A device for the production of a transformer is disclosed, comprised of at least two electrically conductive windings (A, B, C) adjacent to one another, and a ferromagnetic core (11; N2; N3) linked to the two electrically conductive windings, formed by wound strip-shaped ferromagnetic material. The device comprises guide members (9) configured and arranged so as to define a closed path linked to the two electrically conductive windings, along which one or more strip-shaped ferromagnetic materials can be wound from at least one coil (R; R1-R18).