This filter was found in an American publication from the 1980s. The circuit can be implemented with any operational amplifier. The power supply must be symmetrical.
The frequency of this circuit depends on the crystal. The transistor supports a modern equivalent. We...
This circuit is from 1992 documentation, but it can still be assembled today, as the components used are...
Found in an Analog Devices documentation from the 90s, this circuit uses operational amplifiers from the...