Review: Ryuzoh’s AK70 Kai – The mod mod

As I mentioned in my AK70 Kai RMAA post, my first listen to Ryuzoh’s personal AK70 sealed the deal. Prior to setting up our man-date at Tsukuba’s Hi5 Burger, Ryuzoh asked if I was interested having him mod my AK70. He’s already modded my Plenue D, my Mojo, and my AK100. The question was nothing but a formality. Of course I would. But how much would it set me back? How long would it take? I’ve already spent a pretty penny on Ryuzoh’s handiwork. I trust it. But, it adds up. Ryuzoh asked me to consider it. If I was game, he’d do it. And this time, after hearing that I was interested, he said he’d do it au gratis.

My personal conversion went like this: after gurgling down half a cup of Coke, I plugged in my earphones and 200GB micro SD card.


I was immediately floored. Kai’s bass is grippy, reaching way around the head and stippling firm texture straight from the bottom. In fact, I’ve not heard a bass like it in a portable. It’s not elevated along a frequency plot, which makes it hard to describe. And while it sounds to me more energetic and bouncy, it doesn’t measure that way. Perhaps it is riding so hard on the Kai’s iMAX stereo image that it juts out from places it earlier never jutted. What I heard can only be described as the difference in visual clarity when you open a screen door: the clarity of the real.

And that still is the most notable difference. I’m sure that Ryuzoh wanted me to hear other things, things like Kai’s totally load agnostic and rock-solid stable frequency response, its much lower loaded THD and IMD, and its biggest measurable difference: -91dB of stereo crosstalk under harsh load at high volumes. Here’s a bone, Ryuzoh. Those things are icing on the cake. They are great. But sussing them comes long after basically tasting Kai’s superb and thwacky bass. I mean, this is bass whose stereo texture clears the shoulders with the same impact as it does at the ear. It’s the mod version of U2’s song, Trash, Trampoline, and the Party Girl.

So, let’s talk stereo image. What that bass best anchors is one of the clearest and widest stereo images I’ve heard in a DAP. I guess the latter is in large part the reason the former is so impressive. Where this has the greatest impact is in live music, whose bass edge always smears into the cacophony of the crowd. It isn’t subtle and even firms up the lower edges of soft guitars. String vibrations crystallise their own space and push to the sides. Stages expand. Distances grow. I don’t notice a noticeable change in Z-axis depth, but stock, the AK70 served up a pretty deep image, so I can’t complain.

At the same volume level and driving the same phones, AK70 Kai sheds 23dB of stereo crosstalk. That’s an improvement of about 33%, whilst driving the Audio Technika ES7. At -91,1dB, it fast approaches the limits of 16-bit audio – and that under load. Improvements to balanced signals are noticeable, but not nearly as drastic. At this point, and with this good of a mod under its belt, I see little reason to use the 2,5mm output unless you’re tied to the plugs and cables and attendant accessories.

Unlike the Mezzo Hifi mods, Ryuzoh didn’t replace the AK70’s DAC. So what you get is still bright, somewhat light, and detailed from top to bottom. But you get more of what that DAC is capable of, particularly under load. That I didn’t expect such audible differences is my issue; stereo crosstalk is one of the most impactfully audible metrics. Combined with the right mix of high THD or soft low-pass filter, crossfed stereo images can put the listener right in the centre of the action. AK70 Kai, on the other hand sits the listener a few metres back, but close enough and with a gentle enough low-pass filter, to ‘feel’ the music. Its firm bass is as visceral as you can get in flatline DAP connected to earphones. It is truly remarkable.

There is a minor and slow low pass filter in there. It isn’t severe enough to offset that energetic stereo image. This will affect how already perky earphones (Beyerdynamic Xelento, Grado GR8e, Earsonics S-EM9) sound. If the standard AK70 was enough for you, likely Kai will be too much of a good thing. If you craved a firmer, liver, and faster textural stereo ground whose icing is textured, live, bass, AK70 Kai is a notable, exciting improvement over the original.

End words

Ryuzoh added coaxial output to the AK100, balanced output to the Mojo, and shined up the Plenue D’s already decent, but more pedestrian innards. AK70 Kai, which doesn’t do anything drastic, preens one of the most drastic base sound enhancements I’ve heard this side of a subwoofer. Ryuzoh nailed this one.

5/5 - (8 votes)


Back before he became the main photographer for bunches of audio magazines and stuff, Nathan was fiddling with pretty cool audio gear all day long at TouchMyApps. He loves Depeche Mode, trance, colonial hip-hop, and raisins. Sometimes, he gets to listening. Sometimes, he gets to shooting. Usually he's got a smile on his face. Always, he's got a whisky in his prehensile grip.

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