⌈ AURORASOUND is a Japanese company founded in 2010 by Mr. SHINOBU KARAKI. Its lineup includes line and phono preamplifiers as well as amplifiers, including headphone amplifiers. We are the first magazine in Europe to test its first ever integrated amplifier. ⌋

HEN IN THE AUDIO WORLD you say "Japan" you almost instinctively hear "tubes". And no wonder, this Asian country is largely responsible for their renaissance in the 1970s sealed by the international success of the Kondo OnGaku amplifier (more → HERE and → HERE). There are plenty of small and quite large companies from this country offering this type of devices.

However, while in the high-end stratosphere it is relatively easy to achieve the assumed results, and I am talking about experienced designers, it is much more difficult to repeat them in lower price ranges and with products that are smaller than a two-door refrigerator. Among the few companies from Japan that I know, Uesugi U•Bros, SPEC, Leben and - you guessed it - Aurorasound managed to do it.

We have already tested the products of the latter in "High Fidelity" many times, so the figure of its founder and designer, Mr. Shinobu Karaki, should be familiar to you. However, it does not hurt to remind and emphasize that his approach to the design of audio components is significantly different from what we associate Japan with - in that he is much closer to SPEC than to Leben. Its creator worked as a semiconductor specialist for 29 years. He gained his experience working for twenty-nine years for the Japanese branch of Texas Instruments.

When he retired early, he returned to his youthful passions - building audio devices and learning to play the guitar. He started as a DIY business, and in 2010 he turned it into a professional job by founding AURORASOUND. Although its offer includes power amplifiers with tubes, all other devices are solid-state. And the tubes in question are controlled by silicon elements, not by electrons emitted in a vacuum envelope.

His latest product has a similar genesis, which has the makings of becoming the most popular device of this brand, the integrated amplifier HFSA-01. Its creator will tell you about it.

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| A few simple words…

SHINOBU KARAKI
Owner, designer

⸜ Mr. SHINOBU KARAKI in his laboratory

I STARTED THIS PROJECT around one year ago. My customers requested a new product, a more popular and versatile amplifier. And I knew it should be a tube one, because tubes can make better sound and better listening experience for customers. I visited my friend’s home who is an influencer in audio and music industry. He was using EL85 pp AMP with Altec speakers. It sound was very smooth and fantastic to play music in small Japanese room.

EL84 has been a very popular tube from 1960s, and there were many amplifiers and sample circuits in the history based on it. It is easy to drive, able to deliver enough output power, and very good performance in terms of THD, frequency response and SNR. But I DID NOT WANT TO follow this old approach. I studied EL84 data sheet, and I found out that it is very easy to drive it using a semiconductor circuit. This is really Aurorasound methodology, good combination of new technology and old technology to make a new sound and new performance. So I developed a new semiconductor circuit to use OPA604 OPAM IC.

HFSA-01 is a „Pre-main AMP”. I integrated in it a phono equalizer, tone control, volume control and power AMP with power regulator and transformers. As it turned out, it is very difficult to find a good placement for these section in a single chassis, as well as ensure a good air ventilation for tubes, and most of all, to achieve a good gain balance among these functions, and difficult to keep good SNR for headphone listening. I spent most of the 505 hours used for development of this project, finding a way to fit a complete amplifier in one chassis.

⸜ Mr. SHINOBU KARAKI’s home system: B&W 801D4, 2-way Amphion, and Altec 604-8G loudspeakers.

Most important parts in the new amplifier are output and power transformers. I asked a Japanese manufacturer to develop new transformers, and tried out 3 designs before finding the best one. HFSA-01 offers 14W+14W output, but output transformers have 20W+20W capability, meaning enough size and weight. Power transformer is also able to deliver enough power, which is very important factor to achieve a good sound in any place, every time and with every music source. HFSA-01 can drive B&W 801D4, 10cm, Amphion 2-way book shelf, and Altec 604-8G speakers, or in other words many designs from modern to vintage ones. But 14W+14W output is not enough to play really loud. SK

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HFSA IN THE NAME OF THE AMPLIFIER IS AN Acronym for High Fidelity Stereo Amplifier, and "01" means that this is the first such product in the company's offer. We are talking about a small stereo amplifier measuring 360 x 145 x 320 mm (W x H x D) and a weighing 10.3 kg. The device offers 14 W per channel and is very versatile. It features three line inputs and a phono input for MM cartridges. The layout of this section was developed on the basis of more expensive Aurorasound devices, for example VIDA Mk II (more → HERE). The features also include a headphone output and a tone control that can be disconnected.

