Ron Sutherland, who released a line of cutting-edge solid-state amp and pre-amps in the 1990s, offers a product which bypasses a computer's soundcard and accesses the digital data stream directly via a USB socket, as found on nearly every post-1998 PC and some Macs. The inspiration is simple: computers are overtaking hi-fi in certain quarters (e.g. colleges) as the source of music, yet they suffer undernourished power supplies, most sound cards are made from scandalously cheap parts, and the environment in which they operate is 'dirty'. More specifically, because volume control in a computer exists in a purely digital domain, the software 'volume sliders' lower level by shedding bits of information. The 12dAX7 adjusts volume solely in the analogue domain, with no loss of information.
Unbelievably given Ron's pedigree, the 12dAX7 is a valve product. And we all know that the digitisation of music adds vile artefacts to the signal; the 12dAX7 uses 12AX7 tubes in a special circuit that 'euphonically restores even order harmonic structure to music.' Each channel in the 12dAX7 contains its own circuit board, 'a type of dual-mono construction unusual in even the most expensive high-end audio products,' according to Sutherland. And Sutherland chose a Burr-Brown PCM2702 DAC as the heart of the unit.
Effectively a preamp-D/A converter housed in a gorgeous 15x8.5x3in (WDH) box to fit in-between computer and hi-fi system, the 12dAX7 is so minimalist that it doesn't even provide on/off; the unit is controlled entirely by the computer to which it's attached, save for a master volume rotary on its 1/2in thick Perspex front panel. Through the panel, you can observe the valves and four LEDs on the PCB: 'mute' which flashes red during warm-up, 'suspend' (also red) which is on until the computer drivers 'find' the 12dAX7, a yellow LED marked 'zero' which glows when there is no audio data coming in, and 'play', which glows green when digital data is available. The back contains only the USB input, phono sockets for left and right analogue line output and an IEC mains socket.