Apex HiFi Sangaku Review

Thanks to Todd from TTVJ for allowing me to borrow and review the Sangaku.




The Sangaku is a relatively new amplifier from Apex and Pete Millett, famous for his Millett Starving Student DIY tube hybrid amplifer kit.  The Sangaku is a tube amp that uses KORG Nutubes, a relatively new component from KORG that is actually a smaller scale vacuum tube that requires less voltage and produces much less heat than traditional tubes more commonly used in amplifiers.  The Sangaku is still a hybrid design with a solid state output stage following the gain stage of the Nutubes from my understanding.  It is also my understanding that while the Sangaku has balanced inputs and outputs that it’s not a fully balanced design and that the tube gain stage is entirely single-ended.  The back of the unit features two sets of unbalanced inputs and a set of balanced inputs as well as single-ended pre-amp outputs.  On the front is a standby switch, an input and gain selector and the headphone outputs.  

Sound Impressions

The Sangaku is a really surprising amplifier to listen to.  Going in I wasn’t really sure what to expect, but from their website and from reading up on Korg’s Nutubes, I understood that Nutubes are supposed to have similar properties to a single ended triode tube, the better implementations of which tend to really have a really big and exaggerated sense of staging.  One thing I noticed any time I used the controls on the unit or connected a headphone, the Nutubes were very sensitive to vibration and had very high frequency microphonics that would ring for at least 10-15 seconds.  Once they went away everything was fine, but it could get bothersome at times.  Overall I find the amplifier leans just slightly warm but has a good overall balance.  The amp was able to drive most of my headphones with ease, but clearly struggled to drive my HE-6, leaving it sounding poorly controlled and distorted.  The amp has a softer sort of texture to it and is quite a smooth and clean sounding amplifier that I think gives up a little bit of lower level impact for that more relaxed and laid back sound.

Bass on this amplifier isn’t quite as authoritative or hard hitting as I normally prefer but quantity is still ample in the midbass.  The subbass region seems slightly recessed and softer, lending less of a solid, weighty sound but still maintaining a somewhat warm overall tilt and sound.  Bass notes don’t always separate clearly and the amps softness ends up making me feel as though I’m losing out a bit on texture and impact in the bass region.  I think the bass is ample for most music, you may notice some of the characteristics of its bass in EDM, especially EDM that uses a lot of subbass.  

Mids on this amplifier are great.  The slight warmth gives male vocals and some instruments a slightly weightier and fuller sound.  The midrange is where I notice that the Sangaku really seems to elongate the sustain of instruments, almost like there is a very loud second order harmonic that rings out beyond the normal length of sustain on the amplifier.  The midrange is really where this was most apparent, later becoming easier to notice elsewhere.  It gives the amplifier a really romantic, slow kind of sound that still maintains really good clarity and separation.  It’s a very unique aspect of this amplifier that I think can make music sound a lot more pleasing and laid-back.  Vocals and instruments come through very clearly, there is good texture and dynamics through the midrange as well though it takes a bit more concentration to catch some of the finer impacts and details in string instruments and drums.  Ringing of strings on guitars and the smack and motion of drumskin isn’t quite as clear as I’d like it to be here, but I can certainly see why someone would trade that for the Sangaku’s overall tonal signature and uniquely romantic kind of sound.

Treble is very clean and just a bit recessed on this amplifier.  Treble comes through very smoothly and with great clarity and impact, but it’s also obvious that treble is not as well extended as it could be in order to achieve the tonal balance that Sangaku does.  While treble is certainly less present, it isn’t as though the amp is completely dark or overly warm sounding, treble is certainly more present than it is on the Mogwai that I reviewed recently.  The amp also manages a surprisingly good sense of air despite its warmer signature.

Staging is quite good on the Sangaku.  While it doesn’t expand the staging the way some of the rarer single ended triode amplifier I’ve heard before do, I find some of that effect is still here.  Imaging is quite clear, despite the “slowness” effect of that extended sustain, the amp actually seems quite quick and seems to image instruments believably in the space it presents.  While I find the amp punches quite well, impacts are a bit rounded on the Sangaku and I feel it can muddy the impact of much quieter sounds in music, some of the smaller details like the opening and closing of valves on brass instruments or the sound that comes from the throat and mouth of a trumpet player, almost spitting as they try to play their instrument.


The Sangaku has been a really enjoyable amplifier to audition.  I really enjoy its slightly warm tonality and the extended sustain effect that brings a bit of romance and “tube-yness” to the music without sacrificing clarity.  While I do find smaller details slightly more difficult to pick out in music on the Sangaku, I still find the amplifier is quite detailed, clean and smooth sounding.  No signs of harshness at any point with this amplifier, making it a very easy listen.  It has been very surprising listening to the Sangaku and makes me curious what other Nutube based designs could be capable of and hopeful for how they could be incorporated in lower power devices like portable devices and still offer some of the flavor of a nice, high end tube amplifier.