This is a really tough review because to my ears this DAC doesn't really have it's own signature. So the best I can do is compare it to my old ODAC and Modi, but all based on memory.
 
First off, Headroom had stopped selling their own brand of gear so I just HAD to buy this. Headroom should reconsider and hire a marketing guru. The small size and plain design doesn't help much. They're built like a tank though and not made out of plastic! Their stuff is much better than all the other Schiit. I skipped it for over a year because I thought it'd just be a side-grade to what I already had. WRONG! Since the Headroom Micro Amp + Astrodyne is the best solid state amp ever made under $500, I had to buy it to complete my "Micro Stack". The Headroom Micro Amp + Astrodyne is so neutral IMO that if you don't like it, maybe you like more coloration (nothing wrong with this) or it's due to the DAC or stock power supply. To me it's like a slightly re-tuned O2 on steroids with all the rough edges taken off. It can drive almost everything, but maybe sweat a little with the He-6. It has 1.21 Jigawatts into 32ohm. OK, it's more like several watts.
 
On the first few days it was not like a night and day difference. I found that some songs sounded basically the same.
 
After maybe 3 months I can say that the Micro DAC is dead neutral, but yet very very revealing of recording bit-rate and quality. Much more so than the ODAC and Modi. On the Modi you feel as if it's a much more smoother and forgiving DAC. Harsh tracks are not as bad and they're easier on the ears with the Modi. I was pretty shocked when I first used the T90 with my Micro Stack and first heard this when I switched to the Modi. The Modi + Micro Amp despite being not as revealing, was actually a nice and musical combo, but holding the T90 back a little (when it comes to how revealing the T90 can be).
 
With the Micro DAC + Micro Amp using both with Astroydyne power supplies, the soundstage of the HD-650 is as large as i've ever heard it. On some more expensive amps the sound can often be warmer and more closed in and congested. The HD-650 with this setup and the right recording can be very very wide open, airy and spacious sounding. You can hear this easily with "The Buena Vista Social" club. You feel as if the instruments are coming at you from all around, up on top of your head and even slightly behind you. All the instruments are very full sounding, as if you can FEEL them. They have much less body on the ODAC and Modi perhaps.
 
In comparison the Modi's sound is slightly more "hazy" sounding. Harder to hear in between things. Still very clear, but less expansive and less airy. Ultra subtle details are harder to hear. You can actually HEAR the clearness of a recording properly with the Micro DAC and on the Modi/ODAC this is a little harder. Some recordings actually can sound more muffled on the Micro DAC, but only due to the recording.
 
When you listen for hours with the Micro DAC you can easily say to yourself "That's probably a 192kps mp3 file" or something like that and you're almost always right. OK, I can't tell the exact bit-rate but it's usually just a low bit-rate. I know there are plenty of lossless files that still sound like garbage due to recording.
 
When I bought this I had my usual expectations. I thought it would probably be bright or thin and harsh. No, it's not. It's just very clear/clean and only reveals what's on the recording. Despite being basically dead neutral, it might actually be a touch warmer than the Modi. It's not actually warm itself, but possibly compared to the Modi.
 
It never sounds thin/harsh or bright unless it's the recordings fault or the headphone.
 
I actually think the Micro Amp + Micro DAC is so good that the Q701 and HD-650 hold it back. To me they're definitely mid-fi, but I would glady use them with an HD-800/T1 or LCD2.
The cost of each unit when new was around $350 (+$60-90 for the Astrodyne PS), but to me they're worth up to $600.
 
As a whole, the Micro DAC is very clean/clear and sort of analytical. Not thin or bright, but just extremely revealing. If you like your DAC to ADD warmth, don't bother with this one.
 
This uses the Cirrus Logic CS4398 DAC chipset and so far I love it! My Ipod Touch 2G uses a Cirrus Logic DAC, but this definitely sounds much more refined and less bright/thin.
 
BTW I'd love to compare this against the Bifrost. I'm pretty sure it would be a side-grade. I'd love to get a review unit, but probably not going to happen. I bet the Bifrost also is like a slightly more revealing Modi, but way better. I'm a huge fanboy of the Modi but the Micro DAC is definitely an upgrade.
 
NOTE: I will update this review the more I listen to the Micro DAC. It's replaced the Modi, but I've kept the Modi since it's still a keeper.

This will be a short review based on maybe on 12-15 hours of use. If you think that's not long enough you can skip it.
 
I was a bit worried that this would be some cheap gimmicky toy amp because of the name. This is instead a seriously good amp! I love it.
 

1. Sounds great with ALL my headphones and does not add any major coloration to any of them. It works equally well with the HD-598, HD-650, K400, DJ100 and modded Q701. It sounded especially good with the hard to drive K400! All my headphones and music sounds as it should.
2. Sounds transparent but it's not cold/analytical/thin sounding. There is a subtle touch of warmth in there. It will be nice for even a DT-990 or SR-325is. This warmth is only noticeable on specific headphones and harder on others. I noticed it on my DJ100 and HD-650. It never ever sounds thin unless it's due to the recording.
3. The treble is well extended and not rolled off. It's much smoother than the treble of the O2 or Magni. About the same as my Headroom Micro Amp.
4. Bass is well controlled and neutral. There is no emphasis I've heard in any area.
5. Soundstage is lacking in width somewhat. With the HD-650 it's less spacious/open and airy sounding than with my O2/Micro Amp. The O2 is less warm though and has more treble sparkle (less smooth). It's possible my brain is just being fooled, but I'm pretty sure it's not. It's still pretty good and not as bad as it sounds. Nit-picking really. I got similar results on many difference sources.
6. To my ears it's a better "all-rounder" amp than the O2/Magni/Asgard/Vali/E9. It does cost more though.
7. It's the 2nd best amp i've heard. It's not as good as the Headroom Micro Amp + Astrodyne but that cost $350 new. It's the closest i've come to it's sound. The iCAN might be a tad warmer though.
8. I have an O2 for my bedroom (backup) and it's not worth upgrading to this as a backup. If I didn't have my Micro Amp I'd be using this as my main amp. It's that good!
9. I'm able to hear changes in all the sources I connect up to it. There is really no real coloration coming from the amp. Just that touch of warmth.
10. If you found the O2 too sparkly, try this (or the Micro Amp)! Is it worth the $140 price premium? Well if you nit-pick about tiny things like me, then yes. If iFi can get it down to $200 in the USA it'd be a STEAL!

Sounds great with the modded AKG Q701. Nearly as good with that as my main amp that originally cost $350. Impressive! In fact, the Vali added nothing to the sound of the modded Q701, which is perfect. I would say the resulting sound is similar to that of the O2 but with very very slightly fuller mids and very slightly smoother treble. We're talking maybe a 2% difference. The Vali sounds dead neutral to my ears with the Q701. I also tried my K400 and the Vali added nothing.
 
I then tried the HD-650 and Koss Pro DJ100. Sounded terrible and no better than an E9. On both the bass was too sloppy and uncontrolled. Any recordings with bass would put a haze over the sound. The problem I had was that the sound with these two was just not clear and very closed in. They never sound this way. There was extra thickness to the mids but yet the low mids were almost fatiguing. On the DJ100 the sound was not smooth at all. On an amazing amp the DJ100 with M50 pads never ever sounds closed in and congested. It's even a closed headphone! On my main setup it sometimes sounds like an open headphone.
 
The best results I got were with a CD player with two Wolfson WM8740 DACs and my Micro DAC with a CS4398 DAC. The problem with the CD player that is it made my HD-650 abnormally thick sounding and too smooth. This obscured detail and just made it sound weird. I think the larger soundstage of this CD player is what helped out the Vali and HD-650.
 
When switching to many different sources it's as if I couldn't even hear their different qualities and Vali was adding in it's own colorations (with HD-650). Maybe the HD-650 is just a very bad match for it. I guess some might like it.
 
I myself would pair the HD-650 and Vali up with a DAC that has a massive soundstage and is sort of lean and bright. I could not get acceptable results with anything I own. If it requires a $500 DAC to get good sound with the HD-650, then that's a complete fail. There is absolutely no reason the Modi should be bad for this setup.
 
