This 1967 modeling circuit mimics the whistle of a locomotive. The steam-shrieking wheezing is set in a 2k2 potentiometer.
This is one of many configurations with a 4-input mixer transistor that can be found on this...
This dimmer was found in the Electronics Experimenter Special projects of 1983. The circuit uses...
The operational amplifier used is the 741, but the configuration is valid for other operational...