Discussion of AC mains isolation transformers

[One and a half]

Thanks John

 

In terms of earthing, if an iso transformer stated the following, would you avoid it for audio applications: "Earthing is NOT carried to Outlet Socket, Hence Isolated and Floating."

 

Would you prefer to see Earthing IS carried to the outlet?

 

Run away from that transformer.

[One and a half]

Run away from which?

Earthing is NOT carried to the outlet socket?

Or earthing IS carried to the outlet?

And may I kindly ask why? :-)

Many thanks in advance.

 

I would avoid that transformer for plugging in anything.

 

The incoming safety earth that comes from the wall must <-- (by many rules on this planet, maybe Russia/China is exception) be connected to the outgoing circuit of the isolation transformer, straight passthrough, no filtering of any kind. This is a safety requirement.

 

These days, the output of the Isolation transformer must be protected by a RCD/GFCI, since the neutral connection to ground/earth is lost when the isolation transformer is used. If there is an imbalance on the output between line and neutral, the upstream RCD/GFCI can't see the problem.

 

I'm surprised by Tortech that the earth is not connected. I bet that 3rd pin is connected to earth.

[One and a half]

How big, John? About 1 kVA for a stereo with PC system?

 

Rule of thumb : (Sum all Watts, VA of audio equipment) / 0.6 = VA of isolation transformer.

 

Watts = Volts x Amps x power factor. VA = Volts x Amps. The 0.6 derating is for the lumpy currents that amps especially draw. Middle Atlantic have guides for more accurate determination of what amps can draw depending on the music content.

 

Peak. The maximum power drawn by an amp is written on the nameplate. In rare cases, there might be a peak rating.

[One and a half]

Hi mate, the one I linked above does have earthing to the outlet, here again: Medical Isolation Transformer IEC 601 and UL 544 Standard for Medical Instruments Australia

 

Tortech confirmed to me that the medical version has earthing to the outlet,

 

whereas the standard (which you linked) does say "Earthing is NOT carried to Outlet Socket, Hence Isolated and Floating"

 

But like you say, perhaps it's not written clearly

 

There you go, if you are testing something, then in some cases the AC needs no reference to earth, but not audio equipment.

[One and a half]

Ah righto, so in this case the only option is the medical version - you'd avoid the standard version?

 

Theyre supposed to be well built, some others have said over on StereoNet.

Sent from my Blackberry DTEK50 using Tapatalk

 

If you are going to Tortech, get one of these. The one sore point is that they don't mention the output balance regulation, which is important. They use NTC thermistors for soft power, a power company's auto-recloser will make mince meat of them.

[One and a half]

Thanks for the reply.

 

That is one point of confusion for me. My amps are rated at 400 watts at 4 ohms but then double (half) depending on 2 ohms (8 ohms) loads. What should I use for your recommended 50 - 60% calculation?

 

In this case, use the rating as stamped on the nameplate usually at the rear panel.

[One and a half]

This post didn't come over.

 

The leakage currents on 120V systems is half those of 230V systems a bonus for audio equipment.

[One and a half]

The voltage drop across 120V mains plugs and sockets is much higher, resulting in many members replacing supplied mains plugs with much higher quality expensive plugs, and even replacing AC mains receptacles with higher quality types too for greater reliability.

 

Perhaps your post, and my reply, were both deservedly removed by Alex C due to the wording of your original post, and my tit for tat reply to you ? .

 

The larger rated wall sockets or more a tighter connection is related to power amps and powered subs. For signal sources 120V with the lower leakage currents would prove advantageous. For my system at home I power the RUR, Icron from 120V supply. The Icron PSU is a SMPS 24V with leakage current of 3mA max on the 120V side. That's about as low for a commercial OTC. Unless the linear psu's transformer has lower AC leakage depends on the shielding used and mitigation of unwanted artefacts as per JS-1 for example.

[One and a half]

But your system at home is far from typical isn't it ?

You also use a couple of Isolation transformers.

 

I design the AC for purpose. The 120V is derived from a couple of Jaycar small ISO transformers, which get a bit warm... used to have 2 x 1kVA 230V-115V transformers, still have them, in the process of rebuilding that network. RS components have a 26kg 2kVA ISO with wireable for 2 x 115V or 400V to 2 x 115V. It needs an enclosure and ventilation though. There's no shielding, so the search continues.

