Originally Posted by Snag1e
+1 on the O2. It's a great amp, and has absolutely no problem with the 702s...even on battery power.
+2 on the O2. Almost as neutral as a Phonitor, plenty of power to spare even on batteries. K702 + a neutral SS amp like O2 is an analytical detail-freak's dream!
Originally Posted by theeyealtering
I've found that the K702 can get loud enough on most things, but just doesn't sound right unless its run off a pretty decent desktop amp. It's amp requirements are totally different from higher impedance headphones, where the concern there is mainly about getting the volume.
Unless you're planning on forking out for an amp, I'd definitely go with the Shure.
Originally Posted by mikeaj
FiiO E7 is limited to about 50 mW into the ~62 ohms of the K702 (1.7V). That's probably more than any laptop except rare exceptions. At higher impedances it's still limited around 1.7-1.9V. Taking the least sensitive of the K701 and Q701 sample data on InnerFidelity and rounding down, that would be around 104 dB SPL maximum from the E7 with those headphones, pretty loud for a lot of recordings.
If you look at the sensitivity data for DT 990 250 ohms, assuming the Pro isn't quieter than the Premium, at a given voltage, the DT 990 250 ohms should be quieter than the K702:
And the voltage an E7 can supply to the K702 exceeds what a typical laptop or an iPod could put into a DT 990 250 ohms (or any headphone).
So the K702 with E7 will be louder than DT 990 250 ohms with a laptop / iPod.
The trouble with that figure is, while it will drive it loud, it will not drive it loud across the entire frequency spectrum and leads to some measure of frequency shift especially at the upper range. K702 has wildly non-linear impedance as frequency goes up. Well above that 62ohm rating at the center. Planars on the other hand are famed for linearity, so they rarely go out of step with the frequency response. K70x gets really wierd when it gets frequency shift.
But you don't need a $300 amp either. O2 and the like should do fine. Maybe (maybe?) even a cMoy or E11, but that's a little more questionable. Despite its amping needs, K70x is a great deal right now for the level of detail and soundstage it provides (assuming you dig analytical sound) at its price point. It's sort of a really, really, really cheap HD800 (an exaggeration, but it's on the same quest for neutrality.)