Kingrex UD 384 DAC and UPower Li Ion Power Supply

$479 for UD 384, $189 for U Power


Dr. John Richardson


I’m always amused at companies that have funny names.  You know, catchy, but funny at the same time.  To me, Kingrex is such a company.  If my Latin is correct, rex is the word for king or ruler, so what we have here is a company that’s really named Kingking, or maybe king squared.  Either way, Kingrex, based in Taiwan, has been around for more than a few years, and as I found out from their website, have covered a great deal of ground in the electronics industry, with products ranging from liquid crystal displays and gaming systems to consumer audio.

Kingrex should also be no stranger to readers of, as one of its products, the T20 Tripath integrated amplifier, spent some time in Publisher James Darby’s home a couple of years ago.  Noteworthy was that in his own comparisons, Brother James found it to best the erstwhile Trends TA integrated, which itself was the winner of the famed Stereomojo Integrated Amplifier shootout.  Quite an accomplishment, I do say.

Here for review we have the newest products in the Kingrex family:  the UD 384 DAC ($479 USD) and its sidekick, the UPower Li Ion battery power supply ($189 USD).  Together, these components theoretically offer a formidable combination:  a DAC capable of decoding native files at mind-boggling 384 kHz/32 bit resolution along with a dead-quiet DC power supply.  To boot, the combination costs $668 USD, putting it squarely in Stereo for Cheap Bastards territory.  I don’t know about you, but cutting edge technology like this at Cheap Bastard pricing gets me pretty worked up.

Within a week of finding out about the opportunity to review these little buggers, a small shipping bag from Taiwan showed up at my door.  I might have missed it if I hadn’t been looking for it.  Inside were two even smaller boxes containing (separately) the DAC and Li ion battery power supply.  Once out on my desk, I was somewhat taken aback at how small these things were!  I had read another reviewer report that a Kingrex DAC could fit handily in his “fag pocket,” which I take to be a very Brit way of saying that the DAC was about the size of a pack of cigarettes, or maybe a deck of playing cards.  The UD 384 was possibly a tad larger, but not much.  Ditto the UPower unit, as it’s housed in the same extruded aluminum case.  All in all, these little guys reminded me at first glance of toys, not serious audio components.

I was eager to find out if the UD 384/UPower combo would actually live up to the high expectations given its impressive technical specifications, as well as the track record of its cousin, the diminutive, but stellar performing T20 amplifier.  I got the UD 384 working right away, burning in using its optional wall-wart power supply.  As with most other components, I chose not to listen critically to the DAC for several days while it underwent the business of break-in.



A few points are worth addressing here from a usability standpoint; There’s only one way to get a digital signal into the UD 384, and that’s with a computer using a USBcable.  That’s right: USBonly.  On the output side, you get two choices.  First, there are analog outputs from the internal DAC, which consist of two gold-plated RCA jacks.  Also available is a single S/PDIF coaxial output, again in the form of an RCA jack.  That means the UD 384 will also function as a high-resolution USBto S/PDIF digital-to-digital converter for those who would like to use it to link a “legacy” DAC to the digital output of a computer.  Fortunately, I found myself in a good position to evaluate both output options, as we shall see.

The UPower unit was a similarly simple device to set up and use.  It has an umbilical that attaches to the UD 384 to provide a nice, steady DC voltage, while the UPower itself is fed from a separate wall-wart when it is in its charging cycle.  There is a simple toggle switch on the front of the unit that lets the user choose between charging and output cycles.  On the rear of the UPower chassis is a USBoutput, presumably to power other devices that might normally be powered via USBdirectly from a computer.   In practice, I just toggled the UPower to its charging state any time I wasn’t listening to the DAC.  That way, it was always ready to go when I was.  The unit is also equipped with a blue LED that illuminates when in the charging mode; very helpful when I was too lazy to look closely at the toggle switch to see what mode it was in.  I found that the UPower got warm to the touch when it was charging, but cooled off quickly again when the blue LED went out, signifying a full charge.  The unit is meant to stay plugged in at all times, as the Li ion battery is electronically isolated from the charging circuit when it is powering the UD 384. 

Given that the UPower and the UD 384 are meant to go together as a couple, all of my critical listening was done with both components in the audio path.  I’ll mention that I never ran out of “juice” while using the UPower during a listening session.  In fact, I accidentally left it on one night, and it was still going strong in the morning when I checked on things.  That the UPower gives a clean DC output is unquestionable, as seen in the oscilloscope traces in which the UPower (bottom) is compared to a competing non-battery supply (images provided by Kingrex).

For all listening tests, my normal system was used.  On the digital side, this consisted of a Mac Mini using iTunes driven by the excellent Channel D Pure Music application.  Coincidentally, Kingrex recommends Pure Music specifically for users of its DACs.  From the DAC/Power supply combo, the analog signal was fed to a Wyetech Coral preamplifier, and from there to my Threshold SA/3.5e amplifier running my main speakers (Shahinian Compasses) and to an ODL HT-2 amplifier driving my Shahinian Double Eagle subwoofer.

