On the Bench (JEJ)
We have a lot of graphs to go through here, so let's get started. For the tests, I used an Audio Precision AUX-002 switching amplifier filter, which reduces the amount of switching frequency noise getting into the Audio Precision test instrument.
At 1 kHz and 5 volts output into 8 ohms (a little over 3 watts, which is a typical listening power), THD+N was only about 0.03%.
At 4 ohms, THD+N went up a bit, but not significantly.
At 20 volts into 8 ohms (50 watts), THD+N was still low.
And at 4 ohms, still less than 0.04%.
IMD was also low, only 0.004% with the standard SMPTE/DIN test, using a combination of 60 Hz and 2 kHz at an output of 5 volts into 8 ohms. The test measures the resulting peaks ± 250 Hz around the upper test frequency.
At 4 ohms, IMD went up, expectedly, but it was still reasonably low.
Even at 20 volts output into 8 ohms, IMD was low, at 0.006%. As the chart indicates, the amplifier needed 1 volt input to produce the 50 watts output into 8 ohms.
And at 4 ohms, less than 0.02%.