MSRP: $2000 USD



  • Soothing midrange
  • Excellent clarity
  • Good resolution
  • Excellent separation
  • Small footprint
  • Solid build
  • Unique but simple functionality


  • Lacks microdynamics
  • Lacks punch and authority
  • Treble is a little dark
  • Bass lacks extension an solidity


Much thanks to Todd of TTVJ Audio for sending this headphone amplifier loaner out on SBAF. I had been curious of the hybrid tube APEX Sangaku for sometime. After hearing and coveting the Apex Teton, I became very curious of Apex’ other offerings and wondered what technicalities belied the house sound that I got a taste of with the magnificent Teton.


Sound dBSPL
Library 30 dB
Normal conversation at 1 meter 40 – 60 dB
Car driving by at 10 meters 60 – 80 dB
Busy city traffic 90 dB
Jackhammer at 1 meter 100 dB
Typical club concert 110 dB
Threshold of pain 130 dB
Jet engine at 30 meters 150dB


The Apex Sangaku is a hybrid amplifier that aims for the ‘single-ended triode’ sound. It uses both vacuum tube and solid state technology. This means that it supposedly puts out mostly second order harmonic distortion which some find to be pleasant. The design uses opamps and when pushing a lot of current it kicks over to class AB. 

The small footprint and low power requirements of the Sangaku makes me wonder if they could have skipped the preamp and some features and made a more portable high end device like Chord but with the same sound quality it already has. I mean this thing takes up very little desk space at only 8.75 inches wide.

On the front of the amplifier is a balanced output and single ended output. These jacks cannot be used simultaneously but are selectable via the output button which functions as a both the gain selector and output selector. I find the output selection method unique but ideal and I have never seen an output selector function like this. I really found it convenient and simple to use.

The back of the Sangaku has three different inputs (1) two 3pin XLRs and (2&3) as RCA inputs. The preamp works uses RCA outputs.

The build of the Sangaku, while a little lacking in impressive aesthetics, is very solid and well put together. The knob turns with good resistance and no part of the amplifier seems loose or cheaply made.


  • BASS PRESENCE       72%
  • TREBLE BALANCE       81%
  • TREBLE EXTENSION       82%
  • BASS CONTROL   89%


The bass of the Sangaku tube amplifier has good clarity with acceptable focus but as a whole it is  not at the level I was expecting from an amplifier costing 2k. During listening with the Sangaku I found the performance in the low band to be of a high end quality but overall was a bit underwhelmed with it’s physicality. When plugging in the HD6XX and modified T50RP I felt like it was rolled off and lacked slam. I switched over to some EDM with my wooden T50 and the bass presence and slam was adequate based on the mixing of the songs and I liked the texture and control but knew from experience with other amplifiers, namely the HE-9 and Cayin, that there was more solidity and heft to be gotten from my ortho and the recording. What is fluid is the transition from sub to upper bass where you will not hear any extra bloat or muddiness. Sub bass extension not as deep as I was hoping for and were I to purchase an APEX Sangaku I would have to come to terms with the fact that bass slam is not really a prerogative of this amplifier.


The midrange of the Sangaku is very linear from the lower midrange through the upper midrange. I hear what seems to be a rise from the lower midrange all the way up to the middle midrange and a very very slight downward slope into the upper midrange. This sounds like an upwards bow in the midrange proper giving it some welcome emphasis. It has a very organic tonal balance that I consider marginally deviated from flat. It’s gentle rise in the midrange proper gives it a very tasteful highlight of chord tones and a sweetness that has a bit of preeminence over other frequencies before and after the mid band. The Sangaku is smooth to a fault but never really sounds overly lush to my ears. It has a very melodically tuneful flow to it that gives it a charming take on musicality.

