This circuit was found in an Electronic Engineering of the 80s. The circuit indicates when a telephone line is being used, being useful in case of extensions.
This circuit came out in an American magazine that no longer exists. It's the Electronic...
This circuit can be added to any audio amplifier design, consisting of a good tone control with an...
Using a 741 op amp with symmetrical source, this circuit was found in a 1982 documentation. The...