Attempt to clean the IC9 opamp voltage. Since the change of filtering capacitor from Samxon GC 470uF 16V to Panny FM 1000uF 16V and added the 100nF ceramic bring down the ripple on the +16V IC9 voltage from 32mV to 27mV, I tried go futher todays.
So I thought - what about LC filter? If I add a L coil, the voltage might be clean! So, I did. I made my first toroid filter, sadly the wire is 0.8mm thick (a bit too thick, IMHO):
...and result? No change in behaviour. And, what is worser, the voltage ripple on IC9 increased from 27mV to 28.3mV...!
I thought things has to be better, but... Probably the coil impedance is too low for the 100Hz - or it might even help the ripple...