HeadRoom Max headphone amplifier Measurements part 2

While the Max's 1kHz squarewave response is good enough to make its presentation here unnecessary, the 10kHz response in fig.4 clearly shows the HF rolloff indicated in fig.1. The crosstalk shown in fig.5 indicates virtually identical performance between channels, and the (deliberate) increase in crosstalk when processing is engaged.

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).