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Discussion of AC mains isolation transformers


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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.

 

 

Right. Aside from floating power supplies, there's really no substitution for a well made heavy iron transformer :) ... with a low interwinding capacitance.

 

If you are spending $$$ for that amp it should be very heavy!

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I received the second network isolator today and connected that. In addition, I have recently purchased two power strips without filtering, surge suppression, etc. These strips take IEC inputs. I'd had old MIT Z-Cords feeding them, but thinking of avoiding filtering, yesterday I substituted two ordinary Tripp-Lite IEC cords. So I've got the strips plugged into the wall with these cords, a couple of the network isolators (inexpensive b/c bought used), a couple of small (about 5" cube) inexpensive iso transformers, and the LPS-1. I had this combo together for the first time tonight and just had time to listen to a few songs, not too loud because my wife had gone up to bed.

 

The sound is effing amazing. Effortless clarity and beauty. All the nuances, all the little differences in the way things are recorded, even from track to track on the same album...I'm loving it.

 

Jud,

I am glad you are having better sq! However, I am confused (and easily, cuz this whole subject has me a little confused). I thought that ONE power strip is the only way you won;t have impedance issues (when using mulitple power strips) and that the power strip plugs into the iso transformer, not directly into the wall. So where are your iso transformers and what is plugged into them (since your powr strips go to the wall) for you to get benefit?

Thx

Ted

 

P.S. I ask about multiple power strips and multiple isos especially because I have multiple uses for my music room and have my video/projector/surround equipment (except exasound mch dac) in the back of the room (due to projector fixed mounted and HDMI feed to pj), and can't reach any possible single power strip for the room. But they coexist because center and secondary preamp (front l/r for movies) 15 ft analog interconnects are plugged into front system.

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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!


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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!

 

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.

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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.


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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...


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a couple of small (about 5" cube) inexpensive iso transformers

 

Which ones did you get, Jud?

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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.

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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.

 

 

You're on a roll today--with two great posts! ;)

 

One thing that I wanted to mention is that John has found that oversizing an isolation transformer too much is something we may want to avoid. If the load is much less than about 10% of the isotrans' rating, the power factor drops quite a bit.

 

 

On a separate, but somewhat related subject that your trans hum post reminded me of:

Transformer ringing.

 

Not talking about these high quality isolation units (though I suppose those do too), but the power transformers in most all our gear. Much of it is a byproduct of diode switching noise, but it is also just inherent with all transformers.

 

Trans ringing and also low power factor (both resulting in harmonics kicked back into the AC line) is most likely the primary reason people hear differences with AC power cables--especially with power amps. Cables are not "improving" the AC delivered to the amp, they are filtering/altering to various degrees/characters what the component is sending back to the wall--in turn effecting other gear.

 

What is crazy is that trans ringing is so easily dealt with but very few designers of commercial audio gear bother to do so. John (and others) have been espousing for years the application of a simple RC (resistor and capacitor in series) snubber across the secondary of all power transformers. He has measured the resonant frequency range of close to a hundred transformers and concluded that an RC consisting of 330ohms/0.022uF is highly effective for most all transformers (despite some people going nuts unnecessarily trying to completely fine tune such for each trans).

 

And I have heard the results of this simple fix first-hand in my own gear (without changing anything else). It is quite remarkable.

 

 

And back to isolation transformers, here is a photo of the custom units we designed and built at Hovland Company--way back in 2002. I came up with the name VoltAire, and we had our favorite local, custom trans winder (Frost Magnetics who produced to our spec ALL of the Hovland power and output trans and chokes) make close to a dozen prototypes for us. They were only about 275VA. They sound terrific with from end gear. I think we sold fewer than 100 of them--mainly due to lake of marketing, lack of 220/230/240V version, and lack of understanding--everyone was so obsessed with power "filters" and myself and my Hovland partners lacked the vocabulary to properly explain the advantage of an isolation transformer.

 

VoltAireBack.jpg

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So Alex, maybe now you can relaunch something like the VoltAire as an Uptone product. There are certainly lots of people following this topic. Are you considering this?

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So Alex, maybe now you can relaunch something like the VoltAire as an Uptone product. There are certainly lots of people following this topic. Are you considering this?

 

Get a Euro or UK firm to make a version to act as a distribution hub....

Your specs ect...just a thought...

 

 

Would not consider it. Government regulatory constraints surrounding AC mains attached gear are too onerous to want to get involved in this arena.

 

Plus, our value-add--besides doing a pretty case--versus the available industrial isolation transformers would be minimal.

 

Besides, John and I have grander ambitions. :) Much more fun to do things that have not been done before!

 

--Alex C.

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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

Just ran the same test with the better quality Power-Mate power meter which arrived Friday afternoon.

 

I needed ear muffs to go to louder than normal listening volumes.

 

I got similar figures to the reading I took last week. RMS current approx. 0.7A, and approx. 180VA.

 

So there will be no issues with my 2.5kVA 0.0005 pF Elgar when it's finally hooked up to my system. This once again confirms that a lot of people over-estimate the power consumption of their gear (I was one of these people until I now have some measured figures).