I imagine that this would be best with a neutral headphone that's not too warm and doesn't have a closed in soundstage. I was thinking that it might sound great with a DT-880 or T90.
 
I'm a bit disappointed in some ways. I can't suggest it for someone new to all this because it doesn't seem like a good all-rounder. If you plan to only use it with very specific headphones with no plans to upgrade, then this might be OK.
 
Despite this sounding great with the modded Q701 I would probably suggest the Magni or O2 instead since it seems to do better with more headphones.
 
I guess you could get this as a cheap toy to play with and that's what it felt like really. Nothing wrong with that.
 
YMMV

6-7 hour impressions. I will update/edit this more as I listen to it more. If you don't like this please GET OUT!!!.
 
These are only impressions vs the bass port modded Q701.
 

1. Slightly fuller sounding in the mids than the Q701m. Barely audible. K712 adds some slight warmth to recordings that are already warm. The Q701m does this less.
2. K712 to me sounds slightly more forward in nature than the Q701m, especially in the low mids. The Q701 low mids are leaner but still nice and full without being too forward.
3. The soundstage of the Q701m is slightly more open/spacious/airy. The K712 is still really very good in this area. On warm recordings the soundstage is noticeably worse. Try the Buena Vista Social Club. That sounds best on the Q701m. The K712 Pro sort of feels like it gives it a slight haze over the sound of that album.
4. The K712 really doesn't sound any smoother or forgiving. There's music that is harsh on the Q701 and other music that's harsh on the K712. Harsh/bright Jpop seems slightly worse on the K712 to my ears due to the more closed in soundstage. This is all random though. Sometimes the Q701 spaces out vocals more so they sound less forward (due to recording). No dang fixing of my poor tracks on either of them.
5. I don't notice any increased bass over the MODDED Q701. I know this will surprise some people. There may be a little, but not worth pointing out. The low bass is still not perfect. I remember the Annie having a little more perhaps, but that's based on memory. The idea of ruler flat low bass to 10hz is good for a laugh! No way! Both sound like they have some slight roll-off still.
6. Both are very very accurate to my ears. None of my music is dramatically altered. Isn't that how it should be?
7. Both headphones are able to reproduce male/female vocals that sound way too distant or way too forward. This seems to confuse some people. Female vocals don't really sound all that much more forward on the Q701. It doesn't magically shove them forward despite what some think. Both have good soundstage depth.
8. The K712 doesn't sound even remotely dark to me. Perhaps a little less treble than the Q701, but again not very audible.
9. Level of detail is about the same. K712 doesn't sound any more revealing.
10. Some music sounds noticeably clearer on the K712, but this is very rare. Maybe if I had ALL HD tracks this would be easier to spot.
11. Modded Q701 sounds very very very slightly more neutral to my ears. Mostly due to it's flatter low mids.
12. In 6-7 hours zero fatigue or discomfort. Nice!
13. I disliked the Annie but love the K712 Pro. No clue why, but I think I was right and it's the improved pads. That's my only idea.
14. I could not really detect any difference between my DACs with the K712 or Q701m. Sound transparent to me.
15. The full low mids of the K712 are really addicting. My brain tells me the K712 is smoother in the low mids, but I think it's fooled due to the warmer sound. Makes sense.
16. Vocals sound a bit fuller on the K712 at times, but not by much. It's VERY subtle. Don't know why but they remind me a little of the HD-598.
17. To me it sounds like a perfect mix of the K702 and HD-650.
18. After dozens and dozens of tracks I did find a couple tracks that sounded easier on the ears with the K712. ONLY some 128kbps bright/tinny/harsh tracks from a singer named "Hitomi". I guess perhaps the K712 is more forgiving of low bit-rate files? I have very few of them. This makes sense to me. I really can't call it a forgiving headphone. Who uses 128kbps mp3 files anyway with such a headphone?

 
RESULT:
 
Both headphones sound great! I highly recommended both.
 
Final overall sound score (mid-fi):
 
Modded Q701: 9.75/10
K712 Pro: 9.75/10
 
For reference:
 
Q701 stock: 9
HD-650: 8.75
Annie: 7
K601: 8
 
I would be happy with either headphone. Due to preferences I prefer the modded Q701 slightly despite no change in score.
 
If you don't like mods or prefer no bumps, I can definitely suggest the K712 Pro.
 
To me you can't really say which is better. All depends on preferences.
 
I have to get this out of the way but there was not more than a 5% difference between the two. Think i'm wrong? Get a modded Q701 and compare them and report back.
 
If AKG can afford to get these down to $325 they'd be a pretty good deal. $400 is kind of high.
 
Disclaimer: My Q701 might be darker/warmer or bassier than the rest. I really don't know.
 
NOTE: My gear has about zero warmth itself that's audible by me.
 
Good job AKG!
 
EDIT: I know they say the K702 and Q701 drivers are the same, but I don't know. I have my doubts. Most likely the K712 Pro uses the best measuring K702 drivers (with different part #). So K712 would possibly equal hand selected K702 drivers + memory foam pads and flat headband. The extras are not exactly free. $350 is a fair deal. When I listened to the K712 Pro with Q701/K702 pads it sounded closer to a K702 than a Q701. I did not install the Q701 outer grill and foam though.

Got the unit in and on day one it randomly sounded OK and then would crap out on me. In total I wasted probably 6 hours of my day off trying to fix issues I thought were a fault of my computer. I kept thinking that I had fixed it and then the issue would come back. First I thought it was interference with my ethernet port, bad usb cable, bad hub, noisy power etc. I tried every combination I could find. I even attached the amp to different wall outlets and with and without noise filtering on my surge protectors. In the end there is NOTHING wrong with my setup.
 
On day one the sound would randomly feel as if all the weight of the music was being sucked out. No life at all to it. Background details seemed to get "lost". Then 5 minutes later (same song) it would be fine. The sound would alternate between sounding good to bad and not due to variations in recording. I could switch to a different amp using the same usb port and DAC and it'd be perfect! On day two at one point it sounded great for 45 minutes and then went back to normal.
 
I thought maybe it was noisy power or something but I got the A2 to be dead silent. I did notice an improvement in sound when I used cables with tons of shielding and USB cables with ferrite beads. It didn't last long though. Yes, I tried many different cables.
 
At times the bass would randomly get bloated and the low mids would get shoved forward somehow. At one point I was sure that my A2 had died. Nope.
 
So I gave my ears and amp a rest and tried again the next day with my HD-650. Same results but even worse sound compared to the Q701.
 
I tried Xbox 360 Optical to E17 DAC to Asgard 2. This combination was awful and warmth overdose. Fallout 3 seemed incredibly muffled and dark. First time I've ever heard bass bleed in that game and I use my HD-650 with it all the time. It felt like everything was abnormally thick/full. More than it should be. E17 has some warmth, but not a lot. Switching to the Q701 was a little better.
 
I then tried a docked Ipod Touch 2G to A2. IMO the 2G is kind of bright. Not any warmth at all coming from it's amp/dac. Similar sound. Still got that muffled/fuzzy sound from my HD-650. Closed in soundstage and lacking detail. Just sounded too dark.
 
I also tried a Denon 1920 CD player to A2. A little better, but the A2 seemed to be giving everything it's own coloration. The bass from each setup wasn't very well controlled at all.
 
 
HD-650/Q701 sounded amazing from the O2 and Micro Amp with not much change between them. I understand that maybe the A2 is not meant to be 100% transparent, but not sure. Please note that I would switch to other amps and everything was perfect so it's not an issue with my ears or setup. At times I felt my ears were playing tricks on me but that's not the case.
 
So in the end I returned it and the unit is fine. I guess the A2 sound is just not for me. After all that time i'm out of about $68. Not a big deal. Return shipping costs about $35 (should have went UPS/Fedex) insured and you have the 5% restock (which is perfectly fair). I wish I could say I just had a lemon but guess not. Perhaps i'm too picky, but I don't think so. I also spent maybe $50 on a new powered hub and RCA and USB cables to make sure it wasn't my fault. Couldn't wait for Monoprice so I had to buy overpriced stuff locally. I even bought a new USB card and no change in the audio.
 
