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I have pulled some CAT6 through the ceiling from one room to a nearby cupboard, for line level audio signal.

See wiring: enter image description here

I haven't used a balun or DI box, and there isn't TOO much hum and hiss, it's manageable.

But something strange is happening with the audio from Alexa, it sounds really bad: a lot of hiss and distortion. When you turn the volume down, the signal to noise is so bad that the hiss is really high, also the distortion doesn't really disappear it just gets quieter.

When I unplug the Alexa and swap it out for audio from my phone, it sounds really clean. So you'd think it's a problem with the Alexa. But...

  • I tried another Alexa and the same problem happens.
  • I turned the Alexa up (and mixer input down) and vice versa, this didn't help
  • So then I plugged the Alexa directly into the amp and it sounds really good
  • I plugged the Alexa back and tried it in a battery pack, rather than into the USB power supply, and the problem is still there.

What is the reason for this?

Should I be using baluns, or a DI box or something like that?

I've heard it's fine sending line level signals over CAT6 - indeed with the phone plugged in, it's all good.

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I will first assume you do not have any of the wires crossed here.

It is unlikely that the cause is in the CAT6 cable, but here's how to test this: send the alexa signal (red) thru the cable to the mixer. Then, instead of plugging them into the mixer, unplug the OUTPUT (blue) lines from the mixer and connect them to the alexa (red) wires. Then plug the blue cables into your amp. the signal path is alexa->red cable->blue cable->amp and play a file. I'll bet you get no distortion, no hiss, and a strong signal.

Furthermore, I'll bet the line level input on your mixer is expecting a much stronger signal at its input terminals than alexa is set up to deliver. If possible, compare the signal amplitude from the roku unit with that from alexa on a 2-channel oscilloscope.

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verify if the cable is making some contact or is open, verify if the plug on both end has a little chip or debris that is distorting the signal. The Alexa device has no output signal filter Here is a link for a device that could help: https://images.app.goo.gl/wy59kAzKFgh9gUZg6

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