The release of "Autobahn" in 1974 saw Kraftwerk moving away from the sound of its first three albums. Hütter and Schneider had invested in newer technology such as the Minimoog and the EMS Synthi AKS, helping give Kraftwerk a newer, "disciplined" sound. "Autobahn" was also the last album that Conny Plank engineered. After the commercial success of "Autobahn" in the US, where it peaked at number 5 in the Billboard Top LPs & Tapes, Hütter and Schneider invested in updating their studio, thus lessening their reliance on outside producers. At this time the painter and graphic artist Emil Schult became a regular collaborator, designing artwork, cowriting lyrics, and accompanying the group on tour.