Discussion of AC mains isolation transformers

[Superdad]

Hi John, a few people on other forums have commented that their Topaz hums...

 

Just teach it to hum with the tunes!

(or put it in another room)

[Superdad]

John, regarding an isolation transformer, something like this? https://www.amazon.com/Tripp-Lite-Isolation-Transformer-Outlet/dp/B00006HPFH

 

Hi Jim:

 

Most of the TrippLite isolation transformer units also have various additional surge-suppression devices--such as MOVs (metal oxide varistors)--which as John explained are not very desirable in out application.

 

Also, to hit the price points they do, I sincerely doubt that the inter-winding capacitance specs of the Tripp units are anywhere near as low as the old Topaz industrial units. Those Topaz units were expensive in their day.

[Superdad]

Hello John and thanks for the info:

 

I have here some possible choices, i hope you can suggest if any of these are good for the job or perhaps any could do it even better:

 

Topaz Line Noise Suppression Ultra-Isolator Part# 91005-31 ~Untested~ S2453

 

 

TOPAZ 91001-12 Isolating Transformer 120V | eBay

 

 

TOPAZ ULTRA-ISOLATOR LINE NOISE SUPPRESSOR 91001-11 | eBay

 

 

 

regards

 

Miki

 

Hi Miki:

 

The first one you linked to a very large 5KVA unit, where as the other two are a more manageable size 1KVA.

 

When buying these used (the only way they come!), pay attention to the cords and outlets as most of the time they are cut, and you will have some work to properly wire them.

[Superdad]

Thanks John. Not sure what VA capacity I need. I have a turntable, CD Player/Transport, Network Player, DAC, Preamp, 2 mono amps, urendu, USB?SPDIF Converter. Any recommendation?

Thanks, Jim

 

Hi Jim:

 

90% of your choice will be based on the draw of your power amps. Without the power amps you easily get away with a 500VA unit. Depending upon the size of your amps, even 2400VA could end of not being enough--or it could be plenty.

[Superdad]

We have the advantage over the USA of double the mains voltage and half the current needed. The doubling of the current seems likely to cause more mains supply degradation ?

 

Yes, but at least we can touch our mains without being nearly killed!

[Superdad]

Due to the nature of the forum system, this intro post will appear below all the earlier-dated ones I just moved out of the UltraCap LPS-1 Troubleshooting thread.

 

--AJC

[Superdad]

Hey jabbr,

 

Could you give an example or two of "reasonable prices" including the output of the units your referring to?

 

It's times like this where I feel the cost of not knowing how to solder.

 

Thanks.

 

Joel

 

Hi Joel:

 

Here is a nice 500VA unit for $120 which has a cord and a duplex outlet. Nice size for front end gear.

Topaz Line Noise Suppressing Ultra Isolator 91095-12 | eBay

 

 

As part of my just completed facility addition we built a utility room (for new high-efficiency, duel-fuel house HVAC system, new mains panel, etc.), and I am seriously considering a big 5kVA (or even 7.5kVA) transformer to locate in there. My office/studio has its own sub-panel fed with 25 feet of 000awg wire from the main panel, so feeding it from a transformer would be easy. And in the studio there are both house-fed outlets and sub-panel outlets which have only hi-fi gear plugged in.

 

I would use the iso transformer as 240V in/out since I run both sides of the line to my studio (someday I'll reconfigure my Hovland RADIA-i power amp trans for 240V operation).

[Superdad]

 

John Swenson,

How does your recommendation for isolation transformers hold for balanced transformers, which, I believe, also function as isolation devices ??

 

TIA,

Dave

 

Not John, but I can say that what are referred to as "balanced transformers" are just 1:1 (or maybe 1:1.08 or or something to compensate for losses) isolation transformers with a center tap for ground. The unknown is what the interwinding capacitances are in comparison to the known ultra-low spec of the Topaz units. The specs I have seen for balanced transformers do not list interwinding capacitances.

