for an amp.
Most IEM's however are sensitive enough to not make that much of a difference between driven from a dedicated amp. I looked up the sensitivity for the HF5: "105 dB SPL at 1 kHz at 0.1 mV". This is an incredibly high sensitivity, so the iPod should be able to drive them quite easily.
Power isn't the problem here.
Another explanation is that the differences you hear are caused by psychological factors. This probably won't be the case when you're talking 'night and day' differences, but when differences seem subtle this can play a larger role than you might think.
In my experience the amp in the iPod classic is really not that bad (I have the 6G 120GB version). I can drive an HD 25-1 II from it with there being hardly any difference between the iPod and an amp.
Could you please elaborate on the differences you hear? How big are they, and of what nature are they, e.g. does it sound clearer/more detailed or is there a tonal difference?
