We found this circuit in the 1983 edition of the Electronics Experimenter handbook. The circuit uses components that are common today, although many admit equivalents.
We found this configuration in a Linear Applications Handbook by National Semiconductor in 1994....
Another useful audio circuit using an operational amplifier is the one shown in the figure. It is a...
Found in English documentation from the 1980s, this 3 transistors siren directly drives a small...