TDA3810 is an old spatial, stereo and pseudo-stereo sound circuit who is hard to found, so I search replacement solution.
In an old romanian book named “Electronica peste tot’ (Electronics everywhere) writted by mr. I.C.Boghitoiu, I found exactly what I want
I design a version for board in Autodesk Eagle PCB software !
Phase shift depends by frequency theu C3 (variable reactance X3 with frequency) and P1 variable resitor value:
This circuit can be adapt to use with operational like TL074:
HERE is board in pdf format !