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Stephen Scharf
Exemplifying excellent build quality and a sophisticated feature set capable of decoding all current digital music file formats, and blessed with neutral and natural tonality, timbral accuracy, outstanding clarity, harmonic subtlety, and vibrant dynamics, the LUMIN U2 is a superb streaming transport, both functionally and sonically.
LUMIN U2 Streaming Transport Highlights
- The LUMIN U2 is a streaming transport that presents music with exceptional accuracy, lifelike tonality, engaging musicality, and very low noise.
- First LUMIN Transport to use a new, all-in-one chassis.
- Utilizes LEEDH lossless volume control.
- Includes the LUMIN Application at no extra cost, which supports online streaming services and includes extensive hardware control including PCM and DSD up-sampling and conversion. The LUMIN app enables U2 functionality as a digital transport as well as a system renderer, allowing access to other compatible streamers and music libraries in the user’s network.
- The latest processor provides greater resampling flexibility.
- New integrated toroidal linear power supply.
- Fiber optic network connectivity provides complete isolation from network digital noise.
- 3 USB ports including a new direct-coupled low-noise USB output.
- Dual-network interface with built-in network switch.
- DSD512 and PCM768 file playback.
- 4 exceptionally low phase-noise crystal clock oscillators.
- Increased capacity for future updates.
- Same surface finish as the LUMIN P1.
The LUMIN U2 is a dual-mono streamer designed to stream music files from sources such as a music server, NAS, Roon Core, etc., downstream to an audio system. As there is no built-in DAC, the U2 functions as a digital music file transport, and an external DAC must be used with the U2. It is designed for customers with the need for music streamer functionality, but wish to have the option of using a DAC of their choice. The U2 will stream music files from an upstream networked-connected music server, NAS, or computer to a DAC using MinimServer or Roon. It can also stream files from a connected USB flash or hard drive using MinimServer or the native LUMIN app. The LUMIN U2 is also compatible with several music streaming services including Qobuz, Tidal Connect, Tidal MAX, Spotify Connect, MQA, Plex, TuneIn radio, and Apple Airplay2.
Supported file formats:
DSD: Up to DSD512 22.5MHz, 1-bit
PCM: Up to 768kHz, 16–32-bit, Stereo up-sampling rates & bit-depths.
Up-sampling option for all DSD256 and PCM 384kHz files
Supported Network Streaming Protocols:
UPnP A-V protocol with audio streaming extension (OpenHome)
Roon, Plex, Qobuz, MQA, TIDAL, TIDAL Connect, Spotify Connect, Apple AirPlay, TuneIn, Gapless Playback, On-Device Playlist
Supported Control Devices:
Apple devices: iOS 11.0 or later
Android devices: Android 4.0 (Ice Cream Sandwich) or later required
Apple Silicon: macOS 11 or later. (download the iOS App from the iOS App Store) Chromebook: Google Play Store required.
Supported Digital Music Formats:
USB: Native DSD512 support, PCM 44.1–768kHz, 16–32-bit
Coaxial RCA, Coaxial BNC & AES/EBU: PCM 44.1kHz–192kHz, 16 to 24-bit; DSD to 2.8MHz, 1-bit (DoP, DSD over PCM)
Digital Interfaces:
USB: Native DSD512 support, PCM 44.1–768kHz, 16–32-bit
Coaxial RCA, Coaxial BNC & AES/EBU: PCM 44.1kHz–192kHz, 16 to 24-bit; DSD to 2.8MHz, 1-bit (DoP, DSD over PCM)
USB Connectivity:
3 USB-A ports including direct-coupled “audio only” USB-A port.
USB flash drive and USB hard drive
Single-partition FAT32, exFAT, and NTFS-formatted hard drives.
Supported Inputs:
Ethernet RJ45 network 1000Base-T
USB storage, flash drive, USB hard disk (Single-partition FAT32, exFAT, NTFS only)
Optical network input:
Industry-standard SFP1000Base-T Gigabit Ethernet
An adapter may be required for the user’s specific switch/cables.
