This time we will build a two channel mixer based on the design presented in the last article.
To keep this simple, I am using a printed circuit board from Radio Shack (part no. 276-159). The design is simple enough, that etching a unique circuit board would be overkill.
Now, to build the mixer.
First insert and solder the resisters to the circuit board. You can insert resistors across any two holes that cross the “break” across the center of the board. The photo below shows the trace side of the board with both resistors in place. One resistor soldered.
Next solder a small piece of bus wire in place to connect the two resistors on what will be the output side of the mixer. This photo shows the component side of the circuit board, with the resistors and jumper (labeled J1) in place.
Next, connect the 1/4 inch jacks. First let’s discuss 1/4 inch jacks and plugs (you can skip this section if you are familiar with the terminals of a 1/4 inch jack).
A 2-conductor 1/4 inch plug has 1 connection for each conductor. The conductors are named the tip and the sleeve and are labeled on the photo below. The tip carries the audio signal, while the sleeve is the shield and ground for the circuit.
The 1/4-inch plug connects with these two conductors. The sleeve makes contact and connects around the edge of the plug. The tip makes contact and connects with a pressure connector further in. There are tabs on the jack to solder connections to other circuitry. The photo below shows a 1/4-inch plug inserted into a jack with labels to show where connections are made.
Now, solder a contact from the input side of each resistor to the tip tab of a 1/4 inch jack. Then, solder a contact for the output side of the resistors to the tip tab of a 1/4 inch jack. Finally solder all the sleeve tabs together using a length of bus wire.
The following photos show the completed circuit from the component side and from the trace side.
For more permanent use, mount the circuit to a facepIate or in an enclosure. If the jacks are mounted on a metal surface, it is not necessary to solder the bus wire to connect the sleeve tabs on the 1/4 inch jacks. This connection will be made through the metal mounting surface.
Here you can hear two inputs to the mixer, and what the mixed output sounds like. As discussed in the previous article, this mixer design produces a the mixed output that is at a lower level than the input signals.
This completes construction of a basic 2 channel audio mixer. If you would like to add additional additional channels, you only need add input jacks, resistors, and tie them in appropriately. Remember, however, each additional channel sill further reduce the level of the output.
If you have any questions about building this circuit, or would like assistance, just let me know.