 

The key though is distance and keeping the transformers and switching nasties away from the audio equipment. This includes the audio playback computer. I thought to install the playback PC on the same network close to the audio gear with a small ISO transformer, but it was a disaster. The SMPS that powered the computer (19V, 6A) threw back so much shite, it affected the USB transmission very badly. Now the computer lives 25m away and there's very little degradation, however it's not eliminated. Currently input to the DAC is AES3, that seems to be the most optimum. Unless there's a really super dooper USB front end built into a DAC, a separate DDC is the way to go like BADA.

 

The SACD player is still king for SQ, but it's a long road to tinker with computer audio.

[One and a half]

snip

 

I am sure there are some very high quality balanced units out there with extremely well made transformers, but they are not cheap. Some are toroids, and some are EI style.

 

Would love to see balanced transformers brought into this discussion as I know a lot of audiophiles have had good results with them. One question is if the results are due to the "balanced" output or due to reduced leakage current. Or is it that one leads to the other?

 

The immediate and obvious change in using a balanced transformer from Equitech was the quiet. Fade outs went forever, it was easy to listen to. Bass improved as it should. Since the noise was lowered, the quality of the sound improved, naturally increasing the volume level.

 

Objectively, measuring low level harmonics (3rd, 5th, 7th....) line to line on the AC side, IIRC reduced by 35db compered to plugging into the wall. The harmonic voltages were in the microvolt levels, there's a graph at CA shows this. Conclusion is the crud (harmonics anyway) from rectifiers and SMPS are indeed knocked on the head on the AC side. I didn't measure any RF, by the time you reach the 35th harmonic and it's all noise floor, who cares.

 

Equitech have a lot of information on their site, but I would not buy from them again. After repeated request emails to buy a larger unit, the questions remain unanswered. Plitron have shyed away from balanced transformers publicly and offer an isolation transformer which supposedly does the same thing...they did at one stage supply Equitech with balanced transformers to Equitech spec. There was another lot in CA that also supplied transformers to Equitech, I will do some research as to the name and post.

 

The reason they are not cheap is to do with the construction of the bifilar windings of the secondaries. To achieve effective cancellation, the voltage regulation must be be very tight from one winding out to the other. To ask that of a magnetic device is a tall ask and complex since the regulation needs to be <1.0%., or better of course.

 

To substitute the balanced transformer, it's possible to use solid state programmable AC voltage supplies with +/- 0.1% regulation, 2kVA for USD5500 a piece (California Power or ELGAR), you need two of them of course. Makes a rotary system a very real prospect. More on this later.

 

I did read somewhere (here at CA?) that balanced transformers restrict dynamics. That's BS. The recordings are the limitations to restricting dynamics, if sized correctly, transformers can withstand quite a bit of overload before they melt and reduce the voltage.

[One and a half]

Just as a follow-up:

 

Can I use this: Power Factor = True Power / Apparent Power

 

Therefore: Apparent Power = True Power / Power Factor = 0.7 / 0.42 = 1.75A = current to be used to size an iso transformer?

 

Allowing for even significant measuring equipment error, if I'm using < 3.5A then it sounds like my 8A (2.5KVA) Elgar Iso transformer should be fine.

 

Voltage at the wall here is ~ 249 Vac

 

Yes, you're on the right track.

 

Power factor is always is equal to or less than 1.00. So Power Factor = True Power / Apparent Power and

 

Apparent Power = True Power x pf and

 

VA (apparent power) = Volts x Amps

 

Watts = Volts x amps x pf

 

If your load is 0.7A at 0.42 pf at 249V, then the Watts = 249 x 0.7 * 0.42 = 73.2 Watts.

 

The ISO transformer in this case is a minimum 73.2 Watts / 0.42 pf = 174VA.

 

If the pf can be improved even to 0.8, the size of the ISO transformer can come down 73.2 / 0.8 = 91.5 VA. Power factor can be improved using a combo of mainly capacitance and inductance. BUT. No free lunch here, possible resonances between the load and the power factor correction gear can occur. The load has harmonics which usually add voltage and also resonate with the frequency of the LC filter, which the capacitor tries to support, so an over voltage occurs. If the load decreases, then too much capacitance can makes things worse as well. Oversizing a capacitor bank can attract harmonics from other appliances in the house or your neighbour.

 

In audio case, it is simpler and less painful to buy a bigger ISO transformer.

 

BTW, you buy electricity in kW, not VA, eg. $0.25 / kWH, not kVA per hour.

