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Silent Angel

Manufacturer: THUNDERDATA Co. Ltd.
Price (when reviewed): 12 990 PLN

RM503, Building 18, No. 1889, Huandao East
Road, Hengqin District, Zhuhai City,
Guangdong Province | CHINA


Provided for test by: AUDIO ATELIER


images Marek Dyba | Silent Angel

No 231

August 1, 2023

The Silent Angel brand entered international markets barely a few years ago, specializing in the production of devices designed to improve the quality of music played from audio files. One of its first products was a server called Rhein Z1. Today we test its new, more advanced version Z1 PLUS.

EW PLAYERS ON THE AUDIO MARKET (and on others) choose various paths of development. There are those who try to get in "with a bang" by offering right away top-of-the-line products designed to offer high-end sound quality, top workmanship and impeccable finish, and therefore costing tones of money. Only later do they use some of the developed solutions in cheaper models, sometimes also finding less expensive ways to apply those solutions. To put another way, they start at the top of the range expanding later (at least for a while) downward.

Most new brands, however, present themselves to potential customers starting with cheaper, less advanced products, gradually improving and developing them, based on the knowledge and experience they gain in the course of their work, using feedback and hints coming from the market, from users and reviewers. Which way is better? There is no unequivocal answer, as we witnessed both, successes and failures, by representatives of both schools. The safer and more often chosen path, however, is the latter - building a brand and customer trust from the ground up, starting with simpler products, which are later gradually developed.

Silent Angel, a brand belonging to Thunderdata Co. Ltd., is one of the representatives of the second way. What sets them apart is how quickly they have been developing. Just a few years ago the basic version of the audiophile LAN switch, Bonn N8 was introduced, and then the Forester 1 linear power supply meant to improve its performance (I still use both in my reference system). Then there was the first audio files transport with a proprietary operating system called VitOS, the Rhein Z1.

Only later more advanced versions of LAN switches followed with the top-of-the-line Bonn NX and Genesis NX word clock in particular (tests → HERE and → HERE; the latter had its world premiere in "High Fidelity"), the better and more versatile Forester 2 linear power supply, but also the slightly cheaper than the Z1 Munich and Bremen file transports.

This year's latest addition to the lineup, however, is a new version of the original audio files transport, which has been renamed Rhein Z1 PLUS. I've dealt with the first Rhein Z1 model several times. I tested it soon after it was introduced to the market, then again paired with the Forester 2 power supply and finally in a whole system together with the N8 PRO LAN switch and the so-called E1 Expander (which is the company's external USB drive meant to store user’s whole music library) and Forester 2 taking care of the high quality power supply for most components in the system. It was a well-made, flawlessly working device that delivered high quality for DAC. Small, sleek, passive (and thus noiseless), with an interesting operating system and the possibility of using Roon, which is always a huge plus from my point of view. In a word, it was an interesting alternative to a "regular" computer, and to many more expensive proposals from Silent Angel’s competitors.

After several years of the Rhein Z1 model's presence on the market, which the manufacturer devoted primarily to the development of its LAN switch lineup, the manufacturer has decided to introduce a new version named Z1 PLUS. This extension of the model's name suggests (as does the price) that it is a more advanced product. So one can expect more functionality and an even better class of signal delivered to the DAC, thus a higher class of sound.

Rhein Z1 PLUS

I DID NOT HAVE ORIGINAL Z1 at my disposal for a head-to-head comparison, but based on memory and photos, I dare to claim that externally both use (almost) the same chassis. Sure, the rear panels are different in both generations, and that's also where the elegant on/off button was moved from the front in the PLUS version. Both housings, however, are square, and small, as they measure just 20x20x6.5 cm.

The chassis of the Z1 Plus is made of aluminum. Looking at the photo, it looks like it was milled from a block of this material, and I can’t complain about the quality of workmanship and finish as these are really good. It's a sleek, nicely looking device, which weighs quite a lot (more than 3.5 kg) confirming how solid is the chassis, and the considerable weight additionally translates into anti-vibration properties.

I should add that two color versions are available, silver and black. The whole thing rests not on feet, but on what could be described as a sort of seal glued to the bottom of the device, that is not too wide, and made of vibration-absorbing material. Most likely many users sooner or later will decide to place the Z1 Plus additionally on anti-vibration feet, or a platform. Silent Angel has such feet in its lineup, and many others are also available on the market, so there is plenty to choose from.

