For the first sound test, I'm using my multi channel Nakamichi power Amp and modifying to suit, my test bed (analogue) active crossover, pictured above. I've swapped out the unregulated KMTech power supply board, for an adjustable regulated PSU from China. I replaced the Chinese caps with Panasonic FC but changed nothing else on the board, these PSU boards are to be used on the final build, so it's a good opportunity to see how they perform.
I made a few changes to the KMTech crossover boards, adding bypass caps on the underside, a 0.1uF Ceramic and a 4.7uF Tantalum in parallel, attached to each power pin on the op amps and run to the ground plane of the board. The Red Wima film/foil caps across the +/- pins were tried, but removed, as they degraded the sound IMO. These boards cross at 310hz and I used 1% metal film resistors and Vishay MKP 1837 1% caps. I also converted the single ended input to balanced, by combining the two halves of the balanced input, using the buffer op amp. I had to cut some of the tracks, add alternative paths point to point and solder a couple of additional parts in place, as can be seen. The boards are single ended, but by creating a balanced input, I can feed them straight from my Pre Amp, which runs balanced outputs, it just simplifies the connectivity and it does run very quite when wired this way.
I used Burson v5 descrete op amps, which I already had, for the Hi and Lo Pass filters, but I changed the buffer to the Sparkos Labs discrete unit pictured above, this mix gives a better tonal balance to my ears. The crossover PCB has pin outs for dual channel op amps throughout, but the buffer makes use of just one channel. The designer did it this way to keep it simple for DIYers and supplies identical op amps for all three locations in their kits, so you can't get it wrong when fitting them. This is a waste of the unused channel at the buffer though and there is a big difference in the price between dual/single channel discrete units. I opted to use a single channel Sparkos unit for the buffer. This complicated things slightly, as the pin outs are different on a single channel unit, so I modified the dip8 socket as shown below to match the single channel op amp to the dual channel pin out of the board. The unused pin locations on the board are not connected to anything, which allowed me to make this change fairly easily.
The modifications to the dip8 sockets are on the underside, so you don't even see them when fitted to the PCB. I had a nagging concern that the unused channel on the stock set up would cause noise, as it is powered up without any input connected, whether it does or not, the mod removes this possibility.