 

The kettle 8.7A at 1.00 pf 249V = 2166 Watts.

 

The ISO to supply the kettle (silly but for exercise only) VA = 2166 /1.00 = 2166 VA

[One and a half]

Thanks so much. I was worried a 2.5kVA iso transformer @ 249Vac could be an issue (undersized) since I thought my pair of subwoofers and integrated might get close to 10A. But today's measurement and your calc of <100 watts consumption by my gear is awfully low. That's a good thing I guess !

 

Just another question. If a 2.5kVA iso transformer itself has a power factor of 0.8, then it's good for 2.5 x 0.8 = 2kW = 8.3Amps.

 

If someone accidentally put a 10A fuse on the inlet of the iso trans (or they thought it should have a 10A fuse on there despite my above calc) and the iso trans had a 9A load applied.... what would happen to the iso transformer? And what could happen to the gear connected to it?

 

An ISO transformer doesn't have pf. The load does.

 

Inrush currents and protection on larger transformers can be an issue. There are ways to get it right, but not tonight Josephine.

[One and a half]

Thanks mate. So a 2.5kVA iso transformer is actually good to provide a full 2.5kW of power?

 

Yes, if the load is a kettle pf of 1.00

[One and a half]

Thanks, John. I'm also curious - wouldn't this also create a larger possibility of more traditional ground loops in the system as well? Due to the different components connected through interconnects being on slightly different ground potentials?

 

Not necessarily. By sourcing all the AC at one point is one step to providing equipotentials.

There will always be a ground loop with RCA connections however. The ISO transformer will keep the certain house AC crud out but the audio components are their own worst enemy.

[One and a half]

Hi John, if I had 3 power outlets fitted to the iso transformer, and had double adapters in each, giving a total of 6 outlets, would that be the same as having a single strip with 6 outlets - in terms of impedance between devices.

 

Seems hard in Australia to find a well built power strip with no filtering, circuit breaker etc etc

 

The chain should look like this:

Iso transformer output -> portable rcd 30mA -> standard 6+ standard plug board with no suppression devices.

Have the power amp and pre amp close to the cable end and the sources can follow whatever you wish.

 

Try to find boards that are 4x 2 instead of 6 x 1.

[One and a half]

This is the hard part to find here in Aus: standard 6+ standard plug board with no suppression devices

 

John S mentioned, no filtering, no switch, no circuit breaker.

 

So I have the option to fit 3 outlets on the iso transformer output. I can then add a double adapter to each (which only has wiring, no filters) giving a total of 6 outlets. Will that achieve the same impedance between devices as a single strip with 6 outlets?

 

And what would be the role of the portable RCD after the iso transformer? Especially if I had a 10A switch/fuse at the iso trans input?

 

Even Bunnings?

[One and a half]

Does the RCD help sound quality in a way? Is it needed even if you have an RCD where the power enters your house?

 

Sent from my D6633 using Computer Audiophile mobile app

 

I will find a previous post explaining why rcd is necessary on the output of an iso transformer and link it in this thread.

[One and a half]

As promised, here is the reason to install an RCD/GFCI.

[One and a half]

Also regarding impedance between devices, can anyone help me with this: I have the option to fit 3 outlets on the iso transformer output. I can then add a double adapter to each (which only has wiring, no filters) giving a total of 6 outlets. Will that achieve the same low impedance between devices, as a single strip with 6 outlets would?

 

Forget double adapters, their connections are too sloppy. There's nothing on the Australian market that does what we need to do.

 

You mentioned an electrician that is re-working the Elgar when it arrives? I thought to use standard 4 Way Outlets and a mounting block.

Put two of these back to back, and wire via shielded power cable to the RCD. A fire resistant timber perhaps would jazz it up. The joining wires can be short, there are only three, so impedance is not an issue.

 

Available here

 

Available here

 

This is what I made before standardising on Oyaide and Furutech Euro standard plugs and sockets, there's nothing much for AU style even from Furutech only one or two models, that's it. Euro gear is rated for 230V and it stops anyone else using a vacuum cleaner out of the system. Choices.

 

Never use NEMA 120V plugs and sockets on 230V systems. You don't pressurise a tyre rated maximum at 30psi and you put in 60psi?

