How to build a passive crossover network
Passive crossover build guide
We’ve designed a crossover before, now it’s time to learn how to build a passive crossover. There are different techniques to building a passive crossover network. Some are basic, some are more advanced and more clean looking. However, I’m going for the middle ground. I mix soldering, crimping, gluing, zipping to make the filter look clean, but at the same time, easy to make.
I’m not going to show you, how the crossover is designed. If you are interested in that, you maybe want to take a look at :
- Passive crossovers basics
- Passive crossover designs with circuit diagrams
- Design a crossover without measuring equipment
- Design a crossover using SoundEasy
Now that we got that out of the way, here is the schematic for the crossover we are going to build :
This is a 2nd order Linkwitz Riley filter. Actually, it’s an asymmetrical filter, with a first order slope for the woofer and a 2nd order slope for the tweeter. The tweeter also has a ladder delay network and an attenuation resistor.
How to build a passive crossover – first step
The first step I like to take is to make the cables for the speakers and binding posts.
I try to use thick cables, as thick as the crimp connector allows. Use appropriate crimp connectors for you binding posts. This should be a short cable. In fact all the cables should be as short as possible. I trimmed them after I took this picture. But the cables for the mid-bass should be a bit longer, and for those I used 6.3 mm spade crimp terminals. (middle row). Tweeter cables should also be a bit longer (for reaching purposes) and use 2.8 mm spade crimp terminals for these. Leave the other ends of the cables stripped for further processing.
The circuit board
First thing to do is to get a board to fit the components of the filter. Easiest thing to do is to use a thin piece of wood. However, even easier than this, is to get a piece of MDF that you used to make the enclosure. It’s a bit thick, but it will do. I like to glue 4 small legs to the board. This is because I use zip ties to fix some of the components. The board needs to be of sufficient size to accommodate the components. However, it also needs to be small enough to fit through the mid-bass hole. This board is 14 cm x 15 cm.
Remember, this is my view on how to build a passive crossover. I like to use zip ties on the inductors, and hide the ends of the zip-ties on the bottom of the board. Never use screws to fix the coils, it will alter the inductor value. Some have a plastic casing with a hole in the middle, and the first instinct is to drill a screw in the middle. In conclusion, don’t use metal fixing solutions for the inductors.
Using the 3 way crimp connector
I like to start with the biggest component, usually the inductor on the mid-bass side (L0). In our case the 3.3 mH one. I place it near a corner and work my way from there, so I don’t waste space. If you look at the circuit schematic, you will see that this inductor is connected to the positive input (amplifier +) and the tweeter section of the filter which begins with capacitor C3.
As a result, I like to use a 3 way crimp connector. This makes it easy to connect 3 components in one spot, using a crimping tool. Furthermore, I can screw it to the board using a small screw. I use a 3 mm drill bit to make holes for both the screws and for passing the zip ties.
Trim one end of the capacitor and crimp it to the connector. Crimp the inductor to the connector also. For the 3rd end of the connector, crimp the positive lead that goes to the positive speaker terminal (the mid-bass).
Placing the components on the board
Here is a pic after I placed some components, and let’s see how to build a passive crossover :
Comments on the above picture :
- Inductors are fastened to the board using zip ties. If the inductor is placed close to the edge, I drill only one hole and route the zip ties along the side of the board. Otherwise, drill two holes.
- Try to alternate inductor positioning. You see that one is placed flat and one is upright. This minimizes influences between the fields they generate. Good practice, not mandatory.
- I used a screw to fix the 3 way connector to the board. This keeps the look clean and fixes the wires closer to the board.
- In the middle, I placed a small ground bar. This is a very convenient place, because whenever you will see a ground icon on the circuit schematic, you will connect it here. Usually, there are several ground connections in any passive crossover build. As a result, being in close proximity to all of the components is a wise choice.
Soldering things up
As much as I love to crimp, sometimes soldering is best. You didn’t think you will learn how to build a passive crossover and avoid the soldering iron, did you? Before we get into soldering, let’s focus our attention to the circuit schematic. You see a lot of lines, which represent wires. However, you have to imagine that there are no wires. You could use cables, but they are redundant, make the design look cluttered and affect the overall resistance of the circuit.
In conclusion, if you look closely at C3, L4, L8 and C7, if your take away the wires, they all converge into a single point. So what I did is, took all the ends of these components, bunch them up in a nice bouquet, twist them with a pair of pliers, and solder everything up.
The same thing I did for the L8, C10, R6. Here, you can easily see on the circuit diagram that they converge into one spot. Connect the rest of the components in a similar fashion.
Where I connect the speaker positive wires (for both the mid-bass and the tweeter), I prefer the usage for crimp connectors. This way I can glue it to the board. As a result, if you pull this wire when attaching / detaching the speaker, it will encounter some resistance. Otherwise, you might pull out the nearest component.
I always leave the soldering for last. Besides, the 2 obvious bunched up components, there is another spot where I used the soldering iron. Some of the components didn’t have enough length in the wires to reach the ground bar. Usually, I use the screws from the ground bar to fasten the wires mechanically, but they were too short. For this reason, I soldered a couple of components on the top of the ground bar.
Last thing to do is to use some glue for the parts which aren’t fixed to the board. Therefore, I applied glue just beneath every capacitor, the resistor and the pink crimping connectors.
Now you know how to build passive a crossover. At least, you have an idea on how I personally do it. Some like to stick the components directly on the back of the box, some use actual PCB’s. You can go as fancy or as modest as your comfort level dictates.