Pre/Power Amplifiers

Sailing past its rated 300W/8ohm, Classé's Delta MONO punished the lab test loads with a full 410W/8ohm and 760W/4ohm, the very stiffly-regulated PSU going on to support 420W, 790W and 1361W into 8, 4 and 2ohm loads under dynamic conditions at very low levels of distortion [see Graph 1, below]. Power into 1ohm cuts at 1203W (34.7A) and the Delta MONO enters standby. Distortion is indeed exceptionally low through the Delta MONO's Class A range, from 0.0003%/100mW to 0.0002%/1W, 0.0001%/10W, 0.0003%/100W and 0.0006% at the rated 300W (all 1kHz/8ohm). Residual noise is low too, and the A-wtd S/N a wide 92.6dB (re. 0dBW) for an overall gain (balanced in) of +29.1dB. The response is flat to –0.05dB/20kHz and –0.6dB/100kHz and output impedance low at 0.01ohm.

The Delta PRE analogue preamp offers a huge 20V maximum output (balanced), a gain of +14.3dB, distortion gently increasing from 0.0002-0.0016% (0dBV, 20Hz-20kHz) and a promising 98dB A-wtd S/N ratio. The response rolls out to –0.2dB/20kHz to –6.4dB/100kHz although the AK4497-based DAC section, with steep roll-off linear phase filter selected by Classé, has its 'own' response of –0.2dB/20kHz, –0.8dB/45kHz and –3.1dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. Set to a 4V (balanced) output for a 0dBFs digital input, the PRE offers a very wide 115dB A-wtd S/N ratio and distortion is a consistent ~0.0014% (20Hz-20kHz). THD falls to a minimum of 0.0002-0.0007% over the top 30dB of its dynamic range [see Graph 2] and low-level linearity holds good to within ±0.1dB over a full 110dB dynamic range. Jitter meanwhile is suppressed to ~50psec across all inputs/sample rates. PM