- Μηνύματα
- 5.581
- Reaction score
- 298
http://www.stereophile.com/solidpoweramps/1006sonic/index4.html
"Peculiarly, the Super T is more linear at low frequencies into low impedances than it is into high ones (fig.5). Above 1kHz, however, the amplifier clearly has trouble maintaining its linearity into all loads. Looking at the distortion content without the low-pass filter engaged, what appears to be subjectively innocuous third-harmonic content is overlaid with spikes that coincide with the signal's zero-crossing points (fig.6). Switching in the low-pass filter smooths these spikes over (fig.7) but doesn't eliminate them, confirming that they are characteristic of the Sonic Impact, not the result of any unwanted interaction between the ultrasonic noise in the amplifier's output and my Audio Precision test set.
What was interesting was that these spikes are not present with the Super T passing low frequencies. Fig.8, for example, shows a spectral analysis taken with the low-pass filter of the amplifier's output while it drove a 50Hz sinewave at relatively high power into 4 ohms. The second harmonic is the highest in level, at an excellent –83dB (0.007%), with the third and fifth harmonics lying at –90dB (0.003%). (These odd-order harmonics disappear if the load impedance is increased to 8 ohms, leaving just the benign second harmonic as the primary spurious component.) But with a 1kHz sinewave at the same power into the same load, again with the 30kHz low-pass filter in front of the analyzer's input (fig.9), the third is now the highest-level harmonic, at –66dB (0.05%), and some high-order components can be seen, correlating with the spikes seen in the waveform graph."
"Peculiarly, the Super T is more linear at low frequencies into low impedances than it is into high ones (fig.5). Above 1kHz, however, the amplifier clearly has trouble maintaining its linearity into all loads. Looking at the distortion content without the low-pass filter engaged, what appears to be subjectively innocuous third-harmonic content is overlaid with spikes that coincide with the signal's zero-crossing points (fig.6). Switching in the low-pass filter smooths these spikes over (fig.7) but doesn't eliminate them, confirming that they are characteristic of the Sonic Impact, not the result of any unwanted interaction between the ultrasonic noise in the amplifier's output and my Audio Precision test set.
What was interesting was that these spikes are not present with the Super T passing low frequencies. Fig.8, for example, shows a spectral analysis taken with the low-pass filter of the amplifier's output while it drove a 50Hz sinewave at relatively high power into 4 ohms. The second harmonic is the highest in level, at an excellent –83dB (0.007%), with the third and fifth harmonics lying at –90dB (0.003%). (These odd-order harmonics disappear if the load impedance is increased to 8 ohms, leaving just the benign second harmonic as the primary spurious component.) But with a 1kHz sinewave at the same power into the same load, again with the 30kHz low-pass filter in front of the analyzer's input (fig.9), the third is now the highest-level harmonic, at –66dB (0.05%), and some high-order components can be seen, correlating with the spikes seen in the waveform graph."