With how it is I imagine it would OK for me with a Grado or Beyerdynamic DT-880 or something considered brighter/thinner. I guess I just didn't like it with the 598, DJ100, HD-650 and modded Q701. I thought the Magni was pretty OK and felt like it sounds better than the Asgard1/2 but it's not warm at all (don't care) to me and is a LITTLE bright/thin. The O2 and Micro Amp are close to perfect. To me the Micro Amp is like an O2 on steroids and with all those rough edges taken off.
 
I feel a bit bad reviewing this but why should I? I spent my hard earned money on the amp and it didn't work out. I use to have a lot of money but now i'm mostly on a budget. I have nothing against Schiit and I love their Modi. I should have just gotten a Bifrost instead.
 
BTW I had an Asgard 1 years ago and didn't like that either so I guess it makes sense why I wouldn't like the Asgard 2. I did feel it was fair to give it another chance.
 
EDIT: The review details are messed up so don't go by that. I gave the Audio Quality a 2 out of whatever.
 
EDIT 2: My only idea as to why this didn't sound good or randomly bad is due to external interference. Not from noisy power or computer etc. None of my other amps have any issues. Probably impossible but that's all I could come up with. Like I said before it SEEMED to sound best with ferrite core USB cables, heavily shielded cables etc.
 
I live in a 3 story building with 12 apartments total.

Mids are nice and full sounding. Not thin or lean at all. If they are it's due to a poor amp match or supposed to be that way in the recording (yeah really). I've even gotten good results with an O2, E9 and Micro Amp. Not much else yet. They sound natural to me. To me this headphone really excels with female vocals. They're very slightly forward sounding. I would say the low mids are more neutral. They're not as forward as those of the Anniversary and I like that. With some recordings the Q701 can sound nearly as warm and full sounding as my HD-650 (try Buena Vista Social Club). You can also have the Q701 change into an AD700 with some tinny/harsh recordings.
 
Treble is not harsh unless it's due to a poor recording. Even then it's no real problem. This headphone won't make harsh/very bright recordings any easier on the ears. For that you can try the HD-598 or HD-650 to sort of take the edge off. I actually think the treble sounds neutral despite what some say. It seems smoother than what I heard on the K702.
 
Bass is fine and there seems to be no large mid-bass hump. Not much bass impact and there is a slight lack of low bass presence (without mod). For this reason I sometimes use my HD-650 or DJ100 for gaming/movies.
 
I don't find them crystal clear sounding, extremely detailed or super revealing. Sometimes they're even a little forgiving of some lower quality tracks. Just slightly. Even Youtube music and Itunes/Amazon samples sound fine (this varies usually).
 
I find them neutral sound with no major emphasis in any area. I actually find them more neutral than the HD-600. HD-600 has more mid-bass and this has some extra treble. What's the difference?
 
Soundstage is what I would call pretty good but not great. It's smaller than the K702 but I actually think this is a good thing. It's not massive, super airy and nothing ever sounds too distant. Imaging is fine and there is no lack of center image for me.
 
This thing is pretty tough to drive. I hate it with portable players. All of them. It gets good enough volume but then it sounds like poop. I can use my HD-650 from my TV headphone jack and get good results (for short periods of time)..with this I need like 90% volume and its not worth even bothering with. Some may disagree but I could hate this with the wrong setup. It seems to sound OK from my E17 but it's just not the same as my main setup. Best setup i've heard it with is what I'm using now (well duh). O2 is 2nd best. I actually liked it with the E9 a lot and the 10ohm output impedance doesn't change the sound in any way.
 
NOTE: This is basically my impressions after 2-3 years of use and NOT the modded version. Don't forget, that version is about 25% better than the HD-800
My impressions of this has not changed since day one. It's my 2nd favorite headphone of all time and I'm never getting rid of it. Not even if you gave me a T1!
 
BTW I'd love a closed headphone that was a clone of this or close. It's NOT the K550! You may need to reduce the soundstage and treble a little but the mids may gain some fullness.

This won't be an in depth review, just a few short impressions. Scored these for $90 at Radioshack. I always wanted to try a V-Moda headphone that wasn't too bass heavy.
 
Since all my portable players were dead I used my O2+Modi (transparent IMO). The low mids were shoved in my bass and these were too bassy. Well guess what? The cause was my powered USB hub crapping up the sound and with the amp/dac and these headphones I was able to detect it. Problem fixed!
 
They have a slight mid-bass emphasis and I was surprised that the low bass extension is very good. The mids are no longer shoved in my face. These actually don't sound dark at all and managed to have very smooth treble.
 
None of my music seemed  colored. The sound was pretty crystal clear too. With most headphones under $150 or so they can often sound fairly muffled or too dark. I actually had just returned an HD-380 and these sound WAY more balanced. I couldn't detect any recession in the mids at all.
 
Unfortunately the deal killer for me is that they were painful to wear. It seems like the design is incompatible with my head. I don't have a horse shaped head or one that's too big. I had to fully expand the headband. They hurt the tips of my ears and feel like a giant claw is grabbing at my head and trying to pull up. I think it's due to the Beyerdynamic style of metal headband. I did try to stretch them out over night but couldn't even take 10 minutes of them. I guess i'm the rare exception.
 
I hope V-Moda reads this because I'd really love a neutral sounding M80 that's over ear. I think the M100 has way too much bass for me probably.
 
So overall, loved the sound quality but hated the comfort. Ended up returning them. Kind of hard to do.
 
I still think the DJ100 with M50 pads sounds better but those are too hard to drive and too picky with gear.
 
M80 actually sounds more balanced than the SRH-840, K240, M50 and definitely the KRK KNS-8400/6400. The low bass is as extended and as present as the DJ100 and KRK KNS-8400. My DJ100 has a little more treble, more forward upper mids and maybe a tiny bit less bass.
 
Almost forgot..the soundstage with the O2+Modi was actually pretty impressive for such a tiny headphone.
 
NOTE: The audio quality rating is for closed headphones in the $100-$200 price range. I'd say they're comparable in sound to the M50, KRKs, SRH-840/940, DJ100, K240 Studio and a few others. Obviously they all have different signatures.

Just a few impressions since nobody really reads these:
 

1. All my headphones work well with it. Everything sounds just like it should. Garbage tracks actually still sound like garbage.
2. Very revealing (yes, I know) and if my recording sounds tinny/harsh/thin it will sound like that (unless I'm using the HD-650) without any change
3. Doesn't sound bright (if it does, it's the recording or headphone) and doesn't require a specific type of headphone for good "synergy" (IMO so far).
4. Doesn't sound cold/thin etc. It's warm (sounding) if the recording or headphone is. Some recordings sound like they have all the warmth sucked out.
5. Sounds crystal clear really. It actually might sound maybe a tad cleaner than my Micro Amp + Astrodyne. Barely audible, but I noticed it.
6. Didn't notice any "larger soundstage" nonsense, but I did get an impression of a little more detail. I think i'm just fooled really.
7. I would say it sounds perhaps 97% identical to my Headroom Micro Amp + Astrodyne. Impressive! The Micro might have a tad more body to the sound, but barely audible. It's not warm!
8. I can't say this enough, but the O2 sounds closer to the Micro Amp than the Schiit Magni (IMO).
9. I don't like the layout and would gladly pay $50 more for a design with inputs in the back. I'll live.
10. If you like a just a slight touch of warmth on your amp I would suggest instead the Fiio E9 or get an E17 as a DAC.
11. I don't really know what else to say. Nothing really WOWs me except for how crystal clear it sounds (with the right music) and how close it is to my favorite Micro Amp.
12. Tested with Schiit Modi, E17 (DAC) and HD-650, K400, Q701 (+Annie pads), Koss Pro DJ 100, HD-598.

1. The coolest thing to me with this is the massive variation in how each recording sounds sometimes. At times it feels as if it's like going from an HD-650 to an AD700. This is with the Q701!
2. So far I like this more than the Fiio E9, Asgard1 and Magni, but it's comparable to the Micro Amp in sound. Is it better? Not sure.
3. Doesn't get hot. I just checked. Had it on the past 4 hours.
4. Might sound .000005% better with the ODAC compared to the Modi. Modi and ODAC sound nearly identical to ME.

