Here some photos of a custom passive line level crossover.
It is a passive crossover to be placed between preamp and power amps for an active system.
The crossover is 2 ways with a fixed corner frequency. Each way can be attenuated in 12 2dB steps, separately for each channel. In this case a crossover frequency of 850Hz was specified by the customer. Finer attenuation steps are possible.
The filter circuits are LCR type with 1st order slope. Attenuation is done with auto former volume controls. The input impedance is 300 Ohm. So a vey low output impedance preamp is needed, ideally a 10Y preamp.