Integrated Amplifiers

The features, applications and specifications for the Ncore module at the heart of the X250T (and X250) are available to download here. Extraudio changed its '200W/8ohm' power output rating during the course of our review – this is a 150W/8ohm Class D module with onboard PSU and, as expected, on test it delivered 2x150W/8ohm and 2x280W/4ohm. Also, because this is a PWM/Class D amp, there is no significant headroom under dynamic conditions, and so the X250T offers 151W, 285W, 275W and 195W into 8, 4, 2 and 1ohm loads at 1kHz/10msec at <1% THD [see Graph 1, below]. This is more than sufficient for most 'sane' loudspeakers.

Distortion also shows a distinctive pattern. From 1-10W it bests Extraudio's 0.008%/1W/1kHz specification by a decent margin at ~0.001% but then increases to 0.007%/20W, 0.06%/50W and 0.11%/100W. However, bearing in mind that most hi-fi amp/speaker combinations are running at or below 10W for much of the time, the subjective impact of this is uncertain. On the other hand, the trend of distortion vs. freq. – from a very low 0.0009% through bass and midrange before a sudden rise above 10kHz to 0.03%/20kHz is entirely typical of this Class D module [Graph 2, below]. Output impedance remains a low ~0.019ohm (20Hz-20kHz), as indicated by Hypex, with an ultrasonic peak of 1.01ohm at 93kHz. The frequency response cannot meet Extraudio's claimed 0.5Hz–350kHz/–1dB (this spec may be for the custom preamp section only) but has a –1dB point at 25kHz and –6dB/100kHz. Finally, the 83dB A-wtd S/N ratio (re. 0dBW) is excellent for a Class D amplifier. PM