XPost: sci.electronics.repair   
   From: spam@spam.com   
      
   On Mon, 6 May 2013 07:08:15 -0700, "Bob F"    
   wrote:   
      
   >Don Pearce wrote:   
   >> On Sun, 05 May 2013 23:04:35 -0700, isw  wrote:   
   >>   
   >>>>>> Looks OK to me. It's configured as a series common mode stopper.   
   >>>>>> What's the problem?   
   >>>>>>   
   >>>>> Will this design eliminate ground loop problems? My concept of   
   >>>>> baluns was that   
   >>>>> they isolated the two ends by placing them on opposite windings of   
   >>>>> a transformer. I am no expert, which is why I asked.   
   >>>>>   
   >>>>   
   >>>> That is a different thing. You need a transformer to kill a ground   
   >>>> loop entirely, but yes, provided there is enough inductance in the   
   >>>> coils this will still make a good job of getting rid of hum from a   
   >>>> ground loop.   
   >>>   
   >>> If there's enough inductance to attenuate 60 (or 50) Hz from the   
   >>> power line, why won't it do the same for similar frequencies in the   
   >>> desired signal?   
   >>>   
   >>   
   >> No, because of the way the windings are arranged their inductances   
   >> cancel each other out for the audio signal, but not for the induced   
   >> hum.   
   >   
   >The windings being on a transformer arranged so that common mode noise   
   cancels,   
   >and the signal doesn't?   
   >   
   >   
   That's it. The windings are wound in the same direction on the two   
   sides. That means that the forward and reverse signal currents on the   
   two windings are always in opposite directions magnetically. So the   
   signal doesn't see any net inductance.   
      
   d   
      
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