This sensitive 5-band circuit was found in a September 1995 issue of Electronics Now magazine. The headphones, for greater sensitivity, should be high impedance.
The configuration shown in the figure makes use of two comparators of the four available on the...
This microphone amplifier operates on battery voltage. The output is in an earphone. The...
Hughes suggests this circuit in a 1968 documentation. The circuit uses old transistors that can be...