This conventional filter circuit is from American documentation from the 1990s. The operational amplifier admits an equivalent and the power supply must be symmetrical.
This transistor circuit was found in Mullard's 1960s transistor manual. The transistors are...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
This high impedance amplifier is from 1985 documentation by General Electronic. The amplifier with...