This tone control was obtained in a Signetics documentation of the 90s. The integrated circuit can be practically any operational amplifier. The power supply is symmetrical.
This circuit can be found in a 1970 Motorola documentation. The circuit can be implemented with general...
This shield circuit with an optical coupler was found in an 90s EDN. The circuit can be used with...
This circuit is from 1977 documentation, and high current equivalent transistor must be used. The...