The quality of the midrange is nicely refined with a soft and creamy delivery. I have read someone use the word velvety and I would agree. The Apex lacks a bit of that raw texture that I can get from the Mogwai and makes some of the realistic roughness that I know is in the recording sound a little glossed over. This subtle smoothing of texture is even in comparison to the HE-9. It can make for a pleasant and relaxing listen with Jazz and vocals but also somewhat troublesome with raw guitar buzzes, EDM synths, and trumpet textures. I do find the Apex nicely refined though and while I did hear a little bit of graininess compared to the HE-9, I only noticed it with the HD6XX which is an inherently grainy headphone. I guess the point is that it won’t help with the Senn HD650 graininess as much as some other amplifiers do.

I did not find voices to suffer from a lack of air and upper midrange presence and ‘hear through factor’ was pretty good on the sangaku. I hold the way the APEX Sangaku does vocals in high regards. There is no extra thickness and a good amount of detail and resolution that make voices really believable to me. There is a tube warmth in the midrange as well as a marked clarity, that while smooth in texture is skillfully resolving. If you have never heard an amplifier in this tier you will hear certain details from familiar music brought out more effortlessly with the Sangaku. However, if you have heard amplifiers in this tier then do not expect the Sangaku to wow you. It acquits itself admirably as it transitions into the treble.Interactive Frequency Chart – Independent Recording Network


From the Upper midrange through the treble there is a decline that is a little steep to my ears. The Sangaku is darker than the HE-9 and most amplifiers I have reviewed recently. It is also a little less dynamic with its universal softness making itself a lot more noticeable in the upper band. Harmonics and air are adequate so overtones stay intact but there is a loss of distinction and crispness that can make headphone pairings of the darker variety very underwhelming. Textures are never coarse enough to sound true to life.  The ZMF Eikon did fair but the Atticus suffers here. The presentation sounds a little nebulous yet never offensive. But the HD650 seems slightly trimmed in the upper treble so I conclude the extension is only fair yet not totally rolled off since as mentioned in the midrange section, voices have enough breathiness.


The Sangaku, while very clear in the midrange, does lack the ability to make music sound as physical as I personally prefer. Tonal heft is not substantial so melodies do not seem to resonate with as much vigor as reality would tell it. Control is decent but the attacks are too gentle and the decay is actually a little different than I was expecting from a tube amplifier and more akin to solid state. These aspects make its sleek sound signature what it is. The Sangaku has a loss of snappiness and nothing I heard ever struck my ears hard with convincing resonance or sustain unless I turned the amplifier up a little louder. In fact, during the time of this review I had the Sangaku moderately louder than I usually listen.  The speed of this amplifier is middle ground and neither is fast or slow which I personally find realistic. I can dig it on certain jazz songs where it’s musicality gains grounds on the sweetness and warmth of the midband and refinement instead of the diction and palpability of its transient response.

Macro-dynamics are decent. I mean in all fairness, if an amplifier has good body, tonal density, and transient response the importance of macro dynamics kind of loses its position of focus from my tastes and I begin to listen for micro dynamics more. I like amplifiers to really pick up the small gradations of volume and provide nuance. The Sangaku does micro dynamics like a solid state, actually I think I would prefer the Cayin iHA-6 in this department on the macro and micro level. The Sangaku is lacking there.

Soundstage on the Sangaku is pretty good. I do not perceive the soundstage of the Apex lacking. It is much smaller than the HE-9 and less deep than the Mogwai but the soundstage is wider than the Mogwai and still keeps from sounding flat in soundstage. The separation is excellent on the Sangaku as is the left to right imaging. It is not tall per se but I did not find the soundstage of the Apex wanting.

Clarity, transparency, and blackness of background are all really good. None of those areas leave me unsatisfied.


MODDED T50RP: Bass was lacking slam on most songs but EDM did fine (because of the tuning of the headphones) and the control was decent. Midrange was very sweet but compressed. The treble smoothness of the Sangaku worked well with the peaks and hashiness of my t50.

HD650: Graininess was evident and the 650 lacked macro dynamics and bass extension. The treble was a little subdued but also lacked body and punchiness. The midbass was not overdone and the warmth from the lower mids to the middle midrange was not too much for the 650. It just sounded like it couldn’t capture the snappiness I know the 650 is capable of.

