Originally Posted by Achmedisdead
The amp is likely beneficial for the OP because it offers lower output impedance than the Classic's headphone-out does....and many IEM's are very sensitive to output impedance.
Good point. In arguing myself out of my anti-iPod prejudice, I'd forgotten how much the output impedance is and assumed that it would be something sane like a Clip's - given that an iPod costs about 8 times what a Clip does, it would seem reasonable.
Yes, that will cause a substantial dip somewhere in the treble. But it is one that Rockbox's EQ will easily fix during pink noise tuning the Shures, so it doesn't really change anything. (If it did, then I'd suggest ditching the iPod for a Clip+ would be a better solution than adding an amp - you'd get the low impedance without the noise of only a single amp, which is very low for the Clip anyway.)
Btw - the dip that you get with typical iems and an ipod due to impedance mismatch is usually of about the same severity as the spike's most people have in the upper midrange due to ear chamber response. And many people have TWO spikes! So that people spend money and go to the trouble of carrying around an amp to deal with one, but ignore the other, probably worse, problem always strikes me as somewhat odd. Especially as EQing with pink noise would take care of both problems.
I suppose there have to be people for who the impedance dip and ear chamber spike cancel each other out with the right IEMs...