My initial listening was done using the UD 384 as a USBDAC, in concert with the excellent (but affordable) Virtue Audio USBcable.  I was immediately impressed with the overall smoothness of the DAC output, feeling that I could listen to it for long periods of time with no apparent fatigue.  My only complaint was the occasional audible “click” or “pop” that I have sometimes heard before when testing certain computer-based DACs.  Typically, this sort of thing signifies momentary loss of lock on the digital bitstream, causing an audible hiccup.  I ended up re-booting my computer at least once daily, especially prior to a serious listening session, as this operation seemed to reduce the regularity of these intrusions; it also just plain makes the music sound better.  Otherwise, there were no drop-outs or other nasties to deal with.

The audible smoothness of the UD 384 was not a surprise to me, as it is said to operate in the asynchronous mode, meaning that its internal clock controls the rate of data transfer at all times by slaving the computer’s clock.  Such an approach is reported to greatly reduce audible jitter when launching bit packets from a computer’s USBport to the DAC.

I spent time listening to all sorts of music via the UD 384’s DAC, but ended up putting together a representative playlist for critical evaluation, and also to make relevant comparisons with other DACs.  What follows are the contents of the playlist, all ripped from original vinyl pressings (by me) at 24/96 resolution:

The obvious DAC that I had in-house to compare with the UD 384 was the original Eastern Electric Minimax DAC, which when still available retailed for $750 USD.  All comparisons were made using the solid-state output of the Minimax, as I felt the tube output might add coloration, making the comparisons less valid.  I also decided that through this comparison, I could kill two birds with one stone.  Remember that the UD 384 will also serve as a USBto S/PDIF converter, so I connected the Minimax to the UD 384’s S/PDIF coaxial output using Signal Cable’s affordable 75 ohm digital interconnect.  I was therefore able to switch between both DACs “on the fly” by just switching the selector knob on my Wyetech preamp.

When reading the comparisons between the Kingrex DAC and the Eastern Electric DAC, one must be reminded that every Stereomojo reviewer who has heard the Minimax agreed that it is one of those few components that manages to punch far above its weight class; it was indeed one of the real bargains in high end audio.  Recall that it finished second in our own DAC shootout just behind the Level 4 Lampizator DAC, which is a cost-no-object, no-holds-barred design.  That said, I was fairly amazed at how well the diminutive UD 384 DAC compared across the board, especially given that it is limited to USBinput, which was something of an Achilles heel for the original Minimax.

Switching back and forth between the two DACs showed very little audible difference in the jazz cuts listed above.  If anything, the UD 384 came across as a bit darker and softer, or rounded about the edges.  There wasn’t quite the same razor-sharp definition of instruments in space that I heard with the Minimax.  However, the UD 384 presented as good a lateral and depth-wise soundstage as the the Minimax.  Definition was lacking in ever so small a way with the Kingrex, with a slight veiling or hooding of cymbals or maracas.  Instrumental timbres were excellent, with plenty of harmonic layering; both DACs did a more than respectable job in this area.

One potential “problem cut” for many components is the MJQ cut “All of You,” (cut #3) which features Milt Jackson playing very closely Mic’d vibes that were also mastered quite hot.  With a lesser DAC, the vibes can get irritatingly lively, taking way too much of a front seat position in the soundstage.  While one can easily discern the recording/mastering technique here, the UD 384 never let Milt’s vibes go over the top to the point of irritation.  If anything, I’d say the UD 384 did a slightly better job of taming the recording than the Minimax did.

On the Brand x (cut #4), there are lots of spatial cues that jump out of the soundstage, seemingly from all directions.  Both DACs did a very nice job of discerning all of the business going on within the highly complex soundstage presented by this recording.  Predominant in the cut is Percy Jones’ electric bass, which with the UD 384 just hung in space between the speakers, as if by magic.  However, I give the nod to the Minimax for providing a slightly better defined sense of attack and crispness to the bass, which Jones plays as if it were a lead guitar, knocking out complex riffs that to me defy explanation.  This is a not a place for even a slight sense of wooliness or over-ripeness.

