This circuit is from a Radio Electronics from February 1959. The circuit has a speaker output and good sensitivity. Power is supplied from a 9 V battery.
This is the circuit published in the August 1973 issue of Radio Electronics magazine announcing its...
This circuit can be used to add a delay to a logic signal as shown by the input and output...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...