This circuit protects the speaker from dangerous direct currents that could damage it. The circuit is from an Electronics Experimenter Handbook 1993 edition.
In the figure we have the way to obtain an operational amplifier with FETs at the input, using a...
This circuit was found in a 1980s documentation. The low voltage circuit uses a PUT. Transistors can...
This circuit shows numbers I II and III when mounted on its side, depending on the position of the...