Assuming that I understand what I think I hear, I think it safe to say that the MA750 is more mid and upper mid detailed than the MA650. And by detailed I mean everything from against-the-bass sound pressure and stereo, to texture, instrument delineation, and stereo width.
Not that the MA750 is all that stereo detailed or casts a huge sound stage. It’s just that its more lively midrange sticks out more against both bass and highs. This helps create a 3D feeling with a deeper Z-axis. I reckon it’s about half a step deep to the MA650’s quarter step. Neither one will get you swimmingly deep into soundscapes but the MA750 goes well beyond what typically I characterize as wall-of-sound sound, whereas the MA650 goes just beyond it. And, while the 750’s mids stick out more with higher pressure especially around the vocals, lateral stereo and stage spread isn’t that much larger than the MA650’s. What it does better (or at least wider) is feather its lateral edges farther and with with good gradation. I think this sort of stage works especially well for small ensemble live music, where, no matter how little, sussing the venue is important.
Mids are bitier, and on some places, wetter, than those of the MA650. Female vocals in particular jump to the fore and get breathy just where they should. The MA650’s are both drier and flatter. They are also a bit warmer until the upper mids. The MA750’s bitey love spreads around. Guitars and metallic strings are more detailed and show greater sound pressure and edge. Again, they don’t give up a lot of texture next to, say, Ocharaku’s FLAT4-Sakura Plus, but they do against Flare Audio’s Flares Pro.
I’m most torn on bass. The MA650s bass has rounder forward edges, and bleeds into the mids a bit more. In comparison, MA750’s bass is neutral with a bit more stereo detail and slightly more texture. But what really drew me to the MA650: incredible warmth and atmosphere aren’t there. The MA750 is less characteristically coloured than the MA650. I think bass quality and quantity will split audio-oriented people more than anything else. Personally, while I personally prefer the warmer, moodier MA650, I realise the MA750 is technically more proficient. That said, I prefer the 750’s more detailed midrange and especially its smoother fade into the highs. It’s got the right pressure and reverb. It is a thing of beauty that even the Flares Pro can’t touch.
Finally, like the MA650, the MA750 leaks some noise into the music. It hisses about as much as an iPhone 4s. While it could be worse, it’s a shame. Astell & Kern’s XB10 – my pick for last year’s roundup – hisses a lot more though. Still, I listen to music at low to medium volume levels, and in every non-dance or metal genre I spin, I hear a constant and low level shhhhhh in the background. Apple’s amazing AirPods also hiss. It could be down to driver/coil sensitivity. If that is the case, it would be smart to make the earphone a lot less sensitive.
The MA750 isn’t perfect, but it could be. Great branding. Great build. Great comfort. Great connection and neutral sound. Sure, next to the MA650, it lacks a bit of character, but who but the hardest core of non-audiophile audiophiles is bothered by that? For me, both earphones are held back somewhat by their low-level hiss, but I’m very sensitive to that.
Otherwise, they are damn fine.