May be used simultaneously with RJ45 network interface (e.g., connect one interface to a router and other interfaces to LUMIN L1 or NAS)
Power Supply:
Linear power supply with internal toroidal transformer
Dual-stage, low-noise linear voltage regulators
Physical finish:
Raw (natural) or black anodized aluminum
Dimensions:
13.8” W x 13.8” D x 2.4” H (350mm x 350mm x 60.5mm)
Weight:
13.2 lbs. (6 kg)
MSRP:
$5,000 USD
Company:
SECRETS Tags:
streamer, high-end, digital transport, LUMIN
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The LUMIN U2 is a slim 13.8” W x 13.8” D x 2.4” H streaming transport with LUMIN’s signature curved sloping front panel. This front panel is machined from billet aluminum, which gives the U2 a high-quality feel and appearance. The front panel also has a small blue status indicator LED display.
- First LUMIN transport to use a new, integrated “all-in-one” chassis.
- The latest processor provides greater digital music file resampling flexibility.
- Support for DSD512 and PCM768 playback.
- Fiber network connectivity provides complete isolation from network digital noise.
- 4 exceptionally low phase-noise crystal clock oscillators.
- 3 USB ports including a new low-noise, DC-coupled USB “dedicated audio” input.
- Dual-network interface with a built-in network switch.
- First LUMIN transport with ultra-low noise rectifier and linear regulator.
- New integrated toroidal linear power supply transformer.
- Increased capacity for future updates.
- New surface finish taken from the high-end LUMIN P1.
All-new digital processing system
- New next-generation hardware and software provide a new digital processing foundation for LUMIN.
- Utilizes LEEDH, an innovative new digital volume adjustment algorithm that eliminates rounding errors.
- Supports up/down digital file sampling up to DSD256.
- Increased processing power and storage capacity provide greater resampling flexibility, audio processing performance, and futureproofing.
Power Supply
The U2 is the first LUMIN transport with a built-in shielded linear power supply utilizing an ultra-low noise rectifier linear regulator and extra-large toroidal transformer. It is also the first digital transport to utilize LUMIN’s new all-in-one CNC-machined chassis design.
The LUMIN U2 rear panel has a wide variety of digital connection interfaces, including AES/EBU, coaxial (BNC and S/PDIF), Toslink optical, a “USB to DAC” USB-A port, two standard USB-A ports (for connecting flash or hard drives), an LC/LC SFP optical port, and an RJ45 Ethernet port. The right portion of the rear panel has an IEC C14 AC receptacle for a 15 ampere C15 power cord and a power ON/OFF rocker switch. The “USB to DAC” port is unique in that it is a direct-coupled, low-noise USB port specifically designed for connecting the U2 to a USB DAC. There is also a dedicated ground terminal on the rear panel for making a connection to the chassis ground for additional noise reduction.
LEEDH Digital Volume technology
The LUMIN U2 uses the LEEDH digital volume technology, which uses more efficient whole number volume values to maintain audio information integrity during subsequent DAC conversion and low processing power requirements to free up CPU resources. This removes the need for a preamplifier in many systems and improves the quality of the signal sent to products such as the LUMIN amplifier (appropriately named, Amp).
LEEDH Processing is an innovation of Gilles Millot of Acoustical Beauty, a French manufacturer of high-end loudspeakers who holds several patents for his innovative designs and technologies. LEEDH is an innovative new digital volume adjustment algorithm that eliminates rounding errors and modifies the digital signal amplitude exactly, without any changes to its shape, and free from any kind of information loss.
Key Features
Because of the significant impact that phase noise and jitter have on sound quality, the LUMIN U2 streaming transport utilizes four exceptionally low phase noise crystal clock oscillators and supports fiber optical network connectivity, which provides complete isolation from network component-induced digital noise.
This is the first LUMIN with three USB ports including a new interface feature, and a dedicated low-noise USB output dual network interface with a built-in network switch. The U2 features LUMIN’s latest digital processor providing greater resampling flexibility and supports up to DSD512 and PCM768 playback.