 
 
TL;DR:
 
Sounds transparent. No, really. I bet you didn't know that! I've heard it with my own ears and agree.
 
9-20-13 UPDATE:
 
Seems like with the Q701 it has a very very very slight hint of treble brightness. Barely audible, but it's still great with bright headphones and won't make them worse really. I've read that upgrading to a different power supply might make the treble smoother. Doubt it, but maybe!
 
Guns in Fallout 3 are noticeably more ear piercing than usual, but not too bad.

Compared to Q701:
(most of this has already been mentioned in other reviews)
 

1. More forward sounding and upfront, except for upper mids (and most female vocals)
2. Warmer and fuller sounding than Q701, but not by much. Sounds slightly more muffled and not as clear.
3. Imaging seems better. I think my brain is just fooled due to flat pads and a warmer sound signature.
4. Way less treble and upper mids took a nose drive.
5. Sounds darker than MY HD-650. Weird.
6. Soundstage seems much smaller and the sound is definitely less airy.
7. The deal killer for me is that most female vocals often sound much more distant.
8. Q701 sounds more balanced to me. So does my HD-650(!)
9. More forward lower mids than the Q701.

1. Less engaging for me with my music collection. Maybe i'm an upper mids and treble addict.
2. Not that much more bass. A little more mid-bass, but that's about it. Any difference in low-bass is barely audible by my ears.
3. I wish AKG could find a way to create that extra fullness but retain the Q701's upper mids.
4. Sounds hard to believe, but SOME subtle background details are easier to spot on the Annie. I think due to the more forward sound and flat pads.
5. Sounds almost more like a closed headphone.
6. Sorry, but it's no HD-650 killer. HD-650 sounds better to me than the Annie, but not the Q701.
7. Perfect for gaming.
8. Seems to be louder at the same volume levels than the Q701.

 
NOTE: All depends on preferences. You'll prefer the K702, Q701 or K702 Anniversary. I think the Q701 sounds the best (for me).
I do use the Anniversary for gaming. I hate to admit it, but for music it generally bores me. I do like it more and more everyday, but i've used it since maybe April.
 
BTW if you want to save some money get a Q701 and some K702 65th Anniversary pads. Same thing.
 
Hopefully AKG doesn't charge a fortune for the K712 Pro. Hopefully it will show up on Amazon for around $350, but unlikely.

This review is mainly for the DAC part only with L7. Mostly in comparison to my Schiit Modi. Just a few random things to note:
 

1. Sounds flat with a touch of warmth. Actually, just slightly more than a touch. It wouldn't be my first choice as a budget DAC if I was using just an HD-650. It seems OK for the K702 Anniversary. Based on memory, the HRT MSII seemed warmer sounding.
2. Everything is nice and full sounding in comparison to my Schiit Modi (doesn't mean it's better). The Modi is a bit thinner, but clearer and with a larger soundstage. Detail seems about the same.
3. Sometimes it sounds very very slightly muffled in comparison to the Modi. Possibly just placebo or just due to it being warmer.
4. Some bad/garbage tracks can be more fatiguing compared to my Modi. I think mostly in the lower mids only. Both measure flat, but Modi sounds smoother.
5. The bass is really good! Doesn't seem emphasized at all. It did on the E10 and I have no clue why.
6. I don't really notice any treble roll-off at all. Apparently there is some when just used as a DAC.
7. Works very well with my Xbox 360 using the Optical Connection. It even seems to drive the Q701 well enough for gaming.
8. Sounded a tad congested or almost too warm when used with the HD-650 (DAC only). Probably just my weird preferences.
9. I really disliked the E10, but felt this is pretty good.
10. The Modi sounds better overall to me, but this has some nice minor coloration so it's a keeper.
11. I have not really tried many headphones for this with the built in amp. It sounded OK with the Q701.
12. Way smaller than I expected!
13. Very musical (not excessively colored or anything).
14. I bought this because I love the Wolfson DAC in my Ipod Classic 3G (monochrome!). This sounds pretty close in sound signature, but even better!
15. Does not ever sound "cold and analytical". I hate anything that sounds that way. My Ipod Touch 2G sounds like that, but the ODAC and Modi did not. The Magni DID.
16. Should be good for anything but the warmest sounding headphones.
17. Might have some slight emphasis in the lower mids (not as much as the E10). Still flat though, don't ask me how.
18. Second best Fiio product i've tried so far. Not a fan of the E7, E10 or E11, but do like the E9 and E5. Wish I never sold the E9!

I will compare the Modi vs the ODAC for this mini-review. They both have the same general "signature" and really just sound very transparent/flat/balanced. I can't really detect any coloration and they don't alter the sound of any of my headphones or make them sound different than how they're supposed to be. I doubt that there is a headphone that would sound bad with the ODAC or Modi. For testing I used the Schiit Magni and Headroom Micro Amp + Astrodyne (both transparent). I used the AKG K400, Koss Pro DJ 100, HD-650 and Q701. It was the easiest to detect the differences with the DJ100 and Micro Amp. All the differences listed below were heard on both amps.
 
After a week of use here are some differences I've noted with the Modi:
 

1. Slightly better Soundstage on the Modi. The Modi seems to have better depth and height, but other than this it seems the same size or very close.
2. Slightly less clear than the ODAC on some songs. The difference is so extremely subtle that it's barely worth pointing out. I could be hearing things.
3. Much easier to pinpoint the exact position of instruments on the Modi compared to the ODAC. This for me was very noticeable.
4. The Modi to MY EARS sounds a little smoother. I know they both measure flat. The ODAC sounds slightly more shouty at times.
5. When you have vocals in front of you that sound slightly further back IN the recording, the ODAC is less accurate. You can't judge the distance as easily. Often the ODAC seems to shove things in your face in comparison. It's much easier to be fatigued with the ODAC. Again, I know they both measure ruler flat.
6. I can't really detect any warmth in either. Maybe the Modi has a touch more, but if so my ears can't detect it. I don't care about this. None of them sound "cold and analytical" though.
7. Both have about the same amount of detail. At times I felt that some detail was easier to hear on the Modi, but now I imagine it's probably the same.
8. Modi is not forgiving at all, just like the ODAC. They won't take the edge off harsh or bad recordings.
9. The mids of the Modi seem slightly more "relaxed" in comparison to the ODAC (still measuring flat). Maybe the Modi is just more accurate to how a recording really is? I think this is why and it's easy to be fooled.
10. I can't detect any difference between the bass and treble. Not after a week at least.
11. The difference between the ODAC and HRT MSII is MUCH greater. Doubt anyone cares, but this might give some an idea of how similar the Modi and ODAC are.

 
Again, I want to point out that the differences are very minor and almost nit-picking. To my ears, the Modi sounds similar to the ODAC but with some slight improvements. With my setup the Modi is maybe just about 5% better. The only way I could be able to pass a blind test here is when testing the differences in the soundstage. The Modi would almost always sound smoother to my ears also.
 
Both are very good and you can't go wrong with either of them. I now prefer the Modi over the ODAC and my old HRT MSII. It's probably not worth selling off your ODAC for a Modi.
 
I'm sure there are plenty of other differences people have heard, but I haven't heard them.

 
Fairly neutral but sounds slightly bright and lean sounding at times. To my ears, definitely more so than the O2.

I had them both within the last 6 months.
 
I felt it sounded good with the HD-650, HD-598 and my DJ100 but just decent with my Q701. For my Q701 with this amp I would probably prefer to use it with a warmer sounding source such as the Fiio E17. I think the docked Ipod Touch 2G to Magni made the Q701 sound a bit harsh/tinny/metallic sounding. Modi to Magni was a little better.
 
I sold the Magni after a few months and switched to the O2. It's slightly better but it does cost a little more. I think the O2 is a better match for brighter headphones, but still not perfect.
 
For very bright headphones the E9 sounds pretty good. It's much darker sounding in comparison and has some warmth but it's not transparent.
 
BTW my favorite budget setup would be O2 + Modi.

I'll try to be brief here, which is nearly impossible for me to do.
 
