Headphones

While Keith was testing the Aperio headphones, its partnering Aperio DAC/preamp was put through its paces in my lab. Testing the proprietary headphone output with its 1.8kV DC bias voltage was impractical, but the ESS9038-based DAC/preamp remains accessible via the USB and S/PDIF digital inputs and balanced XLR analogue line outputs. In practice this turns out to be a textbook implementation of ESS's latest Sabre DAC and one that clearly benefits from the brand's proprietary jitter suppression technology to the tune of <10psec at any incoming sample rate [see inset Graph].

The maximum line output is 2.66V from a fabulously low <200mohm source impedance, delivering a wide 112dB A-wtd S/N ratio and THD that falls as low as 0.00008% over the top 20dB of its dynamic range through bass and midrange [black infill, top inset Graph]. Distortion is almost inevitably higher at 20kHz but its minimum of 0.0004% over the same 20dB is impressive [blue infill, top inset Graph]. A steep linear phase digital filter is selected, offering a 99dB stopband rejection, and a response flat to ±0.02dB with CD/48kHz sources, a steep cut-off of –0.7dB between 43-45kHz (96kHz media) and –8.6dB between 70-90kHz (192kHz media). The only oddity: this line output is phase-inverting but is corrected in the Class A driver amp to the Aperio 'phones, where the output is phase positive. PM