MBL Noble Line N11/N15 Preamp & Monoblock Power Amps Lab Report

Lab Report

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


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max current is 31.6A


Distortion vs. freq for N11 (re. 0dBV, black) and N15 (re. 1W/8ohm, blue; 10W, pink; 100W, red)

Continuous power (<1% THD, 8/4ohm) 352W / 615W
Dynamic power (<1% THD, 8/4/2/1ohm) 402W / 786W / 1.50kW / 1.0kW
Output imp. (20Hz–20kHz, pre/power) 96ohm / 0.016–0.04ohm
Freq. resp. (20Hz–100kHz, pre/power) +0.0 to –0.2dB / +0.0 to –4.5dB
Input sensitivity (for 0dBV/0dBW) 323mV (pre) / 116mV (power)
A-wtd S/N ratio (re. 0dBV/0dBW) 101.1dB (pre) / 82.0dB (power)
Distortion (20Hz-20kHz, 1V/10W) 0.00006-0.0003/0.0004-0.0095%
Power consumption (idle/rated o/p) 25W/665W (21W, preamp)
Dimensions (WHD, Pre/Power) 450x150x450/450x150x425mm
Prices (Pre & Monoblocks): £11,500/£13,900 (each)

MBL Akustikgeräte GmbH & Co. KG
Berlin, Germany
Supplied by: Stranger High Fidelity, Real World Studios, Wilts
07702 155847