How to improve power supply?

How should I "Mu metal the transformer"?

Use toroidal transformers - very small magnetic field outside.

All transformers should be wrapped with one or two,layers of mu metal, a highly permeable alloy. Toroidal transformers are no exception. In addition, if feasible, should be decoupled from the chassis by removing the bolt and by placing a layer of cork beneath the transformer, isolating the sensitive circuit boards from the transformers.

Geoff Kait
Machina Dynamica

Good morning Geoff and a big thank you. Listening to classical gets better for me with every refinement. I will look into Mu metals to find the most appropriate and post it here. Using the cork makes perfect sense. Maybe there's a sandwich with cork that can be more effective. Looking into it. Enjoy the day :-)

Try a couple sheets of Sorbothane, with the cord between. Be certain that the bolt(s), holding the x-former, remain(s) free floating(isolated from the chassis) as well. Good info: (http://www.sorbothane.com/standard_product_guide11.php)