Originally Posted by juantendo8
Let me just correct you on one thing. The AKG K501 is actually very power hungry and demanding on an amplifier. It fact it is very noticeably harder to sufficiently drive than the K701 and HD600/650. I own and love the K501, but if you are looking to get away with a miniscule amplifier (power-wise), the K501 is one of the worst headphone choices. Its harder to drive than my planar modded T50RP.
you are right about the K501 being rather inefficient and hence requiring a headphone amp, But they offer the amp a fairly high impedance load that any entry level amp with enough juice can deal with correctly (I was very happy running the K501 off a PIMETA).
The K701 are more efficient than the K501 but have a middling impedance (62 Ohm): I am no expert but it is apparently harder for an amp to provide enough current than enough voltage, and low impedance requires more current for a given power level.
Here is a good thread on this
FWIW, I got my first "top-end" amp (a Corda Opera) because I was not happy with how my (beloved) Woo 3 drove the K701.
Edited by calaf - 9/4/12 at 7:35am