Discussion of AC mains isolation transformers

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Thanks for your post John.

 

Indeed a true isolation transformer is quite safe. In fact, before there were GFCIs, hotels used to have "shaver-only" outlets which contained--you guessed it, a small isolation transformer.

 

But it turns out that many (likely most) of the in-a-case with outlets units presently sold as "isolation transformers" in fact are not. Due to NEC (and probably EU) requirements--along with a desire for even greater common-mode noise attenuation--they are most all bonding one leg of the secondary to ground. This of course defeats the safety aspects of a "floating secondary" as John describes above.

 

Again, I am not talking about just running the input ground to the chassis and through to the third pin of the output outlets. I am saying that the TrippLites, the Eatons, and many others are connecting one side of the secondary to ground! That is why there are lots of videos by techs and old radio repair guys showing people how to "re-float" their TrippLite "isolation" trans units--since that is important for safety for those folks.

 

Of course the old stock industrial Topaz units are not doing this (though if I bought one prewired with cord and outlets I would check it).

 

And perhaps the "grounded neutral secondary" pseudo isolation units offered to the public these days would indeed benefit from a GFCI.

 

Here is a page from the current Eaton "Power Suppress" series (you can see the secondary being grounded), and all the TrippLite "Isolator Series" pages state "Secondary Neutral Bonding."

 

[ATTACH=CONFIG]30782[/ATTACH]

 

 

This is a top thread and appreciate all the input.

 

I have a question as I'm thinking to pick up a Topaz at some point. In relationship to floating and/or connected to secondary grounds - I would appreciate if someone can explain from the diagram what the S1 and S2 wiring and the chassis to core wiring are achieving.

 

 

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[tapatrick]

[ATTACH]30932[/ATTACH]

 

This is a top thread and appreciate all the input.

 

I have a question as I'm thinking to pick up a Topaz at some point. In relationship to floating and/or connected to secondary grounds - I would appreciate if someone can explain from the diagram what the S1 and S2 wiring and the chassis to core wiring are achieving.

 

 

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Okay there doesn't seem to be any comments to my question on Isolation transformer wiring. I understand the core connects to chassis therefore to the ground but does anyone know why the shields ( S1 & 2 ) would connect to the neutrals?

 

Thanks in advance!

 

 

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[tapatrick]

Thanks Cornan & Middy.

 

 

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[tapatrick]

I found these with a simple search but I think if you have to question any part of wiring anything electrical then pro help is a minimum. Do the company who made these still exist in some form? They should have a tech help department.. with people asking this all the time....Even some surplus suppliers must have manuals wiring diagrams.

You can't complain about bad sound if your dead..... Be safe[emoji4] and good luck

 

 

https://forum.audiogon.com/discussions/wiring-an-isolation-transformer

 

http://www.diyaudio.com/forums/power-supplies/104346-please-help-isolation-balanced-power-question-2.html

 

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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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[tapatrick]

The S1 and S2 are shields. Depending on the source which could come from a UPS PV inverter or a generator, H4 can be connected to ground. It's a convenience thing.

 

For USA: [standard house wiring]

 

Input

120V ac Hot -> H1 + H3

 

120V Neutral --> H2 + H4

 

Ground from 120V --> S1 + Chassis (remove the link H4-S1)

 

Output

120V ac Hot Sec --> X1 + X3

 

120V Neutral Sec --> X2 + X4

 

S2 --> chassis

 

Output Ground --> Chassis + X4 (retain link X4-S2)

 

For EU/AU

 

H3+H2

230V hot --> H1

230V neutral --> H4 (remove the link H4-S1)

Ground from 230V --> S1 + Chassis

 

Output

X3+X2

230V hot --> X1

230V Neutral X4 + S2 + Chassis

 

For balanced output 115-0-115

Output

X2+X3 + chassis

 

Remove X4 to S2

 

S2 to chassis + X2

 

In all cases, use a GFCI or RCD on the output. Grounding the secondary keeps the potential of the chassis voltages of the equipment at the one low level. Floating the secondary elevates them, why would you do that?

