This filter has the components calculated for the frequency of 1 kHz but can be changed. The input resistor can be 100k and the source symmetrical. Any operational amplifier can be used.
This circuit was found in February 1976, Radio Electronics magazine. The circuit is powered by 12 V...
This circuit was obtained in a 1973 publication, being implemented with TTL technology. The...
Found in a 1969 documentation on neon lamps, it actually takes advantage of the durability of the neon...