This circuit protects the speaker from dangerous direct currents that could damage it. The circuit is from an Electronics Experimenter Handbook 1993 edition.
Based on an integrated circuit of the time, this circuit appeared in the October 1979 issue of...
We found this circuit in a 80s documentation. The operational amplifier is from the time and the...
This is an improved circuit from the earlier version also found in the April 1972 Radio...