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For this review, I used the LUMIN U2 with music files sent from an upstream music server, an Akasa-cased NUC Roon Core located in another room. Digital music files from the Roon Core are sent using a Shunyata Research Sigma Ethernet cable to an Uptone Audio EtherREGEN Ethernet switch, and subsequently downstream using a single-mode 1310 nM Planet Tech (PT) optical transceiver in EtherREGEN’s SFP* optical port via Corning ClearCurve single-mode LC/LC optical fiber to a matching PT optical transceiver in the SFP port of the LUMIN U2 located in the listening room’s main audio rack. While the U2 also supports network connectivity via copper Ethernet cables, I’ve consistently found that using optical fiber for networked audio connections is notably more accurate, quieter, and natural-sounding than copper Ethernet, and used optical networking for this review. (*–SFP: small form factor, pluggable)
The LUMIN U2 transport was connected using its new and innovative “dedicated for audio” USB-A port to a Soulnote D-1N DAC with a Shunyata Research Alpha USB cable. This new DC-coupled USB interface was specifically designed by LUMIN for connecting networked audio components with very low noise, compared to a standard USB port. The D-1N’s analog output was connected using a Shunyata Sigma V2 RCA interconnect to a LUMIN P1, which was connected to a Constellation Inspiration integrated amp with Shunyata Venom-X XLR interconnects. The output volume of the Inspiration was set to unity gain, with the actual listening volume set using the LUMIN P1’s LEEDH digital volume control, which I’ve found to sound superior to the Constellation’s analog volume control. In this configuration, the LUMIN U2 functioned as the digital music file transport, the LUMIN P1 as the system preamplifier, and the Inspiration integrated as the power amplifier. All components in the main audio room were powered with a Shunyata Everest power distributor and Shunyata power cords: Omega QR-s for the LUMIN P1, Sigma NRv2 for the Inspiration amp, Alpha NRv2 for the Soulnote DAC, and Venom-X for the LUMIN U2.
The Constellation integrated amp powers Harbeth 30.2 40th Anniversary loudspeakers using Shunyata Alpha V2 speaker cables resting on Shunyata Möbius cable elevators to mitigate the effect of floor-borne vibrations. The Harbeth speakers are placed on Resonant Woods speaker maple speaker stands which place them at the reference height for listening.
The first impression the LUMIN U2 gives is one of tonal accuracy and harmonic richness, outstanding clarity, and a relaxed and musically engaging presentation. The tonality is slightly on the warm side of neutral, with body and fullness providing a natural and organic quality that adds authenticity to voices and instruments. The LUMIN U2 presents the music with accurate, defined, and nuanced reproduction of timbre, the attribute that distinguishes, for example, a woodwind from a stringed instrument playing the same notes. These qualities are most notable on well-recorded and mastered vocal & classical recordings, where the LUMIN U2 provides superb detail characterized by sophisticated and refined reproduction of instrumental overtones and lifelike vocals.
Pepé Romero, “Recuerdos De La Alhambra • Jeux Interdits • Asturias”
The Spanish guitar solo fantasia, Malagueña, composed by legendary Spanish guitarist Celedonio Romero, and performed by his son, Pepé Romero on the album, Recuerdos De Alhambra [Philips B0000040VR] has energetic pacing, a fulsome, woody timbre, and finely delineated harmonic structures as Romero rips his way through this classic guitar composition with impeccable technique. There is so much resolution and definition and sheer virtuosity on display that the first time I heard it, I thought two guitarists, Celedonio and Pepé Romero, were playing, but no, it’s just Pepé. As the only musician, the stereo image is precisely focused on Romero, but the trailing edges of notes can clearly be heard decaying into the performance space. Romero moves from a forceful, fast, and dynamic passage to a very beautiful slow, and delicate passage with refined technique and exquisite phrasing, nuance, and control. The mastering is such that can hear deeply into the recording, the subtle shadings of timbres and notes flying with perfect articulation off the sound box of his guitar. It’s dazzling and quite beautiful.
Mary Gauthier, “Mercy Now”
“Mercy Now” the title track by Mary Gauthier on her 2005 album, Mercy Now, [Lost Highway Records B0003570-02], a beautiful and plaintive song about family, church & country, and humanity, is skillfully recorded and mastered with a rich tapestry of sounds, from Gauthier’s gruff voice, clear, sonorous, and pitch-perfect in counterpoint to her backing acoustic guitar, fully grounded by backing drums as Gurf Morlix’ steel guitar layers a plaintive whine on top, the rhythm section with Brian Sander’s cello driving forward, fully resolved but with just enough restraint not to overpower Gauthier’s voice, but layering in the message of mercy and suffering. It all comes together as a darkly beautiful and moving song, full of pathos and loss.
