This circuit was obtained in a Popular Electronics of the 90s. The circuit uses integrated from the time, uncommon today. Note that the speaker has a higher impedance than ordinary speakers.
This circuit has already been explored in other articles on this site. The high power is due to...
This circuit was obtained in a 1978 magazine, but it can be easily assembled. What the circuit does...
This circuit is from a 1988 documentation, but uses components quite common today. The circuit...