Soulnote D-1N D/A Converter Review.

Exemplifying excellent build quality and a rich feature-set capable of decoding all current digital music file formats, and blessed with neutral yet natural tonality, timbral accuracy, outstanding clarity, harmonic subtlety, and vibrant dynamics, the Soulnote D-1N is a superb DAC, both sonically and functionally.

The Soulnote D-1N is a fully balanced discrete DAC using independent monaural modes equipped with a non-oversampling mode and a non-negative feedback power supply for the highest-quality reproduction of digital music. Soulnote’s design approach uses a method of designing products based entirely on the actual sense of hearing, which they claim eliminates any bias of past conventional common sense about audio and brings out the soul that lives in the music, hence the name of the company, Soulnote.

This approach is based on a postulate of its chief designer, Hideki Kato, of what may be described as a “counter-concept”, which Kato refers to as dynamic performance. For example, the adoption of Soulnote’s non-oversampling (NOS) mode for PCM playback in digital-to-analog conversion as well as a non-NFB (without negative feedback) circuit in amplifiers comes from this postulate.

While using this approach can decrease the measurement result in what Kato refers to as “static performance”, he claims a remarkable improvement can be obtained using what he refers to as “dynamic performance”. Soulnote believes “dynamic performance” is based on keeping the accuracy of the original waveform on the time-axis as the most important requirement for music playback. As such, in the design process at Soulnote, actual listening to the product under development dominates the design and refinement of a circuit design and informs the selection of parts and the mechanical construction of the DAC.

The Soulnote D-1N is a slim design with a very attractive front panel “ribbed” milled front panel. Along the second rib is a series of very small LEDs that indicate information such as sampling rate, lock range, and the selected input. At the left is also a small power button, and at the right, are small circular buttons for selecting the four lock ranges and the inputs, respectively. In the middle of the front panel is an embossed chrome-plated Soulnote badge. The overall impression is one of a very refined, clean modern design that would fit into any décor. The rear panel has inputs for AES/EBU, normal and “direct” COAX, and a USB-B input. There is a single pair of balanced XLR and single-ended RCA outputs and a standard C15 IEC power cord receptacle.

The Soulnote D-1N uses the ESS9038PRO DAC, the highest-specification 32-bit DAC from ESS Technology, Inc., in a dual-mono configuration for the left and right channels, which provide an impressive 140dB of dynamic range. Soulnote’s original-design discrete non-negative feedback amplifier, which extends into the MHz region, receives up to 120 mA of current from the DAC’s power supply and amplifies this current for the analog output. The combination of the ES9038PRO chipset and the D-1N’s discrete non-negative feedback amplifier produces what Soulnote claims is a dynamic and lifelike music playback quality that cannot be obtained from conventional op-amp-based circuits.

The D-1N is compatible with digital music files up to 32-bit/768 kHz PCM and DSD512 (22.6 MHz). In addition to compatibility with these high-resolution sound sources across a range of PCM and DSD formats using its USB input, the D-1N also supports input from S/PDIF and AES/EBU interfaces.

Clock system

Because phase noise and jitter can have a significant impact on sound quality, the D-1N’s word clock uses ultra-low jitter crystals with less than 1 picosecond of phase jitter. The word clock system is also mounted as close as physically possible to the DAC chips which Soulnote says enables an ideal clock wave-pattern.

Another feature of the Soulnote D-1N is that the user can choose one of four lock ranges for the D-1N word clock’s lock range to match the clock accuracy of “upstream” transmitting devices connected to the D-1N (such as music servers, network bridges, streamers, etc.).

Finite-Impulse Response

Pre- and post-echoes are artificial “sounds” created by data calculations before and after the data is interpolated. They make waveforms like sine waves appear smoother, but calculation algorithms can affect the sound quality or ambiguity and be added to the time axis. To counteract the effect of this, the Soulnote D-1N outputs an impulse output waveform with a finite impulse response (FIR) oversampling filter (D-1N analog output).

NOS mode utilization

In addition to the conventional FIR oversampling mode, the D-1N also uses an impulse output waveform when configured in non-oversampling mode (D-1N analog output). The non-oversampling mode cannot be used with DSD. This waveform can only be achieved by combining a non-negative feedback (non-NFB) discrete amplifier with exceptional transient response performance. Because music waveforms are actually a series of impulse waveforms of different heights, the non-oversampling mode eliminates any ambiguity in the time-axis information, creating a more realistic and natural sound quality and an expansive listening environment for the human ear, which is extremely sensitive to the time axis. Soulnote also says this approach provides extremely low noise levels for the analog outputs, with no difference in levels between the two sampling modes.

Bulk PET USB interface

USB audio components generally transfer data using the asynchronous data transfer method.The D-1N is unique in that it utilizes Bulk Pet, a new Bulk Transfer method developed by Interface Corporation. A key feature of Bulk Transfer is the ability to control the transmission data volume and transmission frequency, which Solunote claims results in reduced data processing loads for music server computers and DACs, resulting in improved sound quality during playback. The use of Bulk PET requires the installation of dedicated drivers on the music server computer, but Soulnote says there’s no requirement to update the DAC’s firmware when using Bulk Pet with the D-1N.

