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Come Together

"You never get a second chance to make a first impression", and the AOpen AX4GE Tube nails it. The simple lavender and blue box features a compartment on the side that protects and showcases the Sovtek 6922 dual triode vacuum tube. Inside lies the board itself, a black PCB with gold chipset heatsink. The expansion area stops at 3 PCI slots, with the remaining real estate dedicated to audio circuitry centered around the tube socket. Documentation is abundant. There is a 74 page booklet that describes the design and implementation of the tube circuitry, covers installation and removal of the tube from the socket, and lists other compatible tubes that might provide a different sound. It also features some musical suggestions and lists the audio equipment and demo material used in the development of the board. The main manual is a 116 page booklet covering installation, BIOS, and bundled software. The Easy Installation Guide takes the form of a double-sided poster, and a fold-out card explains how to use EzRestore to protect your operating system installation. AOpen includes a single 80 conductor ATA cable and a floppy cable, but instead of the boring gray they are black with a gray stripe to indicate Pin 1. The other accessry is a slot cover that holds gold-plated stereo RCA out jacks, and a 1/8" stereo input. Without repeating sections from the documentation, it's noteworthy that AOpen has sourced components from well-respected audio parts suppliers. Apart from the Sovtek vacuum tube, AOpen utilized parts from Kimber Kable, Cardas, REL Multicap, and WIMA.

The Package in blue and lavender

AOpen took a KISS (Keep It Simple, Stupid) approach for the audio circuitry that is often seen in high-end components. The shortest signal path with the fewest parts leaves the least chance for noise to taint the sound. Thus, there is no SPDIF jack on the slot cover with the RCA out and stereo in. There is a header on the board that connects to an AOpen SPDIF bracket. Unfortunately, the bracket was not included in the motherboard package. The tube is used for the output of the two main channels. The board is capable of producing up to 5.1 channel analog sound, but only the front left and right channels will be produced through the tube. To have more tube channels, the board would need more tubes. With the separate SPDIF bracket, the board can send a Dolby Digital or DTS DVD soundtrack to an external decoder.

A sleeping beauty in its cocoon

I began by comparing the tube output (RCA jacks on slot cover) with the standard AC97 (1/8" jack on the ATX back panel). I quickly noticed that the colors on the RCA jacks were reversed - the right channel came from the white instead of the red. The easy fix was to swap the plugs on the RCA cable. With that out of the way, the tube was a clear improvement over the plain AC97 output. The tube provided a wider soundstage and more detailed placement of instruments. The placement was apparent on the Overture from "2112"; not only were the guitars and bass in the right places, but the arrangement of the drum kit was clear. The snare drum was centered correctly, and beats from each tom came from a different spot. The tube also did well the the lengthy, multi-guitar introduction to "Two Step", with each guitar coming from a different point on the stage. Bob Mould's "The Last Night" is a mid/slow tempo breakup song with acoustic guitar, electric bass, organ, and drums. The tube's wider soundstage was again apparent with quieter material, and the tube created a slightly more intimate feeling with the song. There is no question that the tube hugely improves upon the sound from the AC97 codec.

To test signal-to-noise ratio, I left the two main channels of the AX4GE Tube connected to the receiver without any sound playing and turned up the volume until noise was audible. The Yamaha receiver measures volume in negative dB, with a top setting of 0. So, -30 dB (about the highest I use for movie watching) is louder than -50 dB (a good level for CD's). The Tube was quiet until about -22 dB, when a hum started coming through. For comparison, my JVC CD changer is silent up to about -8 dB.

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