As I mentioned earlier, Silent Angel's audio file transports use passive cooling, which means that they are devoid of any moving parts (not to mention HDD drives). Passive cooling means no fans, which is important insofar as even the quietest ones start to make noise after a while and need to be cleaned and sooner or later replaced. Of course, since we are dealing with a computer, its heart is the processor (4-core Intel Quad-Core CPU J6413), which gets quite warm during operation. In addition, there are other heat-emitting components on the motherboard, so there is no way around without cooling.

It is provided with the help of a copper heat-sink, and the manufacturer also mentions the use of graphene in the cooling system. The element that transfers heat to the outside is the whole chassis, which noticeably heats up during operation of the device. The ribbing of its sides, visible in the photo, is an element that improves the aesthetics of the device, but at the same time increases the surface area used for heat dissipation. The manufacturer also boasts the use of an even more effective solution to protect the device from electromagnetic interference (EMI) - presumably this is a special mat visible in one of the photos. Source of EMI are many of the components that make up the device, such as the processor, RAM chips, network card, etc., and whole books have been written about the negative effects of EMI on the operation of electronic devices.

The aforementioned rear panel of the file transport significantly differs from that known from the original version of the Z1. In the PLUS version you'll find there two gigabit Ethernet ports (instead of one), two 3.1 USB ports, and one 2.0 for connecting external storage media, a dedicated USB port to serve as an audio output (to connect to the DAC's USB input), a USB Type-C port, an HDMI port (albeit for service purposes only), and a DC power socket (12 V). Let's add two more novelties: the aforementioned on/off switch of the device, as well as a new connector allowing usage of an external word clock (this, among other reasons, is why the company's Genesis GX offers as many as four outputs), plus a toggle switch to choose internal or external clock.

There are even more differences between the older model and the latest one. I've already mentioned the CPU - it's a different, faster model than in the predecessor (although both are Intel quad-core units). The original Z1 came with 8 GB of RAM as standard, 16 as an option, and the Z1 Plus already has 16 GB on board, expandable (for an extra charge) to 32 GB. The Z1 came with a standard SSD, the Z1 Plus already features a newer (and faster) generation of NVMe drive. Not only does the new Z1 Plus have a suitable connector for an external clock, but the one built-in is also a higher-end TCXO unit than in its predecessor.

I recently tested the top LAN switch from this manufacturer, the Bonn NX, also equipped with a high-end TCXO clock, and yet connecting an external clock (Genesis NX) brought further improvements. Thus it is safe to assume that equipping the Z1 Plus with this connector gives users the opportunity to upgrade its performance. The USB port labeled as audio output is supported by a noise-reduction solution, and this too is a more advanced solution than the one used in its predecessor.

The newer, more advanced hardware components allow Z1 Plus to handle up to 32-bit PCM files with sampling rates of up to 768 kHz, meaning its capabilities compared to the original are the same in this regard, but for as for 1-bit DSD the new file transport enables playback of DSD512 files (the predecessor maxed out at DSD256). More powerful components also mean that the Roon Core DSP seamlessly converts the PCM signal to DSD256, which is good news for supporters of this format.

The device invariably runs under Silent Angel's proprietary operating system, VitOS, in its latest version. It's a Linux-based software optimized for music playback. The system supports programs such as Roon, Spotify Connect, Apple AirPlay 2, Tidal, Qobuz and others, and it is also MQA-Ready. The manufacturer notes that the increased computing power of the Z1 Plus makes it possible to run very demanding (in terms of hardware) NAA HQPlayer on it. As an option, customers can order their server with an additional 4TB NVMe SSD for storage of audio files, but they can just as well store them on a NAS or computer hooked up anywhere in the house to the same network, or the so-called Expander, E1, an external USB drive offered by Silent Angel.

The proprietary VitOS Manager app can be used for control, although Android users can use, for example, Bubble UPnP, and apple users can use MConnect (or other similar apps). Roon Core is also installed by default on the device, although to use Roon you need to purchase (or already own) your own license. I make no secret of the fact that I have been a fan of this software for several years, so any device that allows me to use it has an advantage over those that don’t, not least because I don't have to get used to a different way of controlling music playback.

Looking at the development of Silent Angel's lineup over these few years, it is clear that their engineers believe in a comprehensive approach to audio files playback. Not only do they offer several categories of their products - file servers/transports, network switches, linear power supplies and an external word clock - but they also make sure they can be combined into an optimal system offering top quality.

