This circuit synchronized by the power grid can be used as a shield. We found it in an 80's Electronic Engineering. R1 can typically be 4k7.
This filter, which rejects frequencies around 1 kHz, was found in the August 1993 Electronics Now...
This is a voltage regulator circuit for currents up to 1.5 A with an output voltage adjustment for outputs...
This circuit uses an operational amplifier that is still common today. The indication is made by...