An apparatus for generating a sinusoid at a pre-set frequency f includes a DC power source with a controllable output voltage, a transformer, a power switch, a sequencer, and an output filter. The power switch is configured to apply the output of the DC power source to the primary of the transformer in either direction or to remain off based on control signals that are applied to its control input. The sequencer applies control signals to the control input in a choreographed sequence to form an oversampled version of a sine wave. The output filter is connected to the secondary of the transformer, and it passes the pre-set frequency f and attenuates frequencies above a cut-off frequency. In some preferred embodiments, the cut-off frequency is 3f and the transfer function of the output filter has a zero at 5f.