HeadRoom Max headphone amplifier Measurements part 2
Fig.4 HeadRoom Max, small-signal 10kHz squarewave into 100k ohms.
Fig.5 HeadRoom Max, crosstalk (from top to bottom at 10kHz): L-R, R-L with filter & processor on; L-R, R-L with filter & processor off (10dB/vertical div.).
The THD+noise vs frequency results, for a 2.5V output into a load of 40 ohms (representative of the headphones likely to be used with the Max), are plotted in fig.6. The distortion here is very low—I was unable to get a recognizable waveform with the fundamental notched out until the output began to clip. This overload occurs quite abruptly; below clipping, only noise was visible on the 'scope.
Fig.6 HeadRoom Max, THD+noise (%) vs frequency at 2.5V into 40 ohms (right channel dashed).