Apex HiFi Audio Sangaku

Pros: Versatile with low high in both SE and balanced inputs/outputs with pre-amp out An amp that leans to towards the neutral side. Compact amp.
Cons: Microphonic tube design that's sensitive to touch. A slightly shallower depth imaging compared to some other tube amps

Thank Yous

A big thanks to Pete Millett for lugging this amp all the way from US for us here in Japan and a further added thanks to Amos/Currawong for shipping it to me from his hometown down south, to me in Tokyo to have an opportunity to listen and review this amp.


Apex Hifi and Pete Millett are names that is well known to the veterans of personal audio. Pete doesn't churn out new amps the way Toyota would revise their Prius, however what he does produce are solid proven products such as the Pinnacle and Teton, and most recently he's leveraged some new technologies in his latest Sangaku amp.
The Sangaku uses the Nutube tube package which employs vacuum fluorescent display technology from Noritake Itron Corp. The package which looks similar to an IC chip with pin outs and glows blue/green fluorescent light when powered on. It's even microphonic like regular tubes. However it seems it doesn't require a long warm up time like regular vacuum tubes.


The amp is a very compact 22.3cm x 23 cm x 5.5 cm designed to be laid flat. Due to the front panel, can't be laid on the side (for those seeking to save space). Pete went for a basic amp only design leaving the user to have the flexibility to use the DAC of his/her preference. The amp is versatile in accepting 1x XLR pair for balanced, and 2x RCA pairs for unbalanced. It has also a pre-amp out at the back, and unbalanced 6.3mm and XLR 4 pin balanced out socket in the front. The input and output selector switches are push buttons that just rotate around the various options. For the 6.3mm single ended and XLR 4 pin balanced out the output selector further provides a low and high gain option.
The volume knob is also smooth with no perceivable channel imbalance.
As earlier indicated in the introduction, the Nutube is sensitive to vibrations like normal tubes. The way the Nutubes are mounted on the PCB and in turn mounted within the chassis, any vibrations on the Sangaku amp would cause the Nutubes to ping. This include whilst plugging in the headphone into the socket, pressing the input/output selector buttons, and in general tapping on the chassis. The good news is that the microphonic ping from the Nature doesn’t ring for long - light taps would settle in about 3-4 sec but a bigger tap would take longer for the ringing to settle. Some sort of dampener on the soles of the amp would help.
Unlike other tube amps, the Sangaku and Nature produces little heat. I can’t count the number of times I’ve burnt my forearms accidentally touching my Zana Deux tubes whilst reaching to the side/back to power it off on or to fiddle with the cords behind. The Sangaku is vented however little heat is produced from within.


My setup is Audirvana Plus 2.6.4 on my iMac to the iFI Micro iUSB 3.0, Invicta 1.0 to the Eddie Current Zana Deux pre-amp out into the Apex Hifi Sangaku (Single Ended connections all the way through). The headphone used is the Focal Utopia cabled with Moon Audio’s Silver Dragon.
The Sangaku is mostly a transparent amp. It doesn’t add colour to the overall signature so having a good source helps. The amp has has a more distinctive left/right separation than my Zana Deux (ZD), but the overall tonal signature doesn’t seem to be as full bodied as the Zana Deux. That’s not to say my ZD is bassy but the the ZD seems to have a bit more “weight” to the signature making the ZD a little more holographic and with a little more 3D imaging than the Sangaku.
However the Sangaku having the distinctive separation gives a (soundstage) wider presentation than the ZD.
The overall signature difference between the Sangaku and Woo Audio WA8 is greater than with the ZD. The WA8 has a noticeably warmer signature than the Sangaku, making the Sangaku sound “light on the feet” by comparison.


