In some examples, a drive signal generator for a fluid ejection element of a piezoelectric printhead, includes a core amplifier to amplify an input waveform to provide an amplified waveform, and a plurality of rail power circuits, each coupled to a different power input of the core amplifier. Each rail power circuit of the plurality of rail power circuits includes a comparator to compare an instantaneous voltage of the amplified waveform to a subset of a plurality of voltage sources, and a switch to, based on the comparing by the comparator, couple to a respective power input of the core amplifier a voltage source in the subset of the plurality of voltage sources that is closest to the instantaneous voltage and sufficient to generate the amplified waveform.