This is the final iteration - a result of 1/2 year of testing and listening.
C1 = any size from
0,1 to 0,22 uF / 250 V x rated or 630 V non-x rated.
Soldered directly to IEC socket.
L4 - finger type ferrite rod, 10 wire turns. 2,5 mm solid copper wire (green/yellow stripes). Tinted copper ends.
L1 - ferrite ring, preferrably 3001 material. From C1 to L1 - wires tightly twisted (2,5 mm solid core).
L1 Winding: two wires wound tightly around core together 3 1/2 times) (not like on the drawing, but both wires side by side).
L2 and L3 - finger sized ferrite rods - 3 turns of each wire. OMIT (skip) these for amplifier outlets.
C3, C4 - 0,01 uF (10nF) X or Y rated foil caps (wima is very good). or 630 V non x rated.
MOV - 275 or better 300 V DC, biggest energy you can find. (big and thick look is a good sign). MOV directly on the AC outlet.
Earth continuity switch: put in on all outlets except one, which must be allways in use (be it an amp or mono amp).
Everywhere possible the N-L wires should be twisted.
If making more than
1 outlet, the C1 and L4 are common. Everything else
remember to solder-tin all copper ends to prevent corrosion. Use tons of hot melt glue to secure everything.
I recommend at least 24 hr burn in and break in under real (or much bigger) load before critical evaluation.