This circuit for the very low frequency range was found in the Radio Electronics magazine of February 1983. The components are according to the frequency range to be amplified.
This simple MW radio was found in a 1975 publication, but it can be mounted with BC548...
This control for bass, midrange, and treble was found in the March 1995 issue of Electronics Now...
This circuit from a 1967 documentation generates 2.5 Hz signals depending on the capacitors used,...