Simaudio MOON 250i Integrated Amplifier Lab Report

Lab Report

Although this ten-year-old integrated has certainly benefitted from component upgrades and a little 'light dusting' since its 'Neo' incarnation [HFN Jun '14], Simaudio's 250i is otherwise a classic example of 'if it's not broken, don't fix it'. It's refreshing to discover the amplifier's performance is as solid and competitive now as it was in 2014, benefitting from improvements in S/N, output impedance and drive into 2-4ohm. Rated at 50W/8ohm and 100W/4ohm, it achieves closer to 2x68W and 2x100W into 8/4ohm, respectively, and there's sufficient headroom garnered by that 320VA transformer to yield 83W, 152W and 250W into 8, 4 and 2ohm under dynamic conditions [see Graph 1]. The Class AB power amp is protected against shorts, so its output remains limited to 56W/1ohm. The 250i's output impedance is now a uniform 0.021-0.029ohm (20Hz-20kHz), increasing to 0.12ohm/100kHz, while the response reaches out from 5Hz-58kHz (–3dB) with a gentle treble roll-off down to –0.5dB/20kHz.

Overall gain is a sensibly restrained +36.5dB while the A-wtd S/N ratio is a deeply impressive 91.3dB (re. 0dBW). This is a very 'quiet' integrated amplifier suited for use with sensitive speakers, where hiss might otherwise intrude, while still possessing sufficient 'grunt' to tackle less sensitive/lower impedance boxes. Distortion is low and well managed too, achieving a minimum of 0.002% from 2W-20W before increasing to 0.004%/30W, 0.008%/40W and 0.016% at the rated 50W (all re. 1kHz/8ohm). Versus frequency there's just a slight rise at HF, from 0.002%/1kHz to 0.04%/20kHz (re. 10W/8ohm) and 0.12%/ 20kHz (re. 30W/8ohm) [Graph 2, below]. Finally, the analogue volume control 'law' marshals the top 6dB of gain from 12 o'clock onwards. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 11.2A


Distortion vs. frequency at 1W/8ohm (black, 5Hz-40kHz), 10W (pink) and 30W (red, 20Hz-20kHz)

Continuous power (<1% THD, 8/4ohm) 68W / 110W
Dynamic power (<1% THD, 8/4/2/1ohm) 83W / 152W / 250W / 56W
Output imp. (20Hz–20kHz/100kHz) 0.021–0.029ohm / 0.12ohm
Freq. resp. (20Hz–20kHz/100kHz) –0.3dB to –0.5dB / –6.5dB
Input sensitivity (for 0dBW/50W) 42mV / 305mV
A-wtd S/N ratio (re. 0dBW/50W) 91.3dB / 108.3dB
Distortion (20Hz-20kHz, 1W/10W) 0.0017-0.026% / 0.0023-0.045%
Power consumption (idle/rated o/p) 20W / 190W (18W standby)
Dimensions (WHD) / Weight 429x89x366mm / 8kg
Price £1900

Simaudio Ltd
Quebec, Canada
Supplied by: Renaissance Audio, Scotland
0131 555 3922