Pre/Power Amplifiers

An established part of the Simaudio stable, the MOON 740P preamp is also the 'squeaky clean' half of this amplifier duo. With the offset at 0dB, overall gain is +6dB (or x2, balanced in/out) and the A-wtd S/N ratio a fabulously wide 100dB (re. 0dBV). Maximum output is a full 20V from a standard 73ohm source impedance while the response is exceptionally flat and extended – within ±0.04dB from 1Hz-100kHz. Distortion is also very low indeed at just 0.0001-0.0003% (20Hz-20kHz, re. 0dBV) – some two orders of magnitude lower than that of the partnering 860A v2 power amp [black vs. red traces, Graph 2 below].

Talking of which... the MOON 860A v2 power amp bested its 225W/8ohm rating with ease at 2x289W/8ohm and although its 4ohm output heads north of 530W it is impossible to measure a continuous <1% THD maximum output without popping the 5A/250V line fuse. Dynamic measurements are safer, revealing a capacity of 297W, 585W and 1.13kW into 8, 4 and 2ohm loads but show a limit of 360W/1ohm [see Graph 1, below]. Distortion increases gently with level from 0.003%/1W, 0.005%/10W and 0.025%/100W up to 0.06% at the rated 225W (all at 1kHz), and at low and high frequencies [red trace, Graph 2] to the tune of 0.008%/20Hz and 0.015%/20kHz (all 10W/8ohm). While this and the mild treble roll-off (–0.6dB/20kHz to –6.9dB/100kHz) suggests some slight 'character' on the 860A v2's part, the fabulous low 0.005ohm output impedance (20Hz-3kHz) suggests great control while the huge 96dB A-wtd S/N ratio (re. 0dBW) promises super-silent backgrounds. Finally, the DC-coupled output option gives a +0.9dB boost at 1Hz (!) while the AC-coupled mode rolls away to –1dB/10Hz to –3dB/5Hz. PM