SPL Phonitor xe DAC/Headphone Amp Lab Report

Lab Report

Key to the Phonitor's analogue performance are the proprietary 'VOLTAiR' discrete op-amps that feature in all its crossfeed/angle/laterality and main headphone preamp circuits. Running off high ±60V rails, the VOLTAiR-based headphone amp offers a 44.5V single-ended output, sufficient to develop an unprecedented 2.95W into 600ohm [black trace, Graph 1]! This voltage falls across lower impedances where maximum output is 865mW/32ohm (or 847mW/32ohm in the Low gain setting) with THD climbing from 0.015%/1mW to 0.018%/10mW, 0.043%/100mW, 0.4%/500mW and 0.7%/800mW/32ohm [orange trace, Graph 1]. There's sufficient current available to support 93mW into a very low impedance 8ohm insert earphone, for example [red trace, Graph 1] but note how distortion continues to increase with reducing headphone load. The effect is particularly marked at high frequencies as THD increases from just 0.0005%/20kHz unloaded (the VOLTAiR amps offer a vanishingly low 0.00005% THD at 1V/1kHz, unloaded) to 0.25%/20kHz into 32ohm.

The response extends from 1Hz-90kHz (–1dB) and gain is +0.5dB (Low) to +12.5dB (High) with ±3.4dB laterality (balance) either side. Residual noise is extremely low at 10µV (perfect for very sensitive 'phones) and the A-wtd S/N usefully wide at 99dB (re. 0dBV). Tested in the high gain setting, the USB DAC/headphone pathway yields a maximum 18.7V output (re. 1kHz/0dBFs) while the choice of fast roll-off/minimum phase filter in the AKM4490 DAC defines the digital/analogue response of –0.4dB/20kHz, –2.7dB/45kHz and –9.2dB/90kHz with 48/96/192kHz files. THD reaches a minimum of 0.0002-0.002% over the top 20dB of its dynamic range [see Graph 2], the A-wtd S/N is a wide 111dB and jitter moderate at 500-560psec (48kHz-192kHz/24-bit). PM


Power output vs. THD into 600ohm (black), 32ohm (orange) and low 8ohm (red) headphone loads


Distortion (unloaded) vs. 48kHz/24-bit digital level over 120dBFs range (1kHz, black; 20kHz, cyan)

Maximum output (<1% THD into 47kohm) 44.5V (single-ended)
Maximum power output (<1% THD) 865mW/32ohm (93mW/8ohm)
Output Impedance (20Hz-20kHz) 1.00–1.14ohm
A-wtd S/N ratio (re. 10mW/0dBV) 99.1dB / 110.9dB
Distortion (20Hz-20kHz, re. 10mW/0dBV) 0.013-0.25%/0.0012-0.0016%
Frequency resp. (20Hz-20kHz/100kHz) +0.0dB to –0.06dB/–1.35dB
Digital jitter (48kHz / 96kHz) 500psec / 560psec
Power consumption 19W
Dimensions (WHD) / Weight 278x100x330mm / 4.9kg
Price £1899 (£2499 with DAC768 option)

SPL electronics GmbH
Niederkruechten, Germany
Supplied by: SCV Electronics Ltd, Herts
03301 222500