Product name: KingRex UD-01 Pro.
Manufacturer: KingRex
Cost: 378 USD.

Reviewer: Nick Whetstone - TNT UK
Reviewed: February, 2011

If computer audio was something that audiophiles could once ignore, it's certainly getting much harder to do so these days. Despite reviewing a couple of new CD players this year, they look to me to be a dying breed, and the trend to look at some sort of computer audio source is growing rapidly.

I remember as a young man interested in hi-fi, that the choice for playing recorded music was fairly simple. You either had a record player, or a reel-to-reel tape recorder (no cassette tape in those days). Of course, the vast majority owned some type of record player or turntable, and for some that's where the simplicity ended, and the hi-fi addiction began. There was a vast range of turntables, from the cheap-and-cheerful ones based on the trusty BSR mechanicals, there were mid-range models, and of course, hi-fi being hi-fi, the exotic top-of-the-range stuff (that the likes of myself could only dream about). Then there was a choice or arms, cartridges and styli. And tweaks galore - even after you had spent weeks setting the damn things up optimally. Some, like Geoff Husband, have never recovered from this ordeal!

Then came the age of the CD. 'Perfect sound forever', or so we were told when it was launched. "Good!" I thought, if it's perfect, all players will sound the same and my anguish at never being able to afford those top-of-the-range-products will finally be gone, and I can really enjoy the music again. But that illusion was shattered the first time that I went to a hi-fi shop and auditioned a range of those new CD players. Then along came separate DAC's, higher-resolution formats, and of course a host of tweaks ranging from the infamous green pen, to the placing of the contents of water-filter cartridges around the inside of the CDP.

And then somebody said "why not use your PC to play music?" In fact I remember reading about such matters on this very site at the end of the last millennium (doesn't it seem a long time ago now?). Once again, I foolishly though that would put us all on a level playing-field. But it wasn't long before that dream too was shattered. Even in the beginning of computer audio, the choice was there. Internal sound card? No much better to have a breakout box and move it out of the noisy computer. Sound cards ranged in price from under 20 pounds to over a thousand, with a range of outputs to confound a rocket-scientist. Then came the USB DAC's, followed by music streaming devices such as the Squeezebox. Now there is talk of improved computer power supplies, special cables, special software, and all sorts of other tweaks to keep our search for that perfect hi-fi going on for another decade or so, until the next format comes along. So progress in one way or another never seems to remove that vast choice that the poor old audiophool has before him. And I suppose in one way that's not such a bad thing as at least it keeps the likes of we reviewers occupied and off the streets. But it does mean that the world of hi-fi is just as bewildering as it ever has been, perhaps even more so now for those who aren't technically minded. As such even more responsibility falls on the reviewer to help the audiophile through the endless jungle of products on offer.

All of which brings me (eventually) to the subject of this review, the KingRex UD-01 USB DAC. While the streaming devices such as the Squeezebox family, Sonus etc, offer probably the most convenient method of playing back music from a computer, there is no doubt that the main development appears to be happening with the USB DAC, at least going by the number that are on the market now. I was quite impressed by the first USB DAC that I reviewed, the cheap and cheerful Trends UD 10 back in 2006. Last year, it was the original KingRex UD-01 that showed me how much things could be improved, and the Item Audio special edition of the (KingRex) UD-01 took things even further, as did the Devilsound USB DAC (all in this USB DAC shoot-out). KingRex appear not to sit still for very long, and they have now introduced the UD-01 Pro, that is quite a bit more than a restyled UD-01.

The difference between the original UD-01 and the Pro version is obvious right from the start. The latter is built into a larger, thicker (6mm aluminium for the front panel) metal case. The larger case is to accommodate an internal linear power supply, that replaces the external SMPS type used with the original (replacing switched mode power supplies with linear types is a consistent trend in hi-fi at the present but may be halted by legislation to limit our increasing consumption of power). The Pro is still relatively diminutive (185 mm wide, 150 mm deep, 50mm high) even with the internal PSU added, and looks good with its illuminated name plate (back-lit in blue). When the Pro receives a signal, the 'X' turns red, a novel alternative to the almost obligatory (over-bright) blue LED. The rear of the case has an IEC switched mains socket, a pair of classy-looking gold-plated RCA sockets for audio output, and a USB 1.0 input socket. The case is still small enough, that combined with the build quality, it remains rigid, and therefore less likely to vibrate.