The Ray Brown Trio featuring Gene Harris, “Soular Energy”
Soular Energy [Concord Records CCD42682] with Ray Brown on bass and Gene Harris on the piano is one of the most natural and organic-sounding jazz recordings I’ve ever heard, it’s been a long-term reference jazz recording for me. A timeless hard-bop album, Soular Energy is beautifully presented with a deep black background against which Brown’s finely articulated string bass provides a counterpoint to Harris’ exquisite piano playing, and the clean and quiet background provided by the LUMIN U2 lets the simple beauty of the mastering shine through with subtlety, texture, and subtly rendered tone colors from the piano and bass. Jazz lovers, if you don’t have this in your collection, Soular Energy is very highly recommended.
Adele, “Live at the Royal Albert Hall”
I’ll have to admit I haven’t followed Adele’s studio recordings all that much; a bit too much commercial over-exposure for my sensibilities, but the first time I heard her live recording of Lovesong [Adele: Live at the Royal Albert Hall, Columbia 88691901199] on my Harbeths, I was smitten. An exquisitely beautiful vocal performance by Adele, Lovesong is exceptionally well-recorded and mastered for a large hall live recording. It starts with the two guitarists, Ben Thomas and Tim Van Der Kull, stage left and right, and Miles Robertson’s organ laying out the melody and rhythm as her voice comes in over the top, followed by the crispness of Derek Wright’s drumming and the swell from the string section. The song builds and develops slowly and beautifully as Adele’s incredible voice, finally set free, soars above the string section. It is an absolute knockout. The feel, ambience, and atmosphere of an outstanding live performance in front of an enraptured audience are captured on the recording; it’s all there, and listening to it with the LUMIN U2 in the system, along with the audience, you feel part of the concert experience.
Johann Sebastian Bach, Arthur Grumiaux, Heinz Holliger, Herman Krebbers, Les Solistes Romandes, Arpad Gerecz, New Philharmonia Orchestra, Edo de Waart, “Bach: Violin Concertos”
After 40 years as a classical music lover, I’ve never tired of listening to J.S. Bach’s Concerto for 2 violins, strings, and continuo in D Minor [Philips 420 700-2], particularly when Belgian violinist Arthur Grumiaux is playing, as on this Decca recording with Les Solistes Romans. Here Grumiaux used his Guarneri violin, Rose, made by Giuseppe Guarneri in 1744. All the classic Guarneri violin attributes: richness, sonority, timbral weight, and exquisite tone are in full evidence, and in the hands of Grumiaux’s virtuosity, fully resplendent, bright and energetic, but never harsh or strident. Each musician in the chamber orchestra is precisely positioned in the soundstage, and with the inner detail and spatial accuracy presented by the U2, you can focus in on each musician in the orchestra and hear them fully resolved against the background of the orchestra as a whole. For example, during the Allegro on Concerto No. 2 for Violin, strings and continuo in E Major on the same recording, as Grumiaux winds down his solo, one can hear clearly hear the first cello come in on the right, providing counterpoint to the violin.
Yeol Eum Son, “Mozart: Piano Concerto No. 21”
One of the best classical recordings I’ve discovered in the last few years is Korean pianist Yeol Eum Son’s recording of Mozart piano concertos, accompanied by The Academy of St Martin in the Fields [Onyx4186]. The last recording the Academy made with famed director Neville Marriner before he passed away, is one of my favorite classical recordings I’ve discovered in the last few years. Of the eight compositions on this record, Variations in C Major K.264, (“Lison Dormait”), is a standout. Son’s sweet, deft touch and virtuosic technique give full credit to Mozart’s genius as well as his well-known musical sense of humor. In Movement III, Allegro Vivace Assai, of Piano Concert No. 21 in C Major, Son, and the Academy engage in the classical music version of “call and response”, and it’s clear that the musicians are having an absolute blast playing this delightful concerto; both pianist and orchestra playing with incredible speed yet delicacy and refinement in this challenging movement, the woodwinds cleanly interlaced with the piano. The piano’s full dynamic range, weight, and power are fully evident, yet fully resolved and defined by every other musician and instrument in the orchestra. A fabulous recording by Onyx Classics Records, Son and the Academy’s super-clean, super “light & tight” playing is sensational. Just a fantastic recording and performance, and one with my highest possible recommendation.
