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DAC + headphone amplifier/preamplifier
KingRex UD-1 Pro + HQ-1

Price: 269 + 590 euro

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


Manufacturer's webside: Kingrex

Text: Wojciech Pacuła
Pictures: Wojciech Pacuła
Translation: Krzysztof Kalinkowski

KingRex is a brand of the company Kingrex Technology Co., Ltd. from Taiwan. Many splendid, albeit small, companies working in the computer branch come from there. They manufacture high quality accessories for our computers, like DACs with USB inputs, headphone amplifiers, miniature amplifiers, etc.
I have run across this company by coincidence, due to a banner on “”, so I approached the test without any prejudice – I knew only the price of their products. And I received two for testing – UD-1 a DAC with USB input and HQ-1 “Headquarters” line preamplifier/headphone amplifier.
Both units are well made and nicely looking, but the DAC has a more attractive fascia. As it turned out, the amp can also be ordered in the better looking version – the front can be milled just as the DAC, and in addition it can be anodized red. Also the rest of the cabinet will be nicer, varnished high gloss black.


Discs used during the listening session:

  • Stereo Sound Reference Record. Jazz&Vocal, Stereo Sound, SSRR4, FLAC.
  • Tron Legacy, OST, muz. Daft Punk, Special Edition, Walt Disney Records, 9472892, FLAC.
  • Cassandra Wilson, Silver Pony, Blue Note, 29752, WAV.
  • Depeche Mode, Hole To Feed/Fragile Tension, Mute Records, CDBONG42, WAV.
  • Donald Byrd, The Cat Walk, Blue Note/Audio Wave, AWMXR-0009, FLAC.
  • Linda Ronstadt, What’s New, Elektra/Lasting Impression Music, LIM PA 046, FLAC.
  • Norah Jones, …Featuring, Blue Note, 09868 2, FLAC.
  • Santana, Abraxas, Columbia/Mobile Fidelity, Collectors Edition, No. 06452, UDCD 775, FLAC.
  • Suzanne Vega, Close-Up, Vol 1. Love Songs, Amanuensis Productions/Cooking Vinyl, COOKCD521, WAV.

The recordings were made from CDs I own, and were ripped using dBpoweramp in AcurateRip mode, and played by Foobar2000 v1.1 from a laptop Hewlett Packard Pavillion dv7, OS Vista, 320 HDD, 4 GB. The signal went through the Acoustic Revive USB 5.0 PL cable, where the signal and power are guided through separate cables.

Japanese versions of the discs available on CD Japan.

UD-1 Pro

I started the session from plugging the UD-1 DAC into my system. From the moment I saw its technical specification I was skeptical about it. This because I always hunt the usage of old type USB receivers and converters, handling only 16 bits and 44.1/48 kHz, in all kinds of DACs, players, amplifiers, etc. Those are usually really old Burr-Brown chips. My battle is related to the potential offered by high resolution files, in which I see the successor of the Compact Disc. I think as follows: why all this ado about the digital media, when we only change the form of archiving, and this to a worse one? If we are to change anything – we should opt for better – this is why I think, that converters handling 24/192 are a minimum, also in terms of USB transfers (optimum would be 32 bits and 384 kHz – those are parameters of the professional DXD recording). And it is not that there will be a lot of such recordings available in a moment – this will for sure not be the case! But I think, that closing us for those formats upfront will not lead anywhere. Do you remember DVD-Audio? When this format would be implemented in all DVD players, we would have many good hi-res recordings more right now. And as it was not – we have what we have, it is too late to change it.

As you can see, the UD-1 is a DAC with a single USB input (this is why this subgroup of DACs is usually called “USB DAC”), handling 16-bits signal with 48 or 44.1 sampling frequency. Even more – the Burr-Brown chip PCM2702 is not only the USB receiver, but acts also as the converter chip. And it is a 16/48 converter!!! – It couldn’t be worse. That is what I thought.
Then my opinion about KingRex started to evolve. First I took a look at its mechanical construction, which impressed me with solidity, used materials and common-sense approach. And it also looks nice, with the backlit logo. Then I took a look at the circuitry inside. And this puzzled me a lot. The heart of the unit was still the Burr-Brown chip, no changes there, but it was used in a way, that amazed me. First the power supply: splendid, much better, than anything we can find even in very good DACs, like the Arcam rDAC or Musical Fidelity V-DAC. Equally important is the clock – a fantastic piece used in hi-end CD players, where cost is no limit. Can you see, where I am hinting at? This should be clear, although before listening, this was only a feeling.

