I tried all the possibilities I had. Unregulated and regulated. Regulated was better but not perfect. The transformer is roughly used on filament PSU. We are pumping 5,2A constantly, and the caps haven't got enough guts to handle that. There is something like 2 or 3 volt sawtooth on the DC...
The drums sounsamples are made with a regulated PSU based on 2 LM350. I had to add a cap (330uF) to the adjust resistor and went with four 4700uF caps ( and not 2 ) to limit the oscilation. Of course, I played with the transformers place and put a metal shield between the toroid transformer and the electronics...
And the hum is still here :-\, small but here...