Hey everyone, this is my first actual 'review', so just keep that in mind and take everything I say with a grain of salt as it could just be an under-experienced newbie audiophile writing this.
So I am using this amp with the only equipment I own as I am a student which pretty much means I have an extremely tight budget.
The Equipment used is:
FiiO E12 Amp (obviously)
AKG Q701 headphones (again, obviously)
Pioneer HDJ-2000 headphones (briefly, for comparison)
Sandisk Sansa Clip+ (rockboxed)
HTC One (w/ various audio mods and poweramp)
Many .flac files and my vast taste of music
My initial impression of the AKG Q701 was 'wow, the need for an amp is really exaggerated'. They worked fine for any type of jazz, pop, trance and some kinds of metal/rock (Dream Theater, and bands that did melodic/symphonic death metal worked best). No seriously - if you like trance music do not hesitate buying these headphones, as it does not need that much bass and because of the extremely thick texture of it, it's easy to hear all of the layers of the track. Anyway, for bassier EDM like electro, dubstep or dnb, it didn't work very well and the same could be said about rap/hip hop. It was adequate for my tastes, however and I was content for a few weeks before buying my amplifier. The bass rolls off so you don't notice it's not there while still providing slight warmth from the lower section, but the best part is the clarity that they give compared to the mid-range headphones that I've tried so far. Jazz works brilliantly with these things. My favourite track to test with these was 'My One And Only Love' by John Coltrane/Jonny Hartman.
When my amp came, I didn't know what to expect. When I plugged it in for the first time, I was really unimpressed. It sounded the same, with a slight volume boost. Disappointed, I started messing around with the settings to see the different options, and as soon as I pulled the gain to 16db, I jumped at how loud it was, threw my headphones off and turned the volume down. This is where I was really impressed. With the bass boost turned on, crossfeed off and gain at 16db, I was finally past content and into impressed that something could sound so full and deep. Even for electro and hip hop, with bass boost the bass was tight and hard hitting. It no longer sounded like a wall of sound and finally sounded like I was immersed in the music. The bass was deep, and the mids and treble were sweet. Every layer of the music could be heard and the clarity was immense. I did not expect much more from my headphones. Nothing was distorted, there were no spots and everything sounded really clean and full.
When I used my brother's Pioneer HDJ-2000 to test the amp, the results were incredible. The bass was not just hard hitting, the mids and highs were clearly audible and the volume was driven to incredible levels. Truth be told, they do not need to go as loud as they did with my brother's Xperia Z, which has a pretty low volume limit. We were very impressed, but I don't see them being as versatile as my AKG headphones, as the bass is a bit too much for some tracks and it wasn't nearly as clear.
Then something happened. After my brother tested, I plugged my headphones back in. Immediately, I could hear the bass sounded muddier and more distorted, while disturbing the soundstage. I was frustrated beyond belief, and I thought that it might be the amplifier's battery being low, as I kept forgetting to turn it off. I left it to charge overnight and tried the next day. Same thing. That evening I tried them again with my phone and it sounded better, like before. I was thrilled until I unplugged my headphones from the amp, still turned on. It let off a noise similar to grabbing the end of a 1/4" cable from a guitar amp while it's still on. Except directly into your ears at max volume. I plugged them back in, and same thing as before. Distorted bass, dodgy instrument separation. Turning off the bass boost function stops this, but also turning the bass too high on my Clip+ and phone provokes it. Until I can get a solution to this problem, I'm stuck with it. If anyone has a solution, it would be greatly appreciated. Even with this problem though, when I plug my Q701 unamped into my Clip+, it now sounds horrible. Volume is way too low, bass is nonexistent, mids and highs sound washed out. Thanks a lot head-fi, now that my standards have been set higher, my wallet will take a serious blow - not that it hasn't already.
In conclusion, if you have a pair of AKG Q701's, do not hesitate to buy this amp -- HOWEVER my experience with extreme levels of distortion may not have been just a one-off, so keep that in mind. Also, these have been the ramblings of a newbie audiophile so don't take everything as pure fact. If I could go back to the quality that I had once enjoyed, I would give this amp/headphone combo a 10/10 purely because I cannot imagine the sound being any better. Also, I really like the sound signature of these cans and the synergy between the two is very complimenting to each other. With the distortion, I'd give it a 6 because the sound is a lot harsher, less clear and overall less enjoyable. The headphones aren't nearly as versatile and only a certain amount of music sounds good without annoying you.
Note: No EQs were created or used in the making of this review. All music was purchased and any resemblance to piracy is purely coincidental.