Overview
Soulnote recently caught our attention at a prominent Hi-Fi show in North America. The sounds being produced were so impressive that repeated visits were made to their listening room to verify our initial impressions. What we discovered with this relatively obscure Japanese brand is very special indeed – creative audio designs that strive to keep the listener engaged at a fundamental level. With three simple and distinct products ranges, Soulnote has a solution for music enthusiasts at all price and performance levels.
Design Philosophy
In the world of Hi-Fi design, following your gut instincts (not just measurements on a oscilloscope) can often yield unpredictable yet excellent results. Chief Soulnote designer Hideki Kato knows this well. Throughout his long career with companies such as Marantz, NEC & Philips, Kato was determined to find out why improvements in static performance (lab measurements) and sound quality did not always correspond. Kato named his hypothesis ‘Dynamic Performance’.
The adoption of the NOS (non-oversampling) mode for PCM digital playback as well non-NFB (negative feedback) circuit in amplifiers stem from this hypothesis. Curiously, he discovered that these design concepts may worsen the lab measurement results, but a remarkable improvement can be achieved during actual human listening tests.
While unmeasurable using conventional methods, he decided that maintaining accuracy of the original music waveform on the time axis is one of the most important considerations for music playback. At Soulnote, listening tests are heavily relied upon to determine parts selection and mechanical construction. This approach is a kind of antithesis against the supremacy of static performance, an approach not widely adopted by other manufacturers.
Amplifier Technology
All Soulnote amplifiers are designed with perfectly balanced non-NFB (negative feedback) technology, and have been fully optimized to give sound quality the highest priority. Voltage feedback has been completely eliminated in the output stage, 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.
Chassis Design
Soulnote has not limited their “hearing is believing” design approach to the internal circuit design. The chassis itself is designed to look spectacular while also maximizing performance, often in ways that are counterintuitive. The top cover, which has a particularly large influence on sound quality, features a dual-component construction that joins the base plate and the aluminum panels at three points so that they do not dampen each other. By grounding it at three points without fixing it to the aluminum portions of the housing itself, this design succeeds in pulling down the sound focus while still keeping it expansive.
In addition to the above, internal spikes ground the power supply transformers. Combining the spikes with uneven cross-sectional aluminum panels to control resonance increases rigidity, and the aluminum panels are not directly bonded in order to eliminate unwanted resonance.
Power Supply
The A-2 power supply utilizes a 600 VA bifilar wound toroidal transformer, the most powerful in Soulnote’s history. Commutating current loops have been minimized by placing ± independent commutating circuits from the fast recovery diode close to the transformer winding. The commutating capacitor employs an ELNA product developed specially for Soulnote and selected for its sound quality. Connecting multiple small capacity capacitors in parallel helps control and optimize frequency characteristics and mutual capacitance.
Modes of Operation
While most will use this strictly as a 2-channel integrated amplifier, Soulnote has designed this product to evolve as your needs change. Not only can it be used as a world class integrated amp, a simple switch on the back panel can enable it to be used as a stereo power amplifier (bypassing the internal preamp circuit), mono power amplifier, and other configurations that could include bi-amplifying of your main loudspeakers.
