This circuit was found in an Electronics World of 1966. It has a range of 5 to 25 000 Hz at 1 dB and the diagram includes the power supply.
This interesting circuit from a publication from the 1970s, measures the intensity of the sound...
This power supply can supply a voltage between 6 and 8 V depending on the load. The transformer will...
This circuit, like the previous one, can be controlled by a microcontroller, functioning as a...