Almost all USB DACs using the Burr-Brown chip I heard before (and I heard a few dozen of them) sounded like trash, or close to that. The main sin was lack of dynamics (my bones were cracking!), washed out colors, no emotions and finally disastrous resolution. A notable exception was the DAC Pro-Ject USB Box FL, which used four (!) separate DAC chips, the NOS Philips TDA 1543. But I think, that it only confirmed the “trash rule”. And because the UD-1 does not use other DAC chips, I was not sure, what I am going to hear.
Let me put it this way: this DAC connected to a computer with CD quality files sounds better, than a large amount of stand alone CD players, even expensive ones. I know what I just wrote – I gave it a lot of thought. But I am not afraid of that statement – KingRex is a company, with which I was never in any business relationship, there is no banner on my site, I do not know anyone there, so even for the conspiracy theory fanatics, the case should be clean. It is just good, and good things should not go unnoticed.
The sound of the UD-1 is extremely saturated. Only twice in my life, with Wavelength DACs I heard sound from a PC built that way. This was a saturated, dense sound. Dynamic and with a splendid tonal balance. This was not an ideal, I will tell about some deviations later. But that what reaches us from the loudspeakers tells a lot about what can be achieved with good, well thought power supply and precise clocking.

The first disc was the Silver Pony Cassandra Wilson, and I was “bought” after listening to it. The sound was fluent and satisfying on each level – intellectual and emotional. Wilson’s voice was a bit higher than in my CD player (Ancient Audio Lektor Air), what made me think for a while, that the computer-DAC combo sounds better. This is not true, but this incident shows the direction I am going. Silver Pony is a warm recorded disc, with a low recorded voice, typical for Cassandra. This is why it sounded so good right from the start. The situation repeated then with Abraxas Santana, where his guitar sounded plain brilliant, and finally with the disc Live Sara K. (although I get bored with her discs, this one I appreciate – the longer I listen to it, the more...). With that kind of repertoire we will have an almost hi-end sound. The tonal balance is shifted towards lower midrange, and the treble is recessed. Not too much, to a lesser extent than in the mentioned Pro-Ject, but it is back. Lower bass is fleshy, but not so well controlled. So most of the sound we can love is in the middle of the spectrum.
The sound is not very resolved, but this was nicely masked with saturation of the timbre. It is very strong; this is not a delicate, pastel sound, but rather a picture with strong basic colors, a very energetic one. Anyway, this not so outstanding resolution manifests itself in slight flowing together of virtual sources and only a mediocre precision of placing them on the sound stage. The shapes of the instruments are also not well distinguished, but here the timbre makes it seem better than in better resolving devices.

UD-1 Pro+HQ-1

So I sat down to listen to the headphone amplifier HQ-1 (I did not test it in the role of a preamplifier). With the Sennheiser HD800 I heard that the sound stage was narrower. The amplifier showed this characteristic of the DAC nicely, but added also a lot of treble to the sound. In general, the upper midrange and a part of the treble are strong here. Maybe this was done to balance the creamy sound of the DAC – but this is just thinking loud. However with Sara K and Cassandra Wilson it was heard, that the accents were placed higher, round 1 or maybe 2kHz. The voices were clearer and stronger, than when I listened to the UD-1 with my Leben CX-300 X(S) Limited Edition.
Still the high culture of the sound was well kept, as was coherence. The bass was condensed and – for my taste – a bit too light. This is the reason, that the rest of the test was done with headphones, which fared much better with the KongRex – the AKG K701.
With the AKG the sound had a lower timbre, and the upper midrange was not so audible anymore. You could listen with pleasure and comfort. But still I lacked some of the dynamics and saturation, I heard from the UD-1 when hooked up to my system. This is why I changed the headphones once again. This time, those were the – HL-5 from the company HiFiMan.
Those are difficult to drive rotodynamic headphones. Ha! This was exactly that, what the HQ-1 was waiting for. It powered the headphones without a problem and the timbre and resolution were finally as I thought they should be. This was still not the vividness I know from the Leben, there was no low bass, but – for the money – it was superb!

Both the devices are fully worth their price and more. The headphone amplifier needs some more activity, but it can also be upgraded with a battery power supply SLAP!, also offered by KingRex. It was really good. But the UD-1 was the device that SURPRISED me. Splendid, saturated sound, good dynamics and timbre. The only problem being, that it cannot decode high resolution files. You can play such files of course, but the computer will detect the capabilities of the USB receiver and downsample them to the 16/48 format, in which they will be sent to the DAC. But when we listen to CD quality material only, or mp3, then it will be difficult to find another DAC in this price range (maybe with the exception of Audinst HUD-mx1, albeit also with some comments), which would sound satisfactory.


