This circuit with the NE602 was found in the February 1997 Electronics Now magazine. The NE602 integrated circuit is not very common these days.
This stage was found in a 1964 Electronic Design. The transistors are of the time and the shape of...
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...
This circuit, which is present in other points of this website, was found in a 90s Hands On...