Discussion of AC mains isolation transformers

[mourip]

I have been using isolation transformers for a while mainly for the supply for my DAC. These are smallish toroidal hospital rated devices. They seem to do the job however they also have an audible hum.

 

For those of you who have one of the larger Topaz units, .5KVA or larger, do you find them to be quiet?

 

Thanks!

[mourip]

How would one know if you were overtaxing a topaz? I have my entire system plugged into the 500VA model, including my amp. Would I hear something obvious or would dynamics be constricted in subtle ways?

 

I would think that the transformer would get hot and you might hear restricted dynamics. I think that many folks do not plug the amp into a conditioner or transformer.

[mourip]

I picked up a 500VA unit yesterday. It is smaller than I expected from the picture. I have to put my ear on it to hear the hum, so not a problem. Spent a few hours listening to favorite tunes. There is an improvement I'm happy to report.

 

Thanks for the report. Good news...

[mourip]

Thanks Middy. I have also searched for Topaz manuals and other threads on the shielding topic but apart from what's on here and other things from googling, haven't found anything in great detail. At least in the time available but I do like to be informed. Thanks for warning, I do not intend to rewire transformers anytime soon!

 

 

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I bought a 1.0 KVA Topaz 91001-31 from Ebay after reading this thread. It came with 14ga captive power cords that were un-terminated coming from both the input and output. I wired a US 3 prong adapter to the input cord and wired a 4 outlet box with hospital grade outlets to the output.

 

When I applied power to it I had 65 volts at the outlets. Our power here in DC is around 125 volts usually. I figured from this that it had been wired as a stepdown from 240 to 120. I scoured the Internet for a good PDF for wiring from Topaz but found nothing. Eventually in a stroke of "genius" I looked on the inside of one of the removable end panels and found a perfect chart of how to wire and set the jumpers. I ended up being short one jumper so I made one. Now I have 126 volts on the input and about 130 on the output. I guess that the transformer is not perfectly 1:1.

 

In my home nearly all transformer hum a bit. I figure that there is an imbalance in our AC. So the transformer hums a bit if you are within a couple of feet of it and if you are within about a foot you can hear a faint buzz. At the listening position these are not a problem.

 

I have also noticed as others have that as time passes improvements have been increasingly more noticeable.

 

Currently I just have just my DAC and tube preamp plugged into it. It replaced a small hospital isolation transformer that was just serving my DAC.

 

Definitely worth the effort.

[mourip]

Good to know Mourip, thanks.

 

Looks like these old Topaz units need a good examination when purchased on eBay.

 

 

Sent from my iPhone using Tapatalk

 

Definitely. Probably your best bet is to buy one with a plug attached and wired on the input side and outlets built into the output side. Also be sure to ask about which voltages it is wired for. I do not think that the hum issue is from the transformer but an issue with my AC.

[mourip]

My Isolation transformers hum is reduced as ground loops are eliminated. The last possible source of a ground loop will be eliminated next week. Nevertheless with the progress made so far, any hum is now inaudible.

 

What should one be looking for in terms of ground loops?

[mourip]

If you got 65 volts most likely the transformer was wired as balanced.

 

 

Sent from my iPhone using Computer Audiophile

 

I measured between hot and neutral on the output side. Should that not show 120v one way or another?

[mourip]

This is how the unit arrived.

 

 

 

I think this is was wired for 240v in and 120v out.

 

I rewired for 120v in and 120v out unbalanced.

[mourip]

Interesting ... so you were measuring between X1 and X2 but the transformer is wired as 2 parallel i.e. stepdown which suggests it was expecting 240v input and 120v output

 

As near as I can figure :-)

 

BTW. It was definitely worth doing. A nice improvement.

[mourip]

2 hours ago, mikicasellas said:

Hi everyone,

 

After following this thread and purchasing my TOPAZ ISOLATOR, i have been using it for a month and very happy with the results, but today i heard an electrical sound/noise, it is the same like when you are close of an electrical plant, like "DZZZZZ" that is coming from my TOPAZ UNIT and i am concerned because i don't know if that is already causing ANY issues or is it normal.

 

Is anyone experimenting these "sound" coming from their Topaz units, i know that in the beginning i did not heard any sound coming from it.

 

Any suggestions?

 

I have a Topaz and a couple of other medical grade isolation transformers in my house for isolating my audio equipment. They all have a physical humm. I assume DC in my AC but the transformers help so much that I do not worry much. I cannot hear it from my listening position.

