Pros: neutral tonality; detailed; smooth; clean; clear; very good resolution; great sense of space and ambience; very good sound localization and dynamics
Cons: could use a bit more bass impact but not really lacking here, just neutral
Below is a review and comparison against a few other USB DAC/AMPs in the same price range. Review pasted from a post I made in the Sennheiser HD 598 Impressions thread.
I've had my 598s for a few months now, and have been using them mostly with my iphone 6 and the E10K. I've never been all that impressed with the E10K. I think my iphone 6 sounds better. Anyway, the E10K, I guess is decent for what it is and its price, but nothing about it really stands out as anything more than "decent" in terms of sound quality. My primary reason for wanting to upgrade was that I think the E10K sounds a bit bright overall and a bit sharp at times in vocals, and lacks bass punch. The bass boost helps with punch but sounds a bit muddy. Vocals can sound a bit grainy at times.
So in comes the Dragonfly 1.2. Blows the E10K away in every aspect, except for maybe volume. I actually compared the Dragonfly 1.2 against a few other usb dac/amps (ibasso d-zero mk2, audioengine D3, cambridge audio dacmagic XS, and Meridian Explorer). The Dragonfly 1.2 sounds better than all of them overall, with a noticeably higher level of accuracy and refinement to the sound. Here's a breakdown of what I liked and didn't like about each:
Audioquest Dragonfly (DF) 1.2: Tested at 24/96 mode with Spotify 320Kbps files. Excels in all aspects of the music. Very neutral, clean, crisp, and smooth sound, top to bottom. Very good resolution and accuracy. Wide, spacious, 3 dimensional sound. Very good detail but never harsh and always smooth. Very good localization of sounds within the soundstage. Very good dynamics, soft to loud. Very good transparency. Beautiful layering to the sound. You hear everything, nothing is lost, and sounds just flow naturally into and out of the soundscape. The only negative, and I'm nitpicking here, is that it could use a bit more bass impact for modern bass-driven, rhythmic genres like EDM, metal, and hip-hop. It has a good neutral bass with some impact, but considering the 598s bass is light to neutral, it's not the best choice for those that listen to these types of genres. Then again, neither are the 598s, so really I think the dragonfly has a very neutral and accurate bass, and any lack of bass drive or rhythm is more a fault of the 598s than the dragonfly, IMO.
When testing, I don't have a sequence of songs I listen to. I just go with whatever I feel like, but I tend to pick songs I'm very familiar with and vary the songs between different genres to get a broad picture of the equipment's abilities. When I plugged in the dragonfly, I was so excited to hear what it sounded like that I just hit play on the first song on the screen. It was a slower Ed Sheeran song, with his vocals featured and of course guitar. The vocals really stood out. Airy, transparent, as if he was singing right in front of my face. Don't recall Ed's vocals ever sounding this good before. Janis Joplin, Woodstock Experience, was a showcase of not only her vocals, but the spacious and wide soundstage. The Dragonfly 1.2 does a superb job of reproducing the ambience and nuances of the recording. The more I listened to the DF, the more it revealed how excellent of a DAC it is, and the more I appreciated what it could do. Percussion instruments especially come through with impact and accuracy. High hats and cymbals sound more realistic than any other DAC/AMP I've heard.
Audioengine D3: Tested at 24/96 mode with Spotify 320Kbps files. I fell in love with this DAC/AMP right away, primarily because I was looking for more bass and less brightness than the E10K, and the D3 has the most fun and rhythmic presentation of all I tried. The bass on the D3 really stands out in terms of impact and it's fairly tight overall. It changed the character of the 598s from a headphone that's better for slower music to one that's actually fun to listen to with faster, bass-driven music like EDM and hip-hop. The juicy bass also improves the experience with classic rock and other genres as well. I spent a good hour and half just listening to various tracks for the pure fun of it.
