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D/D converter USB-S/PDIF/DAC + battery power supply
KingRex UD384 + U POWER

Price (in USA): 479 USD + 189 USD

Manufacturer: KingRex Technology Co., Ltd.

Kingrex Technology Co., Ltd.
13 F-3, No. 136, Min Quan West Road | Taipei, Taiwan

tel.: +886-2-2557-2156 | fax: +886-2-8226-2626


Country of origin: Taiwan

Text: Wojciech Pacuła
Photographs: Wojciech Pacuła
Translation: Krzysztof Kalinkowski

The Taiwanese company KingRex is a manufacturer of small, sleek devices, designed mainly to work with computers or similar equipment. I do not know if you remember, but some time ago I tested two devices manufactured by that company – UD-1 Pro, a DAC with USB input, and the HQ-1, a line preamplifier with a headphone amplifier (test HERE). Both devices appealed to me, especially the DAC, which had an old D/D USB-S/PDIF converter and DAC, which I never expected to be so musical – the Burr-Brown PCM2702. Already then it could be seen, that the company knows the one and the other about digital technology.
Shortly after the publication of the test I received another shipment, this time with the converter UC192, converting USB signals to S/PDIF, AES/EBU or I2S, which allows to connect a computer to any DAC and play even 32 bit 192kHz files. This way we can bypass the lack of a USB input in a DAC.
But before I could make the tests it turned out, that the company prepares something even newer – a DAC and D/D converter in one box, allowing to decode the signals up to 32 bits and 384kHz (however without 352.8kHz) and send out a digital S/PDIF signal starting with 16/44.1 up to 24/192. Even more – we can purchase also an external, battery power supply, with two output voltages – 7.5V and 5V, which can supply power to the mentioned DAC, as well as other DACs or headphone amplifiers, also from other manufacturers. The only thing that this combination cannot do is to convert DSD, the coming novelty. This kind of signals need to be converted to PCM in foobar2000 first, which has a plugin for this, and then send to an external DAC.

So we get a powerful tool. The UD384 allows to play DXD signal, in which most files from sensible companies are recorded – for example those from First Impression Music, Fidelio Musique or L2 (I am talking about the PCM signal with 32 bits and 384kHz). On the company page you will find a full list of allowable formats, together with some free samples in DSD and PCM up to 24/384.
The UD384 is not only a DAC. This is also a D/D converter with asynchronous mode, switchable in the drivers, which we receive in a small pendrive. Like I said, currently DSD signals cannot be played. At least on PC. Because on the MAC it seems possible – KingRex recommends to use the program Pure Music, which decodes the DSD stream.
The KingRex can be powered from a wall-wart power supply or a batter one, what – as experience shows – is an ideal solution for low power consumption devices.
It is also hard to see what is more important in this device – the decoding of the USB stream and conversion to S/PDIF or the DAC function – clearly the company emphasizes on multi-functionality. In the test I took a look at both functionalities separately.


Recordings used for the test:

  • T-TOC Data Collection Vol. 1, T-TOC Records, DATA-0001, 24/96+24/192, WAV, ripy z DVD-R.
  • Vinyl Magic for High Fidelity, sampler, DVD-R,, 16-24-32/44,1, WAV, ripy z DVD-R.
  • Al Di Meola, Flesh on Flesh, Telarc, 24/96, źródło: HDTracks, FLAC.
  • Brian Eno, Craft On A Milk Sea, Warp Records, WARPCDD207, 2 x 180 g LP + 2 x CD + 24/44,1 WAV
  • Cassandra Wilson, Silver Pony, Blue Note, 29752, CD; rip FLAC.
  • Charlie Haden & Antonio Forcione, Heartplay, Naim Label, 24/96 FLAC.
  • Depeche Mode, Personal Jesus 2011, Mute, cdbong43, MS CD; rip FLAC.
  • Kankawa, Organist, T-TOC Records, UMVD-0001-0004, Ultimate Master Vinyl, 4 x 45 rpm 180 g LP + CD-RIIα + 24/192 WAV;
  • Lars Danielsson & Leszek Możdżer, Pasodoble, ACT Music, ACT 9458-2, CD; rip FLAC.
  • Mikołaj Bugajak, Strange Sounds and Inconceivable Deeds, Nowe Nagrania 001, 45 rpm LP+CD+WAV 24/44,1;
  • Milt Jackson Sextet, Invitation, Riverside/Mobile Fidelity, UDSACD 2031, No. 01828, SACD/CD; rip FLAC warstwy CD.
  • Patricia Barber, Companion, Premonition/Mobile Fidelity, UDSACD 2023, SACD/CD; rip FLAC warstwy CD.
  • Simon & Garfunkel, Bookends, Columbia/Sony Music Japan International, SICP 1484, CD; rip FLAC.
  • Stan Getz & Joao Gilberto, Getz/Gilberto, Verve, 24/96 FLAC.
  • Stardelay A New High Fidelity, Ozella Music, OZL22006CD, FLAC 24/44,1 (2008).

