Network Audio Players/Servers

Astell&Kern’s SP2000T player [HFN Jun ’22] employed a pair of ES9068AS DACs per channel with the option of three digital filters, while the latest SP4000 model leverages a pair of AKM’s two-chip AK4191/AK4499EX upsampling/DAC solutions per channel, and offers six user-selectable digital filters. The new player bests this legacy model in all respects, not least in its compatibility with files beyond 96kHz and its marked reduction in digital jitter – down from 630psec to <7psec here across all 48-192kHz sample rates. The SP4000 offers both single-ended and balanced line out options (to drive active ‘full-sized’ systems or active speakers) with settings for 1.4V, 2V, 2.5V and 4V in balanced mode. In practice its max. output is nearly twice as high – 7.8V, with a massive 121dB A-wtd S/N ratio, at volume setting ‘150’ all from a vanishingly low 1ohm source impedance.

Like the SP2000T, the SP4000’s line output is phase inverting [Graph 2] while stopband rejection and high frequency response are all determined by choice of filter. ‘Sharp’ (linear phase fast) and ‘Short Delay Sharp’ [minimum phase fast, black traces Graph 2] yield the flattest responses of –0.1dB/45kHz and –0.1dB/90kHz with 96kHz and 192kHz media, respectively, while ‘Slow’ [linear phase slow, red traces Graph 2] and ‘Short Delay Slow’ fall to –8.3dB/20kHz, –10dB/45kHz and –8.5dB/90kHz with 48kHz, 96kHz and 192kHz files. Resolution is held to within ±0.2dB over a full 110dB dynamic range [red trace, Graph 1] while THD dips to a minimum of 0.00015-0.0005% over the top 20dB of this range, remaining consistently low at mid and high frequencies thereafter [Graph 1]. A pair of these AKM DAC chipsets is capable of lower still, but this is of technical interest only. PM