This circuit was found in a 90s Popular Electronics. It produces a muted tone similar to that produced by a bell. The signal must be applied to an amplifier.
We found this circuit in a European publication from the 1970s. The transistors are made of...
The TAA131 used in this circuit is not very easy to find today, but an equivalent low power audio...
This circuit was suggested by National Semiconductor in its Linear Application Handbook. The...