Moving on to classical, I found the warmth of the UD 384 to pay dividends when listening to string passages.  Both solo and massed strings were presented in a satisfyingly lifelike manner that I found both highly engaging and easy to listen to over the long haul.  In contrast, the Eastern Electric DAC may have added a bit more body or sheen to the upper registers of the violins and violas that brought them slightly more to the forefront of the recording.  Put another way, I think the warmth of the UD 384 may contribute to a slight dulling of the string sound, casting it in a bit of a constrictive aura.  A specific classical cut that I have used to ferret out differences between the two DACs is Sir William Walton’s “Cappricio Burlesco” (cut #6), in which the orchestra is more distantly mic’d than in other Lyritas I own.  Here, the orchestral forces are laid out in array well behind my speakers with the listener feeling more like he is seated in a rear balcony than in a front row center orientation.  The overall sense is more of a blending of sound with some hall reverberation, thus making it harder to pinpoint individual events taking place in the soundstage.  While this cut is very satisfying to hear via the UD 384, I got more out of it listening through the Minimax thanks to its more incisive nature providing the sense of detail that this particular recording demands.  With the Minimax, the brass instruments burst out more readily during their fanfares, making the performance that much more exciting.

I wanted to finally try out the UD 384 with ultra-high resolution digital downloads.  This wasn’t such an easy task, as not much music is available for easy download at resolutions above 96 kHz.  I was able to download a few files from Norwegian label 2L’s digital test bench as 354 kHz DSD files.  These the UD 384 handled with aplomb, provided that the minimum sampling rate in Pure Music was set accordingly (forgive me please, as sometimes I can be a bit of a slow learner).  Ditto the excellent Reference Recording HRx series, of which I have a few examples, all at native 176.4 kHz resolution.  Again, the UD 384 was unflappable in its ability to handle these files.  Ultimately, I can’t say I hear specific differences between 176.4 kHz samples and 354 kHz samples attributable to the difference in the digital sampling rate; the differences I did hear arose more from recording and mastering choices on the part of the engineers and producers of these files.  However, I give kudos to Kingrex for engineering a “future-proof” DAC that can handle these ultra-high resolution files so easily, as ultimately they should become more accessible to interested audiophiles and music lovers as time progresses.

A few more words are in order regarding the UD 384 as a USBto S/PDIF converter.  In the end, I felt this application might well be the greatest strength of our little combo.  With the Eastern Electric Minimax DAC’s S/PDIF input fed from the UD 384’s digital out, I felt that I was getting all of the information I typically get from the Minimax when using my Metric Halo ULN-2 for the same purpose.  In short, the Minimax sounded as good as I have ever heard it sound.  The advantage of the UD 384 (besides its cost) is that it will pass higher resolution digital files (up to 24/192) than the ULN-2 will, thus opening the door to processing capabilities of the Minimax DAC that I haven’t been able to tap into up to this point.

As I finish up this review, I’ve been reflecting on how sometimes it’s a shame to have to compare products to their peers.  I know it’s necessary, as it gives readers an important point of reference.  I’m sitting here right now listening to a digital rip of an old Norgran monophonic record from the 1950s (just for my own pleasure, mind you), and it sounds just lovely through the Kingrex DAC/power supply combo, warts and all.  The sound is smooth, smooth, smooth, I feel relaxed, and it’s like the performers are here with me; I’m transcending time.  Even if a particular product isn’t     perfect, that doesn’t mean that it can’t be enjoyed, and greatly.  I’ve decided that the UD 384/UPower is just such a product.  I want to listen to it (or through it), as it gives organic meaning to the music it’s reproducing.

As an overall package, I can heartily recommend the Kingrex UD 384/UPower combo, especially at the combined asking price of $668 USD.  My initial inclination was to recommend it primarily as the digital heart of a desktop or office system, but over my extended time with it, I conclude that it is worthy of doing time in an audiophile main system, especially as a first-timer’s USBDAC.  There are a number of supposedly very good DACs at this price point (many of which I have unfortunately not had the opportunity to hear), but the Kingrex stands out with its battery supply option as well as its ability to process files at native resolutions up to 384 kHz.  I suspect that many listeners will also cotton to its small footprint, simple operation, and overall visual cuteness.  On the downside, the UD 384 doesn’t offer the interface options and other bells and whistles (e.g., headphone output jack) that many of the over $1000 DACs I have had in-house boast.  Nonetheless, I suppose that many users may not want to pay for all of that, wanting instead a simple, straightforward solution to the complex problem of coaxing bits from a computer and turning them into beautiful, meaningful music.


For all you cheap bastards out there looking to get into the fun of high-resolution computer audio, I can’t think of a better choice than the Kingrex UD 384/UPower combination.  On the pro side, it’s small, cute, versatile, and it provides a smooth, pretty sound you can listen to all day long without a hint of fatigue.  It also serves as as USBto S/PDIF converter that will let your favorite DAC (if you already have one) be seamlessly integrated with your computer so you can do the hi-res download/playlist thing that all the cool kids are doing these days.

There are very few negatives; the only ones I could come up with are the occasional popping sound I get when the UD 384 is interfaced to my computer, and also the fact that the DAC isn’t the last word in resolution compared to DAC's at higher price points.  But you really shouldn’t obsess about these things at this price point, as the Kingrex is more musical and enjoyable than it has any right to be.

 So, Kingrex, it looks like you have done it again.


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