This circuit protects the speaker from dangerous direct currents that could damage it. The circuit is from an Electronics Experimenter Handbook 1993 edition.
Available at Mouser Electronics this component of Diodes Incorporated consists of a voltage...
Found in Radio Electronics this circuit uses a fotodiac to drive a triac. The circuit can use...
The first circuit was suggested by Analog Devices (www.analog.com) in its Application Note AN-411...