This circuit from the 90s, found in an Electronic Engineering can be used as a shield since its control is digital with TTL logic of 5 V. The components used are still common today.
This amplifier with complementary symmetry output and good sound quality was found in...
This circuit should be placed between the signal source and the input of a recorder or amplifier....
Found in an Electronics World of 1968 this circuit can use current SCRs and the diodes are...