There is relay a matrix designed to switch between active and passive speakers in a music shop. There are actually two matrices, each in a different showroom. It has been observed that one matrix switches speakers almost inaudible while the other makes a quiet but annoying click. Here is a screenshot of a signal recorded at the output of the speaker relay matrix. This is matrix switching line signal for active speakers so it was possible to record it directly:
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| Recorded distortion on the output of the matrix, at the beginning and ant the end there are disturbances which I believe are 4 bytes digital transmissions coupled on the audio signal. |
Because of the location and surrounding equipment only one rack with a matrix can be opened, namely the one which generates audible disturbances, it looks like this:
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| Wiring arrangement in the matrix |
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| Single module of the relay matrix |
In reality a single module is more complicated (I assume GND is switched too) but it describes the idea. A complete matrix is built in two rows and wired like this:
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| Current wiring of 10 modules in the matrix (outputs not shown because they are shielded on the other side of the panel) |
See how many times digital signal cable is crossing and running parallel to analog signal wiring. I believe there is magnetic coupling between digital and analog lines. To make it worse, both are wired without shield, such arrangement is actually prone to cross-talks and requires longer cables. I suggested changing arrangement to something like this:
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| Improved wiring of 10 modules in the matrix |
In the improved wiring concept there are shorter cables, and there is no unnecessary zigzag. I believe this will remove unwanted disturbances on the switched analog signal. Rearranging is possible because every module has its own configurable address, I am not even sure what exact type of the digital transmission is used. Maybe daisy-chain order can be changed even without readdressing modules. I will update this post when it's done.
