The integrated circuit used is uncommon today. We found this configuration in Motorola's 1990 Linear Databook. The triac can be any of the TIC series.
This circuit for the car was found in the April 1990 Radio Electronics magazine. The speaker is...
We found this circuit in a Texas Instruments documentation from 1973. Other operational amplifiers can...
This circuit was found in a 90's EDN. The circuit has a well-known configuration. The voltage...