This circuit is from an American manual from 1975. The transistors are types of the time, but equivalents can be used, as well as the relay that can be according to the supply voltage.
We found this circuit in a 1981 publication. We applied an audio signal, for example, a music...
The circuit presented was obtained in the 1994 Linear Applications Handbook from National...
An inproved version of the circuit CIR129E is shown here. The resistorR1 must be at least 5 times...