Sutherland Engineering 12dAX7 USB DAC/preamplifier

Computers and vacuum tubes go together like Trent Lott and flyaway hair, right? The last time filaments glowed in computers was during the 1960s, when a computer was a building. I remember laughing at the ponytailed computer-science dweebs back then, who spent their college days playing nursemaid to a football field's worth of electronics capable of little more than adding two plus two. Chained to a computer half the day, as most of us now are, guess who had the last laugh?

So if you're going to be plopped in front of a screen all day, the least you can do for yourself is squeeze some decent sound out of your computer—especially if you work at home, or in an office where you can pump up the volume. Adding a high-quality satellite-subwoofer system like Acoustic Energy's Aego2, Eminent Technology's LFT-11, or Cambridge SoundWorks' Megaworks 210D would be a good place to start.

But there's much more you can do, and if your computer is equipped with a universal serial bus (USB 1.0) port, you can do it without messing with internal soundcards, which, while offering upgradeable audio, still must operate in a difficult environment. The high-frequency noise produced by digital processing does bad things to both the power supply feeding the audio circuitry and to the post-conversion analog signal on its way out of the computer.

USB 1.0 offers single-jack multi-function connectivity with reasonably high-speed data transfer, so even without a dedicated digital audio output jack on your computer, you could still take the D/A conversion and the rest of the audio circuitry out of its foul environs—if, that is, you could get an outboard DAC with a USB interface.

Now, thanks to Sutherland Engineering's 12dAX7, you can, and because it uses smooth-sounding 12AX7 tubes in its analog preamplifier circuit, you can also round off the audio jaggies inherent in MP3 recordings and make them not exactly listenable, but less noxious to the ear.

Even if your computer doesn't have a USB port, you can add one. Keyspan, for example, makes a Mac/PC-compatible USB 2.0/FireWire card that fits into PCI expansion slots for $99, complete with installation software. [USB 2.0 is backward-compatible with USB 1.0 devices.—Ed.] Yes, some computer dweebs will be satisfied with nothing less than the higher data-transfer rate of IEEE-1394 (FireWire) connectivity, but for CD playback, USB 1.0 will do fine.

The 12dAX7
About the size of a standard rack-mountable audio component, the PC/Mac-compatible 12dAX7 will not be welcome on an overcrowded desk. But assuming you have the space, its transparent Plexiglas face—displaying the circuit boards, LEDs, and glowing tubes—will make a neat addition to any workstation, and a real conversation piece.

A chassis of cold-rolled steel provides a rigid platform for the dual-mono modular design, which uses printed-circuit boards of high-quality FR-4 fiberglass. There are modules for the power supply and digital circuitry and two for the tubed gain stages. Name-brand parts are used throughout, including 1% Dale metal-film resistors and Wima polypropylene film capacitors. There's also a toroidal power transformer, and Russian-made 12AX7 tubes with a claimed life expectancy of "at least" 10,000 hours. The digital circuit is based on Burr-Brown's surface-mount PCM 2702 chip, a 16-bit two-channel DAC with an integral 8x-oversampling filter and a USB 1.0 data input port.

Hookup is simple: you run the supplied USB cable from your computer or USB hub output to the 12dAX7's USB port, run analog cables (or an RCA/RCA-to-stereo-miniplug cable) from the 12dAX7's RCA jacks to your amplifier or powered subwoofer-satellite system, and plug the 12dAX7 into the wall via the IEC AC jack. (Yes, you can even play with power cords. Knock yourself out.) Computer operating systems include bit-trimming digital volume controls that should be cranked full on or you'll be diminishing the digital resolution reaching the 12dAX7's DAC. The idea is to control volume in the post-conversion analog domain using the 12dAX7's analog volume potentiometer.

When I switched on my computer, the 12dAX7 came to life: during the short warmup period, the turn-on relay clicked, the filaments glowed, and the yellow Mute LED came on. By the time my Mac G4 computer was booted up and ready to use, the 12dAX7's Suspended light had begun to glow as the computer looked for peripheral devices. Then it was the Zero LED's turn, until I inserted a CD into the Mac's CD-ROM drive and pushed Play. When the bitstream hit the 12dAX7, its green Play LED fired up and music poured from the speakers. When I shut the computer down, the relay clicked again, shutting down the Sutherland.

Sutherland Engineering
P.O. Box 1633
Lawrence, KS 66044
(913) 841-3355