Hi Peter, > On 19 Sep 2017, at 00:41, Ullrich Peter <Peter.Ullrich at kapsch.net> wrote: > > The 5532 oscillate quite easily if you forget to add the decoupling caps near the power pins. I do have two 22nF caps as close as possible in the circuit. I just wonder if an oscillating opamp really can trigger the mains hum we are experiencing? Michael.