Pre/Power Amplifiers

Although promoted as 'The most powerful amplifiers ever developed by darTZeel', the NHB-468 is no more powerful than the previous NHB-458 [HFN Jun '12]. Like its predecessor, the '468 still smashes its rated 450-465W/8ohm specification by delivering 550W/920W into 8/4ohm loads and rising still further to 625W/1017W, respectively, under dynamic conditions (all re. 1% THD). DarTZeel's protection circuitry now limits output to 565W/2ohm and 305W/1ohm [see Graph 1, below] but its output impedance is unchanged at 0.3ohm and its response remains extremely extended to –0.04dB/20kHz to –0.55dB/100kHz. The A-wtd S/N ratio is only 1dB less at 86.2dB (re. 0dBW) but the new '468 really shows its true colours in respect of distortion. Not only is this now predominantly 2nd/3rd order (instead of 3rd/5th/7th in the '458) but it is both impressively consistent both vs. output level and frequency [see blue, pink, red traces, Graph 2]. Under continuous conditions, distortion is typically 0.073-0.15% from 20Hz-20kHz across 1W-300W/8ohm.

The partnering NHB-18NS preamp has also evolved since last tested [HFN May '08], the +10.2dB gain now +5.6dB (–6dB setting), +11.55dB ('0dB') and +11.25dB ('Pro'). The response remains super-flat out to –0.3dB/100kHz (Pro) and –0.15dB/100kHz (0dB) although the A-wtd S/N ratio has fallen slightly from 83.9dB to 80.8dB here. Distortion, however, is now significantly lower, especially at low frequencies, thanks to the transformer-coupled inputs being replaced with an active stage. As with the NHB-468, distortion is now impressively consistent with frequency – now just 0.0023-0.0032% across a wide 5Hz-40kHz [see black trace, Graph 2]. PM