Pros: small size, build quality, features, spaciousness, liveliness
Cons: Slightly underpowered for hard to drive headphones, no marking on volume knob
I was looking for a work solution to drive my relatively low impedance headphones I use at work (Shure SRH840 and Grado SR225e), while also being able to feed my powered desktop speakers (BOSE companion II). As I don't do critical listening at work, I didn't need the highest level of audio quality, but I needed something small and portable so that I could easily put it in my briefcase when leaving for the weekends, etc. I also wanted it to look okay, but have a fairly small footprint. I looked at a lot of products and ended up trying this and the HiFiman EF2A. They both seemed to fit my needs of a AMP/DAC combo in an attractive, small package.
My expectations were that the HiFiMan would sound better and look better on my desk while the Audioengine would be more easily transportable.
While the HiFiMan did look somewhat better, it looked kind of ugly from behind, and didn't have a convenient spot on my desk. The Audioengine on the other hand, while not being a talking piece, was much more convenient on my desk, and its design aesthetic gelled well with my Macbook Pro, Bose desktop speakers and the headphones I was using it with. The HiFiMan looked somewhat out of place.
Soundwise, I expected the HiFiman to sound better, but that turned out to not be the case at all. If anything, the humble D1 blew the HiFiMan away. First, with low impedence, easy to drive headphones, the HiFiMan was mostly useless, as it had major channel imbalance issues up until you got past 1/4 power. However, for easy to drive headphones, much past 1/4 power was at earsplitting levels. The d1, on the other hand was perfectly balanced at all levels. Sound on the D1 cut out when it was below 8 oclock (I know there aren't markings on the D1, I'll explain below), but was completely balanced and noise free at all levels. The HifiMan, on the other hand, had an extremely narrow band where it was usable, and you had to constantly adjust it based on the recording.
Further, given the headphones I was using both had 1/8" terminations, I decided that there was no use even spending any more time with the HiFiMan, and sent it back after just two days (I had originally planned to spend a week with each and maybe even keep both).
As the D1 burned in, the sound continued to gain more spaciousness and the bass tightened up. At this point I've logged about 100 hours on it, and the sound seems to have stabilized.
Now, the first con is that the volume knob had no markings on it whatsoever, making it hard to see what your volume level was at, at a glance. Especially given that I will sometimes move this around, it was easy for the volume knob to be turned way up, without knowing. However, I solved this by simply pulling out a sharpie and making a small dot on the knob when it was turned all the way down. I put the mark at 7 o'clock when it was turned all the way down. After doing that, I found that with my SRH840 and SR225e, 9 o'clock was my normal listening level. 8 O'clock could be used for soft listening, 10 o'clock for "slightly loud fun." After about 12, things were uncomfortably loud on those headphones.
With the HD650, 12 O'Clock was normal listening level. However, with the HD650, is where the limitations of this guy started to show up. While the D1 would get the HD650 loud enough, it didn't have the same bass power as a full desktop amp with a dedicated power supply. The HD650 was a tick slower than when it was well powered. It wasn't bad sounding by any means, but the USB powered supply just couldn't give the HD650 quite the juice/headroom it needs to really shine. However, I never bought this to use with the HD650, which is my go to at home critical listening phone. Just thought I would point that out. With tough to drive headphones, it's merely "good" and not superb. Would I hesitate to use this with the HD650? Not at all, it still worked fine with them, and did dramatically improve them vs. no amp. But, there was certainly a noticeable difference with a nice, fully powered amp.
A further benefit of the D1 is that when you plug your headphones in, it cuts the non-amped out. So, you can plug in your desktop powered speakers and make use of the DAC and volume knob on the D1, and not worry about turning your desktop speakers off when plugging in your headphones.
Now, as to the sound, with the headphones I use this for, the SR225e and SRH840, it really tightens up the bass. That's the most noticeable benefit, you get fast, punch bass that's not quite there when those are straight out of the macbook's headphone jack. Further, there is a smoothness to the highs that really is pleasant. The midrange is rich. Soundstage is slightly expanded, you get a nice depth to the vocals. You can hear when singers even slightly move toward and away from the mic.
It is also dead completely black quiet, no noise whatsoever. Should be a given, but with sub $200 DAC/amp combos, that's unfortunately not always a given.
In a lot of ways it kind of has an almost tube like warmth, without the noise, difficult load management and unreliability you often get with tubes.
It's small size also allows me to easily take it home, or lock it in a drawer at work, thus have complete peace of mind with leaving it at work.
I can't believe how good this thing is, given the size and price. I'd happily pay $300 for it, but am sure glad I didn't have to. It was exactly what I was looking for features wise and sounds incredible. I in fact bought a second one for at home, and am considering adding a few other audioengine products (their bluetooth transmitter) because of the positivity of this experience.
Is it a perfect amp? Of course not, don't be silly. But if you are looking for a quality amp for headphones that aren't extremely hard to drive, it's great. It provides plenty of current that lower ohm headphones need. It has a great DAC and a fun sound. In a sleek, quality build. For sub $200.