Update: in its original version, I mistakenly labelled the lead for the final graph 'single ended' measured at a volume of 136/150. It should be 'balanced' at a volume of 149/150 (as seen in the graph itself). This was a cut/paste error. My apologies.
For reference:
ohm image: RMAA: Astell&Kern AK70 24-bit — ohm image
MST Audio: http://info.m-s-tech.jp
I consider myself something of a skeptic. Not a real skeptic. I let narratives carry me away far too often, and question things I’m down with far too seldom. But I try to make it a point to distain the belief in listening and believing. For audio stuff: that test has to be hardware, standardised, volume-matched, and snarky.
But before I could do all of that, get snarky, etcetera, I had a burger with Ryuzoh, modder extraordinaire behind MST Audio. We had fizzy drinks. With cold, fizzy fingers, I picked up his mod and my AK70, listening back to back at volumes as matched as I could make them. The impression I had at Tsukuba's awesome Hi-5 burgers is the impression I have now: bass, glorious bass. According to Ryuzoh, this mod is the culmination of everything he’s tried over the years, and to my ears, is something of a home run. Ryuzoh doesn’t strike me as a bass head. And his AK70 Kai isn’t exactly a bass monster. Instead, its bass is harder edged and more shouldery than stock. Its stereo image is boxier and more textured than stock. In some ways, it is like nothing I've ever heard.
But what I hear isn’t borne out in measurements. Differences compared to stock exist, but mainly in load stability, though with some definite stereo improvements and far lower THD and mildly improved IMD. So I’m confused. His AK70 Kai sure as hell sounds better and more detailed than stock, but what is behind it? I've not finished a full-on balanced comparo, and will revisit single ended measurements with Jupiter, which has been out on loan.
One thing I've noticed, and which still disappoints me is that even modded, the AK70 still hisses far more than it should. That's the first thing I wish would be addressed and I'm not sure why it isn't. Hiss aside, this is an impactful modification that, at least to these ears, and in no small part, to these measurements, makes a difference.
Note: Originally, I measured the AK70 at VOL 136 (single ended) and 149 (balanced). Next week, I will update this article with VOL 149 for single ended and add Campfire Audio's Jupiter.
Source: Astell&Kern AK70
ADC: Lynx Studio HILO LT-TB
Computer: MacBook Pro 21015; 2012 27" iMac
Cables: 1,5m Hosa Pro 3,5mm stereo to dual 3-pin XLR (around 8$)
Loads:
NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880/600
24-bit single ended @volume level equivalent to iPhone 6 max output (136/150)
NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880
24-bit balanced no load (@VOL 149/150 +6dB)
End words
I’m not done yet. I’ve a bit more work to do, including re-measuring the AK70’s playback of loaded square waves. But I’m almost there. And, I’m sure that my opinion of Ryuzoh’s mod won’t change. It is his best effort to date. And it is made on such a nice base DAP.