Pre/Power Amplifiers

Tested in its standard guise (see boxout, p41, for 'Unity Gain' mode) the N11 preamp offers a +9.8dB gain and vanishingly low distortion of 0.00006-0.0003% (20Hz-20kHz re. 0dBV, balanced in/out). Full output is 10V from a 96ohm source impedance, the A-wtd S/N ratio is a respectable 101dB (re. 0dBV) while the freq. response extends from sub-1Hz to 100kHz within ±0.15dB.

The fully balanced operation of the partnering N15 monoblock(s) is just one reason behind its claimed, superior, common-mode rejection. In practice it is remarkably 'clean' and free of PSU hum and noise to the tune of –86dBV (10-500Hz) even though the smooth increase in white noise from the Class D modulator takes this to –71dBV with an A-wtd S/N of 82dB (re. 0dBW, 20Hz-20kHz). MBL rates the power output as 300W/8ohm and 560W/4ohm which, in practice, turns out to be a very generous 352W/8ohm and 615W/4ohm with sufficient headroom (almost unheard of in a Class D architecture) to sustain 402W, 785W, 1499W and 1001W into 8, 4, 2 and 1ohm loads, respectively, [see Graph 1, below].

Moreover, MBL has pushed out the inevitable rise in inductive output impedance to beyond 60kHz, the low 0.016ohm achieved across the audioband increasing, finally, to 0.3ohm/90kHz and 2.5ohm/100kHz. By the same token, the global feedback that's central to the Ncore modules ensures the N15's response is unaffected by speaker load, reaching out from a sub-1Hz bass to –0.5dB/20kHz and dipping to –5.5dB/60kHz. Distortion, too, follows a similar pattern – 'flat' at a very low 0.0004% from 20Hz-2kHz, rising to 0.01%/20kHz then 0.23%/40kHz (all 10W/8ohm) [see Graph 2, below]. PM