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ESL transformer question
ESL transformer question
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Old 18th November 2013, 11:04 PM   #1
BuyDIY is offline BuyDIY  United States
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Default ESL transformer question

My first ESL build, and I am trying to decide on the correct transformer.
From what I have read on the forums, a toriod is the way to go for a hybrid.
I have been looking for a 230v 2x6 transformer with no real luck.
It has been suggested that the Antek AN-0509 works great, but it says discontinued on their website.
Could anyone recommend a different transformer?

Also, my panels are curved, 12"x40" (30x100 cm), 1mm front & 1.1mm back spacing. I have no way to measure, but I estimate 1.4nf panels..... Does this sound about right?

I'm thinking my curved panels have to much curve to them. What would be the theoretical limit on a curved panel. My panels are currently 30 arc.

Any insight to the above questions is much appreciated.


Last edited by BuyDIY; 18th November 2013 at 11:15 PM.
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Old 19th November 2013, 05:51 AM   #2
Calvin is offline Calvin  Germany
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Toroids ar just one way to go. It can also be the way in many cases, but there are always other options.
There have been many comments about which toroids might be useable and which may not be useable. I still prefer the single primary, single secondary versions, as they are really "idiot proof" regarding internal flashover issues.
1.4nF sounds reasonable for a panel of the given dimensions.
30, or +-15 is ok. More than that and tensioning of the diaphragm and mounting it correctly becomes increasingly difficult.

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Old 19th November 2013, 03:52 PM   #3
CharlieM is offline CharlieM  United States
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I'm using tandem Multicomp/Farnell 50VA 230V/2x6V toroids purchased from Newark in my esl's and they are fantastic. At Newark, the Farnells have been replaced by VTX brand, with same part number as THESE

I would to with the VTX's above. At least the high voltage side (most prone to flashover) is a single winding. Besides, the chances of finding single-primary/single-seconary trannies available for shipment to the US is practically zero.

Last edited by CharlieM; 19th November 2013 at 04:10 PM.
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Old 19th November 2013, 05:22 PM   #4
BuyDIY is offline BuyDIY  United States
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Calvin/Charlie, thanks for all the information you have provided.
I have another question that I am hoping you can answer.
I was looking at the Antek site, and even though the AN-0509 are discontinued, they have the AS-0509 which is stated as Audio grade.
Now, I am a newbie at this, but would'nt these work too?
From what I read the AS versions has a shielding, so maybe this sheilding would be prone to arcing?
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Old 19th November 2013, 09:28 PM   #5
X83 is offline X83  United States
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The AN series is the non-shielded version which works better in reverse as a step up transformer and the AS series is the EMI shielded version which are more prone to short out with higher voltage use. Also the 0509 toroid is a 9V unit and I believe most people are opting for the 230/6V ratio for most ESL applications.
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Old 19th November 2013, 09:52 PM   #6
BuyDIY is offline BuyDIY  United States
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Thanks X83 for clearing that up for me.
I'll keep looking for a good deal. I might just go with Charlie's suggestion and buy the VTX brand.
I'll search a little bit more, if I get lucky and find some in the States I'll be sure to post them here.
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Old 19th November 2013, 10:51 PM   #7
BuyDIY is offline BuyDIY  United States
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I found this company that is 3-4 hours away from where I live. They can custom wind a transformer, and I was wondering what would be the ideal toriod if it was custom wound?
I would like to give those specs and see what they come back with in price.

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Old 20th November 2013, 04:14 AM   #8
geraldfryjr is offline geraldfryjr  United States
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Which company are you referring too?

Typically they charge a lot for just a few pieces and you would need to commit to a large batch in order to make it cost worthy.
I have not yet inquired about such costs yet as I am just now understanding on what values to start with.

I would start with the largest core that you could afford and shoot for a primary impedance of about 8 to 32 ohms or so at your lowest frequency of operation.
This will help keep the amp happy without too many complications and losses of having such a large amount of total turns involved.

Your common 240v/6v X 2 power toroids that we are using now (at a 1:80 step-up ratio) will allow for operation of about 300hz to 360hz with 40Vrms of input voltage.
The impedance of such a setup is in the order of about 2 ohms or less at that frequency.

Keeping your crossover frequency above about 400hz to 600hz will greatly help to keep your amp from going into the danger zone, especially if you like to crank it up a bit.

Thus in order to raise this impedance to a safer level at that frequency (or lower), it would require about 2 to 6 times the amount of turns found on one of the smaller cores that many have been using.

Increasing the amount of total turns also raises the parasitic capacitance of the transformer and this is not good.

Thus using a larger core will allow for your transformer design to have a higher impedance at the lower frequency's that is safer for the amp using around the same amount turns to as much as 4X of total turns while not raising the transformers parasitic capacitance as much.

You want to limit your HV winding's to single layers with no winding overlap!! And with lots of insulation in between the layers as well.
This will greatly help to keep the transformers capacitance to a minimum.

I have covered this in many threads already but if you have any questions about this, Please do ask!!

It is a little hard to grasp at first but with time you will find that it is not at all a mystery of how the transformers work, although there is much more involved than just the transformation ratio.

Alpha Core has some very good prices on some very large quality raw cores to work with.

Silicon Steel Toroidal Cores - In Stock

It is very possible to hand wind such a transformer using a large core like the #140 or #160 or larger and be very cost effective per performance.
It is just tedious to do, and, if you have ever unwound a toriod core then you know what you are in for.

I have been working on this for quite sometime.
But since this is just a hobby for me I have had a lot of other pressing projects that I have been trying to do as well, sorry for the delays.

Do stay away from the shielded types as warned!!

