AOpen AX4B 533 Tube

Wednesday, September 25, 2002


Every once in a while, but not very often, the market is lucky enough to be graced by the arrival of a very special and original product.

AOpen, which has often been at the forefront of innovation, has surprised us this time around, by releasing just such a product.

The beast in question is none other than the AX4B 533 Tube, which, as its name indicates, incorporates audio-out capabilities that are tied-in with a good old-fashioned vacuum tube. That's right, a vacuum tube. Surprising as it may seem, this innovation (sic) will come as quite a delight to high-fidelity audio enthusiasts, who swear by the capabilities of the little bundles of glass -- a subject we'll be exploring during our analysis.

Other than that, the AX4B 533 Tube is nearly identical to the AX4B Pro 533 which we reviewed earlier. The only major difference is that the "Tube" has been stripped of both its RAID controller, and three of its PCI slots in order to make room for the new audio circuit.

Otherwise, except for a few minor changes, the AX4B 533 Tube is a twin of the AX4B Pro.

While the new board does come without the Realtek RTL8100B network controller of its predecessor, it does retain its Ethernet capabilities, thanks to the integrated network circuitry of the i845E Northbridge.

So, without further ado, let's get on with the review, shall we?

Characteristics of the AOpen AX4B 533 Tube
Support 533 MHz FSB Intel Pentium 4 socket 478 CPU
Form factor
ATX 30.5cm 24.4cm
3 PCI - 0 ISA - 0 CNR - 1 AGP - 6 USB 2.0
3X 184-pin DIMM sockets DDR SDRAM slots for up to 2GB
of DDR200, DDR266, DDR333.
100Mhz to 248Mhz in 1Mhz increments
Vcore adj.
1.1v to 1.85v in 0.025 increment
VDram - VAGP adj.
Audio chipset
Realtek ALC650


The AOpen AX4B 533 Tube's audio circuitry is driven by the Realtek ALC650 integrated circuit.

The least we were expecting was the C-Media CMI 8738 which is by far superior to the ALC650 but we re deceived to found out that it was not the case and we really wonder why the ALC650 was chosen in place of the C-Media 8738 especially when we consider all the problems that had the engineers to develop a tube audio output circuit for this mainboard.

Now, that being said, let's turn the conversation to matters of the infamous vacuum tube.

If you listen to the word on the street, chances are that a few ignoramuses of the worst kind will claim, in full confidence, than the worst transistor-based amplifier ever turned out of a factory could beat the world's best vacuum-tube amplifier hands-down. All that proves, however, is that human ignorance can reach stupefying heights if left to its own devices, and so it's perhaps high-time that we set the record straight.

Vacuum-tube amplifiers have always produced better sound than transistor amplifiers, and, even if we've never been able to pin-down the exact reasons why, the differences in sound-quality have long been known. No matter then that tube-amps have higher levels of harmonic distortion than transistor-amps; it's the sound-quality that matters, and that's where the tubes deliver.

Personally, I have my own pet theory as to why tube-amps sound better. My theory is that the voltages applied between the cathode and plate of the vacuum-tube are so high that they have the effect of allowing weak audio signals to ascend and make themselves felt. The voltages in transistor-amps, though, are so low that similar signals would be drowned out.

Also, the flow of electrons from the cathode to the plate circulates in an ideal medium -- a vacuum -- while the flow of electrons in a transistor must work its way through a material substance -- which may explain why some of the detail of an audio signal is lost or tainted in transit.

The audio circuitry of the AX4B 533 "Tube is based around a double triode vacuum tube, and the output signal is taken from the cathode rather than from the plate like it is usually the case on most of the tube amps.

The tube in question is of Dutch design and Soviet manufacture, and goes by the name of the Sovtek 6922 or with the designation of ECC88. It is of excellent quality, and offers an incredibly rich audio experience.

Music is reproduced with crystal clear quality, and with a level of detail that made my eyes moist as I was brought back the days of my very first vacuum-tube based amps some 30 years ago. While that probably betrays my age, I'm not ashamed to say that my experience with all things electronic stretches back as far as times when the vacuum-tube reigned supreme.

Heck, I could sit hear and wax poetic, writing chapter upon chapter about the good ole' days, but that's probably outside the scope of this particular article.

I would, however, like to thank AOpen to have had the sense to design this little treasure, and allow a new generation of neophytes to finally experience the musical work of a good vacuum-tube, and compare it to the much different experience of a transitor-based systems.

I'd also like to note that the tube in question produces only 6 watts of total heat dissipation -- 4 watts from the filaments, and 2 watts from the plate. So, though it will due its part to encourage global warming, the effects will be less than dramatic. In fact, you can even press a finger to the valve while it's in full swing without burning yourself. That's a far cry from some tubes I've known, which would take the skin of your finger, and the hair off your knuckles almost instantly...


The AX4B 533 Tube's design is a Jumperless affair. That means that user's won't need to play with on-board jumpers to get the board up and running.

Configuration, in fact, is accomplished from within the BIOS, and most frequently from within the "Frequency/Voltage Control" menu.

Once there, user's will be presented with a number of options, including the ability to set the FSB frequency to between 100MHz and 248MHz in 1MHz increments.

The clock multiplier value, unfortunatly, cannot be set manually.

The Vcore voltage is adjustable however, and can be set to any of the values indicated in the table above.

Finally, as expected, a number of memory timing options can be tweaked from the "Advanced Chipset Features" menu. That includes the ability to set the operating frequency of the memory bus manually, or to set it to "SPD" ("Serial Presence Detect"), which allows the system to determin the proper setting automatically.


Next: Technical details

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