Crane Song INSIGNA - 500 Series Tube Equalizer ModuleINSIGNA is a tube equalizer in a 500 series package, using a dual triode circuit with a 12AX7 tube. The eq has 24 db oct high pass and low pass filters each with 7 frequencies. The top and bottom band are shelving each with 8 frequencies. The mid band is peaking with 8 frequencies. The three bands work by using buffered RC circuits in the negative feedback path around the tube amplifiers. The result is a fat sounding eq rich in second harmonic triode