APEX HiFi Sangaku Headphone Amp 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.

Korg Nutube

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.

APEX Audio Sangaku

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.

APEX Audio Sangaku