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Senior Shackster
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Discussion Starter #1 (Edited)

KingRex UD384 USB DAC and UPower Review
MSRP: $479 + $189 USD

Desktop and personal audio is a passion of mine that started many years ago with a pair of low end Sennheiser headphones. From there my head-fi system eventually grew into something more special with the addition of some Audio Technica ATH-A500 headphones and a Behringer DAC.

This system lasted for about 3 years as I made my move from Canada to the United States, however at some point I decided it was time for a proper speaker system at my computer. It didn't take long for this desire to become a reality as I purchased a pair of Onix Reference 1 loudspeakers in excellent condition from an AV123 forum member, and found myself in need of a desktop amplifier. This was the moment I would make my first acquaintance with KingRex - a small Taiwanese audio company that makes some very innovative products. My hunt for the perfect small form factor (SFF) desktop amp was fairly broad but I ended up settling on the KingRex T20U - a Class-T amplifier that can push ~15W per channel and integrates a Burr Brown DAC.

That little DAC/Amp has lived on my desk for the better part of 3 years, and I still find myself enjoying it thoroughly. It shouldn't be too surprising then to learn that KingRex was a logical jump for me when looking at DAC solutions for my PC audio rig.

Unsure of exactly what I would be reviewing, I reached out to KingRex and was offered the UD384 DAC and UPower products for my review. The items arrived promptly in factory packaging - fairly small white boxes with power supplies, warranty cards, and in the case of the UD384- a small white USB stick containing drivers and some sample files.

About the devices


UD384 (32bits/384Khz USB DAC )
Input: USB x 1
Analog output: RCA x 2 (Rx1 Lx1)
Digital output :SPDIF x 1
Sampling rate support :44.1Khz, 48Khz, 88.2Khz, 96Khz, 176.4Khz, 192Khz, & 384Khz(384Khz for USB DAC only)
Supported bit rate: 16 / 24 /32bit
USB:2.0 high speed
Adaptive Clock Generator for Audio Streaming Synchronization
Asynchronous mode changeable through DFU Tool
Power requirement: 7.5V/250mA
Size: 110x82x24mm
Suggested MSRP : $479/pc


Pure DC output battery power supply unit
I. Two output :
A. 2.5mm DC jacket: 7.5V DC output
B. USB A :5V DC output(through linear regulator)
II. Major component: High quality Sanyo Li-ion battery.
III. Power volume: 2600mA/hr. Included special design for isolated protect circuitry for two
Li-ion batteries.
IV. Using fully high quality aluminum for styling & cooling.
V. Low battery indicator design for charging reminding.
VI. CHG/DC OUT switch. Fully isolated the charging and discharging. It will free the AC noise
from the charger.
VII. Parallel charging- each battery cell could charge to its maximum by the design.
Suggested MSRP: US$189/pc

The UD384 is a very small ~4x3x1" asnychronous DAC (or USB -> S/PDIF converter) that supports either S/PDIF or analog RCA output, and takes a USB input. In my case, the analog RCA outputs would be used. The U Power is an optional lithium ion battery pack that charges via wallwart but when switched to DC OUT mode will output clean 7.5V power to the UD384.

The UD384 supports sample rates ranging from 44.1 kHz to 384 kHz (384 being a USB only option), with either 16, 24 or 32 bit word lengths.

The U Power and UD384 are built to sit on top of one another, and a small one foot power cord is provided to connect the two. Unfortunately, cables come and go from both ends of each product, meaning completely "clean" wiring setup is hard to manage, however this is a fairly minor issue in the grand scheme of things.

KingRex recommends Foobar 2000 and WASAPI on a Windows 7 PC - a setup I use on a daily basis but will explain for those new to PC Audio.

Install Guide

You can get started by inserting the USB stick and installing the KingRex drivers, a process which takes approximately 5 minutes. Once this is done, head on over to foobar2000.org and download this free player. Foobar 2000 has been around for years, and is quite popular because it can be skinned with highly functional and attractive layouts. The real strength of the software however is the near endless list of free plugins which allow everything from iPod syncing to ripping CD's or last.fm scrobbling. In this case, the WASAPI plugin allows bit perfect streaming to a USB DAC such as the UD384.

