A timepiece oscillator includes a sprung balance assembly including a balance with a rim, which is returned by a balance spring and pivoted with respect to a structure, on a first side by a torsion wire, fixed by an anchoring element to the structure, and on a second side, opposite to the first side, by a contactless magnetic pivot. The balance includes a first pole embedded with the balance and the torsion wire, this first pole having a symmetry with respect to the axis of the sprung balance assembly, and cooperating with a second pole included in the structure, for the magnetic suspension of the first pole, and to exert on the distal end of the torsion wire, opposite to this anchoring element, a magnetic force for tensioning the torsion wire.