NAD C 298 Class D Power Amp Lab Report

Lab Report

True to tradition, and despite being a Class D amp, NAD has engineered some useful headroom into the C 298 which supports peaks of 265W, 526W and 750W into 8, 4 and 2ohm loads with 450W/1ohm limited by current protection (21.2A). Note how there is no abrupt clipping point but, instead, maximum power is 'feathered' across 40W of 'extra' output as it approaches 1% THD into 8/4ohm loads [see Graph 1, below]. This is the modern-day equivalent of NAD's 'Soft Clipping'.

Otherwise, the continuous 235W/8ohm and 475W/4ohm power output is well in excess of NAD's 185W/8ohm and 340W/4ohm rated spec. for the C 298 – this conservative 'paper spec' is good to see, particularly as many Class D amplifiers seem rated very close to the wire these days. Bottom line? The NAD C 298 will go louder and prove more capable of driving difficult speakers than you might expect. The very low sub-5mohm output impedance will also assist in keeping bass tight while ensuring the C 298's response – flat to within ±0.04dB/20Hz-20kHz – is unaffected by swings in speaker impedance.

Distortion is fabulously low through bass and midrange frequencies at 0.0004%/1W, 0.0002%/10W and 0.0006%/100W, the inevitable rise at HF delayed here to above 10kHz, albeit only reaching a mere 0.003%/1W, 0.0065%/10W and 0.030%/100W at 20kHz [see Graph 2, below]. Again, these Purifi Eigentakt modules buck the trend of more traditional Class D solutions whose high frequency response and distortion are markedly influenced by speaker load [see HFN Aug '21]. Noise, too, is lower here than typical, the C 298 yielding a respectable 88.1dB A-wtd S/N ratio (re. 0dBW) for an overall gain of +28.7dB. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 21.2A


Distortion versus frequency versus power output (1W/8ohm, black; 10W, pink; 100W, red)

Power output (<1% THD, 8/4ohm) 235W / 475W
Dynamic power (<1% THD, 8/4/2/1ohm) 265W / 526W / 750W / 450W
Output imp. (20Hz–20kHz/100kHz) 0.005–0.004ohm / 0.001ohm
Freq. resp. (20Hz–20kHz/100kHz) +0.0dB to –0.04dB/–11.5dB
Input sensitivity (for 0dBW/185W) 104mV / 1418mV
A-wtd S/N ratio (re. 0dBW/185W) 88.1dB / 110.8dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.00019–0.0065%
Power consumption (Idle/Rated o/p) 25W / 430W (1W standby)
Dimensions (WHD) / Weight 435x120x390mm / 11.2kg
Price £1700

NAD Electronics International
Supplied by: Sevenoaks Sound and Vision, UK
01732 459555