Question: Dc on the Mains from three phase?

[sefi]

Our D. menber Mr. Joshua_G
told me that hus Isolation tranformer Stpo "DC on the mains"

And that the DC comes from:
The thing to remember about this three-phase and two-phase power delivery system is that the loads on each phase must remain balanced or you can get a DC offset to the AC voltage.
A quatation from:
SoundStage! Max dB - The High-End Mythology of the Toroidal Power Transformer (07/1998)

the 4th para.
my question is where the DC came from - AC?

[DF96]

To get DC from AC you need a rectifier. Three-phase AC imbalance alone will not produce DC. However, if there is DC imbalance then you can get DC. So ultimately the source of DC on a three-phase supply is the same as for a single phase supply: transformerless PSUs.

[zigzagflux]

Balance on a two or three phase system has ZERO effect on the presence of DC. Completely independent of one another.

Take your residential panel and load up one phase with 50 A, with no load on the other phase. You will not measure DC as a result.

DC comes primarily from half wave rectifiers present in vintage equipment. There are very few devices that you will find that still do this. At times the earth will carry DC that can affect larger distribution systems with multiple grounds, but this is irrelevant in residential DIY audio.

It is true that transformers are able to block DC. In my experience the problem of DC is largely overblown. Some meters will interpret DC with the presence of even harmonics, but this is technically not correct. Even harmonics are still AC with zero DC by FFT.

Maybe you have torroidal power transformers that are particularly susceptible to tiny amounts of DC.

[sefi]

So you dont took the soundstage site seriosly, I dont.

I live in country wehre the mains are 230V so "we have half problem"

and in my hous I chekd 0.1VDC on the line - bot problem at all.

[zigzagflux]

Originally Posted by sefi

So you dont took the soundstage site seriosly

I do not. The page is a mixture of truth and clear misunderstandings of power, with poor semantics at times. The rest of the site, I haven't read.

Even your 0.1VDC measurement is suspect, depending on the meter used. Rule of thumb is don't bother worrying about DC unless you see behavior that indicates otherwise.

I will inject a full disclosure statement, however. I use shielded EI transformers "whenever practical". It becomes impractical when the transformer is located within, say, my preamp with transformer coupled outputs. To avoid magnetic field pickup, I will use a torroidal transformer for my power supply. In those rare cases, I will use an upstream isolation transformer with grounded center tap to feed the power of my torroids. To remove DC? maybe, but moreso to eliminate risk of AC line noise getting through the torroid, which it can do quite easily. My house uses an AC drive for the well pump, so there is plenty of noise to contend with. Removal of DC is merely a side benefit.

To each his own, but personally I would only use a power torroid when there is absolute need for it.