Search for solutions to the power supply noise problem

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    • #95715
      AvatarChongs
      Member

      I have what is surely a classic problem with regard to power supply switching noise and audio but I am unable to sort myth from reality with regard to what I found so far on the topic.

      Setup:

      I have a notebook with an external power suppy and/or battery
      A radio receiver which has its own power supply (i.e. not fed by notebook SMPS)
      the radio receiver feeds an audio signal into line-in of the notebook
      the radio receiver is controlled by the notebook via RS232 ( http://www.kynix.com/Parts/3231833/RS232.html , etc.)
      Problem:

      If I unplug the notebook from its power supply and run it from battery everything works perfectly
      But if I use the notebook SMPS, I hear a tremendous amount of noise in the audio
      Can anybody tell me where the problem is likely to lie? There is a lot of talk about ground loops but I have difficulty believing they really exist in such a small-scale installation.

      Am I right to assume that it is likely a problem of a varying ground level in the notebook and the fact that the line-in input of the notebook is non-differential? Or is there a more likely explanation?

      What is the best solution? Use an opamp to construct a differential input amplifier and feed its output to the line in? What do I use as ground reference for the opamp?

    • #277798
      CharlesBennettCharlesBennett
      Participant

      Unfortunately, laptop power supplies can be very noisy electrically. I have had this in the past and found the best way was to run the laptop on battery power when working with audio..

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