2way Active Crossover circuit

This active Cross over is fairly straight forward. It consists of a buffer
and two 3rd order, 18 dB per octave filters. One low pass and the other
high. The cross over frequency is set at 2Khz and is designed for AEK's
400watt per channel PA/Keyboard Amp systems. Obviously only one channel is
shown here.

The line level audio signal enters the buffer where it is inverted out of
phase. This is to compensate for the filters which will invert the phase
again thus returning the signal to it's proper phase. The filters are
more-or-less standard low and high pass filters respectively however, extra
capacitors and resistors have been added in order to get the tolerance down
to a minimum using only E12 components.

This circuit may not be of terribly much use to anyone as it was
specifically designed to suit the applications. It is not variable or
switchable for two reasons. Firstly, it didn't need to be since the
properties of the speaker system were already known. And secondly, the
extra complexity was put into the accuracy of the crossover rather than
it's flexibility. The filters are matched in respect to each other as well
as can be expected using only E12 components. If switching were to be
employed to give a range of frequency options, a compromise would have to
be made on filter accuracy.

The only other way to make a universal crossover design and maintain
accuracy would probably be to use Switched capacitor filter building
blocks. In theory, two 18or 24dB per octave filters could be constructed
such that they tracked each other by being locked to the same clock. This
would be a nice experiment but I haven't had the opportunity to prove this
technology for this kind of application. My primary concern was the break
through of switching noise using such a design.

Therefore this design represents the simplest approach I could take and
still get the desired outcome.