 

Turns out I don't get anywhere near the specified maximum power consumption of 1100W for my integrated amp !

 

All of my amplification is Class D by the way (the power amp section of my integrated and the subwoofer sections of my powered speakers) apart from the Class A pre-amp section of my integrated. And my speakers are rated at 93db sensitivity too.

 

I most definitely could have got away with a 1.0kVA iso trans so I quite obviously may have over-sized it. Good to know I have head room though if I add a power hungry projector in future to the system ! Their typical consumption figures (not max consumption) are ~300-400W

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Jud,

I am glad you are having better sq! However, I am confused (and easily, cuz this whole subject has me a little confused). I thought that ONE power strip is the only way you won;t have impedance issues (when using mulitple power strips) and that the power strip plugs into the iso transformer, not directly into the wall. So where are your iso transformers and what is plugged into them (since your powr strips go to the wall) for you to get benefit?

Thx

Ted

 

P.S. I ask about multiple power strips and multiple isos especially because I have multiple uses for my music room and have my video/projector/surround equipment (except exasound mch dac) in the back of the room (due to projector fixed mounted and HDMI feed to pj), and can't reach any possible single power strip for the room. But they coexist because center and secondary preamp (front l/r for movies) 15 ft analog interconnects are plugged into front system.

Hi Ted. I imagine a single power strip (or a sufficient number of wall outlets) is the ideal situation. But I have only a single two-outlet plate behind my system, and way too much audio-visual equipment for a single strip. So I've got two strips, each connected by a plain 2 foot 14AWG TrippLite power cord to the wall (where I've got a multi-outlet adapter plugged into that single receptacle).

 

I listen to my main system using Audirvana+ with my laptop, and HQPlayer running on a desktop upstairs through an NAA (a CuboxTV). The source of music for both is an external HDD connected to the desktop upstairs. To access the HDD for Audirvana and to provide access to the NAA for HQPlayer, I have a router downstairs. The router has two Ethernet cable connections, one to either the laptop or the NAA, depending on which player I'm using, the other to a PS3 (not running when I'm listening, but on standby). To prevent leakage currents from using either of these Ethernet connections as part of a route through the system, I have Baaske isolators on both.

 

I also have two of the small B&K Precision 1604A iso transformers placed to try to keep leakage currents or other hash from power supplies from circulating through the system. I have the SMPS for the laptop plugged into one, and the El Cheapo that energizes the LPS-1 plugged into the other. Since the El Cheapo feeds the LPS-1, perhaps an iso transformer isn't needed there as much as it might be, for example, to plug the SMPS for the router into, or some other piece of equipment. I may experiment a bit with that.

 

Finally, I've got an old MIT Z-1 unit plugged into the wall, since it is supposed to help increase power factor.

 

I plan to get a large iso transformer for the entire system to run from, but that's going to wait for our next house.

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@Superdad

 

The simple RC works very well, I will buy a handful and try them out.

 

The 330 Ohm resistor should be a plain carbon type, there's no need for precision, plus the wirewound types often go open due to dv/dt over a long period of time connected to AC mains.

 

For the 0.022uF cap, poly should be fine, they withstand repetitive voltages as well.

 

The differences in AC cables could well be the interaction of the cable and the effects of crud coming back from the transformer either as a reflection of RF, low end harmonics, diode pulses and on.

 

Louis Motek of Lossless Audio in this article explains that their (and would assume everyone else's) AC power cable consists of a T network of resistance and in parallel, capacitance, not just in one value but more or less an infinite number of these networks in the cable. As RF frequencies move through the cable, they are affected by the RC networks and are attenuated to a degree depending on the geometry of the cable and clearly the marketing spin to add some spice.

 

On a different topic, the thought occurred to have multiple ISO transformers say for each audio component, correctly sized. The problem with that is there could be reflections going everywhere in circles, and it only needs one small SMPS or even linear supply feeding a Microrendu to unleash the monster within. I will ponder on this and work out a drawing. Certainly the hardest issue is working out the size of the transformer that's commercially available and at least rated to 80% to make it work producing Watts, not consuming them to make VAR.

 

PS Audio manufactured harvesters that would consume this waste into light, but I haven't seen them for 230V systems. An LED would contribute more noise when it switches, so more drama to worry about come to think of it.

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@Superdad

 

The simple RC works very well, I will buy a handful and try them out.

 

The 330 Ohm resistor should be a plain carbon type, there's no need for precision, plus the wirewound types often go open due to dv/dt over a long period of time connected to AC mains.

 

For the 0.022uF cap, poly should be fine, they withstand repetitive voltages as well.

 

.

 

I usually use a 1% 1/2W metal film resistor (they are only a few cents) and Orange Drop polypropylene for the cap.

 

John S.

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PS Audio manufactured harvesters that would consume this waste into light, but I haven't seen them for 230V systems.

 

Some years back Silicon Chip magazine did an article on LED "harvesters" and thoroughly debunked them.

It was so long back that I have forgotten the details.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

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