Network Audio Players/Servers

What Cambridge Audio once called Class XD (Crossover Displacement) is reborn in its Edge A integrated [HFN Nov '18], Edge W power amp and now the Edge M as 'Class XA'. It's a novel method of bypassing the crossover distortion produced when music signals 'cross' from positive to negative-going (and vice-versa) and the complementary pairs of power transistors momentarily switch off. Class A operation – maintaining sufficient quiescent current to keep all output transistors 'on' at all times – is the brute force method, but it's inefficient and costly.

Cambridge's elegant alternative doesn't eliminate the transition between NPN and PNP transistors, but simply shifts it away from the zero-crossing point of the waveform – hence the original name 'Crossover Displacement'. It does this by applying a negative bias current, shifting the position of the crossover point without creating a DC offset. Where crossover distortion is most audible, at low signal levels [black trace, Graph], Class XA/XD moves the crossover point below the maximum negative swing of the audio waveform, yielding the benefits of pure Class A without the heat. PM