VTL MB750 monoblock power amplifier Measurements part 3
VTL MB-750, triode mode, spectrum of 50Hz sinewave, DC-1kHz, at 178W into 4 ohms (linear frequency scale).
VTL MB-750, triode mode, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 122 W into 4 ohms (linear frequency scale).
The THD+noise vs output power (1kHz) curves are shown in figs.9 and 10; Table 1 lists the discrete clipping levels (using 3% THD+noise as a clipping point).
VTL MB-750, triode mode, distortion (%) vs output power into (from bottom to top): 8 ohms, 4 ohms, 2 ohms.
VTL MB-750, tetrode mode, distortion (%) vs output power into (from bottom to top): 8 ohms, 4 ohms, 2 ohms.
VTL MB-750 Clipping
(3% THD+noise at 1kHz)
|8||236 (23.7)||426 (26.3)|
|4||266 (21.2)||454 (23.6)|
|2||65 (12.1)||56 (11.5)|
While the MB-750 is undeniably a powerful amplifier, our sample did fall noticeably short of its rated power at a reasonable distortion level—though at a voltage level closer to 120V, the power output in triode mode increased by about 10% from the above values. Still, most users are unlikely to hear any audible power limitation, even in triode mode.
The VTL MB-750's test-bench results, though not exceptional, are more than respectable for a very-high-power tube amplifier.—Thomas J. Norton