ABSTRACT
In Fig. 15.1, the cutoff frequency is well above 4000 Hz but has a serious resonant rise at 2252 Hz. This gives a 0.281 dB gain at 400 Hz, which translates to a 3.3% voltage rise. But this is calculated for ideal conditions, and the rise is much more than 3.3% in operation. Note that this condition is not a problem at 50 or 60 Hz. The dB gain is zero. Actually, this filter was designed for 60 Hz, so there would be no problems. There is insufficient power at these 60-Hz harmonics to cause problems in the 2250 area.