Part of the idea of the balanced transformer (60/0/60)--at least as espoused by the manufacturers of such--is that the leakage currents balance (cancel?) each other out.

 

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?

 

I did get in on the deal that Larry arranged a year or so ago with Bridgeport Magnetics, scoring a 1kVA, 8-outlet balanced isolation unit in a very nice 3-inch tall, thick aluminum case for a terrific price. Embarrassingly, I have yet to try it out.

[Superdad]

I'm copying below the post that John just made in the other thread as it is as relevant (maybe more so) here. Don't think he is trying to put a damper on discussion of isolation transformers, but as usual he is bringing at bit (a lot?) of clarity to the big picture:

 

 

OK, this talk about isolation transformers has gone far a field from my original intent. It was supposed to be about ways to decrease the effects of leakage loops.

 

The PRIMARY part was to decrease the AC mains impedance between devices in the audio system. Many people have power conditioners that as a byproduct of filtering line noise significantly INCREASE impedance between outlets. My recommendation is to get rid of these power distribution devices and use a simple power strip that just has wires between outlets. No filters, no MOVs.

 

BUT that can lead to a situation where noise from the rest of the house and neighborhood can get into the audio system and it leaves the system unprotected from AC line surges.

 

This is where my recommendation of a SPECIFIC type of isolation transformer comes in, these have extremely low inter-winding capacitance and carefully designed magnetics which result in a very high amount of noise suppression AND very good surge suppression in one simple device. Most isolation transformers do NOT have these parameters.

 

This is NOT the only way to do this, there are other devices that filter the line noise and provide surge suppression, BUT it needs to be something that you can drive the power strip with.

 

So look at your power conditioner, if there is ANYTHING other than wire between outlets you will not have the lowest possible impedance between audio devices. If the power conditioner just has its "filtration" upstream of any outlets and just wire between outlets it will probably give good results.

 

But be aware that very few power conditioners will be as effective as the specific isolation transformers mentioned.

 

So a few ways you can do this:

 

a power conditioner with all the filtration/surge suppression before any outlets and all outlets connected with just wire.

 

A filtration/ surge suppression device with a simple power strip plugged in.

 

A special isolation transformer being used as a surge suppressor/filter with a simple power strip plugged in.

 

The third option is, in my opinion, the best way to go for most people.

 

This should give you a way to determine whether a particular system meets my criteria.

 

NOTE I am NOT saying you HAVE to do any of this!!!!! The LPS-1 is a very effective tool for breaking some leakage loops, the above is a way to decrease the negative sonic impact of other leakage loops which cannot be broken with an LPS-1, such as a DAC with its own PS, preamp, poweramp etc. Once you hear what dealing with some leakage loops, which the LPS-1 can do, you might want to think about decreasing the impact of others. This is a way to do that.

 

John S.

[Superdad]

Hi

 

Isolation transformer by they inductance are known to impact the sound spectrum of amps and preamps. I have one and i don't use it anymore because of this. None of you had this kind of issues ?

B.

 

Yours was likely too small and also not of the caliber of the Topaz units under discussion. Yes, a transformer will always increase impedance by a few percent, but sized right it will be very little at the 50/60Hz frequency we care about, and the benefits--again with the ultra-low interwinding capacitance of the good ones--when applied in the manner John explains, outweigh the slight impedance issue.

 

And I say that as someone who has disliked many a "power conditioner" and always plugged my gear direct into the wall.

[Superdad]

Very nice. Which power strips if you don't mind me asking?

 

Not Jud, but IIRC, he may have ordered one of these based on John's recommendation.

 

Audio Catalog

 

They are very nicely made and the price is hard to beat. But I think they took a long time to arrive.

 

Another decent no-filter-element, heavy-duty USA power strip series is this one from TrippLite.

