The circuit uses operations that are no longer common nowadays, as it is a configuration obtained in the Linear Applications Handbook of the National Semiconductor of 1994.
We found this interesting circuit in a 1969 American documentation. It shows a solution with...
Here is a high-quality intercom for demanding readers. The circuit is from a 1982 documentation. Of course,...
This circuit can be found on this website in similar versions. The power supply is given in...