Horace Parlan, “On the Spur of the Moment”
This results in a captivating experience listening to Alan Yoshida’s re-mastering of Horace Parlan’s hard-bop jazz album, On the Spur of the Moment, part of Audio Wave’s superb series of XRCD24 Blue Note reissues [Audio Wave Music AWMXR0008]. Here the U2 excels in rendering the tonal complexity, body, weight, and power of Parlan’s piano while never sounding edgy or hard, but smooth, natural, and refined. This classic album also has Stanley Turrentine’s tenor sax sounding warm and earthy while Tommy Turrentine’s trumpet sets a bluesy vibe with George Tucker on bass and Al Harewood on drums providing a weighty yet detailed backing foundation. Whether capturing the subtle nuances of Harewood’s subtle brushwork on the cymbals or articulating the warmth and richness of Turrentine’s sax, the U2’s treble performance is highly engaging and sweet, but without veering into excessive brightness or hardness, ensuring a harmonious tonal balance.
Count Basie and his orchestra, “88 Basie Street”
Bluesville on the Count Basie Orchestra’s 88 Basie Street [Pablo 2310-901] starts as a duet between piano and bass. A muted trumpet enters, all brassy and warm, but with virtually no bite, and things fully get up to speed when the full horn section comes in, the orchestra ramps up, and the band…swings. Basie’s piano is so well-mic’d and mastered that it’s just flat-out gorgeous on the LUMIN U2, full of body and life-size in the soundstage, while the pitch-perfect tone and timbral articulation of Cleveland Eaton’s bass and Dennis Mackerel’s brushwork on the ride cymbal provide the bass line and backbeat. Just a stunner.
Bruno Coulais, “Himalaya: The Rearing of a Chief (Original Motion Picture Soundtrack)”
I referenced Bruno Coulais’ soundtrack for Himalaya: The Rearing of a Chief in my review of the Soulnote D-1N DAC, and on the track, Norbu, using the U2 as the streamer in place of my reference LUMIN P1, all those attributes mentioned are still fully present: fast, clean percussion where speed, power, and dynamics are the order of the day. This is an impressive track showcasing the LUMIN U2’s outstanding ability to render impactful bass drum crescendos with superb clarity, textural definition, and transient response providing a stable low-end foundation for the overlaid and finely-layered and nuanced female vocals.
Summarizing the experience of listening to these wonderful recordings into a “larger whole”, one of the most notable attributes of the LUMIN U2 is its ability to resolve high-resolution details with finesse. In addition to providing excellent detail retrieval, the U2 refrains from overemphasizing these details to the detriment of the overall musical presentation. Instead, it seamlessly integrates intricate musical nuances into the overall flow, creating a listening experience that feels both natural and effortless. The U2’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 LUMIN U2 is an exceptional and versatile transport and the foundation for a superb digital streaming-based system.
- Compatible with all high-resolution PCM and DSD digital recording formats.
- Natural, accurate presentation of tone and timbre with excellent imaging and spacious soundstage.
- Exceptional transparency, low noise floor providing superb resolution and detail.
- Functional and versatile connectivity features
- Effective resonance and vibration damping and ground-plane noise reduction.
- Excellent build quality and high overall engineering specification
- Well, this must be a first, because honestly, I can’t think of anything. The LUMIN U2 has all the functions and features that I can think of for a digital transport. And it’s superbly engineered and executed, as well.
For me, the bottom line is really simple: the LUMIN U2 is a superb digital transport. In addition to being exceptionally well-designed and engineered with a broad feature set that accommodates any DAC and virtually all digital music file formats, the LUMIN U2 provides flexible and versatile functionality and superb audio quality. 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, natural yet “relaxed” musical presentation that emerges from a deep black background and very low noise floor. If I were looking for a digital transport/streamer for use with my DAC of choice, I’d get the LUMIN U2 Transport and call it a day. I think it’s one of the best-designed, best-engineered, best-implemented, and best-sounding digital transports I’ve ever used or heard and, as such, has my highest recommendation.