This circuit was found in the March 1997 Electronics Now magazine. It uses a common analog indicator and the transistor is a general purpose one.
We found this circuit in a Radio Electronics. The circuit can be seen elsewhere on this site. The...
Found in old American documentation, this filter has a 8 dB per octave attenuation. The formulas for...
The circuit presented is from the Linear Applications Handbook of the National Semiconductor of...