Power Supplies

The AC mains power supply for the Soulnote D-1N is a robust 260 VA large-scale toroidal transformer, which provides power for the amplifier-class non-NFB power supply. With a high voltage swing capability of ±43 volts, Soulnote claims the discrete non-NFB power supply provides detail and precision in the spatial presentation and lifelike and energetic music dynamics.

To power the DAC circuitry, the D-1N is equipped with eight different power supplies using Soulnote’s high-speed discrete regulators. The DAC’s peripheral circuits employ independent power supplies for the left and right channels for both the analog power supply and the digital power supply. The Soulnote D-1N also contains a power supply for the word-clock crystals, another for the USB interface, one for the logic board, and one for the S/PDIF differential receiver. These eight power supplies use Soulnote’s original high-speed discrete regulators that prioritize sound quality to maximize the high-voltage capability of the ES9038PRO chipset.

Also noteworthy is that transistors in the D-1N also operate at higher temperatures than are conventionally used in other DACs because Soulnote claims functionality and sound quality generally improve when the transistors are operated at higher temperatures.

Because of the emphasis Soulnote places on sound quality, the top cover, chassis, and other components do not employ vibration isolation. The Soulnote D-1N also uses metallic footers to provide higher sound quality due to better mechanical grounding and dissipation of vibrational energy than conventional plastic or polymer footers.

For this review, I used the D-1N USB input with content sent from an upstream remote music server, an Akasa-cased NUC Roon Core located in another room. Digital music files from the Roon Core are sent using a Shunyata Sigma Ethernet cable to an Uptone Audio EtherREGEN Ethernet switch. These files are then sent using a Planet Tech (PT) optical transceiver in EtherREGEN’s SFP optical port via Corning ClearCurve single-mode 1310nM LC/LC optical fiber “downstream” to a matching PT optical transceiver in the SFP port of a Lumin U2 streamer located in the main audio rack in the listening room.

The Lumin U2 receiving the music file is connected to the Soulnote D-1N DAC’s USB input with a Shunyata Delta USB cable, and the Soulnote’s analog output is connected to a Lumin P1 using a Shunyata Sigma V2 RCA interconnect. The Lumin P1, functioning as the system’s preamplifier, is connected to a Constellation Inspiration integrated amp with a Shunyata Venom-X XLR interconnect. The integrated amp is set to unity gain and playback volume is set using Lumin’s LEEDH digital volume control. All components in the main audio room are powered with a Shunyata Everest power distributor using Shunyata Omega QR-s, Sigma NRv2, and Alpha NRv2 power cables.

The Constellation integrated amp powers Harbeth 30.2 40^th Anniversary loudspeakers using Shunyata Alpha V2 speaker cables resting on Shunyata Möbius cable elevators to mitigate the effect of floor-borne vibrations.

The first impression the Soulnote D-1N gives is one of tonal accuracy, harmonic richness, outstanding clarity, and a “relaxed”, but very engaging presentation. The presentation is just on the warmer side of neutral, with body and fullness providing a natural and organic quality that adds authenticity to voices and instruments. The Soulnote D-1N is blessed with accurate, sophisticated, and nuanced reproduction of timbre, the attribute that distinguishes, for example, a woodwind from a stringed instrument when playing the same notes. These qualities really stand out on well-recorded and mastered vocal and classical recordings. The overarching impression is that the Soulnote D-1N provides a rich, fulsome, musically dense, tonally neutral presentation with sophisticated and refined reproduction of instrumental timbre and lifelike vocals.

The Soulnote D-1N truly shines in its ability to resolve high-resolution details with finesse. In addition to its capabilities to provide excellent detail retrieval, the D-1N refrains from overemphasizing these details to the detriment of the overall musical presentation. Instead, it seamlessly integrates intricate nuances into the musical flow, creating a listening experience that feels both natural and effortless. The Soulnote D-1N’s high-resolution capabilities are not simply showcased as standalone virtues, but rather as integral components of the overall musical composition.

With cutting-edge engineering, a broad feature set, and the capability to play any format digital music file with reference-level audio quality and with an engaging and natural musicality, the Soulnote D-1N is an exceptional and versatile DAC and an excellent value proposition.

The bottom line is really simple: I love this DAC. In addition to being exceptionally well designed and engineered, the Soulnote D-1N provides outstanding audio quality for all the sonic and musical attributes audiophiles may obsess over. It has neutral yet natural tonality, accurate and refined reproduction of vocal and instrumental timbre, a wide, deep, and tall soundstage, precise and stable imaging, a controlled and defined bottom-end, and this sonic tapestry emerges from a deep black background and very low noise floor. I think it’s one of the finest DACs I’ve ever heard and, as such, has my highest recommendation.