Eliminating RFI


Dear All
I am experiencing problems for the first time with RFI through my Singlepower headphone tube amp. I have concluded that it is due to an unclean power supply as I do not pick up this interference using a wall plug in another room in the apartment and as I have also swapped out power cables and interconnects in the room to no effect. Most of my equipment is UK 240 volts and I run the mains (Brazil 110 volts) through the transformer to the equipment - however, I have never experienced any problems with this equipment - but as the headphone amp is 110 volts I am running it directly through the Brazilian mains (without the transformer) and I am now having problems.
Does anyone have any suggestions for me to eliminate this interference? I need to keep all my gear in this room so moving it all to another room is not an option unfortunately.
Many thanks
James
vicks7