Once Foobar is installed, grab the WASAPI plugin here:


Install this by copying the dll into the components folder inside your foobar2000 install.

Once this is done, open up Foobar 2000 to be greeted by this home screen. Hit Ctrl+P or File -> Preferences to open up the preferences pane. You'll now have an option under Playback -> Output for Device: WASPI .

Selecting this will enable bit perfect playback.
That's it!

The UPower requires a few hours to charge as it is a battery power pack - so with the included wall wart plugged in, I left it to charge overnight. In the mean time - I decided I would begin plugging it into my head-fi rig, an O2 desktop headphone amp built by JDS Labs, and a pair of AKG Q701 headphones. KingRex suggests you connect the DAC directly into the motherboard via a USB 2.0 port, so I happily complied and began to load some favorite sample tracks from my library of FLAC files.

Listening Impressions:

Sophie Millman - In the Moonlight - Prelude To A Kiss [FLAC - 192kHz]

Sophie Millman has the sort of husky classic jazz voice that high end audio salesmen absolutely love to use to convince you to buy expensive products. Her recordings happen to be especially good - especially in the case of the 88 kHz HDtracks release of her "In the Moonlight" album.

The first thing I noticed with the UD384 was the low noise floor - and by low I mean non-existent. I couldn't hear even a hint of noise. Perhaps this is a result of using the U Power, but whatever the cause it was very impressive. Millman's voice was smooth and natural, sounding as clean as I could possibly imagine with thick silky mids and warm accompaniment. Contrasting with my usual Behringer UCA202 DAC - it was a noticeable improvement, primarily becuase there was no noise floor. This was pure music and I was very impressed.

2L - The Nordic Sound - Track 13 - Antonio Vivaldi: Recitative and Aria from Cantata RV 679 - Che giova il sospirar, povero core [FLAC - 384kHz]

KingRex included some 384kHz content on the USB stick from 2L records, which was up next in my listening queue. The track included was the above - and it was provided in bitrates ranging from 44/16 all the way up to 384/24. Playing back via my WASAPI output, the 384/24 content played back perfectly (and bit perfect too!). The sound is best described as utterly lifelike - with the noise floor so low and such a high quality recording, it becomes remarkably hard to mentally differentiate what you're hearing from a live performance.

Harpsichord tones had the natural plucked reverberation that one hears in person while the strings clearly resolved on either side of the listener with perfect separation. A/B'ing between the 192 and 384 kHz content I couldn't tell an appreciable difference, largely I suspect because those subtle differences exceed the resolution of the human ear.

Joey Satriani - Satchurated [Dolby TrueHD - 96kHZ]

This Blu-Ray is a great recording of Satch playing live and features some great sonics. Having thrown a lot of mild and laid back music at the UD384, I felt it was time to move to something with a little more speed. Satchurated is a great production with plenty of Satriani guitar work, fast drumming, active cymbals and a lot of ambient noise from the crowd. The UD384 handled Satriani with equal aplomb, delivering the same neutral, high quality playback that I had experienced with the other tracks, once again with that awesomely low noise floor. On the higher quality recordings, this really lets you realize just how much other information the microphones are picking up and it's a pleasure to listen to.


While an outstanding value and a great performer all around, the UD384 does have a few caveats. In the interest in ensuring all of you are adequately informed, i'm going to lay them out here in a bulleted format:

  • The KingRex UD384 only supports up to 192 kHz / 24 bit playback when acting as a USB->S/PDIF converter. This is an inherent limitation of S/PDIF following the AES/EBU specification.
  • The model of UD384 I originally received does not support 352.8 kHz natively. This is a limitation of the chip used. Granted - there isn't a lot of content out there above 192 kHz these days, but it is worth knowing. Since my original review sample KingRex has provided a replacement unit that supports 352.8 kHz, buyers however should be certain they receive the correct hardware version if this is a concern.


The UD384 and U Power make a stunning combination as a PC audio transport. The UD384 is not without its faults - but the overall sonic character, low noise floor and good value still merit top marks. Comparable DAC's that I have heard are similar in price but have noise floors substantially higher. The U Power is a worthy sidekick for the UD384 - improving the overall noise floor considerably while also subjectively improving the sound. Hard as it can be to select the perfect product for a PCAT, in my case this little combo fits the bill perfectly. Recommended.
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