The K701, more than any other dynamic can I have yet heard, sounds like whats upstream of it. Shouty, edgy, harsh, sibilant amps and sources will sound exactly that way with the 701. A lot of HD650 amps and setups sound pretty bad with the 701 IMHO, emphacizing and energizing the high frequency stuff through a headphone that really doesn't need emphacis there that at all. That also includes high voltage / low current OTL tube amps, which IMHO dont have the current reserves to amp/damp these drivers
dynamically. So its slmost more about maintaining spectral accuracy and dynamics... more so than sheer loudness of sound. A Sansa clip will play these cans plenty loud (at least for my listening habits).
They are the only headphone I own that are neutral, and demanding enough to completely reveal sonic differences in all my amps. They have a flat, closed-in, one dimensional soundstage under amped with my
18V cmoy (although I think a higher current OP amp than the 2107 would do better). My
24V Larocco PPA (627-2107-627) is a little "dry sounding". Upper midrange and vocals are kind of distant sounding, kind of lacking energy for prog-rock and metal bands. Ambiently it does the far out stuff
very well, clearing center stage and pushing sounds far out to the sides. For new age and ambient music it sounds great, Enya sounds like a concert hall. Its my fave amp for that kind of stuff. My
mister-X pimeta with the same OP amp compliment as the PPA, running at 24V is a little more closed in sounding than the PPA, but also has a warmer overall sound. A little bassier, and lower midrange / vocals have a more "in the chest" kind of sound. Pretty cool effect for prog-rock and metal.
Millet hybrid, has similar sonics as the pimeta... except It adds even order THD from the tubes. I can SAFELY adjust plate bias voltage to either increase or decrease tube-THD. Really cool design... all the pete Millets are this way. It also opens up tube rolling possibilities. Skip the
smaller OTL amps like the earmax, morgan jones and the likes. Not all together bad sounding with output transformer coupling (mod). Volumes though are a bit limited, and theres a lack of bass impact/extension for those times when you want to play it really loud. Which is really really strange, because my earmax with Sylvania and telefunken tubes adds quite a bit of bass impact and extension with my koss A250. The A250 like the K701 a 65 ohm can noted for being bass-shy. I think its the 701s lack of efficiency that throttles its performance with small OTL amps.
I think good K701 starter amps are tube hybrids like the millet and LD1+, for $150-200 they open up tube rolling possibilities and the k701 is neutral/revealing enough to hear the differences in tubes and with the millet different tube bias voltage settings. Neither will set you back a whole lot $$$. They have sufficient current reserves from their solid state buffers for low-Z cans like the 701, Denon and Grados.