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.
We found this circuit with a Q factor of 25 in the Linear Applications Handbook by National...
This circuit was found in a Japanese publication from 1971. The circuit uses components from the...
When this circuit is activated the LED flashes for a moment indicating that the function has been...