Integrated Amplifiers

While Soulnote makes no claims for Class A operation, the A-2 is richly biased (idle consumption is 170W) and idle temperature is ~43°C on the top plate and ~30°C from the main chassis. The ‘no NFB’ claim is hardly reinforced by the A-2’s excellent thermal stability – THD barely shifts from 0.025-0.027% at 1kHz/10W over 30mins as the amp heats up – or the usefully flat 0.069ohm output impedance (20Hz-20kHz), but distortion is not super-low even if this is confined to simple 2nd/3rd harmonics with a hint of 4th, 5th and 7th. Soulnote rates the A-2 rather vaguely at ‘0.03%/50W’ but that’s not too wide of the mark with 0.02-0.03% [pink trace, Graph 2] and 0.055-0.1% [red trace, Graph 2] at 10W and 75W, respectively (re. 20Hz-20kHz). Importantly, while THD is impressively uniform with frequency, and increases from 0.01-0.09% from 1W to 100W, it’s lower still at just 0.002-0.004% at 100mW [0.1W re. 20Hz-20kHz; grey trace, Graph 2].

The A-2’s (ultrasonic) response flatness depends on volume position, not level, so from ‘2-20’ it is –0.06dB/20kHz and –0.7dB/100kHz; from ‘21-25’ it is –0.1dB/20kHz and –1.15dB/100kHz; from ‘26-35’ is –0.18dB/20kHz and –2.6dB/100kHz (all re. 1kHz at 10W/8ohm). In all instances there’s a very gentle shelving of bass to –0.05dB/100Hz and –0.08dB/20Hz. Incidentally, gain is lower than the usual +40dB at +30.7dB, making far better use of this volume control with modern digital sources. And power? The A-2 beats its 100W spec. at 2x128W/8ohm and 2x210W/4ohm while offering an increased 150W and 295W into 8/4ohm under dynamic conditions [see Graph 1]. However, this is limited to 368W and 188W (13.7A) into 2 and 1ohm loads, respectively, by electronic protection [blue and green traces, Graph 1]. PM