Abstract: An amplifier system for energizing a d.c. motor from a power source in response to an error signal includes a bridge circuit including a first switching transistor pair for supplying a first current from the power source through the motor in one direction and a second switching transistor pair for supplying a second current from the power source through the motor in the opposite direction. A zero crossing detector determines the sign of the error signal and enables the first transistor pair when the error is positive and enables the second transistor pair when the error is negative. A current sensing resistor senses the first and second currents through the motor and provides a motor current signal representative thereof. An absolute value circuit provides an absolute value error signal representative of the magnitude of the error signal.