class AB
mechanical noise is minimum, if I put thr trafo on the floor, its quiet. Set the trafo on some sheet metal, it starts making a buzzing noise. So I thought as simple test, when the trafo is far enough from the sheet metal, so it stops buzzing, then it would not induce that much into the housing either and subsequently into the housing and the circuits.
When I disconnect thr trafo and frrd the amp via a lab power supply, the speakers have a small pure 50 Hz hum. If I leave the trafo indide the housing and connet to 240V but not to the rectifiers/caps. Feed in from lab supply. Then there is a buzz in the speakers, the kind of sound like a step down transformer nearby. Mostly high frequency. Now I got 2 way speakers connected, it tends to come from the high frequency end. Rectifier is not connected, just to get that one eliminated as source.
I was hoping, eliminating the pysical noise (the housing stops vibrating, since it gets less magnetic field) would also eliminate the noise coming from the speakers.
Crossover is a separate board, disconnected. Has seperate power supply, disconnected.
Its starground.
I cannot see anything on the scope, but its annoying, can hear it from 2m away