That's why the Genesis GX clock offers four outputs allowing it to serve up to four devices. It's why the top-of-the-line switch, the Bonn NX, and now the top-of-the-line audio files transport, the Z1 Plus, are equipped with proper connectors allowing you to enjoy the benefits of a high-end external clock. It's also why the Forester F2 power supply was developed, which can simultaneously power several of these devices offering yet another performance enhancement over standard power supplies.

With all this, the lineup consists of devices from various price shelves, which gives users the opportunity for gradual development, arriving at an optimal solution that allows treating quality audio files as an equivalent source to physical media.


˻ HOW WE LISTENED ˺SILENT ANGEL Z1 PLUS was tested in my reference setup. At the beginning of the test it was powered by a standard switching mode power supply, which is supplied by the manufacturer, but later I used my Ferrum Hypsos power supply in the Signature version as an upgrade. To the Silent Angel Bonn 8 switch powered by the Forester 1, the Z1 Plus was connected using David Laboga Custom Audio Digital Sound Wave Sapphire LAN cable, and to the LampizatOr Pacific 2 DAC with a USB cable of the same brand (David Laboga Custom Audio), but the top model Ruby.

From there, the signal was transferred via a Soyaton Benchmark RCA interconnect to the GrandiNote Shinai integrated amplifier and further via a speaker cable from the same Soyaton series to the GrandiNote MACH4 speakers. Audio files were played from the NAS (with linear power supply) and from QOBUZ. I used my custom server featuring JCAT USB Card XE and notes from a recent listening of the original Z1 (in the whole Silent Angel setup mentioned above) serving as references.

I started the Z1 Plus test after taking a break from listening to audio files for several days. During this time I tested two brilliant phono preamplifiers and, to be honest, they played so good that I didn’t want to loose any time for any other, than vinyl records, medium. Both phonostages, the new LampizatOr VP4 Silver and the fantastic Doshi Audio Evolution Phono Preamplifier, offered the very top quality performance. Hence, the return to audio files was not easy, although it was forced by the need to return both preamplifiers. Although the recent upgrade of my Pacific to version '2' brought another significant (!) improvement in many aspects of its sound, it does not change the fact that I love the sound from vinyl the most.

So to get a little used to a different medium again and to refresh my memory on the sound obtainable with my audio file transport, I first spent two days with it in the system before swapping it for the Silent Angel.

And at some point the listening sessions, as I mentioned earlier, I replaced the latter's standard switching mode power supply with the excellent Ferrum Hypsos hybrid PS from HEM, a unit in the Signature version. The Forester 2 would undoubtedly have been an excellent option as well, but I had to return it shortly before this test, so I had to manage with what I had at my disposal (which was a great choice anyway).

STARTING Z1 PLUS in the system is trivial - all one has to do is to connect the LAN cable, USB cable (an external clock if one is available) and finally the power supply, press the switch on the back panel and the oblong horizontal blue LED on the front of the device informs us that the server has been started. When it lights up with a solid light, it means that the Z1 Plus is ready for use.

Next, it's just a matter of connecting to it with the help of a selected control program. It can be the company's VitOS Orbiter application, it can be Roon's "remote control", it can be one of many others - there is something for everyone including lots of free apps. Then, one has to select the source(s) of the files, maybe enter passwords and logins to local servers, or streaming services, and it’s time to start listening. I'll just point out that direct comparisons between transports were not possible, because I was using my Roon license on both - so I had to log out of one to log in on the other. So only longer listening sessions with one or the other were practical.

The files were played from a local NAS. I store a fair number of albums on it, so indexing them took quite a long time. Without waiting for this process to finish, I started listening with the albums that showed up in Roon first. My system "fed" with the signal from the Z1 Plus did not seem to need any warm-up, there was no audible accommodation in the system period. Right from the start, Silent Angel served me the sound (that's a simplification, of course - it delivered the signal to the DAC, which is how it let the system sound) I like - balanced, dense, saturated, smooth yet open, full of air and impressively spacious. Of course, a lot of the credit for the final effect goes to the system as a whole, after all, that's how I built it, but without a signal of sufficient (high!) quality, getting such a result/sound would not be possible. So it was clear from the start that I was dealing with a promising, or, to put it plainly, classy transport.

There was not even the slightest trace of nervousness in this sound, no digital haze, no artifacts associated with inferior digital sources. Instead, the sound was very smooth, coherent and natural. It encouraged me to listen to the music, to become emotionally involved while relaxing (although that also depended on the type of music), and not necessarily to analyze the sound as such. This is exactly how I perceived my system from the very beginning, in which the new Silent Angel transport replaced the one I use on daily bases. In a word, we spent a highly enjoyable evening together, which was a rather promising beginning of an acquaintance.

