Hey Guys,

I doubt there's much interest anymore in active analog crossovers. But, I still fancy analog gear.

This also ended up being a much more involved project than I had originally anticipated. Looking back, if I had known how much work this was going to take, I'm not sure I would have embarked on this.

Nonetheless, I've completed this project and I'm very pleased with the results. I thought I'd share my story. Even if you don't learn anything from this, hopefully you'll be entertained

My goal was to have two KT DN800, in 4-way mode. I had purchased three units, set in 2-way mode. I ended up cannibalizing one of the units.

The units were originally set to cross at 1.2kHz. I had decided that a simple decades-based crossover would work well in my setup: 80Hz / 800Hz / 8kHz

I was unable to find the software for calculating these crossover points. But I did find an electronic copy of the manual. This helped me calculate the correct component values. One of the main reasons why I chose the decades-based crossover points was being able to use the same resistor values for everything.

My immediate challenge with this was converting from 2-way mode to 4-way. The guide wasn't super obvious about this. I also had several versions of the filter boards. Only one of which seemed to match the component layout in the manual. I made some educated guesses and thankfully came-up with the correct layout on my first try.

I basically stripped all of the components from 8 filter boards. This is where the project starts to get tedious:

I decided to solder sockets for the opamps. I figured since I'm gutting these crossovers, I might as well upgrade the opamps. I also decided to drastically lower the high-pass filter for the low-end signal. Here are the boards, populated with my calculated values:

You will notice that I opted for single-channel SOIC-8 opamps, rather than the composite chips. Two reasons for this... First, single channel opamps tend to have better performance, compared to their composite brothers. Second, I believe this also helps with channel separation.

What's even more sad, I couldn't find any adapter boards for the 4-channel opamps. So, I ended up making those PCBs. Just when you thought this project couldn't get anymore tedious

I did a quick check of the frequency responses of my crossover points. Much to my amazement, not only did this even work at all, everything was responding in the expected ranges. I reached the image limit for this post. I uploaded these measurements in another post...

I figured, why stop here? Why not refresh the limiter boards? I decided to upgrade the opamps and replace all of the capacitors in the signal path:

And since I've updated the limiter boards, why not update the main boards? Originally, I tried swapping out the +/- 18V regulators, in favor of +/- 15V. It opens the door to a whole lot more opamps (i.e. AD797). And I've done this successfully in other analog active crossovers. But, the KT DN800 was not liking this idea.

So, I instead dropped in 1.5A +/- 18V regulators. I know what you're thinking. What's the point? The fuses are rated for 1A. But, my thought was a higher-rated voltage regulator would have less voltage droop.

The new regulators worked just fine in my first crossover. However, in my second crossover, the power kept shutting off (after about 30-60 seconds). This led to about a half a day of swearing and troubleshooting. I couldn't understand why the first crossover was working, but not the second.

My initial thought was "I must have a short somewhere". But, I simply could not find one. And I wasn't blowing fuses. Then I noticed that each crossover had a different looking toroidal power transformer. I decided to measure the voltage coming off of each one. Sure enough, the first crossover read +/- 24V. And the second one was reading +/- 36V. This input voltage was causing my regulators to overheat! This was resolved by cannibalizing the power transformer from my third crossover. Problem solved.

Here is the main board completed:

Since I made so many changes, I figured it would be a good idea to tune the limiter boards. I used a function generator and an oscilloscope:

Thus concludes my story to active analog crossover perfection...