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

1121nad400.lab1

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

1121nad400.lab2

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

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