Auris Audio Euterpe Headphone Amp/DAC Lab Report

Lab Report

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


Continuous power output versus distortion (black, into 25ohm load; red, low imp 8ohm load)


Distortion versus 24-bit digital signal level over a 120dB range at 1kHz (black) and 20kHz (blue)

Maximum output (re. 0dBFs into 47kohm) 2.1V (preamp out, 1% THD)
Maximum power output (25ohm, 5% THD) 425mW (headphone out)
Output Imp. (20Hz-20kHz, line/headph.) 695ohm/ 68/272ohm
A-wtd S/N ratio (0dBFs; re. 2V/10mW) 101.7dB / 80.3dB
Distortion (20Hz-20kHz, re. 10mW/25ohm) 0.8–17%
Freq. resp. (USB, 20Hz-20kHz/45kHz) +0.0 to –1.2dB/–15.6dB
Digital jitter (USB, 48kHz/24-bit) 380psec
Power consumption 25W (2W standby)
Dimensions (WHD) / Weight 160x283x230mm / 4.1kg
Price £1499
Auris Audio
Supplied by: Elite Audio Ltd, Fife
01334 570 666