In the figure we have the typical circuit of a Baxandall tone control applied to an operational amplifier. The operational can be of any type.
This circuit was found in a 1992 publication, using an operational amplifier not very common...
This is a amplifier for XTAL high impedance earphones or piezoelectric types. Current drain is...
This circuit is from the LM111 manual of the 1980s. The component no longer exists, but...