ZMF ATTICUS: very similar results as the 650 but I felt the excess bass of the Atticus lost too much of its body and its ability to sustain a rumble down low felt considerably weaker than what I was used to on the Mogwai.

ZMF Eikon: The Eikon did much better than the rest of the headphones here. The Sangaku adorned the Eikons midrange with a little more sweetness which was welcomed and the Eikon was able to retain its tight bass and sound open enough to remain very enjoyable. The mogwai was a much better pairing for the bass of the Eikon but I still enjoyed this pairing.

Enigmacoustics Dharma: Sounds very detailed and decently spacious on the Sangaku. The treble decline was obviously in the D1Ks favor and it worked out really well. Most of the frequency range of the Dharma was well supported by the Apex except for … yup the bass. The Dharma bass is already garbage as it is so once I ventured outside of some jazz and folk music, things became severely unpleasant. This severity is more due to the Dharma and less the Apex but the Apex did not help at all and I felt like it made bad worse.



The Mogwai has better slam.  Kick drums sound quicker and snappier on the Mogwai. Neither are bass monsters but the Mogwai has stronger slam better extension, control, and solidity. Bass easily goes to the Mogwai regardless of pairing


The Sangaku is more balanced to me in the midrange. It has a sweetness in the lower mids and middle midrange but the upper midrange sounds a little shelved in comparison. The Sangaku is romantic and more effortless with good resolution. With the tubes on loan the Mogwai is thicker and denser sounding with more command behind the tones but also a little less refined and while the attack sounds clear and tones resonate more strongly on the Mogwai, the Sangaku has more finesse and grace which makes the Mogwai sound like it’s a bit too strong. The Mogwai also has a peakier upper midrange as well as lower treble with a more concentrated sound. Nonetheless I prefer the Mogwai’s tonal density and upper midrange bite as I find the Sangaku just a little too smooth. Merit by merit they are photo finished with the Sangaku slightly ahead because of its balance and clarity although the Mogwai caters more to my tastes and pairs better with my Atticus. 


Neither sound really airy to me but the Sangaku sounds darker because of the lower treble smoothness yet slightly more open. The Mogwai sounds like it has good treble presence but a steep roll off in the upper treble. In comparison the Sangaku sounds dark throughout the treble with a steady decline into the upper treble. Textures are more raw and thick on the Mogwai even here. Music has more coarseness on the Mogwai but more smoothness on the Sangaku. The Mogwai easily better body and impact in the treble though and sounds a lot more life like with much better bite. 


Sangaku sounds a little wider but flatter in depth with equal separation to the Mogwai

Macro and microdynamics easily go to the Mogwai. It is more nuanced and punchy at the same time but because it is thick sounding it lacks the finesse and easy listening factor the Sangaku has.


Hard to tell but on one song I felt I heard sounds I have never heard before with the Sangaku. Even though it is dark and smooth, it has a lot of resolution and inner clarity with a very clean sound. The mogwai is clear but I felt the Sangaku actually one upped it here. On the other hand, what ever texture is there the Mogwai brings out with more conviction and it’s weird because the Mogwai seems like it has better texture.


The mogwai is a more powerful sounding amplifier not just in signature but headroom. It is hard to believe that that thing is only 1.8w into 32 ohms. I think Justin is being very modest.


Sangaku sounds more refined and mature with more of a clean and silky sound to it than the Mogwai.



The short story is that the Sangaku has a beautiful midrange with clarity, refinement, and inner warmth that I find uniquely charming. As personal priorities would have it though, I would prefer this sound signature to be more emboldened by a snappier, and more pulse driven sound that could make my music more cadenced. I do prefer the tonality of this amplifier to the pro iCan and consider its mid band more balanced and open. While not as supremely clear as the HE-9, the Sangaku hold its own. It’s real competitor is the SPL Phonitor as they have a lot of similarities but the SPL unit has more bass, and denser tones while the Apex has a more graceful sound with cleaner bass. I can see this amplifier working very well for some people and some headphones, but it is not a one for all kind of accessory. I rate the Sangaku as very good, just not 2k good. To each his own.

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