UD-1 Pro

The DAC is small, but it has a splendid, aluminum, milled front panel. It has a laser cut logo, which is backlit – the whole logo is blue, while the last letter “X” is red or blue, depending on the status of the input (active – not active). Besides that, the fascia is clean. On the back plate there is also not much to be found – there is one USB 1.1 port, type B a pair of gold plated RCA terminals and an IEC power socket integrated with a power switch and fuse.
The electronic circuitry is mounted on one PCB – 2/3 of the cabinet is taken by the power supply. It is based on a large toroidal transformer, with resin damped insides, and with two 16V secondary windings. Those are used to supply symmetric voltage to the analog output stage. The voltages are separated, have separate rectifiers, stabilizers and filtering capacitors – 8 pieces, 2200μF each, what is absolutely unique in such devices.
In the digital section, the main chip is the Burr-Brown PCM2702. This is an old, 16 bit 48/44.1 kHz IC. Next to it, there is a pure beauty – big, temperature and mechanically compensated clock TCXO 12 000 MHz. The I/V conversion happens in a single chip, which houses also a low-pass filter, and at the end, in the buffer there are two more ICs. All the chips are placed in sockets, and have covered markings. However, from other sources we know, that those are: Burr-Brown OPA2604 as the filter and 2x Texas Instruments TL072 in DC-servo. The whole circuit is very well made and really worked out, given the price of the unit. There are even Pi filters at AC power input.

Technical data:
Input: USB 1.1
Input signal: 16 bits/44,1 and 48 kHz
Dimensions: 110 x 75 x 33 mm
Weight: 207 g

HQ-1 „Headquarters”

HQ-1 is a headphone amplifier/preamplifier. It is housed in two enclosures – one with the amplifying circuitry and one with the power supply. They are small, and their fronts are made from thick aluminum. My version had a classic black fascia, without milled logo, however I saw on the company page, that there is a splendid looking, red version available, milled just like the DAC. Attention is drawn by a nicely looking, steel volume control knob, which can be found in many Taiwanese products, like the Furutech DAC. Most probably the manufacturers use one supplier, or KingRex is making OEM products for other manufacturers. In the middle there are two blue LEDs. One signals activation of the RCA output, lighting up, when the unit is in preamplifier mode, and the other one is active, when we select the headphone amplifier function. Between them, there is a switch, looking similar to the LEDs. To the left, there is a gold plated headphone socket – “big jack”, 6.3mm.
On the back we have a pair of RCAs on the input side, a similar pair on the output and a gold plated XLR socket from the Swiss Neutrik, which provides power from the external power supply. The circuitry is mounted on one PCB, which covers the whole bottom of the unit. The signal runs from beginning to the end in dual-mono topology. From the inputs the signal runs to the front, to a large Alps “Blue Velvet” potentiometer. Then it is initially amplified in small transistors, and later we have large transistors, bolted to heat sinks - K214, MOSFET, a pair per channel, single-ended. Those are coupled with the outputs via large Wima polypropylene capacitors. The switching between preamplifier and headphone amplifier mode is done in a sealed relay from Takamisawa. The resistors are high grade, just as the capacitors – the polypropylene and the electrolytic ones. p>

The power supply is similar to the amplifier. On the fascia there is only one blue LED, on the back a XLR socket from Neutrik and an IEC socket with a mechanical power switch. Inside there is a large, solid toroidal transformer with a single secondary winding. The voltage is rectified in very large rectifying diodes and the stabilized in the integrated stabilizer JM85RS National Semiconductors, bolted to a large heat sink. Then we have three filtering capacitors with a capacity of 4700μF each and five smaller ones – 2200μF each. It really looks splendid. The power is sent to the amplifier using a short, shielded cable, terminated with expensive, solid, gold plated Neutrik plugs. When needed, this cable can be exchanged for a longer one – we will find them in any music instruments store.

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



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  • Loudspeakers: Harpia Acoustics Dobermann (tested HERE)
  • Headphones: Sennheiser HD800, AKG K701, Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro, 600 Ω version (reviewed HERE, HERE, and HERE)
  • Interconnect: CD-preamp: Acrolink Mexcel 7N-DA6300, article HERE), preamp-power amp: Wireworld Platinum Eclipse
  • Speaker cable: Tara Labs Omega Onyx, tested HERE
  • Power cables AC (all equipment): Acrolink Mexcel 7N-PC9300
  • Power conditioning: Gigawatt PF-2 Filtering Power Strip (reviewed HERE)
  • Audio stand Base – under all components
  • Resonance control: Finite Elemente Ceraball under the CD (article HERE)
  • Pro Audio Bono platform under CD