Electronics > Beginners
Phono cable and common mode noise filter?
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IDEngineer:

--- Quote from: SL4P on June 03, 2018, 07:01:21 am ---I haven’t seen a single mention of the word ‘phase’, which is critical to the success of balanced circuits. The source and propagation of the +/- legs must be phase coherent, or the CMRR will be negligible.
--- End quote ---
Another excellent point, and one of the reasons diff pairs are often twisted - to insure they follow the same path and have the same length for phase coherence. However, if you review the technical level of this thread, it will become apparent that phase coherence isn't the largest issue on the table.  :)
Loboscope:
In Home-audio-applications noise picked up by a cable is nearly never a problem, at least it is very seldom. Because the length of the cables is very restricted, there are nearly never severe sources of noise that will introduce noise into cables and normally there will be no levels less than line-levels. If there will be noise anywhere, I would first check the source and the amplifiers, as it has been mentioned by several posters before.

The balanced system for cables, inputs and outputs has been introduced for and is widely used by professionals, for example on stages, in studios, broadcast etc.
For example an open-air concert of a symphonic orchestra + choir: At least 40-60 microphones will be used (very low output signal level!), the cable length will easily add up to 1 km of even more. There will be lots of power cables too, for example for the lights, DMX-cables will be found too, etc. etc.
So you can imagine, that there will be tons of possible sources of noise that will introduce noise into the mass of audio-cables with mostly very low signal levels. So it is indispensable to have a cable-system that will be as immune as possible against this external sources of noise.
But even here, the symmetric audio-lines will not be capable to eliminate noise that will be introduced by a source, for example a defect microphone.

But at home, as I said, the will be simply no need for balanced systems. A proper shielded cable will do its job as I think at least in 99% of all cases.
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