Once upon a time, I was building a sound system, and wanted to have separate amplifier for each way in each channel. It was back in the old days in the mid 90's, when I was at highschool. I got a circuit with a 6dB/octave filter. I said... nice, but what about the phase response? Basically it was a bunch of Sallen-Key elements.
Years went by, and my knowledge grew, and I realized that Sallen-Key filters is not suitable for this application. I went to a tutor at the college, and asked what to do. He was "very" helpful and said: "go search on the Internet." The other said: "ah... you are young... go get a girl... don't mess around with linear circuits..." Isn't it nice? Well, I was checking commercial products, and found the Rane corp. They are so nice to publish all their schematics! So, I started to develop a card, with two crossovers, and installed it in my 4 channel amplifier. It was really really good, I organised lots of parties with it, during my college years.
Well... well.... years went by... again.... Came a diplome, came CERN, and I learned that integrated things are not too good, and should make every unit separated. And then came the minor in acoustic at the university, and they made a lot of things clear to me about the subject. Finally, in the summer of 2005, I totally redesigned my crossover. It is now built into a 1U rackmount case, has two channels, three ways, is equipped with delay lines, subsonic and ultrasonic filters, etc... Each crossover filter is built based on the design of Linkwitz-Relay 24dB/octave filters. The results were good, so I took the unit to a competition at university, and got a third place. The original card was given to a very nice friend of mine.
So, here you go, if you like it, use it! If you modify the schematics, and/or the PCB, please send me a copy of it. I might learn something from your work!
The design is as simple as it can be. However, it's not just "five minutes with the soldering iron heats up..." I had to make a few modification to be able to build the crossover. First, I could not get quad potentiometers, as it is needed for the original design. However, I had old modular rotary switches, and I used them. (This was the reason I started to build the whole unit!). The other things, is that I didn't know that I could have got PCB mounted XLR connectors. I replaced the connectors by screw mountable parts, and wired them up. After I sent my layout to the fab house, got to know a place, where I could have bought the connectors. Bad luck...
The schematics and PCB layout was done by the gEDA tools.