I bought this headphone last month and previously had two pairs. Those pairs had really anemic upper mids and had bloated mid-bass. This pair does not. I even used my old reference tracks I tried previously and this pair has a quite balanced sound signature. Not dead neutral or completely uncolored, but I would say it's just smooth sounding. Possibly one of the most musical headphones i've owned.
 
This headphone for me makes a lot of my crappy recordings that are harsh and fatiguing a bit easier on the ears. I don't ever get bombarded by treble or anything else. No shouty vocals or whatever else. It also doesn't make any very warm recordings worse by making them sound congested or less clear. I've found that they also seem to have better bass extension than my HD-600. Punch me if you want, but the bass on THIS HD-650 seems more controlled than that of my HD-600. It's closer to the bass quantity of my HD-580 (same driver I know).
 
Despite being very forgiving for bad recordings (only the garbage with the mids/treble cranked to max in the studio) it still need higher bitrate files. You can still tell the difference between high quality recordings and bad ones despite being both in FLAC.
 
These are very detailed. Nothing is missing, but all that detail is not shoved in my face. As hard as it is to believe, my DJ100 and HD-650 benefited more from my ODAC than the Q701. No idea why. The HD-650 seemed to become more revealing and detailed. The Q701..not as much.
 
This is a good headphone for when I just want to listen to my music and not be bothered by recording flaws. I can listen to these all day without fatigue.
 
The soundstage is better than that of the HD-600/598 IMO, but it's not larger. Better imaging etc. I think the ODAC is playing a role here too. Never thought such an improvement was possible unless my ears are playing tricks.
 
The sound is nice and full sounding, but not excessively warm. I thought I hated warm sounding headphones, but now I guess not.
 
This pair also doesn't seem to have sucked out upper mids, but at times there seems to be a very slight peak. Maybe a tiny one. I know this goes against what nearly everyone says. This pair also doesn't seem dark. The treble is very good and not lacking. It has slightly less than my DJ100.
 
Despite making my bad music sound a bit better than it should be, it still is quite accurate to how the recording is..sometimes. You often don't realize how bad the recordings are until you switch to a different headphones such as the KRKs, DJ100 or Q701.
 
I gave it a 1/5 for value. It's worth $400, but $500 is nuts! My $80 DJ100 with the same setup isn't that much worse and often even better in some areas. Both have some similarities. The DJ100 just has slightly more forward mids and more treble. DJ100 has better low bass. Sounds a little clearer too sometimes. Both are now my top 2 favorite headphones.
 
This review might be off the general consensus, but I don't care. This one is much more balanced than the others i've heard.
 
Setup was Headroom Micro Amp (not a portable amp an drives it with ease) from ODAC. I always use FLAC files. I previously used the Asgard with the HD-650, but found the Micro amp way better.
 
BTW this is as close to my DJ100's sound as I could find. My DJ100 sounds like a weird mix of an HD-650 and maybe a Sextett. Maybe the 650 and another AKG. The DJ100 is definitely a little more forward sounding, but still smooth sounding (with my setup, which I think is very neutral). I only mention this because I always wanted an open headphone that had some similarities to my DJ100.
 
NOTE: if this was priced at $350 retail it'd definitely get a 5/5 for value.
 
If you're curious I'd rank my Sennheisers as:
HD-650 > HD-580 | HD-598 > HD-600
 
Weird, I know..not a ton of difference between the 580 and 600. 580 just sounds better than the 600 to me. Clearer and with slightly more forward upper mids and maybe less bass.
 
Strange as it sounds, I tend to prefer the AKG type sound, but the HD-650 is just addicting.
 
EDIT: The only change after use I've noticed is that the lower mids smoothed out a bit. Out of the box they were a bit "shouty". Kind of like the PX100-II (for me) without an amp.
 
I also think it's a mistake to do many A/B comparisons of these headphones with something that's dramatically different (like a flat studio monitor). With crappy recordings the HD-650 will always sound better and it's easy to be fooled.
 
Oh yeah.. I also use these for gaming! 40 hours into Dark Souls and even use them for movies. The HD-650 can't match the soundstage of the Q701 though. HD-650 is obviously much warmer and a tiny bit bassier.

I found these brand new at a local thrift store brand new for $30! To me due to them being very colored to my ears, they're not worth that. Their sound signature just doesn't play well with my ears.
 
They do feel like the bass is a bit excessive. I think it seems worse than it is due to a severe lack of treble. These aren't as dark as the TMA-1, but maybe close. Some of my favorite tracks seem to sound a bit murky and almost congested. Total lack of sound clarity, but some other tracks are fine.
 
I was shocked at how fatiguing the mids are on this thing. It's not only the upper mids, but also the lower mids. I never had a headphone this fatiguing in the mids. This is also with many ruler flat sources and amps. Most of the time vocals felt as if the person was shouting in my ears.
 
To bring any sort of balance to this headphone I had to EQ down the lower/upper mids and crank up the treble a tad. Didn't need to touch the bass. At this point it now has a decent enough sound. I just can't believe these retail for $100! Wow! I should note that I love headphones with slightly forward mids. These actually make my DJ100 sounds like some sort of neutral studio monitor, which it's not.
 
Instead of these I would suggest the Koss UR-55, UR-22v, DJ100, Beyerdynamic DT-235 or even the KSC75. The PX100-II is also good when well amped. Even the XB500 sounds better when VERY well EQed. With that you crank up the treble and EQ down the bass.
 
It could be i'm sensitive to this forward of mids, but who knows.
 
NOTE: BTW I think this enclosure is just holding back the sound/driver perhaps. These actually seem to have surprising good sub-bass. It's even more present than my KRK KNS-8400. I bet the Uptown is far better. I bet the enclosure and pad design is what's hurting the treble.
 
10/5/12 UPDATE:
 
These are awesome now! 5/5 stars! Just kidding.
Since I hated these since day one I dismantled them and noticed 2 black tabs on each side of the driver. On the Inner Fidelity website, his pair has them removed.
 
Maybe mine has a manufacturing defect? I removed the tabs exposing the white fabric paper. Unfortunately it's near impossible to get them back together. Must require magic. It's impossible and took removing the "screen".
 
Now they sound decent. A little more treble, less shouty mids and more balanced bass. Is this a defect? Maybe Philips can tell me. Unlikely they hang out here. If ALL downtowns come with the black tabs in place than no wonder I hate them. It's super easy to remove them, but DON'T DO IT! Opening the headphone up ruins them mostly. I got lucky.
 
 

These are just some very early impressions since almost nobody reviews the super cheap Koss products under $30 other than the KSC75 etc.
 
First impression from a Clip+ was that the bass was a bit bloated (not the Clips fault). I stopped using that immediately and switched to my Headroom Micro Amp and ODAC (both very neutral). I don't know if they'll sound as good with portable devices. Maybe an amp is a good idea? Remember..early impressions.
 
The sound is quite full and kind of warm sounding for a $18 headphone. There's quite a lot of bass, but not overkill. Except for the slightly boosted bass, it sounds fairly well balanced. Not like a studio monitor. These actually have more than enough treble so far it seems like.
 
With harsh garbage tracks they're a bit fatiguing in the upper mids/treble I think. It seems to not smooth them over at all and make them any easier to listen to.
 
I'm listening to the Nine Inch Nails song "Besides you in time" and am surprised how good these sound for $18!
 
They're more balanced sounding than the Philips Downtown I just got. More treble, less bass and more neutral mids. I don't have to feel like vocals are too shouty. Comfort is better too.
 
Yes, despite the Downtown retailing for $100, these are better.
 
First full sized $20 headphone i've heard that wasn't a piece of junk! These are even $12 online..crazy.
 
Not sure about build quality, but it's VERY plasticy. Well duh, it's $20. Comfort it's a 4/5 for now, but it may go downhill. The pads are not that deep at all and kind of small.
 
BTW I wonder if this uses the KSC75 driver? Probably not, but I should inspect it.
 
I also tried the UR-29 and UR-20 and this sounds much better than both of those IMO. I don't remember the UR-40 much. I'm also a fan of the UR-55 and of course the Koss Pro DJ100.
 
EDIT: I just noticed that my Pearstone Velour pads fit So do the M50, M40 and V6 pads. The M50 pads would ruin the sound probably and make them too treble happy.
 
