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Sound section of the AOpen AX4B-533 Tube Motherboard

Audiophile's output stage on the Sovtek 6922 vacuum tube (Made in Russia)

Here is an advertising composition from the AOpen's site.









The box is divided into two parts, one containing the board and the other - the Sovtek 6922 tube and a bracket with CARDAS cables.























The sound subsystem of the motherboard consists of:

Realtek ALC650 AC'97 codec;

Vacuum tube (twin triode) Sovtek 6922 (Made in Russia) which can be replaced with any similar one;

ELNA capacitors in the power circuitry of the tube;

CARDAS copper cables between the amplifier and connectors;

REL MultiCap capacitors in the sound section;

VISHAY resistors.

The Realtek ALC650 features such advantages as a low price, 6-channel support and easy integration into a motherboard with modern chipsets. And according to AOpen, the tube can add something that will smooth away imperfection of the cheap converter and make sound enchanting.

Here is the circuitry of the tube stage on the triode.









The tube doesn't look so romantic in operation as it looks on the ads. It doesn't give much light and doesn't winkle with time in music. :)









The tube stage gets enabled with a jumper onboard and a special option in the BIOS.

















The tests were carried out in the Windows using the DAC of the codec on the motherboard.

The software is ordinary. An icon emerged in the tray enables a software sound manager.

























































Test listening

The tests revealed:

In spite of my worst expectations the sound wasn't the worst of its kind!

As compared with the original, the codec coupled with the tube stage gives soft sound with a smoothed "attack" and a little blurry details, and noticeable distortions at a high volume level;

The sound is more interesting than in a pure codec but Hi-End is still far away;

Acoustic compositions with live recording sound best of all; the tube doesn't cope well with electronic music where aggressive attack and details are very important.

The motherboard with the tube hasn't passed the tests with the Sennheiser HD600 headphones. In spite of the dedicated 1/4" connector for the headphones the output stage is probably unable to playback without reloading. The sound cracked at any volume level.

Objective tests







The AFCs for 50% and 100% volume levels coincide,

the frequency response is normal







The noise level doesn't reveal noticeable pickups from high-voltage circuits of the section







The harmonic distortion level is 1..2%

- it's typical of tube equipment

Conclusion

Maxim Liadov (maxim@ixbt.com)



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