The Pro is still a 44.1/48 kHz 16 bit DAC but as most of our recorded material won't be of higher resolution, that will be fine for some years to come yet. Like the original UD-01, it uses the Burr-brown PCM2702E DAC chip, and provides dual-channel storage for improved internal buffering. It also has a low-pass filter and DC servo, designed by KingRex for its special output section. The UD-01 PRO also boasts an upgraded 1ppm TCXO clock to improve timing and reduce digital jitter. For those interested in the power consumption (and we all should be by now) it is an environmentally-friendly 5 watts.

The UD-10 Pro does not require any drivers (I mention that because increasingly, USB DAC's do now come with their own drivers) and it was recognized straight away by the Ubuntu operating system on my music PC. I simply had to select it as the output device, open up the music-playing software which in this case was 'Exhaile', and select what I wanted to play. I connected the output of the UD-10 Pro to the ONIX A55 amplifier that was connected to my modified Mordaunt Short Pageant speakers, and I was ready to go.

I had high expectations for the UD-10 Pro, having heard the original KingRex UD-10, and I wasn't disappointed! Detail was there in bucket-fulls. Bass was tight and deep. Clarity was excellent and I found on tracks where I normally have to try and hear the exact lyrics, that I could hear them with much less effort. Everything else was very good but I'll detail some of the things that I wrote at the time of listening.

Ennio Morricone, 'A Fist Full of Dollars' - the sound effects of the whips and bells were more realistic than I had heard them before.

Pink Floyd, 'Dark Side Of The Moon' - there was more 'presence' in the music, reminding me of listening to this album on vinyl. Deep tight bass. Drum hits more clearly defined. More 'breath' on the female vocals.

Van Morrison with John Lee Hooker , 'Gloria' - bass better defined, more space between Morrison and Hooker vocals, all vocals easier to perceive.

Talvin Singh, 'Vibraspace/Monsoon - bass tighter and deep, all elements better separated, control better when turning up volume.

Van Morrison, 'In The Garden' - Acoustic guitar strings better defined and with more 'polish', ie cleaner sounding, vocals more prominent, percussion clearer, some reverb that I hadn't noticed before.

John Denver, 'Take Me Home Country Roads' - More 'body' in Denver's voice, also sounding a bit deeper and stronger, great beat, clearer lyrics fuller presentation of backing, backing singers better defined.

Roger Waters, 'Amused To Death' - Q-sounds much more prominent, clearly defined, and further out from speakers into room. In 'It All Makes Perfect Sense Part 1' the piano appeared to be floating in space and further projected into the room, the deep pulsating beat was more prominent, all vocals much clearer.

Patrick Hawes, 'Tres Amores' - the individual vocalists in the choir much easier to pick out.

Rebecca Pidgeon, 'Fhear a Bhato' - wider sound stage than I remembered, lyrics clearer, violin placed further away from RP.

Beth Neilson Chapman, 'Angels By My Side' - More emotion in voice, piano notes better defined and 'fuller', drum beats better defined, everything better separated.

