No portable amp will do the K702's justice, are you serious about wearing the K702's in public.

kirr45, you need to do some searching for more information on k702's.  They are very hard to drive and require (in my experience) about 325 hours of burn in time.  They are good EXTREMELY open and allow any sound from the outside to come in and therefore would be terrible to be around other people in.  Your music will leak out very easily.  These are really headphones to be used at home.

Now, if you're truly set on using the k702 when you're out and about so everything thinks your awesome-o, know that they probably won't sound their best since the k702 needs a lot of power, and you will greatly boost the chance of breaking them because they're large and unwieldy.

Are the k702's good headphones?  That is all personal preference.  Many claim they have no bass, and when you underdrive them, they do have no bass.  When you burn them in properly and feed them the amount of power you need, they have deep punchy bass.  Their mid-highs are natural sounding for music like classic, but when you play a file that has perhaps a dark female sound sort of like Karen Carpenter, the mid-highs can sound really not so great.

The K702 does need a lot of power because of its low sensitivity (dB per mW), but its relatively low impedance ensures many amps will feed them a lot of power. A portable amp can do them justice, as long as it's a fairly powerful portable amp with low output impedance. They don't require any burn-in, real differences over time are subtle at best.

If you only listen on the go, get a pair of more efficient closed headphones. Denon D2000 are very efficient but not very closed, with low sound isolation. Sennheiser HD25-1 II isn't as efficient as the Denon but better than the K701, and has great isolation. You might want to consider IEMs.

I will not allow this to become a burn in discussion but many people can hear audible differences at points between 100-350 hours with k701/2's.  Whether its the headphones or yourself it doesn't matter, if its audible its audible I don't care what you say.

There are only a small handful of portable amps that can drive 701/702's even half-way decently (SR71 A&B, Stepdance, etc) and these will cost as much as a many desktop amps.  These are in no way portable phones, so  if you have your heart set on them you will definitely need a desktop amp.  They do a lot of things tremendously well, but would not be my first choice if I were to own only one set of full size headphone. 

Quote:

Originally Posted by Il Mostro 

There are only a small handful of portable amps that can drive 701/702's even half-way decently (SR71 A&B, Stepdance, etc) and these will cost as much as a many desktop amps.  These are in no way portable phones, so  if you have your heart set on them you will definitely need a desktop amp.  They do a lot of things tremendously well, but would not be my first choice if I were to own only one set of full size headphone. 

The $90 Fiio E7 will put something like 1.5Vrms into the K701's 62-ohm load before clipping, which is enough to reach 108dB peaks. That's only 32mW, but it's enough. Guess how much the Sennheiser HD800 needs to reach 108dB? 13mW! The Fiio E7 puts about that much into 300 ohms, too. Not too shabby for a $90 portable with a DAC.

Of course, if you and the OP subscribe to the belief that there's something special about more powerful amps even when that power isn't used, I suppose a portable amp isn't enough.

Quote:

Originally Posted by Head Injury 

The $90 Fiio E7 will put something like 1.5Vrms into the K701's 62-ohm load before clipping, which is enough to reach 108dB peaks. That's only 32mW, but it's enough. Guess how much the Sennheiser HD800 needs to reach 108dB? 13mW! The Fiio E7 puts about that much into 300 ohms, too. Not too shabby for a $90 portable with a DAC.

 

Of course, if you and the OP subscribe to the belief that there's something special about more powerful amps even when that power isn't used, I suppose a portable amp isn't enough.

There is a difference between sheer quantity and quality.  I own 702's and a wide range of amps (and DACs).  You can look at the numbers, I will continue to trust my personal experience and, most of all, my ears. 

Quote:

Originally Posted by Il Mostro 

There is a difference between sheer quantity and quality.  I own 702's and a wide range of amps (and DACs).  You can look at the numbers, I will continue to trust my personal experience and, most of all, my ears. 

What is that difference, though?

Quote:

Originally Posted by Head Injury 

What is that difference, though?

You are kidding, right?  LF extension, soundstage, imaging and detail are all effected by different amps with these phones.  Also, I would not use these with a cheap portable DAC -- I have experimented and this approach does not work effectively.  The 702's have always sounded their best to me with a good DAC and amp. 

Quote:

Originally Posted by Il Mostro 

You are kidding, right?  LF extension, soundstage, imaging and detail are all effected by different amps with these phones.  Also, I would not use these with a cheap portable DAC -- I have experimented and this approach does not work effectively.  The 702's have always sounded their best to me with a good DAC and amp. 

But how does an amp and DAC help with these things? For example, the E7 has a very flat frequency response, down only about 0.2dB by 10Hz, and I've already demonstrated that it has enough power and a low output impedance. So what is it about another amp that extends low frequencies further?

Quote:

Originally Posted by Head Injury 

But how does an amp and DAC help with these things? For example, the E7 has a very flat frequency response, down only about 0.2dB by 10Hz, and I've already demonstrated that it has enough power and a low output impedance. So what is it about another amp that extends low frequencies further?

A DAC can affect sound quality in a myriad of ways, but you're right that it as no effect on relative ease of driving speakers/headphones.  However, an amp's ability to deliver current is vitally important to it's ability to effectively drive speakers/headphones, especially difficult ones, and that's the characteristic which makes the difference that you are debating with Il Mostro.

And no, the Fiio E7 can't deliver enough current to drive the K702s well (if at all).  Very few portable amps can.  RSA Hornet at a minimum, SR-71, Stepdance, etc, all expensive.  The only cheapo that will probably work is the iBasso P4.  Reportedly (and I believe the reports) it'll sound great as well.

And yes the headphones and amps will need significant break-in time to sound their best.