Pros: Packs a great sound in a small transportable package.
Cons: A tad on the heavy side for daily on-the-move use, better plug protection for clumsy ppl like me
Analog Squared Paper is small business run by Kageyuki Shikada. He makes each one of these amps by hand and they're effectively made to order. I won't belabour the specs and details of this amp as ianmedium has done a wonderful job at covering all of that in the Analog Squared Paper thread and in his review of this product. But I'll get into what this amp has done for me.
Shikada-san was extremely generous to loan me the TU-05b and TUR-06 for reviewing and I'm very thankful to him for such an opportunity.
Getting Straight Into The Sound
I'll admit from the start that I'm a noob when it comes to tube amps at the time of writing this review. I've only purchase my first headphone tube amp (Zana Deux) beginning of May 2013, and I've borrowed my friend's Shindo Labs Corton Charlemagne for my home speakers during the same duration. Prior to that, I've dabbled a little with the Woo Audio WA7 and an occasional demo of the portable ALO Audio Continental series, as well as Fostex HP-V1.
Although those portable tube amps were nice, the TU-05b really is in a league of its own and borders on being a desktop tube amp instead. It delivers a full sound that gives a large sense of space in terms of soundstage and imaging. The amp was pre-tuned to low/mid gain and I didn't need to turn up the volume to get that fullness and richness of the sound. Another immediately notable quality is the smoothness in rendering that's typical of a high end quality tube amp that's often read about. This tube amp reinforced what I've always read about the infamous "tube signature".
In terms of its frequency response, my particular TU-05b capped at around 30Hz however the maker assures me that with some modification the sub bass can extend lower. However, even for what it can deliver at 30Hz is extremely pleasing with the fullness and richness of it's bass presentation. There's this purr to the bass which almost gives it a life of its own. The quality continues to extend to the midrange and vocals especially are, again, rendered smoothly with an analogue-like texture. I've read a lot about how some amps can sound "digital", by listening to the TU-05b, I can understand the contrast much better. The treble continues with it's smoothness and airy highs without any sibilance. It's probably one of the clearest trebles I've heard in a portable/transportable (irrespective of OpAmp or tubes).
Practicality and Use
This amp though is by no means a practical amp. It's about 1kg, and at least for me, probably not so easy to walk around with. However if I'm going specifically to sit down at a coffee shop for an hour or two, that could be a case scenario of practical use. In Tokyo where "anything goes" no one would probably care if one had something like this on the table but in other countries, it may catch a stare or two. It's definitely quite a funky looking amp which probably screams out a certain level of geekiness but also style (to my mind anyway ;-)).
I did have a problem with the TU-05b and I need to deeply apologise Shikada-san for my clumsiness. In taking pictures, I removed the PostIt labels from the ports. I accidentally attempted to plug the headphone cable into the charging socket as I wasn't paying attention and inadvertently short circuited the TU-05b. Of course I'd offer to pay for the damage I've done to it but it also got me thinking of how the charging port could be improved to prevent idiots like me doing such a thing again. I must say that I've never done such a thing before to other devices (well most other devices are USB charging) but looking at something like the CLAS -dB, Rx Mk3, or DX100's round charging socket, it's not so easy to short circuit the batteries for those as at least one of the two connection points are more recessed. I think this is one area that could be room for improvement. Again, most people probably aren't as clumsy as me but further prevention couldn't hurt.
To my mind and my ears, this amp will not fail to impress and for the kind of sound it's able to deliver, and will continue to satisfy for a long time. As such, I personally see this amp to be a worthy investment. In addition, if one wants to play with the sound for a little variety, this amp is very open to tube rolling. ianmedium has done quite a lot that which he's shared in the thread. This amp will not bore.
TUR-06b on the left (to be reviewed later), TU-05b on the right