That being said, the D3 loses out in many other aspects of the musical presentation. For one, its organic, warm, bassy tonality, comes at the expense of some detail, resolution, and transparency. Some sounds get lost in the music. Treble is far too relaxed. Dynamics are poor (sounds are compressed into almost the same volume). Soundstage is rather small and compressed as well. Surprisingly, vocals on some tracks don't sound as smooth as the DF 1.2, and have a certain edge to them. So other than the fun, bassy, rhythmic factor, the D3 has less going for it than most of the other DAC/AMPs I tried.
Meridian Explorer: Tested at 24/192 mode with Spotify 320 Kbps files. The Explorer sounded very good overall. I would rank it 2nd behind the DF in overall sound quality. It's a bit smoother and less detailed than the DF in the treble, and maybe has a tiny bit more bass impact. The 2 are fairly close sounding. However, the DF excels at all the things I mentioned above in its review. The Explorer seems to have just a bit less of everything else, but still very good in its own right. Also, considering it's about 2.5 times larger than the DF, I was expecting a more powerful amplifier, but surprisingly, it was the weakest amp of the bunch. Had to have it at 50-60% for moderately loud volume, whereas the DF would be around 30-40% for the same volume level. So very good sound quality overall, but doesn't impress like the DF does.
Cambridge Audio DACmagic XS: Tested at 24/192 mode with Spotify 320 Kbps files. Has a very good, clean, smooth sound to it. However, nothing about this DAC/AMP really stood out or impressed. Everything was good, but not great. Bass impact was just okay. Treble didn't shine. Resolution was just average. Soundstage was not immersive Vocals were pretty good, smooth and full. Again, other than a nice, clean, smooth sound, nothing about the musical presentation really stood out or impressed. For that reason, this was the DAC/AMP I listened to the least. I prefer the sound of my iphone 6 over this, but probably prefer the XS over the E10K.
iBasso D-Zero MK2: Tested at 24/96 and 16/44.1 modes with Spotify 320 Kbps and iphone 6 (as AMP only). So this is a full blown portable headphone amp and dac with battery, unlike the simple inline USB dac/amps above. Obviously, this one had the most power, volume, and drive. In terms of SQ, it sounded very good and organic when used as only an amp connected to headphone jack of my iphone 6. You could really crank the volume and feel the rhythm and drive of the music, and the vocals had a weighty full sound to them. This was actually my 2nd favorite listening experience behind the Dragonfly connected to PC. The Explorer had the 2nd best overall sound quality from the PC, but the D-zero connected to the iphone 6 was the 2nd best overall sound experience, primarily due to the rhythm, drive, and full, rich, organic sound. I still prefer the detail, resolution, spaciousness, and accuracy of the Dragonfly, overall.
The real test of the D-zero came when I used both its amp and dac, plugged into my PC. Initially, I had set the mode to 24/96. I listened to some 90s EDM tunes and immediately noticed that the music sounded too bright. There is a wide range of the treble that is accentuated over that of the mids and bass. The D-zero also had pretty good bass impact, but it's overshadowed by the brightness. I found myself cranking the volume to feel that good bass a bit, but then things sounded too bright, and I found myself lowering the volume which lead to not feeling the bass as much. Some songs even sounded a bit harsh. Of all dacs, this was the one that lead to listening fatigue rather quickly. Changing the mode to 16/44.1 for music seemed to lessen the brightness a bit, but it was still obviously too bright. Still, the brightness isn't terribly excessive, and I can see some folks with less sensitivity to high frequencies, or ones using warmer or darker sounding headphones, actually enjoy this amp/dac very much. The brightness does lift a veil off of the 598s and increases transparency. I particularly enjoyed it when watching movies as I heard little details in the background that I didn't hear with other dac/amps. Overall, I think the Dragonfly is a much better DAC, while the D-zero is a much better amplifier.
In conclusion, the Dragonfly 1.2 is the best dac/amp combo I've tried yet under $150 (current prices). It excels in virtually all aspects of the musical presentation, whereas the others had more shortcomings, or had not much about them that really stood out. I highly recommend if you're looking for a small portable, usb dac/amp for use with a computer, that you definitely at least try the Dragonfly 1.2 with any others you're considering