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Positive Feedback ISSUE 61
may/june 2012


The KingRex UD384: Music in a Tiny Box
by Andy Schaub


"Go west
paradise is there
you'll have all that you can eat
of milk & honey over there
you'll be the brightest star
the world has ever seen"

—Natalie Merchant, "San Andreas Fault"

So, a while back I asked Drew Baird at Moon Audio if he had any 24/192 capable USB DAC's with balanced output for under $500 that I planned to use at work with my Blossom headphone amp and Denon 5000 cans. Sadly, he said no; however, he did say that if I was willing to go unbalanced only and give up certain features like lights indicating what sampling rate the DAC was processing, the KingRex UD384 was rather remarkable in that it could go to 24/192. In fact with a soon to come firmware update it could go up to 32/384 and also process DSD files. The basic unit was around $500 and he could send along—on a trial basis—some nifty accessories; like the matching KingRex power supply that replaced the paltry wall-wart supplied by default plus, and this is the really cool part, a battery-based power supply that guaranteed full isolation from unsightly AC.

Now with my PS Audio Power Plant 10 and my triple stack of Equi=Tech balanced transformers, I have pretty damned good power; but full isolation from the AC line? That was just too good to be true. In any case, I took the KingRex into work and played it through the "UNBAL" input of my Blossom headphone amp using just the wall-wart plugged into a Power Wedge 112. My point of comparison was the similarly priced—but balanced—HRT Music Streamer Pro (which only goes to 24/96). I immediately noticed warmth to the KingRex that Music Streamer Pro lacked. Did that mean the KingRex sounded bloated? No, not really. It just sounded warmer and rounder, a little more tube-like, which is pretty amazing for something that (a) costs about $500 and (b) is definitely about as far from tubes as you can get. At first I thought I heard the occasionally ticking or popping sound; but Drew assured me that he had just used this exact UD384 himself without any problems and I did discover over time that the popping was an anomaly, perhaps something in the recording (a 24/96 download from Channel Classics) or maybe sunspots; but it wasn't really reproducible. So the unit was sound (so to speak).

After a day of listening at work I decided I had to bring the UD384 home and hook it up with a real power supply in my digital music server in lieu of my Sonicweld Diverter HR, Locus Design Core S/PDIF cable and original Berkeley Audio Design Alpha DAC. Now I'm not going to tell you the little UD384 with a real power supply (also made by KingRex) blew me out of the water. It didn't. It lacked some of the air and ambience of my reference system; but my reference system is actually pretty pricey, so the fact that I could listen to the UD384 at all actually impressed me quite  a bit. Sample albums included Le Pas Du Chat Noir by Anouar Brahem at 16/44.1 and Lonely Woman by The Modern Jazz Quartet at 24/192 as well as Little Broken Hearts by Norah Jones at 24/44.1, all of which performed quit admirably for a USB-based DAC that now was in the $1K range (with the external power supply). Although the treble remained sweet, there was a tendency to overload my amp a little creating trace amounts of distortion, a forgivable sin but something that might best be dealt with by some inline attenuators since the UD384 has no adjustments.

kingrex ud384

Just when I thought I had pretty much concluded everything I could about the basic sonic signature of the UD384, I remembered the battery power supply, so I charged it up and connected it. Listening again to the 24/192 version of Lonely Woman I noticed a greater sense of midrange "air" and a slightly sweeter treble plus slightly—and I mean ever so slightly—less distortion. I played most of the 24/96 version of Tigerlily by Natalie Merchant and I will say that the percussion was dead on. Somehow, and this was just me farting around with iTunes folks, a track from Little Broken Hearts snuck in there; and it sounded great. Then back to more Tigerlily which played quite admirably. So the battery seemed like the best way to go; but I still had to experiment with some other features of the UD384, like processing DSD files and seeing if it could handle ultra-high resolution tracks.

Since I had no DSD files (with the extension .dff), I bought an album from Channel Classics, specifically Rachel Podger playing the Mozart Violin Concerti, Sinfonia Concertante with the Orchestra of the Age of Enlightenment under Pavlo Beznosiuk. It also included some work by Haydn. I decided that rather move the files onto my main system, I would move the KingRex to my backup system consisting of Tri TRV-88SE with a pair of Micropure minimonitors and an Essex 12" subwoofer. It would simplify the comparison and I could play it in a system more likely to be a match for the type of system the UD384 would find itself in. Since these files are a little different, I had to play them directly from Pure Music, bypassing iTunes. The cables were Audio Note AN-Vx interconnects with Eichmann Silver Bullet plugs and copper Audio Note Lexus speaker cables in a bi-wired configuration.

Again, I used the battery pack both out of convenience and because I found it had the best sound quality in the main system. Unfortunately, I had some technical difficulties getting Pure Music to play the .dff files through the UD384. Mostly I heard pops and ticks with no music; so I wrote to Channel D, the makers of Pure Music, and asked them for help. In the interim, I was able to perform a side by side comparison of the battery-powered UD384 against the AC-powered Rega DAC using an Audiophilleo 1 with a Locus Design Core S/PDIF cable, in both coming from a Locus Design Axis USB cable all from a 27" Quad Core iMac modified to boot off of an SSD. I only played a few bars of the 24/192 download of Bill Evans' Waltz for Debby and realized that the treble from the Rega DAC really was much sweeter with much more air and ambience; however, we're talking about over $2K of equipment in comparison to under $1K for the KingRex with the battery; and I hadn't given up on DSD yet.

So Monday morning comes and I contact Channel D who kindly takes over my iMac and sets up Pure Music to do DSD straight through to the DAC. It's a little complex but covered in the documentation; the bottom line is that we just couldn't get it to work unless we let Pure Music do conversion to PCM and not play my .dff files as pure DSD, which I later confirmed with Drew Baird was the only way it would actually work. So—technically speaking—the UD384 does not support straight playing of DSD files. Normally I would say something like, "serious bummer"; however, the sound of the .dff files converted to PCM at 88.2kHz was really quite heavenly in my office system, which has a very critical pair of mini-monitors. It had a purity and liquidity that I had not heard from the UD384 yet. And, that, my friends is when things started to get fairly amazing.

I am sitting here at my 27" Quad Core iMac (yes, the one with 16GB of RAM and a boot SSD) and am happily listening to Rachel Podger and the Orchestra of the Age of Enlightenment play Mozart and Haydn with this sweet, melodic sound coming from Pure Music's DSD to PCM conversion at 88.2kHz. And I have to say, there's nothing that bothers me about the sound at all. It's liquid and almost tube-like. And there's neither the slightest trace of distortion nor hint of digital grunge. So is it Pure Music or the UD384? I would say, under the circumstances, the answer is yes. Out of practical necessity, I had to go back to the Audiophilleo 1/Core/Rega DAC combination. And you know, while the treble was a bit purer, I missed the warmth of the UD384. And it's not like I have only the mini-monitors. There's a 12" Essex subwoofer hooked into the system. So I would say that when it all was said and done, I really enjoyed the sound of the UD384 with the battery pack and while I quickly acclimated to the Rega DAC again, I wanted to turn up the subwoofer a bit. Sadly, the time had come to return the goods to Drew, so I finished listening to Mozart and Haydn with greater resolution for sure, but perhaps with slightly less fun.

Kindest regards,