This high input impedance tone control circuit was found in American documentation from the 1980s. Equivalent operational amplifiers and FTEs can be used.
The circuit in the figure is based on an LM101A; diodes can be replaced with equivalents. The...
This circuit, with magnetic sensor, uses an operational amplifier of the time. The circuit is from...
Found in a 90s Popular Electronics, this circuit checks if a remote-control transmitter is...