Mixer-systems for up/down-converting frequencies comprise many components: in case of balanced quadrature conversion, some parts will show a fourfold repetition (insight). By creating a three-phase mixer-system (10,40), less components will be necessary (basic idea). The sub-signals in the group of sub-signals at the sub-outputs have phase differences being present between two subsequent sub-signals within an interval of 100-140 degrees, which makes these sub-signals already (substantially) balanced. In case of said phase differences being each within an interval of 118-122 degrees, the sub-signals are even better balanced, and when being 120 degrees, the sub-signals are perfectly balanced. A group of transistors (11-13,14-16,17-19,41-43,44-46,47-49) per sub-input (1,2,3) switches and/or amplifies the sub-signals at the sub-inputs. In an active mixer-system (10), said groups of transistors (11-13,14-16,17-19) are switched by further transistors (20-22). In a passive mixer-system (40) said groups of transistors (41-49) are in dependence of the group of sub-signals at the further sub-inputs (4,5,6) switched from low/high to high/low impedance.