The Pearstone pads stretch a bit and give you slightly more room inside them.
 
EDIT 5000: I've been listening to these the last 2 hours(!!) with the Pearstone Velour pads. Ultra comfortable and the sound is impressive. Sounds better than many $100 headphones that i've tried. Right now it sounds quite well balanced, but with a slight tilt toward being a tad trebly.
 
 

NOTES: SKIP THIS FIRST PART
I had a heck of a time getting this to sound right. It made me aware of nearly THREE problems with my setup. Not even kidding. My desktop computer's rear USB port does not work with this. A powered USB hub is required. Next for some strange reason I have to use high gain on my Q701 with this dac and my Headroom Micro Amp. With 8% volume. If not, the Q701 is too fatiguing. This never occurred with my HRT MSII. On that, Medium was fine.
 
I'll keep this short (EDIT: whoops guess not). First impressions of this over my HRT MSII is that it sounds much more balanced. Yet strangely any of my garbage tracks suddenly don't sound so bad. It seems to take the edge off them. Why? I have no idea. On 5 of my CD players these same tracks are just awful and much worse. Way more fatiguing. I'm listening to a song right now that was unbearably bad on my HRT MSII and CD players and now it's quite listenable...even on the Q701. You could say those 5 players are just more revealing or colored, but that's unlikely to be true.
 
The idea that this makes the Q701 sound less warm or more revealing or analytical is nonsense. With my Q701 I still retained it's warm and full sound. If anything, it's treble is even more smooth and easier on the ears. The Q701 now sounds closer to neutral than before. I would say in comparison the HRT was a tad warmer, but only slightly. Again, it doesn't make the Q701 any leaner in the mids or anything like that. This is really the best i've ever heard the Q701.
 
I find the ODAC gave the Q701 a slightly larger soundstage with better imaging, but the difference isn't huge. I was actually confused with the difference in imaging. My X-Fi Go Pro does seem to give the Q701 a slightly larger soundstage than the ODAC. Don't really care though.
 
I actually find this DAC very musical and smooth sounding. Maybe it's the headphones and music too. All my garbage tracks are not put under the microscope at all. They sounded much worse on the HRT MSII. I actually think that thing might be more revealing of bad recordings.
 
I've not had this thing magically change any of my headphones in major ways. Generally they sound just like they should, but even better in many areas.
 
The biggest improvement in sound was with my $80 Koss Pro DJ100. Mostly improved soundstage size and better bass. Not more bass, but just better bass. I didn't even think that was possible since i've never heard the bass as good on any other DAC. I did experience a bit more detail with the DJ100, but I didn't feel ever that anything was being shoved in my face.
 
One reason I sold my HRT MSII is that I didn't like it with my HD-598 and HD-580. I just have weird preferences I guess. At first I blamed my amp, but i've found it's more transparent than I had originally thought. Less colored than the HRT MSII (which is still fairly neutral). The ODAC is really so much better IMO with my two Sennheiser headphones. It doesn't make them warmer or give them any extra bass. I think if I ever tried the HD-650 again, this is the DAC which would make me like it even more.
 
BTW it's general "signature" is close to my onboard sound, Sansa Clip+ and X-Fi Go Pro DAC. Obviously this is a huge upgrade, but all of them sound pretty flat to me. Blind A/B test would be stupid easy though.
 
SCIENCE GUYS IGNORE THIS NEXT PARAGRAPH:
 
I could never ever hear a difference in DIY (cheap) cables until I got my HRT MSII. It was stupid easy to tell the difference (less so with interconnect cables). Nothing major. With this I can't hear an ounce of difference. Only if the cable is a very high capacitance wire (such as Canare). My guess is that the ODAC is just no super duper revealing detail monster like the HRT. No idea here. I'm perfectly happy with my $1 Monoprice cables. Consider this a bonus. I can't really figure this one out (for myself).
 
 
Now that i've found a budget amp that plays well with EVERY headphone i've ever tried, I think i've finally found the DAC to go with it. I don't know why, but every single popular amp or DAC on Head-Fi i've tried has had some weird coloration to it or only sounds best with specific headphones. I hate that. Maybe I just have very bad luck. I'd also prefer to not feel the need to buy a DAC/amp every year and would rather spend that on headphones or new music.
 
BTW I think maybe this has very slightly rolled off highs. Probably not, but I guess it's possible. Not like the E10 though...this seems far more balanced than the E10. E10 didn't sound neutral, yet measures flat. Strange.
 
 
10/17/12 UPDATE:
 
I've now been using this since 8/20. Never imagined it'd be such a nice upgrade from my HRT MSII, but it is. Unlike the HRT, this thing (like my amp) plays well with every headphone. Sounds equally good with every single thing.
 
Lately I did notice that it's even less warm sounding than my Clip+. I took my KRK KNS-8400 downstairs to my main setup and it just wasn't the same, but still good. Yeah..I just called the Clip+ warm sounding!
 
I'd say my favorite headphone with the ODAC is the Q701.
 
For the record, I still don't find the ODAC excessively detailed or too analytical. Detail level is just where it should be. The HRT did seem to be more detailed. Why? Not sure. Maybe it's just due to a little more coloration and my brain being fooled. Who knows..
 
With this ODAC, my Q701 sounds as smooth as the HD-598. Nothing in it's frequency jumping out at me too much. Not thin or analytical, but quite musical.
 
 

I don't really like this. My impressions of it have been like a roller coaster. First it sounded good, then just ok, then terrible and back and forth. It will sound good on some headphones, but then on other ones it will sound like garbage. I don't want a DAC or AMP like that really.
 
If you don't agree with my impressions, then that is OK. These are just my opinions and how I heard it.
 
These are for straight out of the DAC:
 
My impression of it is that it makes the lower mids of my headphones (sound) much too forward. My DJ100 magically sounds as if it has even more fatiguing mids. The DJ100 should never sound this way. It's not that bad. Then the bass is quite bloated. Again, It's not THAT bad, but it's a huge distraction and is extremely annoying. It's clear that something is "off" because I've never heard the DJ100 sound this colored. The DJ100 and 598 will sound much less balanced with the E10. I will note that the DJ100 with this sounds very slightly better with the high gain option. A little more clear too.
 
I've found that this makes the HD-598 sound a bit more muffled and something just sounds off. I also got the fatiguing mids and couldn't take it anymore.
 
What makes no sense is that it doesn't actually sound like it has any lack of treble. At one point it clearly sounded like it had more than my HRT MSII. Something has me fooled perhaps.
 
To make matters worse, I could not get this thing to make any of my headphones with forward mids to sound normal when using the line out to any amp. Out of nowhere I tried the headphone out to amp and it sounded a little more balanced. Why? I have no clue. Even the soundstage seemed larger and the sound even clearer. Why the difference in sound between the two jacks? No idea. Should sound the same right?
 
I think for ME this dac/amp might only be a good match for some headphones. Maybe the Q701 or any headphone that isn't too warm or bassy. I think I might be sensitive to forward lower mids, so maybe this is why it bothers me. I imagine I would hate this with the HD-650, M50 or anything with a larger mid-bass hump. I also didn't like it too much with the PX100-II. I bet it may be impressive with the Koss A/250 or DT-880.
 
I prefer the E5 or even E11 to this as an amp. As a DAC I actually prefer the $35 X-Fi Go Pro. It sounds much more balanced sounding and plays well with all my headphones. I've seen graphs of the E10 and it doesn't look bad, so I don't know why it sounds so weird to me.
 
Maybe i'm just too picky and need to try the E17. Again, differences in impressions can be due to different headphones. I'm sure I can find a headphone I love this with.

My first desktop amp I got was the Schiit Asgard. Can't believe I went so long with just weak portable amps. I bought the Asgard for the HD-600. Found it drove that perfectly, but made my K702 and K601 sound like poop. ATH-AD2000 also sounded bad too. D2000 however was pretty impressive on it. Went with the E9 and found I preferred the K702 on that, but still liked the Asgard for the HD-650.
 
My goal was to find an amp that sounds equally good with BOTH the HD-650 and the K702. I remember one night comparing all my amps for the HD-650 and it actually sounded the best out of my cheap Total Airhead. How the heck does that happen?! This was for gaming and music. This made me want to give the Micro Amp a try.
 