And so on. Now going back to the original UD-01, I listened to the same tracks again. Using a basic 12v SMPS with it, there wasn't quite the same level of sophistication. It was still very good but I would have no problem in saying that I just preferred the UD-10 Pro. Replacing the SMPS with a good 12v linear supply, it was much harder to be so sure, although ultimately, there is just that nth degree of extra detail and clarity from the Pro. The question then arises, is it better to go for a UD-01 at around 160 pounds, or the UD-10 Pro at 450 pounds? And that question is made even more difficult with Item Audio adding their own modified UD-01 into the mix as well at 225 pounds. Of course, we have to also remember that the Pro comes with its own linear power supply built in. If I take an example of a linear power supply from the Item Audio (KingRex UK distributor) site while I am on there, I (conveniently) find the KingRex PSU at 170 pounds. Assuming that is roughly the same thing that is built in to the Pro, it makes the costs as follows:

1. KingRex UD-01 (+external PSU) 330 pounds
2. KingRex UD-01 SE (+external PSU) 395 pounds
3. KingRex UD-01 Pro (PSU built in) 450 pounds

To make matters even more complicated, Item Audio are bringing out an SE version of the Pro (don't these people have any consideration for we poor reviewers?). But as regards the UD-01 Pro, it's another great piece of kit from KingRex. At the price, the UD-10's have been clearly the best USB DAC's that I have heard, although an audition with something much more expensive (that is the subject of another review) has shown me how much further these USB DAC's can be improved. Computer audio has certainly put the excitement back into the hobby for me, although I can sense the frustration of those of you who are still trying to come to terms with the concept of PC based audio, and are ever more bewildered with the increasing choice of equipment. If you are one of those people, take it from me that the UD-01 Pro is a very good USB DAC!

Product name: KingRex UD-01 Pro SE.
Manufacturer: Item Audio.
Cost: 575 UK pounds (900 USD) .

Reviewer: Nick Whetstone - TNT UK
Reviewed: February, 2011

Well, the SE version of the UD-01 Pro arrived before I submitted the original review so I decided to extend this review to cover that too.

Item Audio are the UK distributors for KingRex, and specialise in PC-Audio systems. They took the original KingRex UD-01 and successfully upgraded it, so it was logical that they would do the same with the Pro version. The upgrades for the Pro version include replacing the output opamps with discrete opamps produced by Burson Audio. The opamps in the servo circuit have been upgraded to OPA627's. The power supply has the diodes replaced with Schottky types. The light on the front panel has been disconnected (LED's produce some noise and leaving them out of a circuit can reduce the noise-floor). The inside of the case gets some Stillpoints RFI absorption treatment, and some copper-shielding, and the case itself, gets some damping in the form of bitumen sheet. Finally, the interconnects, a pure silver type, are hard wired to the unit, before the whole lot is cryo-treated. The idea with the IC's is that no connector, at any price, matches the sound quality produced by soldering the IC directly to the PCB.

So apart from the lack of illumination behind the KingRex badge, the SE version looks the same as the standard version (unless you look underneath to find some damping material on the base). As far as a PC is concerned, it is the same beast as the standard version, so simply plugging it in (in place of the standard version) meant that it was ready to play music.

I wondered if I would easily hear any improvement as the standard version Pro is so good, but I did, and straight away. The sound is slightly more focussed with the Pro SE. In fact it reminded me of the difference when listening to the same tracks played in 24/96 format compared to 16/44.1 format. I would also say that bass was a fraction deeper and tighter. After listening longer however, I found there was something that I didn't quite like about the SE. There was a mid-range leanness that made instruments like saxophones sound a bit thin. I went back to the standard UD-10 Pro, and the leanness wasn't there at all. I swapped back and forward a couple more times, and landed up concluding that I preferred the sound of the standard model.

Is it worth the extra money for the SE? Well as it seemed to make many of the tracks that I played through it, sound more like they had been recorded in a higher format, I initially decided that it was. However, I couldn't personally live with the sonic signature. I don't know if it is down to the Burson discrete opamps, or possibly the silver interconnects. And as the latter were soldered, I couldn't swap them for another set. It is a big jump in price, and there are a lot of top-quality components in the SE (including the silver IC's that cost quite a bit if bought separately). It's possible that some listeners may prefer the sound of the SE but I would strongly recommend anybody considering one, to compare it against the standard version before making the decision to buy it. By the way, if you already own a UD-01 Pro, Item Audio will upgrade it at a cost of 245 UK pounds (385 USD).