3-way active crossover - version 1

Rohit Balkishan Dubla

Description:

The schematics above show two 12dB/oct 2-way active crossovers with LR2 alignment. The circuit in figure 1b is connected to the low-pass output of figure 1a to realise a 3-way crossover. Thus the output marked "HI" in figure 1b is the mid-range output. I chose to do it this way instead of making a new 3-way unit since this one is going to replace the earlier 2-way version and I didn't want to waste the existing 2-way crossover. The circuit in figure 1a is described here. Referring to figure 1b, U1A forms the input buffer; U1B and U1C form the high-pass and low-pass sections respectively of the crossover. U1D inverts the low-pass filter's output to correct for phase inversion between the filter sections - this is true for all 12dB/oct (i.e., 2nd order) filters sharing a common crossover point. With the resistor/capacitor values shown, the crossover frequency is about 312Hz and the filters are 6dB down at the crossover point. U2A is a peaking 2nd order high-pass filter (Gpk = 6dB, Fpk = 30Hz). This is optional and is used specifically for my speakers to extend their low-frequency response. This filter's response when combined with the response of my speakers results in a 3dB peak at about 70Hz and the low -3dB frequency is about 30Hz. Switch SW1 is a DPDT type for stereo, and allows switching between the EQed (ON) and flat (OFF) low-range outputs.