Outboard DACs

This product is a story of two halves: a dual-ESS9018-based USB DAC/preamp with solid-state and triode-tube output option, and a very capable analogue headphone amplifier. The latter has 'Low' and 'High' output options, ostensibly to match low and higher output headphone impedances, but both settings have the same high-ish 10ohm source impedance, potentially exaggerating swings in response with low/variable impedance headphones. Into a 'flat' 25ohm load there's a 2.5dB signal loss but the response extends from 9Hz-65kHz (–1dB). In practice, 'Low' and 'High' set the HA500H's overall gain at +7dB and +13dB, respectively, and determine the maximum output voltage into high impedance loads (4.6V and 9.1V) together with the maximum power into lower loads (448mW and 1650mW/25ohm). Very low impedance phones are well served too as the HA500H delivers a full 1350mW (1.35W) into 8ohm [see Graph 1] – sufficient to drive the super-sensitive Avantgarde Primo Duo XD speakers! Distortion is very low at 0.0004-0.002% into high impedances, increasing with decreasing headphone impedance and lower frequencies to 0.008%/1kHz and 0.025%/200Hz and 0.048%/20Hz (all 10mW/25ohm).

The DAC/line output offers 4.13V at 0dBFs (balanced XLRs) with a maximum A-wtd S/N of 114.2dB and distortion falling as low as 0.0002-0.005% (20Hz-20kHz) over the top 30dB of its dynamic range [see black/blue traces, Graph 2]. Responses reach out to ±0.01dB/20kHz (Fast digital filter), –2.9dB/20kHz (Slow) and ±0.04dB/20kHz (Minimum phase) with CD/48kHz data. The tube buffer has little impact on S/N but THD increases to 0.13-0.50% at maximum output [see red/green traces, Graph 2] while the low frequency response rolls away to –1.0dB/20kHz. PM