 

[One and a half]

snip

I had schaffners filters but since i optmised my digital chain with battery decoupling and network isolation, i have much less harchness in SQ and i realize i probably liked before the schaffner for their low pass action on audio spectrum and digital harchness more that their ability to filter ac noise. They probably do it well, but they colored the sound too and affect the dynamics.

I just removed them.

 

The Schaffner filter needs to supplied with a balanced power supply, common the neutral to ground and it loses its effectiveness.

 

The most important point on the Schaffner filters and devices like them, is that it isn't a filter. It's a low pass selective mirror, it reflects frequencies in its domain back to the origin. On the line side, to the rectifiers, on the load side also back to the rectifiers on the load device, but it will not mix the two systems for RF. The attenuation of frequencies vary but they start throttling EMC above low MHz values. It will pass 50/60Hz and low order harmonics very well.

[One and a half]

It has it's power lead on the same surface as the outlets though. Behind the furniture it wouldn't be visible at all.

 

And it's the only type of board I can find with no circuit breaker, no switch, no filters.

 

Wouldn't work? Apart from the visual aesthetics, any other issues with using it to plug Hi-Fi into?

 

The 3m lead would not be shielded.

[One and a half]

Here are informative pdfs on leakage currents, especially those caused by SMPS. Wondering what frequency leakage currents can be, and they form part of the EMC spectrum up to 30MHz, but can bottom by regulation to 100kHz. That doesn't mean the lower than 100kHz frequencies aren't there, it's only a limit of compliance.

 

I would have thought the higher RF would be mitigated by audio components in one way or another, so these frequencies should be covered by reflecting the noise back to the source. It's the lower frequencies that cause the problem, supposing they have greater energy.

In essence and reality hits home here, to remove the leakage currents on the AC is not so easy based on filtering. That's most likely why power conditioners with L and C get the frequency wrong and cause a worsening of SQ. I found this out the hard way by installing a Monster power Center on the upstream of a balanced transformer. There must have been a resonance of the harmonics from the audio equipment reactive adversely with the L & C of the power conditioner. The bass vanished and the performance just sucked the life out of recordings, so bad idea there.

 

The way around this is to corral the AC leakage currents so they follow some path of our choosing and not into audio devices. Ony way is the practice of star-ring the components never goes out of fashion, heh the Naim Hydra is a good idea but needs some DIY at voltages that bite to make sure the AC leads are the same length, if possible especially for sources, but can't be avoided in all circumstances. Not easy for the hobbyist though.

 

Hopefully these discussions may shed some light on techniques that work for everyone.

 

Don't forget the built in transformers of audio equipment of reputable quality have shields between windings and in some cases, enveloped shields over the winding. Inherently this provides for voltage suppression and avoids an easy path for leakage currents to enter.

 

 

2004NOV16_POW_TA.pdf

 

Electromagnetic-Interference-EMI-in-Power-Supplies.pdf

 

APEC-2002.pdf <-- From Henry OTT

[One and a half]

The discussion on this thread is in line with Naim recommendation which is always to avoid using any power conditioners, circuit breakers and surge protection for best performance. In North America, Naim recommends the Wiremold L10320 which I currently have two of these and they are excellent sonically and the build quality is first class. This is a nice read to get some background info on why Naim recommends a plain power strip by Stereophile Listening #153 Page 2 | Stereophile.com

 

You would have to ask why the Hydra didn't work in the North America, where the power strip does. That extra bit of copper makes a difference?

[One and a half]

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?

 

Measure with a Kill-A-Watt...

[One and a half]

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!

 

Why transformers hum

 

Toroid

 

- Loose windings around the core - Fix - Replace with one that has better construction

- Overloading - Fix - Reduce the load

- Harmonics - Cause losses in the transformer and heat to rise - Diagnosis - Connect only a table lamp (no flouro, energy saver rubbish lamps, the old bulb type) close to the rating of the transformer. If no hum, then plug the audio load in again to confirm detrimental harmonics exist. Fix - Easiest is a larger transformer, perhaps twice the electrical rating.

- Not enough load - Too little load and there's only reactive power drawn, combined with harmonics causes audible noise.

 

Box type shape (E)

 

- Loose windings - Fix - Connect a load (like a portable heater, lamps) that's close to the rating of the transformer, let is run for several hours to get warm/hot. Plan ahead and have screwdrivers/spanners/allen keys prepared, then switch off power, then immediately tighten all the frame screws that hold the laminations together as quickly as possible.

 

Other noises - Refer to toroid above.