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I am building a mono, internet enabled, WiFi radio and I have a problem.

I am running into what I believe may be a grounding issue. When I turn the system on, I hear all kinds of noise coming from both my computer component and my WiFi dongle.

  1. I know that the WiFi dongle is contributing to the noise because if I remove it, some of the noise is gone.
  2. If, I use a completely different sound source, such as a battery powered MP3 player, I get very little noise.
  3. I am thinking I may need a ground loop isolator, but curious as to whether anyone else has suggestions.

Here is a diagram of my circuit (sorry it's a bit crude) NOTE: I am providing extra power to the USB hub because I do not believe the computer (it's a pogoplug) can output enough power over a single USB.

http://i.imgur.com/ZGBAtYi.jpg

I am using Zaph's filter (as my receiver is a HiVi B3N)

enter image description here

And I am using a stereo to mono summing box here:

enter image description here

Finally, I am using this step-down transformer (LM2596S).

I found this question and think it may discuss a related problem, but I am not sure how I should proceed to fix my issue.

UPDATE: I have tried the following layout with the raspberry pi and notice the same noise problem. Also solved by using two seperate AC/DC adapters.

enter image description here

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This may or may not fix the problem that you asked about, but instead of hacking the power to a bus-powered hub, I think you should use a self-powered hub that has its own correctly-designed AC adapter. If you have to power the system on 12V, you can then look at what the AC adapter provides and derive that from your 12V supply.

Also, I'd be tempted to use higher-valued resistors for the passive stereo->mono mixer. More like 5k-10k for the mixing resistors and skip the ground resistor entirely. The amp probably has one already. I'd be nervous about 470Ohms overstressing the sound card. Much better than the short that I've seen from countless non-techies, but I'm not sure it's enough.

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