I was fortunate enough to be part of the Sangaku loaner from the very kind Todd from Todd The Vinyl Junkie. Right up front this is a $2,000 amp, my expectations are high. Listened through my usual source, Gumby and Mutec MC1.2 DDC. 

I've been a Pete Millet and Apex audio fan for a while, building several of project on his DIY site. I was quite excited to try a high end tube amp using a new type of tube, the Korg NuTube.
The Korg Nutube runs cool to the touch, lasts 10,000 - 20,000 hours, and cant be rolled with other tubes (yet?), removing the biggest fear of most users new to tube amps. No more kids / cats / nervosa excuses fellas.

My "How to write a audio review for dummies" manual insists that I start talking about the physical characteristics of the amp before I start on how it sounds, so here goes... Sangaku is much smaller and lighter than I anticipated. When it arrived on my doorstep I was pretty convinced it wasn't a top of the line amp, just too light and too small of a package. Well I was wrong, Sangku is in fact a thin and trim amp. I was already getting clues that I haven't experienced a tube amp like this before.

Three inputs on the back 1 bal xlr, and 2 rcas, with a rca pre amp out. On off switch is on the back, but on the front there is a power button that switches between ON and STBY for standby. Next three blue LEDs select the input. Lastly there is an output selector button, UNBAL LOW, UNBAL HI, BAL LOW, BAL HIGH, and PREAMP. No constant pre amp! As you can see in pic in previous post, each tube has 2 square while lights per tube that glow when powered on. High quality build, would expect no less from Apex.
 
HERE WE GO! GONNA PLUG A HEADPHONE IN I found myself tapping my toes, bobbing my head, getting lost in the music - Now that I got the big three audiophile cliches out of the way- ACTUAL IMPRESSIONS THAT MATTER - SOUND!

I started out listening to Sangaku with HD800 (sdr, cork, and rug liner - balanced, low gain). WOW. WOW Again. I'm getting a rush. This sounds like a tube amp!?! Not warm wet laid back BH Crack tube amp, and not dry etch of Schiit Valhalla2. This has great neutral sound, tiny bit of edge, but thing that popped out at me was the classic tube imaging and stage that only good tube amps can provide. Stage is forward, tall, and wide. Not unrealistic, not too in your face, feels natural. Several times I looked over my shoulder to pinpoint where the sound was coming from. This is good. I thought to myself this might just be HD800. Need to try something else. Natural choice? HD650.

HD650 (common mods -bal, low gain) - Yuk. What happened? This doesn't sound right. Stage, imaging and tube characteristics are still there, but now i have bloated bass that bleeds into the mids. Boomy. Try 4 or 5 more tracks to confirm. Yup. I honestly haven't ever heard a tube amp that doesn't do well with hd650. Next...

HE560 (bal, high gain) - My other newer addition that helps me determine amp characteristics. These sound fantastic. Best I've heard these sound to be honest. Speed, clarity, warmth, tight bass. This little amp has power to push harder to drive planars, and push them really well. Well if it can power HE-560 it can power....

HE-6 (bal high gain)- Nope. Nope. Nope. Doesn't sound terrible, kinda sounds similar to how HE6 sounded on the Jot. Headphone can get loud, but it doesn't have the air it should, sounds slow and veiled. Bass is a bit muddied. Something that HE6 owners are familiar with...

Late addition - forgot I have HD580's. Much better. Cleaner bass / mids. Sounds pretty good, but not great. I think these sound better with Black Widow. I think HD600 will be similar case. Bloomy bass is gone, tightened up. Weird. I don't have a good explanation for any of this.

Ok, back to common characteristics. Sangaku has power, enough to drive he-560 well. Should cover most headphones out there. HD800 sounds great, but HD650 doesn't. Conclusion is Sangaku is a a bit of a warm tone that can affect warm cans. Not warm and lush, but slightly leans on warm side. Gumby & HD650 was just too much. Again, pairs fantastically with HD800 and HE560, probably due to their dry or brighter nature. Amp is fast and clean, has an edge, but no fatigue. I listened to album after album for hours on hd800, which is not an easy thing to accomplish (as reference Elear's 10k spike killed me). The height and depth of the stage and precise imaging stole the show. I imagine this is what great tube amps have that SS can never replicate. Slightly mid forward, but not overly full, certainly not lean or dry.

There not much for cons, tubes are microphonic. I frequently swapped out cans, and the last click of the XLR pings the tubes just right and you get a bit of high pitch ringing for 4 seconds or so. Not a big deal, just strange and new. If this amp were lacking anything it would be sub-bass, would love a little more punch or thump on the low end. But I would say its full and tight throughout the bass range, just lacking a bit of subbass. I might also be coming from a amp with subtle subbass and its not a fair fight.

Apex has a winner on their hands. Thanks to Todd I can see this amp coming back to me in the near future.