This active tone control circuit was found in American documentation from the 90's. The transistor can be general purpose or low noise with high gain.
This circuit uses two transistors and can be powered by just two small batteries. The frequency is given...
This circuit was found in the February 1985 issue of Radio Electronics magazine. It is based on an...
This circuit from Ferranti was released in 1969. It makes use of the company's transistors that admit...