This circuit was obtained in a 1970 engineering documentation. The operational is the 741, but other operational ones can be used. The power supply must be symmetrical.
We found this source with the CI 723, common at the time, in a 1989 paper. Power transistors must be...
Often, unauthorized people use the phone to make improper calls. A control for this is achieved with...
Found in an 80's documentation this circuit uses an integrated from the uncommon era today. Other...