McIntosh MC1201 monoblock power amplifier:
Measurements part 2
Note the rise in distortion in the mid-treble with our simulated speaker load, which suggests that the big McIntosh is uncomfortable with loads possessing moderately high phase angles. (Fig.4, taken from the 8 ohm tap, is the worst-case example.) However, this may well be of academic interest, given the amplifier's enormous power reserve and the fact that the distortion content is almost entirely third-harmonic (figs.5 and 6). Note, by the way, the enormous power levels at which these two graphs were taken; this was necessary to raise the harmonic distortion out of the amplifier's very low noise floor. Even though the third harmonic is well-defined in fig.5, its absolute level was just 0.0045%! Intermodulation distortion (fig.7) was also astonishingly low, even at the 800W level at which this graph was plotted.

Fig.5 McIntosh MC1201, 8 ohm tap, 1kHz waveform at 455W into 8 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.6 McIntosh MC1201, 8 ohm tap, spectrum of 50Hz sinewave, DC-1kHz, at 805W into 8 ohms (linear frequency scale).

Fig.7 McIntosh MC1201, 8 ohm tap, HF intermodulation spectrum, DC-24kHz, 19+20kHz at 805W into 4 ohms (linear frequency scale).