Network Audio Players/Servers

Driven directly via its single-ended headphone socket, the QP2R's maximum output is 40mW/25ohm or 5.5mW/600ohm at <1% THD (the maximum volume setting is '110' for a 0dBFs digital signal before clipping). Tested in 'maximum gain' and its notionally Class A 'high bias' modes, distortion from the QP2R via the HB2 hub is very low at 0.00025-0.00065% and only slightly higher at 0.0005-0.0095% via the headphone output (20Hz-20kHz). Distortion increases with output into lower headphone loads but 0.0008-0.014% is still very low indeed at, for example, 10mW/25ohm [see Graph 1]. It's also possible to achieve a slightly wider 106.3dB A-wtd S/N ratio via the unloaded QP2R's headphone output than via the HB2 at 104.5dB, while the former also enjoys a much lower source impedance of 0.5-0.6ohm versus 209ohm for the HB2's line out.

A sub-1ohm output impedance is key to the QP2R being able to drive low, variable impedance headphones/earbuds without further modification of the overall frequency response. In practice, while Questyle states that the QP2R is compatible with files up to 384kHz, and that its S/PDIF digital outputs are downsampled to 192kHz, its analogue output looks to be downsampled still further to 96kHz. So while CD/48kHz files are replayed across 20Hz-20kHz (±0.2dB), the response of files at 96kHz, 192kHz or greater have the same –3.3dB/45kHz response. While the QP2R's power output is readily beaten by the likes of the Chord Mojo [HFN Jan '16] or Oppo HA-2SE [HFN Dec '16], its distortion and noise performance is state-of-the-art, as is its jitter suppression. No other portable players or hub-powered DACs have achieved <10psec [see Graph 2]. PM

Maximum output (re. 0dBFs into 47kohm): 1.87V (HB2 line out)
Max. power output (re. 0dBFs into 25ohm): 40mW (headphone out)
Output Impedance (20Hz-20kHz): 500-600mohm
A-wtd S/N ratio (0dBFs; re. 2V/10mW) : 106.3dB / 101.2dB
Distortion (20Hz-20kHz, re. 10mW): 0.0008–0.014%
Freq. response (20Hz-20kHz/45kHz): +0.0 to –0.18dB/–3.3dB
Digital jitter (into 25ohm / 600ohm): <10psec / <10psec
Power consumption: 3100mA/3.7V battery
Dimensions (WHD) / Weight: 65x134x14.5mm / 200g
Price (QP2R/HB2): £1199/£599