Testing of current Instrument Transformers relieson low-distortion wideband generation, in particular for themodern exigency of extending testing in the supraharmonic range(up to 150 kHz). Whereas single-tone amplitude accuracy andcontrollability has been mostly considered so far, low-distortionfor non-linearity verification and transient behaviour in presenceof commutating semiconductor devices are also relevant. Thedesign of a stable, accurate and low-distortion amplifier is dis-cussed, featuring 15 A output and sub-μs rise time in the presentrealization, but scalable to higher current. Design solutions wereselected that can be easily replicated, including minor variantsto adapt to different exigencies. Preliminary experimental resultsof the prototype are reported.