Discussion of AC mains isolation transformers

[zilch0md]

5 hours ago, Cornan said:

 

Sorry to hear that the Ghent Audio DC cables did´nt make an audible improvement in your setup Mike. Mine with JSSG surely did! Anyway if you want to order starquad RCA cables this post by John Swenson might interest you:

 

Good luck!

 

 

Thank you Cornan, but that particular JS post you've quoted, makes no mention of star-quad RCA interconnects, but he does offer a great explanation of the reduced inductance enjoyed when using star-quad DC cables - as I had mentioned, quoting him, actually, in my post this morning, lamenting that I can not hear any audible improvements when using the Ghent Audio star-quad DC power cable to supply 7.0V to a USB Regen.  

 

So, as I had said before, I'm disappointed that the star-quad DC cable's ability to reduce inductance yielded no audible improvements in my particular application, but I've not, at any time said, a star-quad cable cannot make audible improvements by reducing inductance.

 

What I have said, only parrots the following JS post, where he recently explained that star-quad DC power cables do not offer the same advantage  of immunity to EMI, that can be enjoyed with star-quad microphone and line-level interconnects (i.e. RCA interconnects) - where the voltages are much lower and, thus, more susceptible to EMI, with the only downside being, as I recently stated (again parroting JS), the possibility of increased capacitance, in longer cable lengths.)

 

 

Mike

[zilch0md]

6 hours ago, Speedskater said:

The reduced inductance only impacts very high frequency noise and interference.

The DC voltage drop is only influenced by the end-to-end resistance. Same goes for low frequency AC.

 

Thanks Speedskater,

 

I was paraphrasing what JS had written, here:

 

 

[zilch0md]

47 minutes ago, Dominique-Tanguy said:

Hi all,

 

i am close to order a Topaz from the USA (91001-11) for the input, it is mentionned 120/240 volts.

 

we normally have 230 volts in Germany, but I measure 215 volts in my house. I am currently using a Isolation transformer from which I get 227 volts at the output when I plug it in the 215 volts from the wall. Can I expect the same thing from the Topaz?

 

cheers,

 

Dominique

 

YMMV, but my 120V, 500VA Topaz 19095-32 increases the voltage about 3% at the Secondary, relative to the input at the Primary, when driving my headphone system, which is putting a very light load on the 500VA Topaz. I've heard of isolation transformers that maintain a true 1:1 ratio, whether unloaded or fully loaded, but I can't imagine how that's possible without including some kind of voltage regulator circuit at the secondary (which would create some noise of its own), in combination with windings that provide the minimum input voltage required by the regulator.  

 

In my admittedly limited experience, and paying attention to what others have said, most so-called 1:1 isolation transformer will give you a higher voltage at the output, especially when not loaded to its rated capacity - which, in your case, would be desirable, given that you're not getting a full 240V from the mains.

 

I have the opposite problem:  I'm using a voltage regulator at the mains to reduce ~127V down to 110V, before my transformers increase the voltage back to where I want it (~120V).

 

I don't want to be the bearer of discouraging news, but the Topaz 91001-11 that you've ordered does not have the low 0.0005 pF inter-winding capacitance of Topaz/SquareD/MGE/Daitron models ending in -31 or -32, as shown in this PDF:

 

http://www.pacificparts.com/vends/mge/images/t1.pdf

 

The 91001-11 is rated at 0.005 pF as shown in this photo:

 

 

 

 

See:   https://www.head-fi.org/threads/topaz-low-capacitance-isolation-transformers-for-affordably-clean-power.857448/

 

[zilch0md]

Oh wow!  I feel so relieved to hear that!  I felt bad, sharing that information with the thought that it had already been shipped. 

 

Thank YOU for letting me know.  :-)

[zilch0md]

2 hours ago, look&listen said:

Uh, I don't think "preached" is the best word. How about "suggested" or "explained" ?

 

I'm good with that, but the Swenson is my shepherd, I shall not taunt.  He maketh me to break down the leakage currents: he leadeth me beside low noise levels.  He restoreth my soul, my R&B, and every other genre.  

 

I'd better stop there, before my system gets struck by lightning.

 

[zilch0md]

22 hours ago, tims said:

Hi,

 

Got a couple of noobish questions regarding grounded neutral secondaries and also balanced supplies that I hope someone can help me with: @One and a half, @zilch0md ?

 

Just discovered my Topaz doesn't have a grounded neutral secondary (i.e. it's floating) and is currently supplying a low power intergrated DAC/amp and a separate music server which according to the info above is not ideal (Warning: Plug only ONE load into an Iso T with a floating neutral secondary). If I understand correctly the way to go is to ground the Topaz secondary neutral to enable more than one load to be connected for better performance?

What if I convert my Topaz to a Balanced mode output; is a Balanced output configuration still good for using more than one load or should only a single load be used as per a floating neutral secondary?

 

Second question: When in Balanced mode, does this mean the Topaz's output is reduced?  My stereo draws around 400-450VA which is close to the recommended limit for my 750VA Topaz and I'm concerned that switching to Balanced mode may not be ideal if output power may come down? I have 240v mains power in my country.

 

Thanks for any replies.

 

Hi tims!

 

Unfortunately, I'm not able to go back and edit the post you are quoting:

 

https://audiophilestyle.com/forums/topic/29662-discussion-of-ac-mains-isolation-transformers-started-wposts-moved-from-quotlps-1-troubleshootingquot-thread/?page=31&tab=comments#comment-704749

 

Quite some time ago, I updated the graphic to correct an error in my understanding, thanks to the teachings of John Swenson.

 

The punchline is that Common-Mode noise is attenuated by Isolation Transformers, whether their secondaries have floating neutrals or grounded neutrals.

 

Here's my current version of that graphic:

 

 

... as found on the first page of this thread at Head-Fi.org:

 

https://www.head-fi.org/threads/topaz-low-capacitance-isolation-transformers-for-affordably-clean-power.857448/

 

In answer to your questions, I personally wouldn't bother to convert to balanced operation, even if it's possible and yes, for safety reason, you should not plug more than one load into a transformer with a floating neutral secondary.  I don't believe any Topaz units shipped with a floating secondary, so yours must have been modified.  I recommend you ground the neutral, but if you don't know how, you should get an certified electrician to do the work for you.   It's either that or just get another one and keep this one for powering a single DAC or any single audio component that uses a switch-mode power supply - both of which are suspect for backwashing noise onto the mains - where a floating neutral secondary can prevent that from happening.