Pre-purchase impressions were that it's probably overpriced and can't possible be any better than what I already had. I always thought it was plastic, but it's definitely not. It's metal and rubber. You could throw it around the house and I bet it'd survive.
 
When I got the amp I was shocked at how small it was. It's tiny! It's about as long and wide as my wallet. Probably the height of two decks of cards. Without hearing it I thought I had maybe wasted my money on such a thing that couldn't possibly sound good. After spending a whole day with it that impression changed fast.
 
I was actually planning to take advantage of their 30 day trial. If it didn't get the pass I'd send it back immediately. Within the first day I found it to be a keeper.
 
The first impression upon listening is how much more powerful it seemed compared to the Asgard and my E9. This thing has zero problems driving the K400, K501, K601, Q701 or even any 600 ohm headphones that i've tried. I know this doesn't always mean much, but no headphone has ever been past 50% on the volume dial. K400 had to go the highest. My Sextett LP (600 ohm) only needs 30% on the volume dial. Q701 maybe around 40%.
 
I've found the signature very neutral. It won't radically change a headphones signature. I've found it to be very very slightly warm (comparable in warmth to my MSII perhaps). The bass is very accurate and doesn't magically add any bass, but does seem to improve it. I first noticed this with my Q701, KRK KNS-8400 and HD-600.
 
I've spent a year trying to figure out it's signature and it's tough because it doesn't seem like it has one. One reason I feel this way is that nearly everything sounds good from it. It won't suddenly make a headphone with forward upper mids sound even more aggressive in the mids than it already is. I had this idea once that it might have very slightly forward mids (maybe upper mids). So little that it's barely able to register with my ears. I'll have to test this further to see if it's my DAC or amp.
 
Bass heavy headphones also don't sound any more bassy. If anything, their bass is more controlled and less bloated sounding.
 
The treble on this amp is fairly smooth sounding. However It doesn't suddenly make any treble happy headphone easier on the ears. No treble roll off that i've heard. It doesn't take the edge off the K702 at all. I haven't heard a SS amp yet that can. 
 
When I had the K702 for this, it seemed to kind of fill in the sound. Made them slightly more enjoyable to listen to and not quite as thin sounding. Slightly fuller sounding mids, but not like the Q701 has. The Micro Amp didn't make me keep the K702, but that'd be virtually impossible with any amp I think. I do think between the Airhead, Fiio E9 and Asgard, I liked the K702 from the Micro Amp the most.
 
I'm not a fan of the HD-650 at all, but it does many things very well. The Micro Amp was enough to push it further into the like category for me. I don't know if there's any amp that could make me love it. I think i'm just one of those who prefer the HD-598 or the HD-600. I generally hate headphones that are too warm. HD-650 is too warm (for me). I also don't like a laid back sound.
 
The build quality on this thing is excellent. It's built like a tank. It's metal and has rubber bumpers around the front and back. I'm sorry to say that i've dropped this thing no less than 4 times from a a height of around 4 feet. It's still working. It also does not function as an extra space heater like the Asgard!
 
Obviously I don't like the 3.55mm only jack, but it's not a big deal. I don't even know if it's possible for them to cram a 1/4" jack on this tiny thing.
 
I've also noticed this thing has a ton of detail. Combine it with a good DAC (HRT MSII is a nice pairing) and it seems to extract every bit of detail out of your songs. I've also found that every little change between cables (yes, i've said it) and DACs to be heard quite easily.
 
When switching between the E9 to the Micro Amp, the sound on the E9 from any headphone is a bit leaner and not as full sounding. Definitely a lot less detail. Supposedly they have the same op-amps (but Micro Amp has 7..no idea why), but they couldn't sound any more different. I don't know why, but my E9 seems to give every headphone an abnormally large sounstage. I don't know how or even if this is possible. On the Asgard, the K702's soundstage was so massive it made all background detail way too hard to hear. Almost like it went missing.
 
I need to compare this thing to the Matrix M-Stage. I bet the Micro Amp would be some serious competition for the M-Stage. My idea is that the M-Stage is more bassy, has a larger sounstage and less treble. Who knows. Has anyone compared both? I bet they sound somewhat similar.
 
The Micro Amp's soundstage (with proper recordings on the Q701) isn't abnormally large. Sometimes it seems a tiny bit smaller than my E9, but sometimes it's easy to be fooled. I kind of like to think the Soundstage of the Micro Amp is more accurate. When I get the M-Stage, i'll know for sure. When comparing them, it's not that much different in size. On the E9 it's a tiny bit wider. Again, could just be something fooling me. E9 seems to do that with all my headphones. No idea how.
 
I will say that with the K501, it's like a total out of head experience with the right music. Very impressive, but that's mostly due to the K501 and not just the amp. When I went into Tennpenny Tower in Fallout 3 with the K501, my jaw just about dropped. Felt like I was really there with all that elevator music surrounding me. K501's soundstage is too huge for gaming though.
 
I've found this to be also OK with most easier to drive headphones. When using my KRK KNS-8400 it doesn't ruin it's signature and just improves everything. The difference between the 8400 between unamped and driven with the Micro Amp + MS2 is quite impressive too. It actually almost sounds like a semi-open headphone. I would say the KRK KNS-8400 with this setup is comparable to the Q701, but maybe even better.
 
Despite being very slightly warm, it's not enough for some headphones to turn them from a cold and analytical detail monster to something that's very warm and easy on the ears. It can't even really help my Koss A/250 much in this area. I do however think it's enough to help the KRKs and Grados. Grado SR-225i and SRH-940 were quite good from the Micro Amp.
 
I think the Micro Amp is good for almost everything, but I would say it's slightly better for the AKG headphones than the Sennheisers, but just slightly. I've yet to find a headphone that sounds horrible from the Micro Amp. Even the 600 ohm DT-770 (bass light version) was great with it. I think the super easy to drive headphones or IEMs might be out of the question for this amp. I don't know and it's best to ask Headroom. I don't use it with any of my portables. DJ100 and KRK KNS-8400s seem OK. Same with my AD700/300.
 
The best headphones for the Micro Amp are the following:
 
AKG K601 (probably the best), K501, K702, Q701, KRK KNS-8400, HD-600/598/650, SRH-940, D2000, SA3000, SR-225i
 
On some headphones that benefit less from amping, there wasn't much change. I probably wouldn't buy the Micro Amp for just a K550 or HD-598. Somehow the KRKs and SRH-940 did seem to improve with the Micro Amp, which was a surprise. Even the soundstage got slightly larger. SRH-940 is a little more musical with the Micro Amp too.
 
So I've had this for quite awhile now. Felt it was 100% worth the $330. If it died, i'd immediately buy another. Basically loved every minute of using this thing. Don't let the looks and tiny size fool you, this thing is quite powerful and can probably drive anything.
 
BTW the version I have includes a huge brick power supply. Not a big deal for me. No plans on hauling this around.
 

9-17-2012 UPDATE:
 
I've discovered more about this amp in the last month than in an entire year. The reason I didn't like it so much with Sennheiser stuff is due to my DAC. I often would blame the amp, but the amp itself did NOT add ANY coloration that I could hear. Basically it should sound like what's connected to it with slight improvements. If I attach my Clip+ it will sound like a Clip+ with minor improvements. The nice thing is that you will hear what's connected and NOT your amp. I like this idea!
 
The slightly small soundstage for me was due to the source and not the amp. I only got a clue when I attached a full sized cd player to my Micro and magically got an improved soundstage.
 
I also have discovered that when connecting this to a Surge protector with filtering, it will bloat the bass and degrade the sound. It requires being connected directly to the wall. I was only able to verify this with my DJ100 closed headphones.
 
I've upgraded my DAC to an ODAC and now everything seems pretty dead neutral now. The Q701 has never sounded better. Exactly how it should sound, but even better.
 
I honestly can now not claim the Micro is bassy or has very slightly forward mids. Any coloration from the amp I can't really hear. Not enough for me to care.
 
Have to admit that out of all the audio gear i've ever bought, this is one of my favorites. I really like it that much. Any complaints i've had about it turned out to be due to an issue with the source!
 
