Teo, so many pieces of gear that I have opened up, and transformer isolated / modified, did not have any such thing to isolate the transformers. It is quite sad, because for little money, it does wonders. As an example, I recently did an Adcom GFA 535 series II, and things improved dramatically.
Quick and free fuse tweak
I read about this once but tonight I tried it and was very impressed with the result. More pling from piano, more thwak from slapped acoustic bass, increased detail and space around performers.
Wrap a short piece of cream-colored masking tape once around the glass portion of a regular AC power fuse making sure not to touch the metal caps. I left a millimeter gap.
Wrap a short piece of cream-colored masking tape once around the glass portion of a regular AC power fuse making sure not to touch the metal caps. I left a millimeter gap.