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29421Re: [softrock40] Re: V9 output to audio card?

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  • Alan
    Jan 2, 2009
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      ----- Original Message -----
      From: "Ken" >
      > By "mains frequecy" you mean the 60 (or 50) cycles of the power line?

      Yes, I thought I was talking the wrong language! Over here we often call the
      50Hz main power supply line "the mains"

      > A "lowish" value (such as in the pF range?)

      That depends on the frequency and the line impedance. 10nF is a small value
      at 50/60Hz so offers a considerably higher impedance than the direct
      connection via the audio cable. Therefore little LF current flows through
      the capacitor.

      > while allowing the "spiky" USB signal to pass....
      > Is there any signals as such on the ground wire of the USB connection?

      The spiky USB signal has to return to ground, so yes, they are there. If it
      is a good low-resistance ground connection they will not be noticed.

      > AND does the ground wire not need to be a DC ground that would be
      > blocked by a capacitor?

      The DC ground is connected via the audio ground.

      > are you suggesting putting this "lowish" value capacitor on all the
      > USB wires to isolate them to prevent any ground loops?

      If there is a good ground return to the USB by way of the audio cable then
      this capacitor may not be needed. I leave the USB ground disconnected to
      avoid a ground loop at low frequencies. The 10nF capacitor just gives the
      spiky signal an alternative route.

      Again I stress that this is just the way I have done it. It seems that to
      get the best results it may be necessary for people to experiment until they
      are satisfied, their conclusions may differ from mine .

      73 Alan G4ZFQ
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