I've seen a lot of IEC inlets with built in emi/rfi noise reduction using uh.. I guess caps and resistor networks? maybe it's that? I have one but it's 6 amp max input so not good for a big iso transformer
Bingo! I think you've guessed correctly! Yesterday, I posted a comment, to
an existing thread at electronics.stackexchange.com, and got this response from a guy named Tony Stewart, whose answers I find difficult to follow, but...
CM = -146dB @ 100kHz , DM= -65dB @ 100kHz Considering attenuation for a Pi Filter at 100kHz, this means it has a good line filter included rated at 100kHz not 60 Hz. It is reasonable. Floating neutral ignores capacitive coupling of CM noise which does occur. . A CM choke and Pi filter Y caps are needed for CM Noise and X cap for DM noise. –
Tony Stewart. EE since '75
I had referenced the MGE PDF (one of the first links I provided in this thread), where the 0.0005 pF models are claimed to offer -146 dB of Common-Mode noise reduction and -65 dB of Normal-Mode reduction. This Tony Stewart fellow, uses the acronym "DM" for Differential-Mode.
I had also asked what influence is had on noise reduction, if any, by floating the neutral of the secondary instead of having a grounded neutral secondary (the latter being what we have with the Topaz/MGE/Daitron transformers.)
My interpretation of his response is that first, it's "reasonable" for the Topaz transformers to claim both -146 dB of CM and -65 dB of DM noise reduction, but the DM NR can happen
only by way of "a good line filter included rated at 100kHz not 60 Hz" - which is basically his interpretation of the MGE PDF's use of the phrase "line noise suppressors."
He goes on to add, somewhat cryptically for my thick-headedness, to say that a floating neutral [at the secondary] "ignores capacitive coupling of the CM noise."
Which begs the question: What does he mean by "
ignores?" Is he saying that a floating-neutral Secondary, in and of itself, will
remove all CM noise that manages to pass from the Primary to the Secondary by way of capacitive coupling? We know (I know) that the whole purpose of the Faraday shield is to combat that capacitive coupling of CM noise, some of which still gets through, of course, even if your inter-winding capacitance is as low as 0.0005 pF. But... What exactly does he mean when he says "a floating-neutral secondary
ignores capacitive coupling of the CM noise?" I have to conclude that there would be no need for Faraday shields in a 1:1 transformer, if all you had to do is cut the ground from the Secondary's neutral - to remove CM noise that comes into the secondary, and since we don't see any such products out there, "
ignores" does not mean "
removes."
So what exactly does he mean by "a floating-neutral secondary
ignores capacitive coupling of the CM noise?"
Unfortunately, they have an extraordinary policy at electronics.stackexchange.com, that prohibits the asking or questions beyond whatever question was posted by the OP of any thread! Give me a break! That's counterproductive! You can't have an expanding discussion. I was told I have to post any related questions, as brand new threads. As yet, I've not bothered to start a thread with the title: "What does Tony Stewart mean when he says, 'a floating-neutral secondary
ignores capacitive coupling of the CM noise?' " LOL
He does go on, however, to say: "A CM choke and Pi filter Y caps are needed for CM Noise and X cap for DM noise," which reminded me of the Topaz Installation Instructions, previously mentioned, above:
THAT is what Tony Stewart calls an "X-cap" - it straddles the output (Line and Neutral) of the secondary - to deal with Normal-Mode/Differential-Mode/Transverse-Mode noise, but apparently, the Topaz/MGE/Daitron transformers
already have some kind of X-cap in place to deal with transverse-mode noise. The PDF I've referenced above is suggesting that an
additional X-caps can be added to deal with the "Special Noise Problem" of "
Extreme Transverse-Mode Noise."
UPDATE on 27 Aug 2017: No - they don't already have any kind of internal Y-Caps or X-Caps! In fact, if you read the first sentence in the graphic immediately above, it says:
"Topaz Ultra-Isolator line noise suppressors are effective in removing both types of noise."
The context of this sentence suggests that the entire product (the whole transformer) is a "
line noise suppressor" - not just some circuit within the product.
Similarly, further down, it reads:
"Topaz Ultra-Isolator line noise suppressors are designed to eliminate virtually all transverse-mode noise that results from common-mode noise on the primary."
Once again, the phrase
"line noise suppressors" is obviously referring to the entire transformer, not to some unidentified components within the transformer.
Now read the part I had highlighted in yellow. They're explaining how an optional X-Cap can be installed across the output of the Secondary, to deal with extreme transverse-noise coming into the Primary, from the mains. This in itself, suggests that no caps are implemented in the design, as shipped.
Nope! The Topaz units must be achieving their specified -65 dB of Normal-Mode noise reduction by way of a proprietary Faraday shield design. (See my later posts, below.)