Not so long ago the Boulder, Colorado-based firm PS Audio touted its PCM-focused PerfectWave DAC and matching PerfectWave Transport as its premier digital audio products, but all that changed with the arrival of the firm’s DSD-centric DirectStream DAC (£5,250, or £5,550, with PS Audio’s optional PerfectWave Bridge module installed).
In the years following the PerfectWave DAC’s release, PS Audio President Paul McGowan was approached by DAC designer Ted Smith. Smith (who has since become a key member of the PS Audio engineering team) suggested a superior-sounding DAC based on a DSD (Direct Stream Digital) rather than a PCM platform. Once McGowan, along with some trusted cohorts from the Pro Audio/Recording Studio world, had a chance to hear Smith’s proof-of-concept DAC circuits in action, the sonic results spoke for themselves, leading PS Audio to embark upon development of the DirectStream DAC. Another key member of the PS Audio team is legendary high-end audio designer Arnie Nudell (creator of, among other things, the classic Infinity IRS loudspeaker); Nudell’s expert ears are used to vet new PS Audio design concepts, subsequent product and firmware revisions, and so on.
The operating principles of the DirectStream DAC are fairly easy to grasp. All incoming PCM digital audio data is first converted to DSD format and then upsampled to 10x the standard DSD rate; similarly, all DSD digital audio files are likewise upsampled to the 10x DSD rate. Then, the 10x DSD digital audio data is converted back down to the double DSD rate for playback. Handling all of this up- and down-conversion is what PS Audio calls its ‘DSD Engine’, which uses an FPGA (Field Programmable Gate Array) as its core processor. No off-the-shelf DAC chips are used in the design.
To drive the outputs of the DAC, PS Audio employs high-speed, fully balanced video switching amplifiers whose outputs are routed through an extremely high quality, wide bandwidth audio transformer that serves, says PS Audio, to provide “both galvanic isolation from the outside world as well as low pass filtering.”
All of the above takes place within an extremely low-jitter (and relatively jitter insensitive) environment made possible by the firm’s decision to use one single master clock for the entire DAC—a clock that, according to PS Audio, is “designed to subtend all possible combinations of sub-clocks, from 44.1, 88.2, 48, 96 (kHz), etc. in order to eliminate the need for multiple clocks…” The clock deliberately does not use “classic edge detection techniques on the digital input data,” but rather uses “a proprietary method of extremely fast sample-and-recognise technology” that is said to minimise sonic degradation related to “cables, jitter, and the quality of the incoming data source.” Moreover, PS Audio has taken special care to avoid noise transfer between sections within the DAC, while paying extremely close attention to circuit board trace layouts to minimise both noise and potential jitter issues.