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Fig 5: The concept of resistive crossover displacement. In and the following cases, the crossover
point is displaced positively by sinking a current into the negative rail.
This method suffers from poor efficiency, as the resistance acts as another load on the amplifier
output, effectively in parallel with the normal load. It also threatens ripple-rejection problems as R is
connected directly to a supply rail, which in most cases is unregulated and carrying substantial 100
Hz ripple. A regulated supply to the resistor could be used, but this would be very uneconomic and
even less efficient due to the voltage drop in the regulator. The resistive system is inefficient
because the displacement of the crossover region occurs when the output is negative of ground,
but when the output is positive the resistor is still connected and greater current is drawn from it as
the voltage across it increases. This increasing current is of no use in the displacement process
and simply results in increased power dissipation in the positive output half-cycles.
