Transformers (1) for transforming primary signals into secondary signals comprise primary and secondary parts that comprise boards (11-14, 21-23) with turns. By introducing distances larger than zero between for example any pair of neighboring boards (11-14, 21-23), parasitic capacitances of the transformers (1) are reduced, and the secondary signals may comprise relatively fast/high voltage pulses having rise times >1 kV/μsec. To reduce proximity effects and any resulting losses, the primary and secondary boards (11-14, 21-23) may be stacked in interleaved ways. Such sandwich constructions reduce leakage inductances. In a particular direction, distances between subsequent primary boards (11-14, 21-23) and distances between subsequent combinations of primary and secondary boards (11-14, 21-23) are to be increased to further reduce capacitive losses in that particular direction. Relatively low voltage differences may be present between relatively close boards (11-14, 21-23), and relatively high voltage differences may be present between boards (11-14, 21-23) that are relatively far away from each other.