Soulnote A-2 Integrated Amplifier
" The Soulnote A-2 has many riches to offer including a purity of sound that makes listening to music addictive, magical,
and full of wonder !”
Michael Lavorgna - Twittering Machines
Perfectly balanced, discrete non-NFB channels
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.
Relay-switching balanced attenuator
The volume isn't controlled by electronics or a rotary slider, but instead incorporates SOULNOTE's original relays in a balanced attenuator system that switches high-precision resistors. This dramatically increases clarity, and allows the sound image to emerge in three dimensions. It also significantly improves quality at low volume levels without fear of gang errors.
An ideal construction
The input signal line has been rationalized by concentrating the input terminals, input selectors, volume, and the non-NFB voltage amplification stage onto a single multi-layered board. The board does not use even a single shield or filter that could negatively impact the sound in order to eliminate every factor that reduce sound quality, such as the effects of vibrations from connecting cables, inductance components, radiation noise, etc. This ideal construction has been achieved thanks to the relay-switching balanced attenuator.
Other Technical Features
4-layer board with 70 micron thick copper foil
Composed of the output stage and the main power supply, the power block features an inner layer stratum of 70 micron thick copper foil as the power supply bus bar and thus minimizes high current loops in the commutating capacitor>>output transistor>>speakers + terminals>>speaker terminals>>commutating capacitor cycle. Eliminating inductance components in high current lines creates outstanding frequency characteristics and stability.
Connectors have been eliminated in the power supply lines as well as the signal lines, and cables are instead soldered directly to the boards for contactless connections.
Chimney-style heat sink
The heat sink uses a newly developed chimney shape that provides extremely efficient cooling with less vibration.
Ferocious power supply
The 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.
4 parallel high-speed output transistors
The final stage is composed of 4 high-speed transistors (2SC2837/2SA1186) with low Cob and high FT connected in parallel. This combines with the strong non-NFB power supply to provide ample speaker driving power. The output transistors have been selected and paired by using a specially designed device that measures the Vbe current value while avoiding any influence from rising temperatures in the output transistors. Perfectly aligning the 4 parallel current transistors creates abundant speaker driving power and clear, precise sonic reproduction.
4-step Darlington configuration
High frequency transistors create a 4-step Darlington configuration to drive the final transistors completely, thereby optimizing the amount of each current. This produces ample drive power for each speaker.
Two types of monaural modes
In addition to BTL monaural mode, you can also select bi-amp monaural mode that distributes the monaural input to the left and right channels.
Power amplifier mode
The power amp mode interrupts the power supply to the microcomputer and bypasses the selector and volume. This increases the S/N ratio. XLR and RCA input can also be selected in this mode.
Housing design that prioritizes sound quality
Spikes ground the power supply transformers directly, and while combining the spikes with uneven cross-sectional aluminium panels to control resonance has increased rigidity, the aluminum panels are not directly bonded in order to eliminate unwanted resonance. 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.
Single non-NFB differential BTL channels
The conventional BTL monaural principle that uses the left and right channels of the stereo amplifier in reverse phases can produce powerful sound quality, but the sound impression tends to blur with sounds tending to clump together because of the effects from GND lines or matching two amplifiers. The BTL monaural principle in the A-2, however, adopts a new approach that partitions the differential output of one non-NFB differential amplifier each for the left and right final stage. This creates an expansive sound with vigorous, yet delicate BTL driving.
Stereo pre-main amplifier, BTL monaural pre-main amplifier, Bi-amp monaural pre-main amplifier, Stereo power amplifier, BTL monaural power amplifier, Bi-amp monaural power amplifier
100W rms into 8-ohms
200W rms into 4-ohms
400W rms BTL Mono 8-ohms
Frequency Response (8ohm / 1W)
3Hz – 240kHz (+/- 1,0dB)
LINE 1, 2, 3 (Balance): 700mV / 16kohm
LINE 4, 5, 6: 700mV / 8kohm
Less than 0.03% (50W / 8-ohms)
110dB (IHF A network)
Dimensions (W x D x H)
430mm x 423mm x 160mm
44 lbs (20 kg)
What they say ...
“…makes listening to music addictive, magical,
and full of wonder...”
"The sound of Soulnote A-2 is very clean, yes, not just clean, it is very clean. The background is pitch black, and each sounding body stands three-dimensionally and embossed in front of the eyes, and the front and back levels are clear. Its voice is very condensed, and it is so dense that it does not appear dry or thin, and it also reveals a warm and sweet taste. The piano has a honey-like amber color, crystal clear and mellow; the violin is as smooth as butter, and has a rich fragrance; the vocals are warm and solid, and there is a body and a posture. Each note is very delicate and carefully crafted. This is like the sweet and melodious sweetness of Yamazaki's single malt, or the rich, deep, steady and harmonious taste of Hibiki..”
Hong Kong Review / November 2022
"A-2 SE SoulNote is an amplifier that has all the features for which we love good audio components. It is warm, rich and saturated. It shows a large space, although without precise location of phantom images.
It is a warm, rich and saturated sound. In fact, it reminds, in a really unique way, the character of my system, consisting of the Ayon Audio preamplifier and the Soulution power amplifier. I started listening from the Master CD-R with unreleased Krzysztof Duda material titled Dudaskalia. It opens with one of the best electronic music tracks, not only by Krzysztof, but in general, with an extremely characteristic leitmotif, under which there is also a very low and dense bass.
On most recordings, this Japanese amplifier emphasized the midrange and saturation. So it sounded incredibly coherent, dense and strong. It was a real spectacle with proper momentum, with powerful imaging and large-scale sound sources. The most important in this sound is the midrange and it sets the perception. Not because the top and bottom are not there, but because the midrange is so emotionally engaging.
Ultimately, it is a beautiful, "golden" sound that never tires, on the contrary - encourages you to buy more albums. What is more is that this device is resolving and differentiating, which will allow us to enjoy the best releases as well as good realizations too. For all this – we award it our RED Fingerprint - our first in 2020 !"
High Fidelity Review / February 2020
"Purity of sound is, in the end, the most appropriate phrase that came to mind to convey the Soulnote’s way with music. The A-2 is also lightning quick, as light on its sonic feet as I’ve heard, making it nimble as all get out while retaining music’s body and color. A combination of strengths that are uncommon in my experience. It is also plenty powerful, its rated 100 Watts (into 8 Ohms) feeling like a lot more through each of the speakers I had on hand during this review period. I attribute this sense of more than enough power to the A-2’s ability to control each of the speakers in use, regardless of their specific load, so things like bass response and upper frequency extension felt at once controlled and limitless in terms of force and speed. Music sounded fully formed with a superb sense of micro-delicacy that gives music drama and surprising scale.
In King Hannah’s hands, the song takes on a more obvious impending doom air, with an electronic whirlwind slowly building in the background with Hannah Merrick’s forlorn lyrics riding over a driving beat. Simple stuff sonically yet you want all of these pieces laid out bare, which the Soulnote does with flair. Quick as a whip dynamics, superb bass control, rich tone color, and a sound image as big and vast as an empty highway at night.
The Soulnote A-2 is the kind of hifi product that speaks to people who are interested in more than what a spec sheet has to say. Or, who need to eat Sushi to know if they like its taste. To my way of experiencing, the A-2 is for people who dig deep—deep into the music they love, the story behind the products they choose to live with, and even how these things look and feel. If you are that kind of listener, the Soulnote A-2 has many riches to offer including a purity of sound that makes listening to music addictive, magical, and full of wonder."
Twittering Machines Review / September 2022