I have found that they are easily prone for failure and here is a link to those tests using a Antek AS-1206,


The shielding also adds to the transformers self capacitance as well by as much as 80pf to 200pf (as measured on my sample) depending on the overall size of the core.
For example, When I took all of the extra winding's that I didn't need on the cores I am using (a Parts Express Buyout), it dropped my cores self capacitance to one 1/2 to 1/3 of what it was when I first started measuring it in the "step-up transformer design" thread.

Here are the impedance curves for just one core (Antek AN-1206) with no extra panel capacitance added,


When you add two cores together by paralleling the primary winding's this will cut the low frequency impedance in half that is shown on the charts (for an example).

And by tying the HV winding in series like we do this also lowers the high frequency impedance due to the increased transformation ratio.

I believe this measurement was done with the HV windings in series just as they would be used.
Therefore the actual impedance for two cores as they are used would be half of what the chart depicts.

These charts are with just the transformer capacitance alone and adding more from the panel will then lower the High frequency impedance even more.

Here are some photos of when it failed,


Testing Your Transformer and Using the Transformer Test Jig

For more info these threads may be of interest to you as well,



This is the beginning of a very intense study I did on using common toroid power transformers.
It is a very long thread, But it deserves a good read through and may answer a lot of questions you may already have,




Last edited by geraldfryjr; 20th November 2013 at 04:32 AM.
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Old 23rd November 2013, 08:12 PM   #9
BuyDIY is offline BuyDIY  United States
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Thanks for the info Jer.

I see most like the toriod, but what is the disadvantages of using a IE transformer?
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Old 25th November 2013, 12:10 AM   #10
geraldfryjr is offline geraldfryjr  United States
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Toroid's are more efficient per size than the IE types.
By as much as 40% to 60%, I forget exactly how much.

EI types are a bit easier to work with as far as winding goes.

However it is difficult to calculate how many windings you can put in the winding space while having a thick insulation between winding layers and alternating them to reduce the capacitance.

Having thick insulation layers keeps the transformers self capacitance to a minimum,But again this is limited to the winding space.

This is a big deal when working with voltages with as much as 5Kv to 10Kv peak (or more).

In the Step-up Tranformer design thread a fellow member designed and built a very nice EI type transformer all hand wound only too later fail due to internal arcing!
I think he attempted this 2 or 3 times, and I haven't seen any other reports since then if he had corrected the issues.

Toroids aren't as limited in this manner.
As there is plenty of room to have thick insulation layers providing you choose a large enough core to work with.
Compared to the EI structured designs it will be about 60% of the size as well.

I believe I have read somewhere that Toroid's exhibit much less leakage inductances.
This means a lot when it comes to keeping the transformers self resonance above the audio passband.
The tape wound fashion of a Toroid core also cuts down on the action of eddy current losses within the core itself.

The most important part is the type of iron and lamination thickness that are commonly available as IE stamping's.
It can be quite expensive to get a quality iron, and, The thinner the laminations are the more the cost goes up, almost exponentially!

It is easier for manufactures to produce tape wound cores than it is to stamp and assemble IE's.

Since today's norm is about efficiency it is common for them to use a good quality iron and thin tape strips for the lamination as all they have to do is roll it up into a doughnut.
Unlike the power IE's of yesteryear with poor quality iron and lamination's that are usually much much thicker such as the MOT's that are still used today.

This is the main reason why good quality HiFi EI transformers for audio use are so expensive.

I have done many tests on the quality of sound of a signal through my common power toroid at 1:1 ratio using the two 120v:120v winding's using just an amp and a speaker and it was quite good!!!
I did this before I tried using it to power my ESL's because of the same question that everybody ask's, "Are They Good Enough to use and is the Sound Quality Good Enough?".

There was just a subtle bit of muddiness on the extreme low end is all.
Even that was barely noticeable and only at a high volume.
This be could improved just by using more iron.
I have concluded this effect to the possibility of the amp having less of dampening affect on the cones movement due to the coupling of the transformer.

I did a study on this which led me to Double, Quad and Hex stacking the cores I was working with.

Providing that the amp could produce a clean square wave, the transformers output produced a very clean square wave as well!!
I was so amazed at this because I have never ever before seen this type of performance out of all of the IE types I had test up to that day including a few Tube OPT's that I have.

I was able to measure the response of the transformer well into the 100's of Khz and as much as into the AM broadcast bands as well.
I regularly see the RF from local radio stations when I am testing them with my scope.
I have never experienced this with a common older EI type designs and core material that they use, at least not into the RF range.

I haven't been able to measure any significant added amount of THD's of the signal as transferred through one of my Toroid Cores except for approaching and well into core saturation as shown here,


In some of the charts you will see some glitch's and irregularities, and those I later have proven to be caused by my motherboards sound system that I was using at the time.
My other sound cards did not do this.

Mostly all of THD the measurements that I did get that were above .1% to .5% were found to be that of my amplifier (Crown DC300a) or caused by the core just as it was going into saturation and that was only about .5% or so.

Therefore the quality of the iron used in today's Toroid Power Cores is very good and the many listening tests (mine as well as others) have proven them to be exceptional as well.

In the cases at above, starting at 600Hz to 1Khz, I wasn't able to measure any added THD's except that of my sound card and amp in the range of .01% to .005% all of the way to 20-25Khz or so.
I believe the limit of my sound card is .005% or so as measured by a calibrated loopback test.

I will do more on this sometime once I get every thing set back up again since all of my issues to stopping were from breakdowns of pushing the voltages as far as I could get them as I have already explained.

Under normal operation it is just the clearest and cleanest thing I have ever heard in my life.
Pretty darn good for some common ole' Power Toroid's.

I hope this helps you.

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