Even on the photos, before amplifier landed in my room, I saw a reference to the iconic device of this type from Japan, the CS-300 amplifier from Leben. I know, it's a different design and a different looks, but that's how I saw it. The design is different in that the preamplifier and output tube driver sections are based on integrated circuits, not tubes. The HFSA-01 is a hybrid amplifier, but with an inverted configuration, similar to KR Audio Electronics devices (more → HERE ⸜ PL).

The output of the device is based on EL84 power pentodes. These are small but great tubes that I know from many solutions. They are inexpensive and easily stocked, also the so-called NOS versions. The tubes work in an ultra-linear push-pull configuration in class AB1. The phono preamplifier and tone control are active circuits based on operational amplifiers. The headphone output is connected to the output buffer of the preamplifier, so it is a semiconductor output.

I mentioned design. Although at first glance Leben and Aurorasound differ from each other, this is only a superficial difference. Both are "children" of the 1970s with their cult of clean, technical shapes straight from the laboratory. Which, I might add, works great. On the silver front of the amplifier there are black, well-chosen volume knobs, input selectors and tone controls, as well as two toggle switches that disconnect the section with the tone control and switch the amplifier to monophonic mode.

There is no remote control.

▌ SOUND

˻ HOW WE LISTENED ˺ The Aurorasound HFSA-01 amplifier was tested in the HIGH FIDELITY reference system and was compared to a split system consisting of the Ayon Audio Spheris III tube preamplifier and the Soulution 710 transistor power amplifier; I devoted a separate listening session to comparing it with the Leben CS-300 Limited Edition amplifier. To listen to the headphone output, I used the HiFiMAN HE-1000 v2, Sennheiser HD-800 and Beyerdynamic DT-990 Pro (600 Ω) headphones.

The HFSA-01 was placed on the Finite Elemente Master Reference Pagode Edition Mk II rack. It was connected to the Ayon Audio CD-35 HF SACD player using RCA Crystal Cable Absolute Dream interconnects, and to the Harbeth M40.1 speakers with Art Series Da Vinci speaker cables from the same brand. The amplifier was powered by the Harmonix X-DC350M2R Improved-Version cable. There were also SPEC RSP-901EX speaker filters in the signal’s path, which their manufacturer calls: REAL-SOUND PROCESSOR.

» RECORDINGS USED FOR THE TEST ⸜ a selection

⸜ CAROL KIDD, Both Sides Now, Impex Records IMP8320, Numbered Limited Edition ⸜ No. 0525/2000, Ultimate HQCD (2020).
⸜ PATRICIA BARBER, Companion, Premonition Records/Mobile Fidelity Sound Lab UDSACD 2023, SACD/CD (1999/2003).
⸜ DEPECHE MODE, Memento Mori, Columbia | Sony Music Labls Inc. SICP-6511, CD (2023).
⸜ KRAFTWERK, 3-D. The Catalogue, KlingKlang | Parlophone 95873424, 8 x CD (2017).
⸜ PAT METHENY, What’s It All About, Nonesuch/Warner Music [Japan] WPCR-14176, CD (2011).
⸜ CAROLE KING, Tapestry, Ode Records/Epic/Tidal (1971/2017).
⸜ MICHAEL JACKSON, Thriller, 40th Anniversary Expanded Edition, Epic/Sony Music Entertainment SICP-31586-7, 2 x Blu-Spec CD2 (2022).

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WHEN I HAVE TIME, before the actual, analytical listening sessions, I sit in front of the audio system with a new product in it and listen to an album I haven't heard in a long time. It doesn't matter if it's high-end sounding or a mediocre one, I'm only interested in music at this particular moment. It's a kind of "calibration". Then I look for emotions in listening, I check if something interests me, intrigues me, or maybe surprises me.

So it was this time. The album I reached for was CAROL KIDD's 2020 album entitled Both Sides Now. This is a tribute album to Joni Mitchell, who released an album of the same title in 1969. This disc was very carefully prepared and released by the American label Impex Records in Japan on the Ultimate HQCD in a limited, numbered pressing. Because everything worked well on it, Coherent Audio’s Kevin Gray's mastering only sorted it all out.

With the Japanese amplifier this release sounded in an open, clear, resonant way. And incredibly energetic. I didn't hear any strain in its sound, nothing seemed forced. Carol Kidd's vocals had quite strong sibilants, such as I know from the "High Fidelity" reference system. It was not an "audiophile" sound in the sense that one thing or other would be smoothed out. Usually tube amplifiers smooth and warm them up a bit, even the Leben CS-600X does it. Interestingly, they are not warmed up by the Leben CS-300. In this respect, it would be very similar in building the timbre of the device. Anyway, the Aurorasound amplifier sounded very lively, a bit like I know it from stage situations.

