If there is no hum. The powersupply is good enough.
You must look at the grounding between source and preamp or preamp and housing. Better is no connection between input plug and chassis and/or connection between preamp ground and housing.
How looks the source/volumecontrol you use?
You must look at the grounding between source and preamp or preamp and housing. Better is no connection between input plug and chassis and/or connection between preamp ground and housing.
How looks the source/volumecontrol you use?
