This simple circuit needs a high gain stage to compensate for losses. It consists of a passive tone control obtained from Electronics Today International of the 90s.
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
This circuit was found in a 1970s documentation. The integrated circuit used is uncommon today....
This filter was found in Exar documentation from the 1980s. The circuit has an attenuation of 60 dB at the...