Soulnote amps are built entirely in Japan. And they are different.
More purist. More resolute. Highly individualistic. Maybe even a bit in the spirit of "times gone by".
The man who had the courage to "walk the path" is Hideki Kato.

Roland Kraft - Stereoplay / Germany

The Soulnote Philosophy


... The intriguing quest for a different Holy Grail ...


by Hideki Kato


In 2005, Nakazawa-san called me to join CSR, where I was in charge of Soulnote design. I was mainly responsible for the design of dc1.0, da1.0, sa1.0, sc1.0, SA710, SC710, and a few more ...

The turning point came eleven years later when I was appointed as Chief Engineer of Soulnote in 2016.

This was a uniquely motivating role where I was entrusted with everything from product planning, electrical design, structural design, sound quality management, and promotion ... all in one place. At that time, Nakazawa had only one thing to say to me :

Make SOULNOTE the best audio brand in the world ... Well, "number one in the world" was Nakazawa's favorite phrase ... and while it may seem like a wild ambition, I had an idea on how to make it happen.


We would properly explain the reasons for the "discrepancy between specifications and sound quality," which is the biggest mystery in the audio world, achieve unprecedented sound quality using methods that other manufacturers would not (or could not) use, and present it to the world. If we could do that, I really thought we could turn the world's perception of value upside down. I understood the reason for the discrepancy between specs and sound quality, and that is the basis of SOULNOTE's current design philosophy.


And now I have the environment to make it happen.

All that remains is to do it.

Initial considerations ....


Discrepancy between specs and sound quality

The specifications (static specs) referred to here are so-called catalog specs such as distortion rate, frequency response, and signal-to-noise ratio. These are easily quantifiable performances, mainly using sine waves for measurement.


In the audio industry, everyone knows that sound quality cannot be judged by specifications (static specs) alone. Also, anyone who likes audio knows that sound changes depending on cables and racks. No matter how precisely they are measured, even though the specs make no difference!

This would seem odd to anyone but an audiophile. In this age of scientific universalism, it seems impossible that people can sense small differences that cannot be detected by precise measurement with high-end measuring instruments. Human hearing is not that good, and the frequency range is only 20 to 20 KHz at best. (But for sine waves! but)


Well, that is why, even though we knew that sound quality cannot be described by specs alone, I think there was still a part of us that could not go against the specs. In other words, the history of audio is such that no one could refute the opinion that "sound is a matter of taste, so you are free to choose, but there is no doubt that a sound with better specifications is a more correct sound.

For example, suppose you were developing a product, and by working on the circuitry, you improved the specs in some way. And suppose the sound has changed. In that case, most engineers would assume that the sound with the better specs is the "better sound. Furthermore, if a major manufacturer develops a new device and no matter how good the sound is, if the specs are inferior to the previous product, the bosses and sales people will usually not allow the release of the new product. This is especially true if the manufacturer explains the sound quality by the quality of the specs.

Let me tell you an old story ...

When I was a student, I loved music, but I had no money, so I built amplifiers and speakers as a hobby. At first I didn't have any proper measuring instruments, but that didn't matter because as long as I could enjoy listening to music, that's all that mattered. For me, it was a proud device that allowed me to enjoy listening to music. It sounded a whole lot better than my friend's high-end amplifier.

However, one day I acquired a measuring device. When I measured it, it was terrible. Then, I wanted to improve the measurement value as much as possible. And as a result of various improvements and better readings, I was very shocked. Listening to music with it is completely boring. Why is this? Since then, I have been thinking about this for 40 years. And then I arrived at a way of thinking.

Imagine for a moment ...

What if I could explain to you that specs don't mean much for sound quality? Furthermore, what if you could explain that improving the specifications may even degrade the sound quality? Don't you think it would be like a change in values?

I can explain this. It is not that difficult. It is all because of a certain curse.

... read on : parts 3 to 12 of Hideki's approach ...

The Soulnote Amplification Line

Soulnote P-3 Reference



A monster preamplifier for truly live and enjoyable music performances! 

The output line amplifier uses Type-R discrete non-NFB balance circuits that have been finely tuned for preamplifier use. It also includes the newly-developed super high-quality naked foil resistors. With 1ohm emitter resistors and 3.9ohm output resistance, it delivers astonishing information detail and S/N presence for superior power preamplifier drive capabilities.


This unit utilizes a dual monaural construction that employs two identical and dedicated sets of I/O terminals, circuit boards, power supply circuits, power transformers, relay drive circuitry, and relay power supplies for the left and right channels. The microcomputer power supply, including the transformer, is also completely separate. A photocoupler keeps control signals completely separate from the relay, the only point of contact with the signal system.


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Soulnote A-1

Integrated Amplifier


To extract the best from the unique characteristics of SOULNOTE's original perfectly balanced, discrete non-NFB circuits, we re-examined every minute detail of our amplifiers for possible improvements, like incorporating ground plane star wiring, centralizing local non-NFB regulators, implementing direct coupling routes, optimizing the tuning of the drive current, and more. This helped us achieve even more vibrancy and speed while also providing a wider sound range. 


In addition to a newly developed bifilar wound, large capacity toroidal transformer with independent positive and negative windings, we have lowered the impedance by connecting multiple high-voltage, small-capacity filter condensers in parallel and incorporating a fast recovery rectifier diode. We have also completely refined the smallest details in order to boost the power supply, such as making current loops as short as possible by placing the rectifier diode close to the power transformer. This further increases S/N and speed.


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Soulnote A-2

Integrated Amplifier


Every SOULNOTE technique has been lavishly incorporated into the current culmination of our perfectly balanced non-NFB technology. This integrated amplifier is loaded with a variety of monaural drive and power amplifier modes, like the new BTL/bi-amp setting. 


SOULNOTE's original perfectly balanced non-NFB channels have been fully optimized and incorporated to put give sound quality the highest priority. Voltage feedback has been completely eliminated in the output stage, the voltage amplification stage, and in the power supply circuits. Because of their impact on sound, DC servo circuits and current mirror circuits have been eliminated, while both the constant current circuits and the bias circuits in the voltage amplification stage employ simple circuitry layouts that only use constant current elements (2SK209) and constant voltage elements (LEDs) carefully selected for utmost sound quality. The power amplification stage is perfectly balanced all the way through the emitter follower output. All this in relentless pursuit of vibrant, expansive, clear, and lush music playback.


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Soulnote M-3 Monoblock

Power Amplifier


Newly incorporated industrial grade can-type output transistors to achieve a perfect non-negative feedback single push-pull structure. Monoblock power amplifier that lets high-end speakers around the world provide playback bursting with emotion. 


We decided that single-end and single push-pull output was indispensable in creating an emotional musical experience, thus eliminating the "blurring in the microscopic time domain" so often symbolized by improvements in sound quality through high-end clocks.

Nevertheless, we still had to overcome the relatively low levels of current provided by the typical single push-pull configurations. As a result, in the M-3 we introduced industrial grade can-type output transistors with a relatively small Cob and large current flow. The driver stage incorporates the same output stage transistors used in the A-2 to easily drive these large capacity cans for a total of four Darlington construction stages.


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