This is a very quick little circuit that I made. Partly I wanted to experiement with controlling the gain of a differential amplifier by changing the voltage on the constant current sink in the tail of the diff-pair.
The circuit uses an astable-multivibrator to drive a longtailed-pair differential amplifier with an input waveform. The tail of the differential amplifier has a transistor acting as it's constant current source, but the current source is not constant, the base of the transistor is driven by a waveform with attack and decay. This results in the gain of the differential pair changing and the output waveform being rather 'chimey'. The attached PDF expains more fully.