Tonal signature and sonic presentation-wise, there is little to fault with the Sangaku. Compared with the Zana Deux and WA8, it’s merely preference of tonal signature and synergy in pairing. For example, with my personal preference, I’m happy with the Utopia with stock pads and the WA8 as the Sangaku is a little too “light” tonally for my preference. However, I believe my opinion would change if I had the Elear pads on my Utopia with the Sangaku- of which I could perceive that to be a decent match. Unfortunately I’ve sold my other dynamic driver headphones.
My minor issues with the Sangaku is more related to the microphonic nature of the amp. I’m more conscious of how I plug in my headphone into the socket, vibrations from its surrounding on the table, etc. 
However I appreciate its size - a seriously compact tube amp that packs a punch in sound.
How do you select the iFI Micro iUSB 3.0 on Audirvana pls ?
@Bbirdmonk you don't. I believe it's a pass through. A+ doesn't even know it's there.
A good informative review. I hope I get to audition this amp at some meet sometime.
Pros: Well-made, excellent headphone driving ability. Great as a pre-amp for active speakers. Flexible inputs and outputs.
Cons: Tubes are noisy when the selector buttons are pressed. No balanced pre-amp option. Not quiet with IEMs.
Video review.​
Big transformers. Bulging tubes. Heat radiating all around the orange glow. That's what we imagine when we think about tube amps. However Pete Millet, long known for his amplifier designs joined us at the 2016 Autumn headphone festival in Tokyo and brought along with him his new and unique amp.
The Sangaku uses the Korg Nutube, essentially a modern re-design of a single-ended triode. To quote the Nutube site:
Nutube, similar to a conventional vacuum tube, has an anode grid filament structure, and operates exactly as a triode vacuum tube. Also similar to a vacuum tube, it creates the same characteristic rich overtones. By applying their vacuum fluorescent display technology, Noritake Itron Corp., a Noritake Co. Ltd affiliated company, have devised a structure which achieves substantial power saving, miniaturization, and quality improvements when compared with a conventional vacuum tube.

Using the Nutube in the Sangaku's hybrid design allows the amp to run using only a small transformer, giving the amp a footprint a bit larger than Apple's Mac Mini, if about double the height. With balanced input and output via buffers (the amp itself is single-ended a hybrid tube/solid state design) and up to 1.4W of power, the Sangaku can easily power high-impedance headphones like the HD-800 as well as planar headphones like HiFiMan's HE1000, Mr Speakers Ether Flow and others. 
Confusingly, the Sangaku has both single-ended and balanced inputs and outputs. However the design is single-ended internally, so the balanced input is converted, and the balanced 4-pin XLR output is essentially the same as the single-ended TRS socket. There's no benefit to using one over the other. 
The set-up of the amp is a little different, however, with the main (hard) power switch at the back and a (soft) standby power switch at the front. With the back switch on, pressing the front power button activates the circuitry and a roughly 10-second delay while the amp warms up. This is faster than my Studio Six which takes about 30 seconds. As well, since the power required by the tubes is small, so to is the transformer, and the amp I felt sounded sonically great from power on, whereas I felt the Studio Six was best after a few hours.
The headphone output selection and gain is controlled by a single button, which selects between the outputs and their gain level, as well as the pre-amp option. Thankfully no noise seems to enter any non-selected option, a problem I've had with other amps. 
Using my Schiit Yggdrasil as the source, the Sangaku has just the right amount of tube euphoria, and delivers music, regardless of the headphones, with a fantastic degree of effortless dynamics and precision. With the HE1000 V2, Mr Speakers Ether Flow and Sennheiser HD800 I felt I could get a very good sense of the space in which music was recorded. Small ensembles sounded close together. Concert halls sounded large, and instrument position was clearly focussed. All this while the amp barely gets to room temperature. The only negative to the design is an audible "ping" from the tubes when the amp is tapped or push-button selectors pressed, but this didn't affect my listening at all. It controlled IEMs too with fine precision, though unfortunately it has a bit too much hiss to be ideal with them.
For preference I liked the performance with the planars best. Maybe it was my choice of DAC and listening preferences at the time, but I didn't feel quite as engaged with the HD800s. I wish I could have tried them with the HD800 S, as they might have been a better match.
I also hooked the Sangaku up to my ADAM ARTist 3 monitors where it did very good duty as a pre-amp, a distinct step above the Audio-gd NFB1AMP that serves that duty. I only wish that the pre-amp outputs were balanced, as with a lot of electronics on my desk, any noise reduction would be welcome. It actually did such a good job that it had me preferring listening with speakers over headphones.
The Sangaku has quickly become one of my favourite amps, striking a perfect balance between precision, dynamics and euphoric sound and I can highly recommend it to anyone with a good source looking for an amp in its price range.
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1000+ Head-Fier
Pros: Clear and open, yet slightly sweet ; Airy imaging with exception rhythmic drive ; Very transparent to source
Cons: Microphonic. Source transparency could be problematic with lesser sources.
First of all, special thanks to Todd at TTVJ Audio for the opportunity to participate in this loaner program.