It looked promising, because it often happens that reasonably priced audio files transports do not quite match the level of my own server, which is not the best in the world, obviously, but I worked on it for years and it plays really well and, importantly (!), the way I like it. Many of the representatives of this type of equipment I've tested over the years cause a marked drop in quality and/or change in the sonic character, which bothered me a bit, at least at first. The thing is not even necessarily that they offer a poor quality performance, just a little inferior to my own sever or even just different - if that happens I have to get used to a different, whether in terms of quality or character, performance. This time, however, such a feeling did not appear at all, which indicated that the sound is at least at a similar level and, in addition, similar in terms of sonic character. Further listening only confirmed these first impressions and the class of the Z1 Plus.

The Z1 Plus does not introduce any form of flashiness into the sound. It's not about the most powerful bass (although listening to e.g. DEAD CAN DANCE I did hear and feel the lowest electronic sounds in my bones), the most resonant treble (although STEVE GADD's cymbals came off splendidly), the largest space (although Noirlac Abbey on MICHEL GODARD's albums was huge! ), or the most palpable midrange (yet on numerous live recordings from small clubs it was brilliant), but rather about smooth, consistent, engaging listener delivery of the music and establishing a connection with its performers.

It so happened that a friend who loves music, who sings beautifully himself, and who has been asking me for years whether audiophile equipment costing a pile of money actually sounds better than the more humanly priced, easy-to-use solutions he uses, showed up at my place literally for an hour. Since he lives at the other end of Europe this was the first opportunity to finally present to him the capabilities of my system. We were short on time, so I didn't play around with going back to my full system, and just played music for him with the Z1 Plus as a source (already confident that it wouldn't let me down). The music my foreign guest selected himself ranged from Pavarotti, to Aznavour, to Kitaro, to performers I can't even remember (he found them on Qobuz).

It only took a moment to see the wide-opened-eyes, and to hear lots of comments such as: "as if Pavarotti were here" or "everything is so close, at my fingertips, so real, tangible". As I mentioned, my guest himself sings very well and has a great musical ear, and that's probably why he not only listened to the music as a whole, but began to even analyze the voice, its texture and timbre, or the myriad of details whose presence in these recordings he hadn't realized before. At one point, there was even speculation as to why there were some imperfections in the sound of the Maestro Luciano's old recordings, with a conclusion that probably microphones or their setup were to blame (after all, this friend is an engineer, even if of a different specialty).

I write about it because it was an interesting experience for me too - to listen to how a man who is not an audiophile, but loves music, immediately was able to describe many characteristics of the sound of my system with the Silent Angel Z1 Plus as the source. Because it is a mature, refined sound, filled with details and subtleties that determine how rich, how full and how realistic the sound is. Because it is easy to judge and appreciate how natural this sound is, when a beloved artist suddenly materializes in the room (even in the perception of a person "untainted" by audiophile/reviewer flowery descriptions), and there is nothing in what flows from the speakers to suggest anything other than (almost) direct contact with the performer. To put it another way, instead of that oft-used phrase in reviews: "even my wife, daughter, son, etc., heard/said...". I used a friend to further convince you how good a device the tested Silent Angel transport is.

At this stage it was also already clear to me that the Z1 Plus offers a significant improvement over the original Silent Angel audio files transport. Which shows that the manufacturer did not settle on initial achievements, but continued to work, gather feedback and suggestions to offer a "sound" of an even higher class. The original device only approached the level of my server after being supported by a linear power supply, albeit not enough for the thought to enter my mind about buying it. The Z1 Plus tested now, on the other hand, even without a separate high-end power supply, delivered a performance similar to that of my unit, both in terms of class and character I might add, paired with one of the best DACs available on the market today, using cables (USB and LAN) costing similarly or more than the transport itself, not to mention the rest of the system. So in theory it was supposed to be the weakest link in this system, but if it was I could hear it.

Genre of music didn't matter at all. I did try many genres, from AC/DC and METALLICA, to PINK FLOYD, PETER GABRIEL, STEVE RAY VAUGHAN and MUDDY WATERS, to PATRICIA BARBER and EVA CASSIDY, Mozart operas and the brilliant Hamilton musical and the soundtracks from Gladiator or Empire Strikes Back, and even a bit of pop (out of curiosity). Where it mattered, I could hear excellent PRAT, when the bass was supposed to go very low and remain saturated with energy it did, when I was about to be immersed in action and emotion of soundtracks, these albums ended surprisingly quick, and when I was about to be enthralled by the extraordinary voice of the opera singers or vocalists, they stood before me as if alive. Even with poorer (technically) recordings, the Z1 Plus did well.

