Soulnote A-1 Integrated Amplifier Review

Hideki Kato has been Soulnote’s Chief Sound Manager since 2016. He came to Soulnote after decades with other companies such as NEC and Philips. Per the Soulnote website, “Through his long career as a designer of audio equipment both in analog and digital areas, Kato-san has been struggling to find out the reason why the improvement in static performance and the sound quality in playback did not always correspond. Kato-san made a hypothesis about a counter-concept which he called dynamic performance.” You can read his detailed narrative here – Soulnote Design Philosophy To help you along, I’ll do my best to summarize his design philosophy below.

It all started when Kato-san built his own amplifier while a student in college. The amp he made in this instance had “improved specifications” over a previous amplifier. The problem was that this improved design sounded lifeless. This was the genesis of his fledgling design philosophy that I will banally call “Specs vs Sound Quality”.

Over many years of ruminating on the subject, Kato-san eventually concluded that most component measurements are measuring static properties, but he felt the life of the music was better reproduced by designing the components with a focus on the “time axis”. He states that the amplitude axis (Volts) and the time axis (T) are all it takes to make music. (I do not agree 100% that all measurements are static because we can measure parameters such as impulse response and square waves, but that is a debate for another day.)

Kato-san goes on to state that audiophiles are too focused on frequency response a syndrome he refers to as “frequency brain”. On the other hand, he feels that proper reproduction of ultrasonic sounds is important in music reproduction. His discussion on DACs and phono stages reminds me how vinyl sounds so good but measures so poorly!

A large part of the design advancements made by Kato-san involve eliminating negative feedback in analog circuits which he understands lowers “static” performance but allows improved time performance by letting the music have more life. He feels that humans have a time-performance or dynamic/impulse bias due to our evolution.

Furthermore, he believes a component’s enclosure is more important than the electrical components!! His approach in this regard is not to dampen or eliminate the mechanical vibrations in the component, but, instead, it helps if you can keep things physically “light” or low mass. He states that too much dampening blurs the waveform on the time axis. So, looking at the A-1, the top cover is designed NOT to restrain the air inside because restrained air acts like heavy rubber – this is not good. He doesn’t want too much dampening and not too much resonance, either. This philosophy leads to a chassis made of a combination of aluminum and steel with a PCB that is not “fixed” but floats. The same goes for the top of the case: it has a suspended method of attachments, so it floats as well.

To sum this all up, Kato-san does not design to measured specs first. Instead, he designs by ear and uses minimal measurements as more of a confirmation of the design. He feels this is respectful to the art and the artist.

As indicated above, the Soulnote A-1 is a very basic integrated amplifier in terms of features. It has four analog inputs (one balanced and three unbalanced). There is only a single pair of binding posts. There are no line-level outputs, processor loops, etc. The A-1 just offers the basics.

Following the same theme, the front panel has a source selector, a gain control, and a simple one-line readout. The A-1 does come with a slick and handy remote that handles these rudimentary controls.

The circuitry is claimed to be “balanced” and with no negative feedback. Other design features involve an intricate internal grounding scheme, a high-speed power supply, contactless wiring, and matched output transformers.

Soulnote also implements a very unique (and likely expensive) relay-switched balanced attenuator. The resulting level settings are quite coarse but are accompanied by a satisfying and confidence-inspiring mechanical “click” of the relays switching as you change the volume.

The case and circuit layout are said to be symmetrical, and the case incorporates all of Soulnote’s unique resonance control schemes.

The whole deal only weighs about 22 pounds which is very lightweight for an 80 wpc Class A/B integrated amplifier. The toroidal transformer visually appears to be undersized for the amplifier’s claimed power delivery.

The Soulnote A-1 integrated amplifier was about as simple to set up as any amplifier I have ever evaluated. It doesn’t have a built-in DAC or DSP. There are no subwoofer outputs and of course no high-pass filters. This amplifier is essentially a very basic unit with four inputs, a source selector, a volume control, and a single pair of speaker binding posts. It is as basic as they come.

I placed the Soulnote A-1 on an amp stand between the main speakers and proceeded to connect everything. Associated equipment for this review is as follows – turntable: Mobile Fidelity Sound Labs Ultradeck with Ultratracker cartridge, Phono preamp: Pass Labs XP-17, Streamer: Roon streaming via a PS Audio AirLens (review pending), DAC: Topping D90, and Speakers: VIVID Kaya 90’s. Cables and interconnects are a mix of Clarus Chrimson and Audioquest.

The Soulnote A-1 comes with a handy IR remote that can handle the most basic functions – input selection, volume control, mute, and display on/off toggle. To maximize the musical reproduction, Soulnote recommends turning off the display as this shuts off the internal digital control of the amplifier. The remote has many other buttons that can be used to control other Soulnote components. This remote is well-made and fits nicely in the hand.

The Soulnote A-1 is obviously simple and straightforward. I hoped for a balance control or a variable line out for a subwoofer. But this amp is excellent for those who want something very simple and minimalist which is its basic gestalt, anyway.

Anyway, this is an approximate 2.5-hour album and I listened to the whole thing!

On “Hands” the tonal balance was spot on. I also noted that the sound was very “tube-like” with its smooth playback. The sound was also very detailed, which made for a very nice presentation all around. On the whole, I really love the way this Soulnote amp handled the bass response. It’s not too dry nor too sweet, it’s just right.

I’m a Jewel fan largely because I love her voice, but she is very easy on the eyes as well. When it comes to her voice, she has a unique inflection technique. Her voice shines on “Down so Long” which was strikingly realistic over the Soulnote A-1 amplifier. I also heard amazing detail in the sound of the backing band on this track.

As mentioned above, the volume control is coarse, but it is possible to find the right level of gain: too little gain and the music was bland; too much gain and things got mushy. The volume control also had a satisfying mechanical clicking noise when actuated due to its design and execution.

I typically had the volume set somewhere in the range of “22” – “24” and I wasn’t sure how high the dial goes. I mention this because this little amplifier has a really big sound. It has ample power for my setup, but bear in mind that my reference amplifier is the Pass Labs INT-25 which is a low-powered integrated. There is something about my system that it doesn’t require gobs of power to light up the room. On the Soulnote A-1, there was plenty of power at hand, but attempts to really crank it up were often met with a vague and mushy sound. So, I kept the gain in the sweet spot for most listening. All the power I will ever need even on these modern recordings. I did wish for a pre-out to feed a powered sub.

The review unit I received was a pre-production sample. Since it was not a unit designed and built specifically for the US market, I will not publish any bench tests at this time. I have requested a production sample so I can test it at a future date. It is important to mention that even this pre-production unit sounded excellent as-is.

Soulnote’s A-1 has been lovingly designed and voiced to provide the most satisfying musical reproduction you could possibly hope to hear.

The Soulnote A-1 integrated amplifier is designed for music first with a focus on the timing of the waveform along with unique mechanical isolation and resonance control features.

I can honestly state that the actual performance of this little amp exceeded anything I could have anticipated, especially judging solely by the manufacturer’s specifications. So, it just goes to show you that as much as we feel we know and understand about this hobby, the fact is there are things going on that just can’t yet be explained under the old ways of thinking. I am sure that through research and study, we will be able to define new tools and methods to evaluate future products. For now, though, the best tools we have happen to be our ears, and my ears really enjoyed their time with the Soulnote A-1 integrated amplifier, irrespective of anything my frontal lobe tried to tell me.