Japanese versions of the disc are available on CD Japan.

KingRex UD384 + U Power as DAC (Digital to Analog Converter)
There are not many DACs on the market that can decode a 32 bit signal, and even less, that can handle sampling frequencies above 192kHz. The most prominent are the, tested in issue 87 from July 2011, Antelope Audio Zodiac Gold with the Voticus power supply (HERE), MPD-3 and MPD-5 from Playback Designs and the DACs from MSB Technology. This time it happened, that I had a system from the latter company, I could make my comparisons with, composed of the drive Platinum Data CD IV, DAC Platinum Signature DAC IV and power supply Platinum Signature Power Base (test in the magazine “Audio”). Beside this system, for Red Book quality files I used the player Lektor Air V-edition as well as the splendid, yet inexpensive DAC Wyred 4 Sound DAC-2 . It needs to be added, that the only DAC accepting DSD signals is the device from Playback Designs – the company dCS has a working prototype, but the production version is not yet ready. I am mentioning this, because the label 2L has already such recordings, and René Laflamme from Fidelio Musique is telling, that he is ready to sell DSD files on Master Flash cards. This is a very high reference point, so to stay closer to earth in the test I used also the DAC HRT Music Streamer II+.

For not even 700 USD we get a very competent sounding DAC. It is not flawless, I will start with that, but when looked at it from the point of other, similarly priced products, it will turn out, that those two small boxes can successfully replace large DACs in many systems.
First a response, why am I talking about 700 USD and not 479 USD of the DAC enriched with the optional 189 USD of the power supply unit. Well, because I cannot imagine, that the UD384 will be working with the wall-wart PSU supplied together with it. The difference between that PSU and the battery shows, what distinguishes audio from AUDIO, hi-fi from high-end (I am exaggerating a bit with the latter, but I want to show you the proportions). With the battery the sound is clearer and more relaxed. It is deeper and more natural. Point.
The KingRex set sounds with a very mature sound, although its timbre is visibly shaped – different than in my Lektor, but also different than in the MSB DAC. It differs from my CD player with stronger treble, much thinner and not as well integrated with the rest of the sound spectrum. The MSB DAC is also brighter than the Lektor, but there it is a result from a different perspective of the sound and not a flaw. Also the bass from KingRex is worse integrated with the midrange. Examples for that can be the recordings from the disc Pasodoble Lars Danielson and Leszek Możdżer (16/44.1) – the contrabass had a clearly softer part of the sound spectrum, somewhere between 100-200Hz. Below that there was more, flesh, power, etc. It was nicely shown by the recordings from the disc Stardelay A New High Fidelity (24/ 44.1), with strong bass drum and bass. Also the re-mixes of Depeche Mode from the maxi single Personal Jesus 2011 sounded strong and explosive. With those this element I am talking about was even stronger audible, as if the high energy of the lower octaves would cause slight detachment of the lowest bass, below 100Hz, from that what is above it.

But there is a range, that makes everything I said seem less pronounced as it might have seemed from the description above – this is the midrange. Listening to new recordings, for example Cassandra Wilson, Sara K. from the beautiful, not so well known disc Don't I Know You from Somewhere, or Patricia Barber it is hard not to appreciate the quality and way of reproducing the human voice. Even more, older recordings sounded even better. Although the treble, very important with the vibraphone, slightly elevated the gravity point on the disc Invitation Milt Jacksona, yet the instrument still reverberated nicely and had a significant weight. But most important was the silky, deep midrange, which made me listen to this tiny DAC for a long time.
Summarizing this part it needs to be said, that this is a very nicely sounding device, which, however, does not handle everything equally well. Its treble and bass are not as good as the midrange, and due to that, the whole sound is not as even as for example in the DAC-2 W4S. This is the reason, that when we are searching for something leveled, the American product, while more expensive, will be a better choice. It will be different in case we can sacrifice something for something else – then it may turn out, that those small boxes will perform better than some big ones.

