Below is my brief review of the Little Dot Mk. II v. 4.0 which I purchased in June of 2018 from somewhere other than Massdrop, hence why I'm not posting this in the reviews section.
Amplifier: Little Dot Mk. II
Power Tubes: Soviet 6N6P Gold Grids (matched)
Driver Tubes: GE Jan 5654w (matched)
DAC: Schiit Modi 3
Headphones: Sennheiser HD58x with custom Canare cable and Dekoni Elite Hybrid earpads
Source: PC streaming Tidal HiFi
Exterior Build Quality: 7/10
The Little Dot's exterior is a bare bones affair, there are exactly eight Phillips screws required to separate its two aluminum halves. The front and back panels have their text thinly etched in and don't match up perfectly with the aluminum shell. The four rubber feet on the bottom of the unit are good enough that I don't worry about the amp sliding around. This little guy is dense and I generally like the exterior, but I don't like that it is sized such that it doesn't really sit atop any DAC I've used thus far.
Board and Component Build Quality: 4/10
This thing has some old school Made-in-China build quality when you crack the two halves open! After one week of normal use with a pair of Sony MDR-7506 and the amp set to the second lowest gain, the rectifier let its smoke out and died. This was a known problem with the newer LD's. I opened the amp to discover a cheap and undersized full wave bridge rectifier rated for between two and five watts. That is completely unacceptable, I replaced mine with a 10 watt unit. I also discovered poor solder joints throughout the board and tube sockets, but the components are generally decent. I re-soldered every connection on the board, sockets, and power plug. All of the components are standard, off-the-shelf items which could be easily upgraded for very little money. The stock vacuum tubes are nothing special, I replaced mine shortly after purchase.
Tube Rolling: 10/10
I can't give the tube rolling ability for the Little Dot anything less than a 10 considering price vs. performance vs. availability. The 6n6 and 6j1 tube layout opens the door to a large selection of tubes across the price spectrum. Vacuum tubes manufactured in the former Soviet Union ($10/EA-$100/EA) are well liked, as are the GE 5654 ($10/EA.)
Sound Quality: 8/10
This is entirely subjective and based on any number of other variables, take anything I say with a grain of salt. My two go-to artists are Mark Knopfler and Daft Punk, both are particularly well mastered. I personally like my Little Dot a lot paired with the HD58x. Bass reproduction is tight with just the right amount of 'kick' for my taste. Mid's are sufficiently clear, I don't have a strong opinion one way or another; I have nothing to complain about. The combination of LD Mk. II and HD58x does result in slightly rolled off treble. This is another positive for me as I'm not a big fan of ultra-high treble that makes my ears feel like they're ringing. Overall sound is clear, perhaps not crisp. This is a OTL vacuum tube amplifier after all, it's slightly muddled by nature. The Little Dot Mk. II as I've configure mine does a good job of adding the human aspect to music we can so easily lose in a highly analytical solid state system. Speaking of analytical, I was not impressed by the performance of my trusty MDR's when powered by the Little Dot. Everything seemed muddy and over-saturated while the headphones seemed under driven. My experience with the MDR-7506's is pretty normal when using lower impedance headphones through a vacuum tube amplifier. The Sony cans simultaneously pick up every little fault in the system while being fed insufficient current.
Returning to the listening experience with my HD58x's, Daft Punk's work on the Tron: Legacy soundtrack is simply mesmerizing. From the driving beat of 'Recognizer' and the punchy bass of 'Arena,' I was thoroughly impressed. Listening to Dire Straits' live work in Live at the BBC and Alchemy: Dire Straits Live I really enjoy how forward Mark Knopfler's masterful guitar playing is through my system. The drum, cymbal, and high hat really drive their music while reinforcing Knopfler's guitar work.
If you're wanting to pair this amp with headphones rated for less than 80 ohms of impedance, look elsewhere. This is an output transformer-less vacuum tube amplifier, it outputs a bunch of voltage and not much current. Your low impedance headphones need a bunch of current and not much voltage. Your needs would be best met by a solid state amplifier, or a hybrid tube amplifier if you must have the vacuum tube sound signature.
If you're not a hobbyist with a basic knowledge of electronics repair, I wouldn't recommend the Little Dot Mk. II. The quality control leaves a lot to be desired, especially if you're in the feet wetting stage of audiophilia. If you are a hobbyist like me, this little guy is a great entry into modifying audio equipment in our conquest of all things music listening. The sound quality is what I wanted in a tube amp with a low price and excellent customization potential.