TRRS Crossover Kit Assembly

If you are looking to purchase the TRRS Crossover Kit, you can find it here.


The TRRS Crossover Kit is a great way to interface your HamShield to a computer, smartphone, or even another HamShield. It does this two ways. First, it cross over the microphone to the speaker, and vice versa. Second, it provides level shifting and the DC isolation required to make a safe, high quality connection to another device.

While the TRRS Crossover Kit is extremely functional for the electronics expert, it also serves as an easy-to-assemble skill builder for people learning how to solder. Not only will you learn how to solder throughhole components, but you will get to surface mount a component. It is remarkably easy too!

Operating Theory

C1 provides DC isolation between the HamShield microphone input and the speaker output of your computer, phone, etc. You will need to also take care that the volume does not cause HamShield to clip, as the HamShield is expecting a microphone input. It is suggested to start at low volume and monitor the output of HamShield with another receiver as every audio device is a little different.

R1, R2 and R3 provide levelshifting of the audio output, reducing the audio amplifier output from the HamShield's speaker output. It is further DC isolated with C2. This lowers the output of HamShield to around microphone level input. However, you will have to experiment with the input gain of your other device. 

Another important aspect is that the circuit is designed to appear as a microphone and speaker headset to the end device. 

The TRRS Crossover Kit exists because we learned from experience that simply connecting a microphone to a speaker and vice versa is never a good idea. The electrical isolation and level shifting is an important key to proper operation.

What You Need

  • Soldering iron with stand
  • Tip cleaner, wet sponge and wire brass cleaner to make your life easier
  • Flux (ideally a flux pen with no clean flux)
  • Solder (lead or lead free)
  • A workbench or dining room table (with permission!)
  • A vice or silicone soldering mat
  • wire cutters (small diagonals) 

Included In The Kit

  • 2x 1.2K resistors (R1, R3)
  • 1x 10K resistor (R2)
  • 2x 0.01uF capacitors (C1, C2)
  • TRRS Jack
  • 4 pin male header (0.1" / 2.54 mm)
  • 4 pin female header (0.1" / 2.54 mm)
  • PCB
  • TRRS cable


Heat your soldering iron to the recommended temperature of your solder. Use flux (ideally a flux pen), and push the pen down on all of the exposed pads, both on top and on bottom.

After you are done applying flux, your soldering iron will likely be up to temperature.

Soldering Pro Tip #1

Throughhole components require a bit of heat to be applied before solder will flow properly. We suggest holding the iron on the solder pad and pressing solder into the hole to fill it. 

Soldering Pro Trip #2

There are a couple of ways to solder throughhole components. The first is to put them into the holes and bend the leads. Make sure the component is flush with the board. While bending the leads are easier, it does leave short barbs that are not straight. Once you get the hang of things, try cutting the component leads flush with the board before soldering. This will result in a very professional, solid finish with little poking through.

Step 1 - Solder the Two Capacitors

Take your capacitors and push them through the two holes labeled C1 and C2. Bend the leads slightly to keep them in place. They are both 0.01uF, so it doesn't matter which one goes where. They won't go down all the way, but you might want to keep them as low as profile to give them a tight, snug fit.

After holding the iron on the pad for a few seconds to heat it up, press the solder wire into the hole. It can take a while to fill up, depending on the diameter of your solder. You will want a nice, shiny dome over your component lead.

Straighten out the leads and cut them with the diagonals.

Step 2 - Solder 10K Resistor

You will then need the 10K ohm resistor. This resistor is unique from the rest, as you only have one. It will have a Brown, Black, and Orange band. 

 Bend the leads and fit them into R2. You will want to bend them again to give it a snug fit. Solder and clip accordingly. 

Step 3 - Solder the Two 1.2K Resistors

You will have two additional 1.2K resistors. They have a Brown, Red, Red marking. Bend them to fit into R1 and R3. Clip them like you did the rest.

 Step 4 - Solder the Audio Jack

The audio jack is a surface mount component. But don't let that scare you. Its large, wide leads make it actually quite easy. 

The audio jack only goes in one way. Simply drop it into place, taking in account the two plastic pegs that will go through the center of the board. This also helps the component keep steady and line up into place.

Apply solder to one of the end solder tabs of the component. This will fix it into place. You just need to apply solder to the top of it and it will work itself around to bond the leads to the pad.

After this first solder joint is applied, you can apply a bit more pressure, as it will likely not move around. Proceed to solder all of the pads in place. Don't forget there are pads on both sides!

Step 4 - Solder the Male Header Onto TRRS Crossover Kit

This is a lot easier with the board on its side. Place in the male header with the leads coming out of the bottom of the board and apply heat to the pad like the other components. Once you get the first pin, it will hold the rest of the header in place. Make sure that it stays even, as they sometimes tend to angle if you are not careful.

You are now done with the TRRS Crossover Kit!

Step 5 - Soldering Female Header to HamShield

Take the female header and solder it to the top of the HamShield in the 4 pin JP3 position. Like before, heat the pad and insert the solder to fill each hole.

Step 6 - Connect TRRS Crossover Kit

You are now ready to use the TRRS Crossover Kit. Simply connect up the board with the jack facing out. You can use the supplied TRRS cable to connect directly to your computer or smart phone.