KingRex UD384 + U Power as DDC (digital to digital converter; USB – S/PDIF converter)
Using a DDC is sensible in places, where solutions built into the DACs are of lower quality. This was some time ago with upsamplers, jitter reducers and now is with USB – S/PDIF converters. Especially because using a device like the KingRex in the role of a converter, we include another cable in the equation – here and S/PDIF cable, which introduces its own jitter. This is the reason, that everywhere, where possible, I try to minimize the amount of boxes, cables and devices. But this is not always possible – a large amount of good DACs does not have USB inputs, or has old type inputs, accepting only 16/48 signal – like the Bryston DAC-1.

The KingRex converter, battery powered, was compared directly to the USB input of the Wyred 4 Sound DAC-2 and the MSB Platinum Signature DAC IV. It is worth noticing, that the UD384 processes signals up to 32 bits and 384kHz as DAC, while the S/PDIF connection limits the sampling frequency to 192kHz. When we need more, we need to use the UC192 converter with upgraded software.

Digital technology is still a big unknown, probably not only for me. It does not stop surprising me and is a never ending source of revelations and frustrations at the same time. The problem is in the fact, that it is still unknown, how to interpret a large amount of measurements and what to pay attention to. Jitter – this is clear. But which one – long term, short term, correlated, non-correlated? This is only the first one of many questions that have no clear answer. This is why listening, or examination by inspection is still the most important thing…
The KingRex system is one of those devices, that make us think about the way we perceive mechanically reproduced sound. It might seem, that when we once set the hierarchy of importance of things, it will be exactly the same every time, with every product. Clearly this is not the case. I said some time ago, that for me the most important thing in the sound, are emotions, some kind of energy, captured in some way by the sound engineer and then reproduced by the stereo system. Much less important are such characteristics of the sound, like even frequency response, its extension, separation, etc. To make things clear – those things are important. But because audio is an art of compromise, if I have to value the individual elements, then first place is given to the musical communication. Due to this it is for me much easier to accept deviations in the frequency response of loudspeakers, even significant ones, than minimal deviations in the sound of the source, especially a digital source.
This is why the listening session of the KingRex was such a surprise to me. It fared well as a DAC, it sounded nice, although its timbre was not fully that, what I personally would be searching for. But when I switched the device in the converter mode (in foobar2000 you need to choose a different device for output as DAC and DDC), with connected MSB and W4S DACs I sat quite some time amazed. Because I heard a sound which was similar in timbre, to what I heard from its analog outputs. I mean I had a slightly underlined treble and in general the tonal balance was moved towards upper midrange. But at the same time I had a slightly better resolution, higher energy.
When the USB signal was delivered directly to the USB inputs of the MSB and W4S I got a much more smoothened, rounded, warmer sound with rather soft bass. It seemed to be very nice, a bit silky. But it was KingRex, which showed the contrabass in a more natural way, I mean it shortened its reverb a bit and underlined the moment of the attack – I know that from many live performances, and this is the way a contrabass sounds in real life. With the Chinese converter it was heard a bit more like live, and not recorded by microphone. The sound directly from USB seemed more palpable, closer to the listener. But with KR it was more alive, more dynamic, more resolved. And this is how I also perceived the other subranges. Every time the KR seemed to be directed towards a precise sound, and the USB inputs in the converters seemed to interpret the signal on their own. In a pleasant way, but probably less real. And that was a real surprise.

I cannot imagine the UD384 without the U Power PSU. With the wall wart unit it sounds properly, but we cannot talk about anything else than hi-fi. With the U Power everything is more natural, you can listen to this better. Such system can be regarded as interesting, with a clear character. But I do not think, that it is much more than for example the rDAC from Arcam. I know, I know – we get the opportunity to play 32 bit files and very high sampling frequencies. But in my opinion this does not justify the advantage of the rDAC, even when its USB input handles only 24/96.
Things are different, when we use the UD384 as a DDC. I would maybe not resign from USB inputs in good DACs, but I would listen, if this would not be a better sound, more dynamic, stronger and more resolved. The slight warmth in the lower octaves disappears, which appeals to our need for analog sound in the asynchronous USB inputs from other manufacturers. But for that we get true bass, better defined and more dynamic.


The KingRex DAC was tested using the computer HP Pavilion dv7 with a dual core processor, 320 HDD, 2GB RAM, Windows Vista and software – foobar2000 and JPLAY. The signal from the computer was output using the cable Acoustic Revive usb-5.0pl.
The comparison was made in A/B/A mode, where A (the reference) and B (tested device) were known. The music samples had a length of 2 minutes each. The UD384 was tested in asynchronous mode.