The tested amplifier did a great job building layers of the stage, rendering the scale of instruments, showing reverbs. As I say, it played effortlessly, as if its fourteen watts were fifty. This was because the dynamic differentiation was exceptional. When in When I Dream the electric guitar with a characteristic effect is heard at the beginning, it was an open timbre, with a lot of information about the depth of the effect, but dynamically filled, if I may say so. And the delicate strings entering at the end of the first minute were shown further in the back of the stage, nicely filling the panorama.

However, whatever I say, or write, you are probably urging me to say something about the bass. Low output and small size of EL84 tubes is a challenge for designers. On the other hand, my powerful Harbeth M40.1 loudspeakers, not very friendly to amplifiers, are a challenge for them. So I hasten to explain: HFSA-01 sounds like a high class, powerful amplifier with excellent timbre and even better bass extension and saturation. Provided that we do not play too loud, at least with medium-sensitivity speakers.

I know the CS-300 Leben very well and I know what these tubes can do. Mr. Karaka's amplifier did not disappoint me, and even showed something more - it showed that you can extract from them not only timbre, but also dynamics and differentiation. The latter was especially evident when I listened to Use Me, a track from Patricia Barber's Companion. You could hear not only the instruments, but also the sound of glasses or bottles in the back, behind the bar. And this informs you that this is an extremely resolving device.

Perhaps even more surprising will be how this tiny amp rocks. Do you remember Naim NAIT? – It's perfectly similar in terms of transforming sound into energy of the device. It seems that the amplifier from Japan has energy stored under its "hood", which it gives back with low bass, played with energy and punch. From the technical side, it is clear that it is about high current efficiency. However, we perceive it as uninhibited dynamics.

What is so interesting is that many, maybe even most, big amplifiers sound slightly muffled, as if all the power was dedicated to controlling the loudspeakers, and the music itself was lost somewhere in all this. Here music comes before technology, but only because technology makes it possible. It seems to be a paradox, but in fact this is how audio components should be designed. Just like before Mr. Taku Hyodo, the founder and designer of Leben, Mr. Shinobu Karaki does it perfectly today.

Ah, how beautiful sounded the PAT METHENY’s guitars from What's It All About! The musician plays a solo here, using four different instruments in subsequent pieces. The first of the tracks resounds with a baritone guitar. And the Japanese amplifier really showed its tone beautifully. Without weighting it down and warming it up. This is not an amplifier that will correct a bright sounding system. In this case, the tubes are used to make the sound as fast, open as possible, but also saturated with harmonics. And also that these harmonics should be time-coherent with the basic sound.

That's right - timing. It is thanks to it that we "see" space. Phase changes, delays in sound reaching our ears, size (volume) of instruments - all these are described by signals with low amplitude and therefore easy to lose. Amplifiers with a simple gain path and low power deal with this issue better than large ones, at least most of them. And Aurorasound does it even better than most small amps.

Metheny's guitar, suspended in a large space with reverbs, was incredibly lively, exciting, energetic. A large space was obtained by saturation of the low bass, but also by timing. Low frequencies do not have as much energy with the HFSA-01 as with more powerful devices, nor are the bodies of the instruments as well described. But it's something you have to sacrifice for what you get, that's life. And, believe me, a short listening session in a good room is enough to understand what we are dealing with.

˻ HEADPHONES ˺ Mr. Karaki's products that I value the most are line preamplifiers and headphone amplifiers. Perhaps because I know them best. There is no separate headphone amplifier in the HFSA-01, and the signal to the headphones is taken from the buffer output after the preamplifier. The sound at their output is shaped mainly by the quality of the preamplifier.

First of all, if we like to listen to music loud, it is better to choose headphones with lower current requirements than HiFiMAN HE-1000 v2. That's why the Sennheiser HD-800 sounded so good and also the completely sensational, old, from the time of my work in the studio of the Teatr im. Juliusz Słowacki in Krakow, Beyerdynamik DT-990 Pro in the 600 Ω version. But when listening at a reasonable level, even the HiFiMANs showed what would appeal to people who prefer this type of listening, i.e. clarity, speed, precision. Dynamic headphones add to that also the bass richness and extension.

But the latter can be dealt with to some extent using the tone control knob. While I did not feel such a need with the speakers, with the headphones adding +6 dB in the low tones filled the sound so much that everything "came back to" its place. This is how I listened to MICHAEL JACKSON's Billie Jean, and then songs from KRAFTWERK’S The Mix, and in general - all the albums sounded great.

The album of the German group comes from The Catalog box and was encoded in a binaural system called Headphone Surround 3D. This is one of the best encoders I know, much better than what Dolby Atmos and 360⁰ Reality Audio systems give us (more → HERE). In contrast, it gives tangible, energetic sources of sound, and at the same time a real, omnidirectional perspective.

