I made an earlier post assuming that the sound of the Bakoon wouldn't be for me. Well, I had the HPA-21 for a week-long audition, and I take everything back. It's probably the best solid-state amp I've heard.
It's a wonderful amp with the Fostex TH900. A lot of reviews talk about linearity and neutrality of it's presentation, but I think it's actually slight U-shaped. Clearly a solid-state type of sound, but not as up-front or in-yer-face as a Burson Soloist, for example.
Also had a LCD-3 (loaner) to try out, and it sounded great. On the TH900 however, the HPA-21 was simply magnificent. It retained the TH900's bass impact and probably brought out a bit more bass layering. Also moved the mids forward a tad and controlled treble effortlessly. Lots of detail and 'sparkle' but never overpowering (I'm allergic to brightness).
Most impressive was the depth it added to the soundstage. I often find that many headphones with ultra-wide soundstages tend to sound a tad aloof and impersonal for my tastes (HD800 or HE-6 being the prime culprits), which is why I like the balance between intimacy and imaging that the Fostex and Audeze headphones provide. The HPA-21 kept those qualities but gave the sound more depth, particularly the midrange. In the TH900's case, it also added a bit of weight to the upper mids which I found most pleasing.
Then there's the sheer detail presented. I use a pretty humble Bladelius USB DAC, which isn't the most resolving thing in the world, but (in my opinion) produces a very organic, analog sound. I'm not really a stickler for outright resolution. On the Bakoon however, it was downright shocking how much more detail I heard compared to other amps, whether less expensive Bursons or the Violectric V200, or even against pricier more-money-than-sense brands (I'm not mentioning names). Also equally shocking was how musical it all sounded without much added colouration. Some amps tend to fight the headphones in terms of sound signature, and you're usually stuck with one side winning out, or worse, a compromise between the two EQs that adds a veil on top of the music. The LCD-3 and TH900 are already quite coloured in terms of their respective house sounds, so in this case the Bakoon presenting extra detail without much colouration was quite pleasing, but it's best quality was that it never once attempted to 'neutralize' either headphone's natural EQ.
I've not had an opportunity to try out the JDM Bakoons or the much-loved GS-X mk2 yet, but I have tried some other supposedly high-end $5K+ amps, and I don't remember them (again, not going to mention the brand names, cos some people might get angsty) sounding as good as what the Bakoon's current output provided. This Akira Nagai chap is clearly on to something. The HPA-21 is currently on top of my want list, though I still really hope to have a go with the Headamp GS-X mk2 one day.
Haven't made a concrete decision yet, but I've started saving money nonetheless.
Edited by kurochin - 11/8/13 at 10:33am