Tube Motherboard No Hoax

Using personal computers to listen to music may be heresy in some audiophile circles, but the practice is definitely on the rise. Recognition of the fact has led at least one maker of computer motherboards to introduce a model with a vacuum-tube audio circuit.

In June 2001, in our weekly online poll, we asked readers, "Do you ever listen to music on your computer?" At the time, 29% replied "Yes, quite often," and 30% replied, "Yes, once in a while." The same question posed a year later yielded 37% who said "quite often" and 24% who said "once in a while." In both cases, 2% of our respondents said they "plan to start." Perhaps more telling, the most negative of our multiple choice answers, "No, hate the idea," showed a significant decline from 16% in 2001 to 11% in 2002.

Even Stereophile Editor John Atkinson has "gone over to the dark side." A few years ago, when one of the magazine's reporters suggested to him that it might be time to begin reviewing sound cards, he dismissed the idea. He has since given several cards positive reviews, and admits that for casual listening, the computer can be pretty darn convenient—despite its lack of audiophile respectability and its obvious sonic limitations.

San Jose, CA–based AOpen, Inc. has addressed some of these limitations with a new Windows PC Pentium 4 motherboard due to hit the streets this summer. An early June announcement from the company touts the audio capabilities of the AX4B-533 Tube Motherboard, so called because of an onboard dual triode, a Sovtek 6922. (A true "tube motherboard" with Pentium 4 performance would be the size of several football fields, dwarfing the early Univac.)

Recognizing that tube amps have long been favored by guitar players and audiophiles—and that there must be some reason for this other than blind faith—AOpen engineers decided to include the tube circuitry as an audio buffer for stereo playback or for the left and right front channels in a surround sound system. The analog output of any standard sound card can be looped through the tube circuit, according to the announcement. We can only speculate as to why company engineers decided to put the tube circuit on the motherboard rather than on an add-on sound card. The reason is probably the need for high voltages; the mystery will surely be solved once the product reaches audiophiles' eager hands.

Audiophile components such as Rel-Caps and Cardas wiring are used where applicable, and AOpen claims to have solved the problems of using tubes in a computer's electrically noisy environment. Generating stable high-DC voltages for the tube's plates was another problem AOpen had to solve, one that likely most of the company's engineers had never encountered. Windows PC computers work entirely off highly regulated +12V and +/-5V DC derived from switching power supplies, themselves inherently noisy devices.

The AX4B-533 is intended primarily for audiophiles, music lovers, and "serious gamers" who want the best possible sound, according to AOpen product manager Al Peng, a self-described "audiophile for more than ten years." Some company engineers derided the concept, but Peng said that their "laughter turned into raves a few months later when we did our first lab demo . . . The reproduced sound was absolutely amazing. It left everyone stunned. What we realized at that moment was how the limitations of typical audio output from a PC as we knew it had come to an end—and what we were pioneering was a way to literally combine the best of two audio worlds, old and new."

The rest of the board is decidedly solid-state, with what AOpen describes as "the latest Intel 845E chipset design" with "DDR SDRAM memory channels delivering 2.1GB of memory bandwidth to the processor—maximizing the full performance of the Intel Pentium 4 processor with 533MHz FSB." The board has four AGP slots, supports four USB 2.0 ports, and provides an Ultra ATA/100 interface. With Intel's 845E chipset, the AOpen AX4B-533 Tube motherboard is said to provide "a revolutionary fusion of old and new technology, producing unsurpassed PC audio output that takes full advantage of the Intel Pentium 4 processor's capabilities."

The AX4B-533 Tube Motherboard has a projected average lifespan ("mean time before failure" or MTBF) of around 50,000 hours on the board itself, about 35,000 hours on the "tube circuitry," and 4000 to 5000 hours on the tube itself. The announcement does not mention whether AOpen has provided a way to put the dual triode in standby mode or to turn it off when not in use. Estimated street price on the AX4B-533 will be around $215.