During the last weeks I finished another little DIY project: an XLR A/B switch box. This thingy has two balanced stereo XLR inputs and one balanced stereo XLR output. Together these are four mono input channels and two mono output channels. It’s a great tool if you need to switch between two input sources like e.g. two DAC’s etc. It’s also ideal for A/B comparison of various input devices. Since it’s a completely passive design it shouldn’t affect the sound. Also the stereo channels are completely physically separated.

The main work was to build the case which was made from aluminium rest of another DIY project.

The wiring and soldering is pretty simple. Here is the wiring scheme:

The input connectors are Neutrik NC3 FXX, the output connectors are Neutrik NC3 MXX. The ground wires of the first channel (A1,B1,C1) and second channel (A2,B2,C2) are soldered together, but not connected to the case. Also there’s no ground connection between channel 1 and channel 2.

Example Use Cases

1. Stereo A/B Input Switch: A1 = A In Left, A2 = A In Right, B1 = B In Left, B2 = B In Right, C1 = Out Left, C2 = Out Right
2. Stereo A/B Output Switch: A1 = A Out Left, A2 = A Out Right, B1 = B Out Left, B2 = B Out Right, C1 = In Left, C2 = In Right
3. 2 x Mono A/B Input Switch: A1 = Mono 1 In, B1 = Mono 2 In, C1 = Mono 1 Out, A2 = Mono 3 In, B2 = Mono 4 In, C2 = Mono 2 Out. Both Mono Outputs are physically separated.

More pictures: