This simple circuit has good gain and can be implemented with any general-purpose transistor. The circuit is from Electronics Now, June 1997. The coil determines the frequency range.
In the figure we have the typical circuit of a Baxandall tone control applied to an operational...
This circuit makes use of older operational amplifiers, but can be designed on the basis of modern...
This circuit that can be assembled in an “aspirin box” was found in the Radio Electronics magazine of...