Below you'll find the measurements from the NuForce Reference 8 amplifier, measured on a professional Audio Precision measurement system. The first plot shows the frequency response of the amplifier, the first sweep was done in a 4-ohm load (Cyan) the second with a 8-ohm load (Green), as is evident from the plot the amplifier has a virtually load independent frequency response.
The second plot shows the intermodulation distortion at 18KHz +/- 250Hz. This plot is clearly showing uneven products between the two test tones which indicates a high even order distortion, this could have been prevented by tying the loop around the entire full-bridge, and not just part of it.
The third plot shows the total harmonic distortion (THD) and noise (N) plotted against the frequency. As is evident the amplifier has a rising THD+N with frequency, much like conventional amplifiers. Other class-D amplifiers, for example UcD, are able to offer THD+N figures virtually independent of the frequency.
The last plot shows the total harmonic distortion (THD) and noise (N) plotted against output power. What is clear here is that the amplifier is abruptly cut off when the output power exceeds 100-watts. This results in excessive distortion levels at high outputs with sources that have a high dynamic range.
Overall these results are somewhat dissapointing; the way the output power is cutoff when it exceeds 100-watts is a genuine concern, as is the high even order distortion products at the output. The other results are not any better than a run-of-the-mill low cost amplifier, which puts the NuForce Reference 8 amplifier firmly into that category.