This circuit makes use of a specific 80's component and was found in an American manual of the time. A matrix keyboard allows you to select one of several music programs.
This circuit is from a 1976 documentation. It makes use of isolated gate MOSFET which is already very...
This setting appears multiple times on the site from different sources. This is from a 2000 manual...
This circuit uses a current regulator from the 90's. This component is uncommon nowadays. The...