 

12 Outlet Vertical Power Strip 120V 15A 6 ft Cord 5 15P 36 in (PS361206) | Tripp Lite

 

Attractive extruded aluminum housing, outlets that grip like crazy, and a 14awg cord. The linked 12-outlet version is $41.

[Superdad]

Which ones did you get, Jud?

 

He got these: Model 1604A, Single Output Isolation Transformer - B&K Precision

[Superdad]

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.

 

[Superdad]

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.

[Superdad]

... shouldn't a properly designed power supply obviate any effect between reasonably well constructed AC cords?

 

Well we think that an RC snubber on a transformer secondary does, by reducing trans ringing back to the wall, reduced the impact of AC cord variations.

 

And the choke filter in our JS-2, by conducting over virtually the entire AC wave cycle (and in combination with Schottky diodes) GREATLY reduces harmonics going back to the wall. So I personally find AC cords have almost no impact on SQ for devices powered from the JS-2.

 

But look at a typical power amplifier: Non-regulated PS and big diodes kicking harmonics back to the wall. No wonder AC cords interact especially strongly with power amps.

 

A regulated, choke-filtered PS for a big power amp will be bigger than the amp itself (though to be fair, most of the real estate in a power amp is already taken up by the power supply.

 

Here is one shot of the interior of the 730W (4 ohms) Hovland Stratos monoblock. Half this 90-pound amp is the power supply (the quasi-C-core trans is suspended in a yoke under the center-front aluminum plate).

 

[Superdad]

Pizza, thick or thin?

 

As long as it's not square in a pan! And no fork and knife please.

[Superdad]

Anyone on this thread who knows If this £290.- 1500 VA balanced power supply would be something good or not instead of a filtered power strip?

 

It also has an inrush current thermistor on it. I don't know if those are a problem or not.

[Superdad]

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."

 

[Superdad]

The only issue is that they can hum a little bit (I KNOW someone is going to ask if they can hum in tune with the music),...

 

Not today sparky, but I did find this fun video of some very musical Tesla coils!

 

[Superdad]

Hi Gents:

 

Happy Friday. I'm taking it a bit easy today. Was going to go to Fresno to pick tile and counter laminate for the UpTone shop bathroom and kitchenette, but there is a storm rolling in and the big Wilsonart laminate store closes in a couple hours anyway. So I'm just catching up on e-mail and forum stuff--and again procrastinating my year-end accounting.

 

Right now there seems to be a particularly nice selection of Topaz iso trans units on eBay, at surprisingly good prices:

http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.Xtopaz+transformer.TRS0&_nkw=topaz+transformer&_sacat=0

 

A lot of the eBay sellers fail to indicate the kVA size of the units they are selling, if they were originally line-cord or terminal models, or the input/output voltage options. But they always list--or you can read from the listing photos--the model number.

So here is a link to the only model/spec sheet I have found to-date:

http://www.pacificparts.com/vends/mge/images/t1.pdf It is from MGE UPS Systems, the last firm to own/sell the line before Eaton bought them. I have seen other Topaz models outside of what is on the list, but it is a pretty good sheet for sizing what you are looking at.

 

Also, I recently discovered that Daitron--a Japanese conglomerate that we have known for a while for their ultra-low-noise SMPS units--has for many years (decades even?) been selling isolation transformers that are exactly the Topaz Ultra Isolators.

See: DaitronPower

 

Look at the photos of this one on eBay:

Daitron J 91005-11 Line Noise Suppressing Ultra-Isolator .005pF

 

Plus, on the current Daitron spec sheet, they are listed with interwinding capacitance of 0.0005pf, just like the best of the original Topaz units.

 

Given that they clearly are using the same end castings as the original, and that Daitron generally does its own manufacturing, I am wondering if at some point in the long and twisted history of the Topaz iso trans line (see this post) maybe Diatron bought some rights and tooling.