The Sangaku is the first Apex Hifi product I have had the opportunity to audition. It is one of, if not the first headphone amps to utilize the new Korg Nutube, which is a miniaturized vacuum tube based on previous Vacuum Fluorescent Display. It uses much less power and generates less heat than traditional tubes. But what is especially unique about the Nutube is that it is technically a directly heated triode. So, the Sangaku is unique in that it is a DHT hybrid headphone amp. Yet it retains the smaller footprint of traditional solid state headphone amps.

For comparison, I have owned a few comparable amps in price and performance over the past few years. Namely the DIY Torpedo III amp, the Trafomatic Head 2, and the Eddie Current Super 7.


Chord Mojo as DAC using a generic 3.5mm to RCA cable from Amazon. Focal Elear and modded Sennheiser HD-650 as headphones. Mostly used the Elear though. Macbook Pro using Vox player and PC using JRiver MC 22.


Build quality seems pretty standard all black Apex style. Nothing fancy. The relay switched inputs and gain with LEDs are a nice touch. Unfortunately, the Nutube is inherently microphonic by nature of being a DHT which never really gets “hot”. Switching inputs or plugging in a headphone results in an audible “Ping!”


The sound of the amp is difficult to describe without sounding paradoxical. The midrange is clean and clear, yet has a sweet slight warmth. Treble is extended and more present than a lot of amps, and in combination with the midrange creates a certain lucidity to the imaging that is slightly reminiscent of (though not the same as) top SET DHT amps. The greatest strength though IMO, is it has an excellent sense of rhythmic drive. This is most apparent with small ensemble Jazz with a lot of rhythmic stuff going on.

One thing that must be taken into account when reading this review, is that I find this amp to be very transparent to source. So much so, that I almost was going to give it a lukewarm review, but discovered my nitpicks were with my source. I recently applied a tweak to my Mojo of adding a large RFI ferrite suppression choke to my USB which made a noticeable improvement to the DAC, and the improvement was readily audible through the Sangaku. The clear and open midrange and treble does not do any favors to digital hash present in the source. Having previously owned the Schiit Yggdrasil and Gungnir Multibit, I can imagine they would pair well with the Sangaku. The amp seems thoroughly resolving enough to take advantage of what the Yggdrasil has to offer.

Therefore, I’m hesitant to try to nail down the sound description in too much detail. Simply because it lets the source shine through. However, it’s not a “wire with gain” so to speak. It does apply it’s own tube harmonics in a tasteful way. And maybe not the tightest bass I’ve ever heard. I deliberately haven’t commented on the bass, because I think it’s just carrying over some of the Mojo, but maybe a touch looser. Again, I think the Gungnir Multibit might be a better match. I thought the Torpedo III had better bass, but I had the Gungnir when I had the Torpedo III.

My only regret with this review, is that I don’t currently have more equipment to try with it. I would love to try the HD800 with it, having owned it twice. I also have no balanced headphone cables at the moment to try with it. I don’t think the amp is fully balanced, but it may have a differential output. I’m not sure though, I’d have to ask the designer.

I do think this amp can really keep up with some of the best out there, but source matters. It brings it’s own unique and addicting flavor to the mix, without spoiling the original sound. If I had to sum it up I’d say airy yet rhythmic. Not the absolute tightest across the frequency spectrum, but still clean and clear. Looseness probably isn’t the best descriptor, but rather it’s the harmonic decay that gives it some nuance and detail to trailing edges of music. This also helps to convey rhythmic information.


This is a tough one for me, and an area I am personally really nitpicky. On sound alone, it competes well against similarly priced amps, despite stiff competition. But when you compare it to the previous Peak/Volcano combo at the same price, it’s clear this amp is more cost effective to manufacture. The copious use of op amps and simple case work, psychologically make it harder to swallow at the price point. I’m guessing that they really just don’t want to have to build a ton of them to keep up with the demand of a lower price, so they are intentionally lower volume, perhaps. It probably has to have a certain margin for it to even be worth Pete Millett taking his time to design. That kind of stuff is time consuming, especially when it’s not your day job.

This doesn’t mean it’s a poor value by any means, it just means there is probably a healthy margin. But probably less so than a lot of big name manufacturers. If anything, this is a testament to Pete Millett’s design chops, that he can take generally pedestrian parts, and make a stellar sounding amp out of it. I really don’t have any problems with the choice of power op amps in the output stage. There is nothing inherently wrong with them, just less flexibility in integrating into a design. But they are implemented well in the Sangaku.
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100+ Head-Fier
Pros: Great sound with HD800, HE560 and other neutral cans
Cons: Not Enough power to drive HE6, sounds odd with warm hd650
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.