This damped oscillator that mimics the sound of a gong was found in 90s American documentation. The circuit signal must be applied to an external amplifier.
September 2016 - It can be obtained from Mouser Electronics modules with 2.4 inch from 4D Systems...
This simple CMOS metronome circuit can be mounted in a small box, providing both sound and light...
This circuit was found in a European publication from the 1980s. The transistors can be the BC548...