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 setting for frequencies around 200 Hz was obtained in a 1975 filter manual. PNP transistors can be...
This circuit was found in a 1987 Radioaficion Microcomputacion magazine. This Spanish magazine no longer...
The 3403 operational amplifier is not common today, but the configuration can be implemented with...