This circuit was taken from an article in Electronics Now magazine in February 1995. The power supply must be dual and other operational amplifier can be used.
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
This circuit was obtained in an old Elektor. It is a reference, since the integrated products of the...
This circuit was found in a European technical documentation from 1991. It is a circuit that must...