Sources of Noise

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32 minutes ago, Ralf11 said:

Noise on the AC line can come from inside your house (or apt.) or from outside it.

 

Consider both differential & common mode noise & methods to reduce. The goal of AC PSU is typically to eliminate everything except 0 Hz  and lower output impedance at all reasonable frequencies  

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1 hour ago, Ralf11 said:

BTW folks - we should probably define common mode, etc. for any newbies

Simply: common mode noise travels across both +|- inputs whether they be cables or AC or DC inputs, whereas differential mode noise is with respect the the voltage difference across the inputs. 

 

All currents need a return path so, for example, when common mode noise enters a circuit along a differential pair, it must return somehow typically along what is called a ground loop. 

 

Google is gives great descriptions.

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8 minutes ago, Speedskater said:

It would take a great technical writer to write a understandable & useful to audiophiles description of 'common mode'.  Heck, different electric/electronic fields have very different definitions of 'common mode'.

 

I don't claim to be a great technical writer, but common mode noise encompassed such topics as "leakage current", as well as good portions  (but not all) of RFI/EMI which many audiophiles seem to be focussed on.

 

Agreed that differential mode noise is much easier to understand, and its also much easier to remove with balanced/differential cables/circuits as well as standard power supply design.

 

Two topics that I've posted on extensively are:

1) use of "ultra" isolation transfomers (e.g. Topaz) as well as balanced power (such as Equi-tech)

2) fiberoptic ethernet

 

Both of these are effective ways to reduce, or in the case of fiber: entirely eliminate, common mode noise transmission, so the take home message is that a good (low interwinding capacitance) isolation transformer can reduce common mode noise on the AC circuit e.g. from your fridge, lights etc etc, and fiber can eliminate common mode noise arising from your NAS, server, switch etc. Of course there are other wrinkles, of course, but those are two simple things.