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This is the 30th in a series of reviews dedicated to the concept of 32Ohm Audio as embodied by the store of that name in downtown Portland/Oregon and described here - Ed.

Srajan Ebaen
Financial Interests: click here
Source: Apple iMac 1TB with AIFF files up to 24/192, PureMusic 1.73 in memory play with pre-allocated RAM, Weiss DAC2, Burson HA160D, iPod Classic 160GB, Sieben Technology dock, Onkyo NS-D1 digital-direct dock
Preamps: StereoKnight Silverstone Balanced [on loan]
Amplifiers: FirstWatt F5
Speakers: ASI Tango R
Cables: Complete loom of ASI Liveline, Crystal Cable Ultra, Furutech GT2 and WireWorld Starlight USB A-to-mini-B cables [on loan], LaCie and Entreq Firewire 800 cables, Entreq USB cable, Black Cat Cable Veloce S/PDIF cable [on loan]
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 1 x GigaWatt PF-2 with matching GigaWatt cord, 1 x Furutech RTP-6
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: $189

See whether this is you in the wanted ads. "Have premium DAC or CDP. Want to include PC audio sources. Need affordable USB interface. Help!"
That's exactly the scenario the KingRex UC192 addresses. As such it's not a dAc—it never enters the analog domain—but a DDC or digital-to-digital converter like the very successful M2Tech hiFace. Specifically it converts USB to coaxial S/PDIF, AES/EBU and I²S. Both S/PDIF paths are coupled with an isolation pulse transformer.

Because there are no standardized sockets for I²S, KingRex carries theirs on an Ethernet RJ45 link (PS Audio and NorthStar do as well, April Music uses S-Video instead). Because there isn't enough room for full-size AES/EBU, KingRex adopted a tiny XLR as we've seen it already on the HRT Music Streamer Pro.

KingRex's chief engineer James Lee suggests the following operating modes - ASIO4All with Foobar 2000 for Windows XP; Wasapi with Foobar 2000 for Vista & Windows 7; and iTunes for Mac.

The UC192 isn't just useful to non-USB DACs. Because it streams up to 32-bit/192kHz files, it can upgrade a DAC whose USB input is limited to 24/96 or 16/44.1 but whose coaxial or XLR input is not. Then such hi-rez signal is processed at its native data density by the actual converter. Ditto CD players with coaxial, AES/EBU or matching I²S inputs. The UC192 does not run asynchronous as was first popularized for consumer hifi by Wavelength Audio (it's been the pro-audio standard far longer). KingRex still relies on isochronous adaptive. Most critics believe it to be the more jitter-prone protocol because the sender (host computer) controls the data stream rather than the receiver (converter). The UC192 of course does reclock the data. Here it is via 1pmm 12MHz TCXO or temperature-controlled oven oscillator with proprietary low-jitter drivers for Windows and Mac. These drivers enable USB 2.0 hi-speed mode and must first be installed first on non OSX machines. There's support for Direct Sound, Asio4All and Wasapi but not full Kernel streaming. The 7.5V power supply is an external switching wall wart that connects via umbilical. The KingRex computer audio transport—henceforth c.a.t.—is housed in a stylish oval cross-section aluminum extrusion with flat end caps.

This type device is obviously popular. It's a stop gap between legacy and computer audio. Ideally you'd want an integrated high-resolution USB or Firewire device like my Weiss DAC2 or Burson HA160D to eliminate the jittery cable interface any DDC adds by design. But the appeal of a c.a.t. is that it retroactively upgrades—just on one feature—what otherwise might be a very satisfying DAC or CDP you'd rather not part with. It's a bit like adding 4-wheel drive to a car that never had it. You can go places you couldn't before but it's still the same old car. From this follows that a c.a.t. makes most sense if it's cheap. At $650 Lindemann's 24/96 device for example seemed steep. Otherwise you might replace your existing DAC altogether. What USB transceiver did KingRex choose? Here marketing manager Christine Wu flags a big top secret whilst their assembly team has strategically removed the chip's markings. Your guess is as good as mine. It's likely not the ISP 1507-A1 Antelope Audio uses in their Zodiac+ because that part supports 480Mbit/s speeds whereas KingRex specifies a maximum of 400.

How does one evaluate a c.a.t.? Stroke it. If it purrs it's good. Not. You'll need a DAC with USB and S/PDIF inputs. If the c.a.t. stream sounds better than USB direct, it has nothing to do with D/A conversion per se. The same converter stage handles either. It'll have to be because the c.a.t. reduced jitter. The best performance here should be expected from the I²S socket since its data stream is discrete and not composite. Alas converters with external I²S are like hen's teeth. It'll be the very rare customer who owns one (not me).

Should one expect miracles from a $189 black box? Not. The asynchronous USB receiver in the Burson HA160D for example ought to be immune to its help. But even a good CD player with a digital input could sound better when fed from hard disk via the KingRex. Laser-based playback introduces its own jitter when the big servo motor currents interfere with the tiny analog currents in the laser diodes. Optical reading thus could come in second when compared to playing back the same CD first ripped to hard drive in an uncompressed format—I use AIFF—then streamed into the player via the USB interface.