The Japanese amplifier perfectly "recognized" its superiority and even such good examples of using the above-mentioned encoders as LORDE’S Mood Ring (ah, that cover :), BILLIE EILISH’S Therefore I Am (ah, that voice:) or CAROLE KING’S I Feel the Earth Move (ah, that cat!) couldn't move me as much as Kraftwerk's music. It had a strong foreground, where the energy of the presentation was concentrated, and clear, tightly filling the "bubble” around me with omnidirectional sound. The Japanese amplifier did a very good job of reproducing this type of recordings, but it sounded equally good on discs recorded in a classic way.

▌ Summary

FOR A LONG TIME, THERE WAS NO small, tube amplifier on the market that would work as well with loudspeakers as with headphones. The Aurorasound HFSA-01 fills this gap perfectly, as if it's always been there. It plays with an open, clear sound of extraordinary energy. Its sound is not muddied or lifeless, as it happens with large devices. At the same time, it has enough authority at the bottom of the band to show the scale of events, the volume of instruments and the depth of the soundstage.

It is not ideal when it comes to building three-dimensional bodies and will not shake the walls of the room. On the other hand, I didn't need it at all. Knowing about its limitations, I accepted them without hesitation. The more so that the Japanese amplifier sounds equally well with loudspeakers as with headphones. I don't know what class its phono preamplifier represents, but knowing other designs from this manufacturer, I wouldn't worry about it. A beautiful example of minimalism in the spirit of zen combined with modern solutions. From us, a saturated, full of red color award the ˻ RED FINGERPRINT ˺.

▌ DESIGN

AURORASOUND HFSA-01 AMPLIFIER is a small, compact design, which has a positive effect on vibration control, but requires expertise in topology to isolate the individual modules from each other.

˻ FRONT AND REAR ˺ The device is mounted on a steel chassis, to which aluminum sheets are screwed from the front and back. In all walls, apart from the front one, oblong ventilation holes were cut out for the tubes placed inside. Decorative elements are wooden stripes on the sides. Usually, manufacturers offer the whole side panels made of wood, like Leben does, and recently NAD and MoFi Electronics, and Aurorasound chose the element used for years by McIntosh, although the Americans made it of aluminum.

In the front there are four nice, though plastic, knobs, two toggle switches, a headphone jack ϕ 6.35 mm (TRS) and a high-class power switch. On the back we see plastic speaker sockets with nice, gold-plated contacts, four pairs of RCA inputs, a grounding clamp and an IEC power inlet with a fuse visible above. The amplifier rests on four aluminum feet with rubber O-rings.

˻ INSIDE ˺ The electronic circuit was divided into modules and assembled entirely on printed circuit boards. There is a preamplifier at the input. From the RCA sockets, as it turns out, not gold-plated and soldered to the PCB, we get to the selector based on Omron relays. After selecting the input, the signals from the turntable input is amplified in low-noise LT1028 integrated circuits, and from the line inputs are immediately sent to the potentiometer. The preamplifier uses very nice components, such as Dale resistors, Wima and Philips capacitors, as well as Nichicon Muse electrolytic capacitors.

The Alps potentiometer (malachite) is placed near the front panel, so the cables are not too short. After attenuation, the signal returns to the tube PCBs. This design is unusual in that the phase-inverting circuit is solid-state, based on integrated circuits. According to the manufacturer, this ensures precise phase inversion of the signal. The output circuit consists of four EL84 (EL84/6BQ) tubes, two per channel, operating in an ultra-linear push-pull circuit. Unfortunately, these are tubes from the Russian Sovtek, and they are from a new production. It is worth remembering that in the future we must have tubes from outside Russia and China.

In front of the power amplifier, next to the front panel, there are output transformers. Like the power transformer, they were designed and custom-made for Aurorasound in Japan. Speaking of the power supply: this transformer is very large and supplies several separate voltages. On the PCB with the power supply there are capacitors for the tube section, two Nichicons, and a voltage stabilizer for the semiconductors, on even nicer Nichicon Fine Gold capacitors.

And there is another board with tone control. Although it may seem just an addition, it is an extremely nice, advanced circuit. It is based on Burr Brown OPA604 integrated circuits and similar passive components as in the phono preamplifier. Here, the potentiometers are unfortunately open, not hermetic.

The whole design is clean, conceptually coherent and exceptionally pretty. Let's not forget about very good, in the vast majority, components. ●

▌ Technical specifications (according to the manufacturer)

• Nominal output: 2 x 14 W / 8 Ω
• Frequency range: 14-40 000 Hz (- 3 dB)
• Total Harmonic Distortion: 0.08% (2 W, A-weighted)
• S/N: 93 dB
• Input impedance (phono input): 47 kΩ
• Gain (phono input): 40 dB
• Power consumption: 150 W
• Dimensions (W x H x D): 360 x 145 x 320 mm
• Weight: 10.3 kg