Both KingRex devices, so the UD384 and U Power, are small boxes, the size of a large cigarette pack each. They are made very solid, using aluminum elements. The sockets are on two sides – on one side we have the USB input type B, with a yellow LED signaling power on and a socket for the power supply, 7.5V DC. The power supply is a small, wall-wart type unit. On the other side we have the outputs, three RCA sockets – two are the analog, unbalanced output, and one is the digital S/PDIF one.
The circuitry is mounted on one high quality PCB. Everything looks good here – from the aluminum chassis, through descriptive writings to electronics. Interestingly the PCB is marked UC384 and not UD384.
The electrical circuit is fairly simple – behind the USB input we have a large DSP chip without any markings on it. The Taiwanese company Tenor (TE7022) and the American Texas Instruments (TAS1020) use the same package for their converters. Here we can see, that this is just a DSP, which was programmed by the company itself. It seems, that the DAC is also integrated in that chip. From there the signal goes to a chip with removed markings. Before the digital output there is a very good coupling transformer PE65612NL, which guarantees true 75Ω impedance on the output and decouples the digital from the analog outputs. The company writes, that those outputs can be used at the same time.
Attention is drawn by the splendid passive elements, like the worked out power stabilizing circuitry, discrete, using transistors, where we have nice Nichicon capacitors, precise resistors, polypropylene capacitors from Wima, and most of all, an expensive, thermally and mechanically compensated word clock. It bears a KingRex logo, but it is a TCXO clock with a 1ppm jitter. Fantastic!

U Power is fit in exactly the same chassis as the UD384. On one side we have the input socket for the external power supply and the switch between charging and playing directly from battery, and on the other side we have two outputs and two LEDs – a blue and a green one. When we switch to “playing”, then the power supply is cut minimizing noise. One output, 7.5V is destined to power the UD384. The second one, using USB type A is 5V. There are two 3.7V batteries used, connected in series, which give 7.4V, so before this output additional filtering circuit could be used, improving the signal-noise ratio. One LED signals charging, while the other power being drawn by an external device.
Inside we have a filtering circuitry and a battery charger. The battery consists of two Sanyo Li-Ion batteries 7.5V/2600mA. The switch I mentioned operates a relay. A nice, clean work.
On a sheet added to the PSU the company states, that during charging, the chassis can get as hot as 50°C, because it works as a heat sink for the batteries and stabilizers.

Technical data (according to manufacturer):


  • device: asynchronous DAC 32/384 and USB-S/PDIF 24/192 converter
  • inputs: 1 x USB
  • outputs: 2 x analog RCA, 1 x digital S/PDIF
  • accepted sampling frequencies: 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, 192 kHz, 384 kHz (384 kHz only when working as a DAC)
  • accepted word lengths: 16, 24, 32 bits
  • input USB: 2.0 High Speed
  • two working modes – synchronous and asynchronous, switchable in DFU Tool
  • power supply: 7.5V/250mA
  • dimensions: 110 x 82 x 24mm

U Power:

  • device: battery power supply
  • outputs: 2.5 mm DC/7.5 V + USB A/5 V
  • battery: Sanyo Li-ion
  • capacity: 2600mA/h
  • indicator for low battery power
  • switch charging/power supply isolating the powered device from mains
  • separate charging of each of the two batteries
  • power supply: 7.5V/250mA
  • dimensions: 110 x 82 x 24mm


  • CD player: Ancient Audio Lektor Air V-edition, review HERE
  • Phono preamplifier: RCM Audio Sensor Prelude IC, review HERE
  • Cartridges: Miyajima Laboratory SHILABE, review HERE), Miyajima Laboratory KANSUI, review HERE
  • Preamplifier: Ayon Audio Polaris III [Signature Version] with Re-generator Power Supply
  • Power amplifier: Soulution 710
  • Integrated amplifier/headphone amplifier: Leben CS300 XS Custom Version, review HERE
  • Loudspeakers: Harbeth M40.1 Domestic, review HERE
  • Headphones: Sennheiser HD800, AKG K701, Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro; 600 Ω version, review HERE, HERE, and HERE
  • Interconnect: CD-preamp: Acrolink Mexcel 7N-DA6300 (article HERE, preamp-power amp: Acrolink 8N-A2080III Evo, review HERE
  • Speaker cable: Tara Labs Omega Onyx, review HERE
  • Power cables AC (all equipment): Acrolink Mexcel 7N-PC9300
  • Power strip: Acoustic Revive RTP-4eu ULTIMATE
  • Stand: Base; under all components
  • Resonance control: Finite Elemente Ceraball under the CD, Audio Revive RAF-48 platform under the CD and preamplifier
  • Pro Audio Bono platform under Leben CS300