Integrated Amplifiers

iFi Audio’s battery-powered xDSD Gryphon portable/desktop DAC/headphone amplifier [HFN Aug ’22] provided the option of four user-selectable digital filters to complement the integral TI DSD1793 DAC. Fast forward three years and not only has the Gryphon’s 3600mAh battery been thoroughly out-gunned by the iDSD Valkyrie’s 4x5000mAh cells but its digital stage is similarly beefed-up with no fewer than two DSD1793 DACs per channel, supplemented with a choice of six custom digital filters. The line output is set to a standard 2V for a 0dBFs digital input where the 96ohm source impedance and 108dB A-wtd S/N ratio match the best and most recent iFi Audio models [the Diablo 2 – see boxout] even though (line) distortion is a little higher and closer to that of the Gryphon at 0.0017-0.039% (re. 0dBFs, 20Hz-20kHz). That said, THD does fall to a minimum of 0.0001-0.0015% over the top 30dB of its dynamic range [see Graph 1, below] while jitter is less than 10psec at all sample rates via the USB-C input [see Graph 2, below], and low-level resolution is good to within ±0.1dB over a full 100dB range.

Response stopband rejection and time domain distortion are functions of the digital filters. ‘Standard’ is a linear phase type with 53dB of alias rejection and a response flat to +0.3dB/90kHz with 192kHz files, while ‘Minimum’ is actually a slow linear phase type that rolls away to –3.1dB/20kHz with CD/48kHz media. ‘Apodising’ and ‘GTO’ behave like fast and slow minimum phase types, respectively, both flat to within –0.1dB/20kHz, the latter dropping to –5.4dB/90kHz and offering a mere 12dB stopband rejection. The ‘BP’ option offers no upsampling or digital filtering at all and rolls away early to –3.1dB/20kHz with 48kHz media but is flatter at –3.8dB/90kHz with 192kHz files. PM