VTL ST-85 power amplifier Measurements part 3
Fig.8 VTL ST-85, distortion (%) vs continuous output power into (from bottom to top): 8 ohms, 4 ohms, 2 ohms.
VTL ST-85 Clipping
(3% THD+noise at 1kHz)
|Both Channels Driven|
|One Channel Driven|
|8||63.3 (18)||64 (18.1)||72 (18.6)|
|4||78.6 (15.9)||77.5 (15.9)||95 (16.8)|
JA repeated this test using a 20% duty-cycle 1kHz toneburst and the Miller Audio Research Amplifier Profiler. The results are shown in fig.9. The lowest distortion is exhibited into 8 ohms (black trace), though the highest power is developed into 4 ohms (red trace, 50.7W for 1% THD+N, 121.75W for 3% THD+N). The little VTL, however, is not happy driving loads lower than 4 ohms, with high levels of distortion apparent even at low powers in to 2 ohms and 1 ohm (blue and green traces, respectively).
Fig.9 VTL ST-85, distortion (%) vs burst output power into (from bottom to top): 8 ohms (black trace), 4 ohms (red), 2 ohms (blue) and 1 ohm (green).
While none of these results is exceptional, they are respectable for what is, in today's market, a moderately priced tube amplifier.—Thomas J. Norton