Headphones

This product is a story of two halves: a single-ended tube headphone amp and an ESS Sabre DAC/triode tube preamplifier – and they are quite distinct. As we saw with the Nirvana [HFN Jun '19], Auris Audio's specifications need to be interpreted with some latitude. In this instance the '0.9W power output' is closer to 25mW at 1% THD, 200mW at 3% THD and 425mW at 5% THD, all at 1kHz into an 'average' 25ohm load [black trace, Graph 1].

900mW might be possible, but at a commensurately higher distortion... Into very low (8ohm) loads, the Euterpe will muster 110mW at 5% THD [red trace, Graph 1]. The maximum voltage output is 5500mV into a high 1kohm load but the response – particularly the low frequency response – benefits from loading. Into high impedances the roll-off begins at 80Hz (–3dB re. 1kHz), falling to –12.5dB/20Hz. With a 25ohm load the bass response improves to –2dB/20Hz while the HF extension is slightly 'sweetened' from –0.4dB/20kHz (high load) to –1.5dB/20kHz (into 25ohm). Noise is not especially low and the A-wtd S/N ratio is 10-20dB behind the best at 80dB (re. 10mW/25ohm).

By contrast, the USB DAC/triode preamp stage offers a more generous 102dB A-wtd S/N ratio, and the maximum output at 1% THD is 2.1V from a high 695ohm source impedance. Distortion falls to a minimum of 0.007% through the midrange at –35dBFs to –40dBFs [black trace, Graph 2] but is typically 20-40dB (10-100x) higher at 20kHz [cyan trace, Graph 2]. The ESS DAC has excellent inbuilt jitter suppression but PSU modulation brings this to (a limited) 380psec here. Regardless of 192kHz etc, incoming file formats the response is determined by the DAC's downsampling to 96kHz, so –3dB/40kHz (or –12dB/40kHz with 96kHz inputs) is the practical bandwidth of the DAC/preamp. PM