Astell&Kern KANN Alpha Portable Player/Headphone Amp Lab Report

Lab Report

As we discovered when testing the A&Futura SE200 [HFN Feb '21], there are gaps in Astell&Kern's published specification. For example, the quoted 'Low', 'Mid' and 'High' unbalanced AMP settings of 2V, 4V and 6V are met at 2.14V, 4.22V and 6.25V but these values are achieved into a high 47kohm load ('unloaded' in the context of a headphone). In practice the KANN Alpha clips at 35mW/32ohm (or 1.06V) in the 'Low' mode and 85mW/32ohm (or 1.65V) in either the 'Mid' or 'High' modes. These correspond to volume settings of '138' and '127' with a peak level (0dBFs) digital input, so the dial should be used between 139-150 (Low) and 128-150 (Mid or High) with caution, not least for fear of generating potentially harmful in-ear SPLs. For the very lowest impedance 'phones the Alpha offers 22mW/8ohm at 1% THD.

The ES9068AS DACs are new to this A&K model and power a fabulous performance that includes a very wide 117dB A-wtd S/N ratio, low levels of correlated jitter (typically ~50psec with all sample rates up to 192kHz) and vanishingly low distortion that falls to 0.0002-0.0005% (re. 0dBV, 20Hz-20kHz), increasing only over the top 25dB of its dynamic range under load (0.001-0.008% at 10mW/32ohm) [see Graph 1, below]. Importantly, the output impedance is a very low sub-1ohm from 20Hz-20kHz, ensuring that the KANN Alpha/headphone system response is not influenced by low and variable in-ear/on-ear loads. With its default linear phase filter, the response is a ruler flat ±0.01dB (20Hz-20kHz), dipping to just –0.6dB/45kHz with 96kHz media. The minimum phase filter cuts above 18kHz to reach –5.0dB/20kHz and the hybrid filter is steeper still at –12dB/20kHz [see Graph 2, below]. PM


THD vs. digital signal level at 1kHz (black, unloaded; grey, into 32ohm) and 20kHz (blue, unloaded; cyan, into 32ohm where 0dBFs = 85mW)


Impulse and HF responses for Linear/Fast (black), Minimum/Slow (red) and Hybrid (green) filters

Maximum output (<1% THD into 47kohm) 6250mV (single-ended)
Maximum power output (<1% THD) 85mW/32ohm (single-ended)
Output Impedance (20Hz-20kHz) 730-1140mohm (single-ended)
A-wtd S/N ratio (re. 10mW/0dBFs) 105.5dB / 117.0dB
Distortion (20Hz-20kHz, re. 10mW/0dBV) 0.001-0.008/0.0002-0.0005%
Frequency resp. (20Hz-20kHz/45kHz) +0.00dB to +0.0dB/–0.45dB
Digital jitter (48kHz / 96kHz) 55psec / 50psec
Battery 5600mAh/3.8V Li-Polymer
Dimensions (WHD) / Weight 68.3x117x25 / 316g
Price £1099

Seoul, South Korea
Supplied by: Armour Home Electronics, Herts
01279 501111