 

Thanks One and a half. That's what I thought, so thanks for confirming. I wondered why it seems to comes with the shields connected to neutral, in and out.

 

 

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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.

 

Good to know Mourip, thanks.

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

 

 

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[tapatrick]

4 hours ago, Middy said:

I wish it said how to get them cheap in the UK. ..

Hi Middy

I managed to get a 1Kva Topaz and shipped to UK for just over £200. Because they are so heavy the shipping is a lot but seller used the eBay shipping partner scheme so if you can make use of that it helps a lot. 

[tapatrick]

I installed a new Topaz 2.5Kva iso trans (0.0005pf) yesterday to replace a 1Kva (0.001pf) and it added a significant improvement over the 1Kva. So the extra lowered interwinding capacitance does seem to make a difference (or maybe the added headroom). Blacker background, cleaner all round sound, more details revealed, Natural voices and better, tighter bass. It does hum a bit even though I added a DC blocker too. I will probably put it in a box next.

[tapatrick]

1 minute ago, tapatrick said:

 

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2 hours ago, esmit said:

I use mine at 230v. It does hum a lot, even with ATL DC blocker before it. How about yours?

Yes does hum a fair bit, more than the 1Kva, which is a expected but its only noticeable when the room is completely silent.

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2 hours ago, One and a half said:

It could be a mechanical resonance that's causing the hum on the Topaz. I have the same model, it doesn't make a noise.

 

Note the four bolts that hold the Topaz together, they are 8mm quite large at either side of the core. Place the transformer over a poor insulator, like timber, this will keep the heat in the transformer. Put a heater on the output, full 2400W power and let the heat build up in the transformer over an hour or two. Switch off the load, and immediately, tighten the four bolts in a cross hatch manner, 17Nm torque should be OK. The bolts are a UNC type, possibly using a 1/2 in socket to tighten, from memory. Let the Topaz cool, and try on the audio system again.

 

The blacker background is the reduction of leakage currents across the windings. Other users have reported that wiring the output in balanced mode reduces the noise (and heat). 

 

Connections for balanced mode:

X1 - Hot 1

 

Join X2 to X3. Wire an earth from the small 3/16 in stud to this point and all shields (the smaller wires in the black sleeves)

 

X4 - Hot 2

 

 

Thanks @One and a half - I will give that a try to tighten the bolts and am thinking to try balanced output too... sounds so good right now.

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1 hour ago, SoundSparks said:

 

Why is the new unit better? Is it because of the lower capacitance (2 times lower) or is it due to the higher power (2.5 times higher)? What is the major contributing factor here?

Should think its a combination of both lower capacitance and power...

 

1 hour ago, SoundSparks said:

 

Should the distance from the gear to the iso trans be taken into consideration? 2' vs. 10', e.g.?

I have mine a metre away from my equipment in an alcove..

 

1 hour ago, SoundSparks said:

 

Is 1000VA iso trans powerful enough for 600VA (total) of connected gear? I.e. is (Total VA)/0.6 = (iso trans power rating) an accurate enough approximation?

Should think that would be enough although some opinions I've read say it needs more to allow for the peaks..

 

1 hour ago, SoundSparks said:

 

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1 hour ago, One and a half said:

For the Northern Hemisphere, this time of year the heater method works well, but not desirable in the summer

...Its well know in audiophile circles that air warmed above 20˚C leads to improved SQ...

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4 hours ago, One and a half said:

Spent most of the the day listening to music, read music, with the absence of noise down in the smallest crevices. Certainly noticeable when its gone, that's for sure.

 

Thanks @One and a half for your nice report on your Topaz install (same as mine just installed 2 days ago too). I confirm with your findings on the effect of noise removal which brings out the best in the music - in my system this brings tauter bass, clearer sound all round, wonderfully natural sounding voices and oodles of delicate details and reverberations leading to greater ease and listening pleasure.