[mourip]

I bought a Topaz 91001-31 iso transformer a bit over a year ago. I wired it up to do straight isolation, not balanced.  It made a very nice difference in my system. Much darker background allowing more fine details to emerge.

 

Today I was finishing building a good quality 8-gang power strip. I tested it with one of those simple AC socket testers that let you know about reversed wiring and ground faults. When I was done I decided to test the Topaz and it's associated hardwired 4 socket power strip. To my chagrin it told me that I had hot and neutral reversed. No problem I thought. I will just opened up my AC plug and the 4 plug box. I must have crossed my wires.

 

I opened up everything and it all looked good so I decided that it must have been the two output connections on my Topaz. I reversed them and now my tester is showing a "ground fault". I searched and searched and found no loose wires and that I had ground continuity from my AC inlet plug all the way through to the outlet box.

 

I finally gave up and left the hot and neutral rewired and put the Topaz back into service. I did test the AC tester on other wall plugs and it showed them to be correct. The plug that my Topaz plugs into also tests OK.

 

Any thoughts?

 

BTW. Here is the power distribution box I built. The box is from eBay and those are reasonably priced Leviton hospital grade receptacles. The box is really well made and costs about $50 and allows you to use your own power cord and choose your own duplex sockets.

[mourip]

19 hours ago, mourip said:

I bought a Topaz 91001-31 iso transformer a bit over a year ago. I wired it up to do straight isolation, not balanced.  It made a very nice difference in my system. Much darker background allowing more fine details to emerge.

 

Today I was finishing building a good quality 8-gang power strip. I tested it with one of those simple AC socket testers that let you know about reversed wiring and ground faults. When I was done I decided to test the Topaz and it's associated hardwired 4 socket power strip. To my chagrin it told me that I had hot and neutral reversed. No problem I thought. I will just opened up my AC plug and the 4 plug box. I must have crossed my wires.

 

I opened up everything and it all looked good so I decided that it must have been the two output connections on my Topaz. I reversed them and now my tester is showing a "ground fault". I searched and searched and found no loose wires and that I had ground continuity from my AC inlet plug all the way through to the outlet box.

 

I finally gave up and left the hot and neutral rewired and put the Topaz back into service. I did test the AC tester on other wall plugs and it showed them to be correct. The plug that my Topaz plugs into also tests OK.

 

Any thoughts?

 

 

 

Well it took a lot of time and head scratching but I believe that I have my answer. Perhaps it will help someone else.

 

As far as I can tell these little AC receptacle testers with the three lights on top and the error codes on the side are faked out by seeing a transformer up stream. I finally dragged out a stock toroidal encapsulated isolation transformer that I bought before my Topaz and tried it. It is hard wired from the factory and I get the same errors. The tester was useful for verifying the wiring of my two power distribution boxes but not once they were plugged into my IT.

[mourip]

7 hours ago, jamesg11 said:

Go figure ... wonder what the ‘upstream’ logic involved with that is?

 

Dunoh! I am very curious also...

 

It is a guess on my part based upon repeatable results but with not enough understanding to be certain. I was hoping someone with more EE knowledge would shed some light on it. All I can say is that using the meter with a transformer in the circuit creates a "false" reading.

 

My only thought is that there is "continuity" between the hot and neutral via the secondary of the transformer which the tester does not expect to be present?

[mourip]

12 hours ago, Ralf11 said:

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

 

Thanks. I have been on Head-Fi for over 15 years but somehow missed that one. A ton of well thought out and clearly presented information building on and clarifying John Swenson's excellent contributions.

 

It is ironic but I find some of the most helpful, cutting edge, and uncontentious computer audio information on HF these days. This would include linear power supplies, grounding, isolation, Dante/AOIP and USB tweaks. Granted some of the initial exploration starts here but they seem to be more able to collaborate for their mutual benefit.

[mourip]

38 minutes ago, sukyung said:

http://used-tools-equipment.com/topaz-ultra-isolator-line-noise-suppressor-91005-31-120-240v-5kva-50-60hz-0005pf/#

input 240v - output 240v - 2400w(5kva)

 

I want to buy a product. What do you think?

 

bryston bdp2 - schiit YGGDRASIL - FREYA - 2 x VIDAR MONO POWER AMPLIFIER - Revel Performa F32

 

220v 60hz

 

Certainly a good price for 5KVA might be overkill. In fact I think that in one of these threads someone recommended that you want to spec the transformer to not be too far over your actual needs. I am running a 1KVA Topaz with probably more current draw than the system you listed and it is barely warm.