Appearance
The build quality is identical to the amplifier, same enclosure, same materials, it's the same. It came with a power cable, but no USB cable.
I suppose this makes sense, otherwise next you'd be expecting them to throw in interconnects as well.
 
The LED's are a softer intensity this time, they are very much the same blue and they light up instantly. Where as the power LED on the amplifier tends to fade in slowly, and shines at this arrogant intensity. It seems strange to have the M-Stage duo, each with their lights shining at varied intensities, though it's negligible and purely cosmetic. There an LED's for the power and sample rate indicators (44.1, 96 and 192). When no source is attached, the lights toggle in succession to indicate that it's "searching" for an input.
 
There's also a filter and input switch, which snap just like the input on the M-Stage amplifier. After an little while the unit warms up, but runs much cooler than the amplifier. To the touch, it's about halfway between dead cold and amplifier hot, so I stack the DAC on top.
 
 
Filter
There's a switch for 3 filters on the front of the panel, "Sharp", "Slow" & "Mute". Out of the box, it was set to slow. Sharp makes the highs sound the slightest bit clearer, though the DT770 isn't renown for it's detail. I found the difference especially noticeable on José González's album, Veneer, where the acoustics sounded a bit flabby on the slow filter. Slow seemed to suit metal and electro genres. The mute setting just zeros the volume (which is nice instead of reaching for your volume or source if the situation calls for it).
 
The volume fades in when you turn the DAC on, for around 1.5 seconds, enough to avoid any unexpected "pop" of ear bashing, headphone damaging noise. I suppose it's a nice feature which some DAC's could tend to skip.
 
 
Listening
I don't have enough equipment to make comparisons, or the adequate experience to provide a review, but to sum up my own experience; the bass has this glorious resonating, deep-and-powerful, one-flavour-of-kickass to it, while the rest of the spectrum seems to take a backseat, occasionally sounding inadequate. I'm sure this is the telltale story of the the DT770's, and although I haven't tried other cans, I'm having lots and lots of fun with this powerful sound. I'm thinking about trying out the HE-400, or saving up for the Schiity LCD-2 combo.
 
One thing I will mention, and perhaps someone can point out why; for happy listening levels, I'm needing to apply gains to the amplifier.
This seems strange to me, I mean, my amplifier is paired with a DAC that was designed to be it's companion... I have the opinion that the gain switches exist purely to save your sanity should you end up with high-impedance headphones. It seems unnatural to set them at anything besides 0dB.

Up until now I was using the DAC within the amplifier (USB version), and I could happily listen with the volume at about 10 o'clock.
With this DAC in the equation, achieving that same level of happiness involves turning the volume all the way around to about 5 o'clock.
So instead, I've applied the first step of gain (10dB), and now the volume I'm seeking can be found around 12 o'clock.
 
I sincerely hope the gain doesn't affect the sound signature, if it does, this oversight is just absurd.

Admittedly, I'm not sure what to expect here. Maybe the output through the amplifier's DAC was unusually loud, or maybe there's an impedance factor when interconnecting the DAC. Regardless, and although I don't have another DAC to compare, it just seems unusual to have the amplifier turned up to 11 before my face features a glimpse of a grin or raised eyebrows.
 
Seemingly, sticking with the 10dB gain makes everything normal, and I'm really enjoying the sound as it settles in. It sounds much smoother than the amplifier's DAC, which sounded harsh in comparison.
 
Noob tip: At first I was a bit concerned that the USB input lacked 192KHz. However, I learned that upsampling from 44.1KHz to 96Khz makes the sound very different. It's a surreal, unnatural sound, but an interesting one. Sometimes I prefer upsampling if the sound needs to be livened up a little, but in most cases the sound is better without conversion. Just a general consideration I suppose, since most music played with this source (MP3, FLAC) is encoded at 44.1KHz, so when you see those inputs with the big numbers, you should really only be considering one thing.
 
 
Op-amps?
The DAC appears to not only have the same form factor, but the same op amps as the amplifier.
I wonder if upgrading the op amps in this DAC would have the same effect as it does in the amplifier? There are 3 OPA2134's on the board (I'm presuming one for each input) (picture), though I have no idea which one is which. Food for thought I guess.

Build
Featuring a simple design, which what looks to be only a few parts, each part is made out of high quality rigid materials that together feel as though these headphones will last a very long time. The headband strap is plether and attached by wrapping around the band and connecting with button clips. The band itself is a very flexible steel substance and offers good tension. I suppose if some find the clamping too tight, it could simply be stretched to reduce pressure.
 
Comfort
With each headphone enclosure being mostly plastic, and the band being quite a thin and light substance, the overall weight of these headphones is fairly negligible considering they are very much a full sized circumaural headphone. I do find after a while my neck tends to lightly cramp, though I suppose this depends per person. Ear cups are not valour but are still very soft and comfortable. I find occasionally they can become a bit itchy (especially with facial hair or in hot climates) but in almost every case this isn't noticeable. The headphone cable is on the left earcup and is not removable, which can be frustrating depending on the placement of your amplifier or source.
 
Sound
I would say the Beyerdynamic DT 770 PRO offers a fairly dark sound with an incredible bass response. Each bass note booms giving somewhat an emphasised sound, though not over the top, but it could be a loose for some tastes. I find the sound is fantastic when paired with electronic, rock, hip-hop, or otherwise powerful or loud music. Unfortunately, depending on the type of sound, often highs will appear insignificant in their representation, and occasionally sibilance is noticed over the smooth sounding bass. Though, considering their price, I would say these are a fantastic entry-level audiophile headphone - they are built and designed for home use, sound fantastic when amplified, and offer a special sound at an affordable price.