Hello folks !
Ditched AGC auto level but opted for DAC via substractor OPAMP to control output voltage for a steady level. Also, with eye glasses I’ ve detected that AD603 out impedance is not 50 but 500 ohms, that only coz THD was way above normal and had to read datasheet once again. Stupid I know, but mistakes are making life greater ! Never had eye glasses in 48 years, but that time has come unfortunately !