An ultrasonic surgical assembly includes an ultrasonic transducer operable to convert a received motional current into a movement of a cutting blade of an ultrasonic waveguide, a measurement circuit connected in a parallel configuration with the ultrasonic transducer, a variable power source operable to supply current through a set of connection points to the parallel configuration and thereby create the motional current in the ultrasonic transducer, and a current controller operable to regulate the motional current by varying an output of the variable power source, thereby maintaining a substantially constant rate of movement of the cutting blade across a variety of cutting loads.