This circuit that appears in several versions in this section and on this website was found in documentation from the 1980s. The transistors can be of any general purpose NPN type like the BC548.
Found in a 90s Popular Electronics, this circuit is interspersed between the filter and the...
This circuit is from an 80's documentation. The integrated circuit is from the time and the...
This circuit was found in a 80s American documentation. The zener diodes determine the points of...