AC Filtering, Grounding Boxes, Linear PSU and Balanced Power.

[zilch0md]

2 hours ago, Speed Racer said:

 

[snip]

 

In the video example, there was 160pF stray capacitance between the primary and secondary windings. Is that the same as 160pF interwinding capacitance? Does that mean that my Topaz has .0005pF stray capacitance?

 

[snip]

 

Wired up to deliver balanced power, there is supposed to be about 20dB more common mode noise reduction. 

 

Yes!

 

Even the Tripp-Lite ITs have Faraday shields, but their design/construction is not anywhere near as effective, with only 1000:1 (60 dB) CMNR vs. 20,000,000:1 (146 dB) with the Topaz 0.0005 pF models.

 

You are the second person, I know, to comment that balanced-mode configuration of the screw-terminal models offer an additional 20 dB of CMNR.  Do you have a source for that information?  I'm not sure I actually need more than 20,000,000:1 attenuation, but I'm curious.  :-)

[zilch0md]

Oh, you started out with it unbalanced?   That's interesting that it is running more quietly now.  From what I've been reading, any hum that can be heard with unbalanced ITs is due to the presence of DC offset coming in from the mains, but I guess your transformer somehow doesn't "see" the DC offset, after center-tapping the secondary for balanced output.  ???

[zilch0md]

Quoting the paragraph below Figure 4. Reducing Common-mode noise, as seen at this page:

 

http://www.mastec.co.nz/JST/PK8.html

 

Quote

With all transformers, stray capacitance, called inter-winding capacitance, can exist between the windings.  It is via this inter-winding capacitance that [incoming] high frequency [common-mode] noise [from the mains] can couple through to the secondary winding. However, when a grounded [Faraday] shield is used to separate the primary and the secondary windings, the inter-winding capacitance is significantly reduced. This effectively increases the impedance (resistance) of the coupling path and therefore reduces the amount of high frequency [common-mode] noise that can couple through to the secondary winding.

 

Thus, the lower the inter-winding capacitance, the greater the reduction of high frequency common-mode noise.

 

Which is what John Swenson has been telling us.  Not just any isolation transformer will do the job.   :-)

[zilch0md]

For the most passionate of students, here's a very well-written article, which, among other things, provides very succinct definitions of the different types of noise. 

 

The author, Marc Dekenah, all but carves 11th and 12th Commandments in stone. 

 

Paraphrasing... Thou shall not use the term "Normal-Mode Noise," but rather "Differential Noise" and "Transverse Noise" is a superset of "Differential Noise;" they are not one-in-the-same.

 

Let the reader be schooled. LOL

 

http://www.marcspages.co.uk/pq/3270.htm

 

Here's an index to several other topics - all, equally well-written and in-depth:

 

http://www.marcspages.co.uk/pq/0000.htm

 

[zilch0md]

I've been doing a lot of research into how the Topaz (MGE or Daitron) Ultra-Isolator transformers could possibly manage to provide -65 dB of Normal-Mode noise reduction in addition to -146 dB of Common-Mode noise reduction (as go the specs of their "-31" and "-32" models, which have the extremely low 0.0005 pF inter-winding capacitance, that allows attenuation of noise in the treble frequencies.

 

Way back on page 13 of this thread, I had posted a graphic of my own creation which, I've only recently concluded, promotes the erroneous contention that a 1:1 transformer having a grounded-neutral secondary (such as the Topaz or less-effective Tripp-Lite units) will attenuate Common-Mode noise (TRUE), while 1:1 transformers having a floating-neutral secondary will attenuate Normal-Mode noise (FALSE).

 

I've held that contention for over two years, but have finally done enough homework to realize that it's absolutely incorrect - and - I've been misleading readers with that incorrect understanding, all along, just as I had been mislead by a consensus of quacks who had made a lot of sense to me at the time.  It's really not debatable.  

 

Back in November of 2016, in the thread titled "Discussion of AC mains isolation transformers..." John Swenson stepped up, without naming names, to set the story straight.  As much out of self-doubt as for my respect for John's expertise, I didn't openly contest his post, but his words did manage to plant a seed in my thick skull, to investigate this further.  

 

It wasn't until I bought a Topaz 19095-32, recently, that I finally started digging into what impact, if any, floating the secondary's neutral has Normal-Mode vs. Common-Mode noise reduction.  I am now thoroughly convinced that John Swenson is correct. Doh!  Both types of isolation transformer, all else being equal, will attenuate Common-Mode noise, not Normal-Mode noise.

 

There is a slight twist, not yet discussed in these pages:  It turns out that grounding the secondary's neutral might improve the Common-Mode noise reduction, ever so slightly, by providing one last path to ground for any remaining CM that has made it through the Faraday shield and is otherwise headed for the load.  A floating-neutral secondary would not provide this infinitesimally small advantage for CM noise reduction.

 

So, here's are a couple of revised graphics, that incorporate corrections to previously "published" versions (along with a lot of other information, which is hopefully not misleading or incorrect in any way.

 

:-)

 

Mike