This circuit was taken from Maxim documentation from the 1990s. It can be implemented on the basis of modern operational amplifiers. Power supply doesn't have to be symmetrical.
We found this circuit in an Electronic Design from the 80's. The generated tone can be changed as well...
This basic tone control circuit employs a Philips NE5538 operational amplifier, but can be adapted to work...
This two-phase stepper motor circuit was found in an old documentation using an operational amplifier...