We found this circuit in a 1968 General Electric publication. The circuit uses an SCR of the time, but any modern equivalent can be used. The relay must have contacts that support the horn current.
This circuit can operate in a 100 dB range with signals of up to 100 MHz frequencies. Similar...
This audio level indication system for microphones was found in Radio Electronics from the 90s....
This circuit was found in a 90’s Electronic Design. The circuit uses components that are still...