In this case, good did not mean absolute fidelity, which would have probably caused me to grind my teeth, but it was rather about marking the lower quality of the recording right away and then focus my attention on the artistic content, music, and on the emotions. As a result, it was possible to listen to such recordings with pleasure as well. During the entire listening experience, I didn't come across a single album that I would have turned off because the sound quality was too poor. OK, I don't have too many of those in my library, as they only serve to verify the fidelity of the reviewed devices, but I keep some, and they too sounded acceptable.

These of better quality and particularly the very best ones sounded exquisite. Clean and dense at the same time, effortless, but with adequate weighting and filling, juicy, with sonorous but not aggressive treble, with brilliantly shown acoustics of recordings, with long decays, full reverberation. The amount of information, saturation of timbre, very good micro-dynamics - all this showed me that the makers of the Z1 Plus managed to effectively minimize the level of interference and noise, in a word, everything that in this type of equipment reduces the quality of the signal sent to the DAC, and thus the sound quality.

˻POWER SUPPLY ˺ So all that was left for me to do was to check if a better power supply in the form of the Ferrum Hypsos Signature would still contribute anything to the excellent performance of Z1 PLUS. These comparisons were a bit simpler, as it was a matter of turning off the Z1 Plus, unplugging one DC power cable and plug in the other. Once turned on, the unit is ready to go in maybe 30 seconds, so each of these operations took no more than a minute.

The improvement obtained with this excellent Polish external power supply was by no means huge, which is only a good indication of what Silent Angel's engineers were able to achieve with a switching mode power supply. There was a noticeable improvement though, in terms of, hmm... additional depth of sound, an even higher level of serenity (understood as a lack of nervousness) and even better organized/orderly presentation especially in more complex, highly dynamic works (such as large classics and operas).

A good power supply costs quite a lot, but after such an attempt, at least immediately afterwards, it is difficult to accept also really good, but nevertheless a little worse sound with a switching mode power supply. So let me warn you that such an attempt will most likely result in an additional investment. I also suspect, although here I'm just theorizing or extrapolating from the Bonn NX test, that using an external clock, such as the company's Genesis GX, will offer another objectively small but subjectively significant improvement. And will provoke yet another expense.... Nevertheless, that's the way it is in this audio game of ours - the pursuit of perfection costs money and you have to reckon with it. And by the way, Silent Angel's products are quite attractively priced compared to many competitors.


THE NEW FILE TRANSPORT by Silent Angel took me by surprise with its class. Sure, I expected a lot based on all my experiences with this brand’s devices, but I got way more than anticipated. Since the manufacturer has decided to stick to the name Rhein Z1 the „plus” should definitely be spelled „PLUS”. After all, the progress compared to its predecessor is so great that a simple "+" or even "Plus" does not cover it.

In its basic form, we get a source that, paired with a high-end "DAC", offers a sound that will boldly compete with many even much more expensive sources. And, in an easy (although not necessarily cheap) way, each user may further improve its performance. Just replace the SMPS for a linear one (or a hybrid one, like Hypsos), add an external word clock and.... you’ll get another step closer to the unachievable sonic nirvana.

Of course, it's not, and probably even with all the possible upgrades it still won't be the best audio files transport in the world, but for relatively (!) little money we get a classy, great-looking and performing source, which can still be improved/enhanced/upgraded in the future. The operation, especially with Roon is easy and pleasant, during the test I had no problems, no software or hardware crashes, no communication problems - the operation was smooth and reliable. So what’s there not to like?

Technical specifications (according to the manufacturer)

CPU: Intel Quad-Core CPU J6413
RAM: 16 GB (standard) / 32 GB (option)
Drive: NVMe SSD, 250 GB (standard) / 4 TB (option)
Ethernet: 1 GbE x 2
USB audio output: USB x 1
USB ports: USB 3.1 x 2; USB 2.0 x 1
USB C-type: USB typ C x 1
Connector for external word clock: 25 MHz x 1
Chassis material: aluminum alloy 6061
Power supply: external 12V / 3A (5.5 mm x 2.5 mm plug)
Dimensions (W x H x D): 200 x 65 x 200 mm
Weight: 3.6 kg