XPost: sci.electronics.repair
From: spam@spam.com
On Mon, 6 May 2013 10:02:21 -0700, "Bob F"
wrote:
>Don Pearce wrote:
>> 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.
>>
>
>Is this design going to avoid ground loop problems? Those signals would just
be
>on the one side, so would they be canceled?
>
>
The ground loop is fixed by the inductance presenting a huge series
impedance to the hum current, which only passes along the ground wire.
There is no equal return current in the signal wire to cancel the
inductance.
d
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