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.
General Electric suggests this circuit in a 1980s documentation. The operational of the time is...
This direct coupled circuit operates in class AB with good gain. The circuit is powered by 12 V....
This circuit is from 1990 documentation, but it is still up to date due to the components it uses....