We found this circuit in a 1994 National Semiconductor technical documentation. The circuit can be adapted to operate with more modern equivalent operational amplifiers.
The circuit shown is only for analog telephone lines. I found it in Popular Electronics (1991). It...
In this circuit from the 60s, the power supply is made with 22.5 V, which is the voltage of the...
This circuit is from 1967 General Electric documentation. It uses SUS which are not very common...