 

Myself, I am considering a big 5kVA unit to wire up for 240V in/out. My custom studio has a dedicated sub-panel--fed from our main panel by 25 feet of big 3/0 (all cryro-treated, including the bug panel and all home-run runs of Hovland Main Line to the outlets). As part of my new building addition (for the UPF--UpTone Production Facility ), I formed a new utility room (for new house HVAC, water, electric, and future solar control). So that is the perfect place for me to install a big humming iso trans to feed the studio sub-panel!

 

Here are some pics:

 

 

The sub-panel from back when I built the studio in 2004.

 

To prove that I'm crazy, a shot of the room between the 2 layers of 5/8" drywall. 760 4-inch squares (that I hand cut) of PolyDamp ADA viscoelastic constrained-layer damping material (really works!).

 

Lastly, John is coming to visit (work/play) in January, so I just added this very firm queen-size sleeper-sofa to the UPF. No more airbed in the studio! (Though with 2 of our 3 kids off at college, we do also have a regular guest room now.)

 

HAVE A GREAT WEEKEND EVERYONE!

 

--Alex C.

[Superdad]

Alex, your utility room has a giant pink alien worm in it.

 

Yes, it is over 9 feet tall. But far friendlier (energy-wise) than the nasty (and I mean rodent-nasty) 30-year old outdoor packaged AC/heat unit it replaced. The old beast nearly killed me a couple of times when gas built up then ignighted--blasting the steel cover panel 30-feet in my direction!

[Superdad]

Ok, perhaps I'm really confused, but isn't the point behind "breaking" the leakage loop to increase the impedance i.e. infinite impedance would mean no loop??

 

What fixes the current? Otherwise why does the voltage increase? I think I must be missing something very basic...

 

No offense jabbr, but you really seem to be going round and round with John on this topic. As he detailed quite completely here, his purpose in suggesting using an isolation trans is not to block leakage currents, but to give some quality noise and surge protection so that people can then safely plug all their gear into one filter-element-free heavy power strip or outlet box, thus reducing the impedance between component power supplies and reducing the problems caused by the unavoidable leakage currents between them.

 

And since you were also talking about medical usage and how iso trans units are used to block leakage to humans, he further clarified his points in this post.

 

Rereading those posts may help clear up your confusion. Or you may then have a more focused question. I know you are really smart about this stuff, so it may be that you are ascribing more to John's suggested use of iso trans than what he intends.

 

It's funny, I've had two 250kVA custom 1:1 trans (with floated secondary) in my system for over 10 years (the old Hovland VoltAire units), but it has become clear to me just this year that the positive action they are having is not from the mechanism I always thought.

 

Ciao,

 

--Alex C.

[Superdad]

I'm having difficulty understanding how, if the power supplies for the amps use low-leakage transformers, of if preceded by a low interwinding capacitance transformer, how can a "low impendance" loop exist between two amps? Even if from the pre-amp out along the interconnect, what is the return loop?

 

Specifically I am asking in the situation where we have a very low capacitance between the AC and the DC.

 

Good question and I'm sure John will attempt to answer.

 

Perhaps that isn't appropriate in this vendor subforum. I thought the point of breaking off this thread from the lps-1 was to allow some non-product based discussion but again as we are still in the Uptone sponsored area I'll back off pushing this issue. I'm not trying to be argumentative, really just trying to understand, and I might not be so smart, but asking for a schematic might understandably be too much.

 

Don't worry at all! Your questions are COMPLETELY appropriate for this thread. We are all here to learn.

[Superdad]

I can firmly recommend anyone with a IT to give it a try. The AHP gold fuse was about $18/pc and SQ wise it is a true find!

 

Fuses? We don't need no stinkin' fuses!

 

But for those who do:

[Superdad]

I'll guess @Superdad re-fuse to say!

 

No, Larry is just trying to fool us into thinking he is not old enough to remember soda can pull-tabs. I'm afraid he might be old enough to remember the time BEFORE soda/beer even came in cans.