This circuit is from a 1968 publication. Here we have several types of resistive sensors with individual adjustments triggering a single SCR. Power depends on the type of sound device to be triggered.
This circuit has a very high input resistance to excite a 0-1 mA indicator instrument. The FET...
The integrated circuits used in this configuration are not common today. The circuit is from the...
The circuit shown uses the 741 operational amplifier, but lower noise and higher gain equivalents...