SPL Diamond USB DAC Lab Report

Lab Report

The Diamond is currently SPL's most accessible DAC solution, sitting beneath the Director Mk2 and Phonitor xe [HFN Jul '21], the latter employing a (very similar) AKM AK4490-based digital solution, with the same AES/USB and S/PDIF inputs, but combined with both single-ended and balanced analogue inputs to service the preamp output. Otherwise the performance of the new Diamond is as robust as we've come to expect from this pro-heritage brand – maximum output is a healthy 4.16V (fixed or variable) from a modest 36ohm source impedance (increasing to 40ohm at 20Hz) while the A-wtd S/N ratio is a wide 113dB, via both S/PDIF and USB-B inputs. The lowest distortion – a minuscule 0.00004-0.0007% (re. 20Hz-20kHz) – is achieved at circa –10dBFs [Graph 1, below, and note the extended –140dB scale] while some (very typical) analogue 'stress' sees this rise to a merely very low 0.0004-0.002% at peak output.

While the AKM DAC offers a choice of digital filters most brands using this chip opt for just one of the five available algorithms in their products, in SPL's case the 'fast roll-off/minimum phase' type which trades any acausal pre-ringing for extended post-ringing. Stopband rejection is a moderate 69dB while the high frequency roll-off increases from –0.7dB/20kHz with CD/48kHz media to –3.7dB/45kHz and –11.1dB/90kHz with 96kHz and 192kHz files, respectively. We've seen moderate levels of correlated jitter from other SPL products but this is reduced here to ~100psec and comprises an extended 'spray' of sidebands originating at ±64Hz [see Graph 2, below] which, I assume, is linked to a clock division or other polling process within the Diamond. The remainder of its 'analogue' performance, including >100dB stereo separation, is solid. PM


Distortion versus 48kHz/24-bit digital level over 120dB dynamic range (1kHz, black; 20kHz, blue)


High resolution 48kHz/24-bit jitter spectrum with low-level sidebands identified with markers

Maximum output / Impedance 4.16Vrms / 36-40ohm (bal.)
A-wtd S/N ratio 113.2dB
Distortion (1kHz, 0dBFs/–30dBFs) 0.00035% / 0.00013%
Distortion & Noise (20kHz, 0dBFs/–30dBFs) 0.0018% / 0.00033%
Freq. resp. (20Hz-20kHz/40kHz/75kHz) +0.0 to –0.7dB/–3.7dB/–11.1dB
Digital jitter (48kHz / 96kHz / 192kHz) 110psec / 90psec / 80psec
Resolution (re. –100dBFs / –110dBFs) ±0.1dB / ±0.2dB
Power consumption 17W (1W standby)
Dimensions (WHD) / Weight 278x57x300mm / 5.4kg
Price £2499

SPL electronics GmbH
Niederkruechten, Germany
Supplied by: SCV Electronics Ltd, Herts
03301 222500