8-31-13:
 
I got in the O2 a week ago and I've been comparing it to the Micro Amp. Both sound extremely similar. The difference? The Micro sounds very very slightly smoother in the treble with harsh/bright recordings and has more detail. Sounds a bit more airy/spacious sounding. Not sure how. You can A/B this forever and hear it. Basically the Micro Amp sounds like an O2 on steroids. I think if you like the O2 you'll love the Micro Amp. The Micro does require the Astrodyne though for the comparison to be accurate. Sometimes the Micro feels as if it might have like 1% more body to the sound at times, but maybe not. I bet some could fail an A/B test.
 
Test was with Schiit Modi (which really is a detail monster IMO).
 
Micro Amp + Astrodyne actually sounds more transparent to me.
 
11-2-14 UPDATE:
 
I still use this all the time and it's one amp that's great with everything i've tried it with. Some amps totally fail at this. To me it's totally transparent, but yet not thin/cold like some "transparent" amps are. Yet it doesn't add warmth really to any headphones. It's far better than the O2 and works better with a larger variety of headphones.
 
They no longer make this but if it dies i'd probably pay up to $500 to get another one. The only thing that came close in sound was the Ifi Ican. I'm sure the Matrix M-Stage might be similar too.
 
BTW this uses the same op-amp in the M-Stage, but it has six of them(!). Someday when I get rich i'd love to put this to the test and try some of the super power hungry Hifiman headphones on this.

Basically this is a mini DAC for your computer with a jack for headphones. From what I've read it has a 7.8 ohm headphone output, which might be unsuitable for IEMs and some portable headphones.
 
I actually bought this to use for my DJ100, HD-598 and other headphones for when I can't use my main DAC and amp. I actually expected to return this or sell it immediately.
 
Really surprised how good it makes the HD-598 sound. Some amazing synergy there it seems like. I actually don't think it's being under-amped because in my experience the HD-598 is very easy to drive. It even gets loud enough (and still sounds good) from my Ipod Classic 3G and CD player. Best of all, the soundstage is quite large and doesn't take away from the mids and make anything sound too distant. So far I think it's fairly neutral and it doesn't seem to change any of the sound signature of my headphones. Not that I can tell..yet.
 
Believe it or not this actually CAN drive the HD-600 and still sound amazing. Yeah..even for me this is a surprise since I hate listening to under-amped headphones. Listened to the HD-600 for several hours yesterday with this and honestly can't hear anything missing. No Sennheiser "veil", no bloated bass, lack of bass or lack of treble. Everything sounds good. Most definitely enough volume too.
 
I would say this sounds better as a DAC than my Nuforce Icon Mobile (Cmedia chipset) and the Fiio E7. My HRT Music Streamer II is better in every way, but that cost me $150.
 
This would be perfect for those that want a simple DAC for specific headphones. I'd suggest it as a starter DAC/secondary or travel DAC. You can even put it on your keychain!
 
BTW I did not install any software and it works just fine! It probably even works in Linux.
 
It doesn't have enough power for the Q701, but still manages to sound decent. You would need to connect it to another amp for the Q701, but that should be obvious.
 
I haven't tried many portable headphones under 60 ohm with this yet. My DJ100 sounds fine with it, but that's a hard to drive headphone. This DAC didn't seem to cause any distortion or mess with it's signature.
 
Not the best sounding DAC ever, but for $40 it's hard to complain! Highly suggested for the HD-598 as a low budget DAC. You don't even need to connect an amp to it!
 
BTW this really does seem to bring out a ton more detail in most of my headphones. Not as much as my HRT though.
 
Most impressive thing is the soundstage. Seems to increase the size of it with specific music. Very similar improvements in size as my HRT, but for $40!
 
I also had good results with this and the KRK KNS-8400. Try this and you'll feel as if you're listening to a semi-open headphone! You'd think the signature would be all screwy, but doesn't seem to change at all.

(science guys feel free to ignore this review. Thanks)
 
As most people know by now, I've always disliked most Sennheiser headphones. They're not bad, but the sound from the HD-600 and HD-650 just doesn't engage me and is not that fun. They're not clear enough, don't have enough detail or treble or are muffled. I previously had the HD-650 and HD-600 twice with various amps. The HD-600 is good, but it's not for me. Loved it for movies and games though, but for music it put me to sleep.
 
When I got the HD-598 I loved it. Compared it to the HD-600 and HD-650 and just preferred the signature of the HD-598 despite the others being "technically better".
 
I recently got this cable in and was shocked at the differences between it and the stock cable. I've always felt that most recables made less than a 5% difference in sound. I do my own DIY recables. Recabling the HD-598 made the biggest difference. I use a cheap wire that costs 60 cents per foot and it sounds better than stock but has the same signature mostly. Even adding a new cable to a Q701 made under a 5% difference. I actually now prefer stock cable. I think it's due to the internal wires still being intact.
 
With this cable the mids are much more engaging and not so anemic. They sound more forward, but I don't know for sure this is the case. Luckily the cable retains the warmth of the HD-600 and doesn't make it less warm. If you use other wire, you can make it even warmer, which is a negative for me. Canare or Mogami does this.
 
Next, i'm noticing much better sub-bass. The low bass rumble in video games is now much more present. I don't know how a wire can add bass and that'd be impossible right? But this is my impression. I've noticed ZERO change in mid-bass quantity.
 
The biggest difference is in sound clarity, accuracy and detail. The HD-600 is now crystal clear. Yes, it was a shock for me. What the heck? There's some detail in there that I can usually only hear on my Q701 and KRKs. Yeah..from an HD-600! So, is the HD-600 now a detail monster? Huh?!
 
With stock cable I've noticed that any badly recording or harsh recordings are not too bad for the ears. They don't sound bad like they should. Some may find this a plus, but I don't want my headphone doing anything to "fix" my music. With this cable, bad songs are very bad and not "tamed" to sound any better. I don't notice any boost in the treble, but it's possible. If anything, it's slightly in the mids and sub-bass. I'd like to think it's just fixing the deficiencies of the stock cable.
 
Now the science guys will also love this, but the soundstage is very much improved. With gaming and specific music it's almost like an out of head experience. Not like the Q701, but pretty impressive.
 
The HD-600 with this cable is comparable in sound quality to the Q701 almost. Q701 will have a larger soundstage, more treble and is slightly less forgiving. A little bit more clear too and less warm.
 
This review was based on about 4 days of listening. Here's the fact: I don't enjoy the HD-600 at all with the stock cable. It just doesn't do it for me. Love it with this cable. Good enough for me. Don't ask me how this is possible.
 
With stock cable on the HD-600 I prefer the HD-598. With this cable I may end up preferring the HD-600 over the HD-598. I need to give it a few more days.
 
I can't put the improvements into a percentage, but it was enough to make me love what the HD-600 is capable of. I'm now a believer that the stock Sennheiser cables are no good at all and really holds the sound back. It was the case with the HD-598 (that I recabled) and now the HD-600. Copper is copper right?
 
Another thing that I found interesting. When using NO dac and a portable player the differences between stock and this cable are harder to spot. When I use my HRT Music Streamer II and Headroom Micro Amp, the differences are stupid easy to spot. I wonder why this is?
 
For anyone that is thinking of getting the HD-600, here is what I suggest instead of buying the $400 new pair. Find and HD-600 used and have someone make this or find a used one. You can even make one yourself if you want. You would end up saving probably a hundred dollars even if you had one made. If you don't believe in cables, even try one with say Belden 1192A or something similar. I remember I once believed cables all sounded the same, but now I don't after making my own (cheap) cables. I think a good amp and DAC play a roll in it too. I actually couldn't tell the difference between K702 cables before I had a good DAC. Don't know why. With some headphones the benefits are small. I guess it depends on the quality of wire.
 
I've tried HD-600 recables with Mogami and Canare and this is much better. Worth the extra money and it's still not too expensive. I'd pay up to $200 for the improvements I've heard (crazy, I know), but not over that. On the Q701 I've not heard a cable that made $100+ worth of difference..yet. I think the benefits of that are chopped in half due to the internal wires though.
 
Tempted to give the HD-650 another try now thanks to this wire...must resist.