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Old 25th November 2013, 03:58 AM   #11
golfnut is offline golfnut  New Zealand
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Hi All

I can add some observations regarding commercial tororoidal power transformers...

First: Small toroids down to at least 15 VA, perhaps lower, make good ESL transformers. If you dont have ready access to low cost specialist ESL transformers, they are a good option.

Second: For a given secondary voltage rating (e.g. 6 Vrms at 50 Hz), smaller cores have higher inductance and therefore lower distortion.

Third: the bandwidth of the transformer depends on winding capacitance, leakage inductance and the capacitive load. Large cores have higher capacitance and lower leakage inductance (small cores have higher leakage inductance and lower capacitance.) In my experience, the unloaded bandwidth of small cores tends to be a bit higher (15 VA ==> 130 kHz) than large cores (160 VA ==> 70 kHz), but the load is a major factor to consider. If you plan to use just two per ESL, more or less any core size will do. If you plan to use up to multiple transformers per ESL to increase input voltage and/or step up ratio you should model the behaviour and select the core to suit to maximise bandwidth.

Fourth: Definitely avoid transformers with twin primaries due to high winding capacitance and tendency for breakdown. Twin secondaries should be connected in parallel to reduce leakage inductance.

Fifth and most important: Choose transformers that comply with the IEC standard (sorry cant remember standard number). They are required to have sufficient insulation between primary and secondary to withstand 4kV dc for 1 minute.

best regards
Rod
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Old 25th November 2013, 11:17 PM   #12
BuyDIY is offline BuyDIY  United States
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I went back to the Antek website hoping by some miracle the AN-0506 was back in stock. But it still said "discontinued" in bold red letters like it was taunting me.
Browsing through the website, I cam across the AN-0206. They are smaller 25va transformers, but I was wondering the disadvantages of using 4 of these per speaker?
Thoughts?
Is there something better then these on the Antek site?
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Old 26th November 2013, 04:05 PM   #13
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Yes, I think that they would work alright.

Keep in mind the above info that Golfnut has provided.

Even though my cores are rated at 200watts each it seems that I do get better THD performance at the lower frequency's just before the saturation point than I did when testing the AS-1206.
But, only very slightly.
I will have more on this at a later time.

As long as your crossover is above 300Hz/360Hz for any size you won't have any issues about this.

I found that I have gotten better results (for the amplifier) from using from using 4 cores with the 120v winding's on each core rather than 2 cores with its 120v winding in series.

This actually gives you a lesser amount of leak inductance than you would with using just 2 cores total.

I am not sure but it also seems logical that the transfomer's capacitance's are effectively in series as well.
When using separate cores this would suggest that it would lower the overall capacitance reflected through the transformation ratio as well.
More on this later too!

The reasoning is that when you have the two separate cores 120v winding's in series you simply add the two leakage inductance's together ( Hence~ Leakage inductance will be 2X ).

Where as if the two winding's are on the same core they share what is called mutual inductance, and, the leakage inductance is goes up as a square of the multiple of the number of turns.

Hence~ If you double the number of turns then the inductance is 4 times that of a single amount of turns if the winding turns are on the same core.

This hold true for the winding's actual inductance as well as the leakage inductance.

So for just one half of the setup, if you use 2 cores then your leakage inductance will be say 2, and, For one core with its two winding in series, it will be twice that at 4, for an example.

The trick is to keep your leakage inductance as low as you can as especially with larger panels (Larger capacitance).

The effect of leakage inductance and the total capacitance (Panel plus the Transformer) determines the resonate frequency of the transformer system.
You want this above the audio band if possible, else it can be dampened using a resistor on the primary side.

This resonance causes a very high peak in the response of the system at this resonate frequency, and, a very low impedance for the amp if it has to produce energy for it.
Literally a shorting action for the amplifier.
You don't want this to happen!!!

I ran into this action in my study (as documented) as it created havoc for my setup from crossover distortions (because the amp could not supply enough current) also the transformer going into (a Tesla action of operation) oscillation and generating High RF Voltages as well.

This caused resistors that I was using to burn up that should not have and a few cheapy DMM's that I was using for measurements rendered burnt and useless as well.

All because of the RF that was generated when the amp could not switch fast enough leaving the transformer ringing at will.

Now to the main part of your question,

Every time you double the input frequency you can double the input voltage into any winding for what ever voltage it is rated at.
This effectively quadruples the power (VA rating) that can be transferred through the core without it going into saturation.

Being that they are designed for 50Hz/60Hz we will use 50Hz for our example because it is the lowest frequency that can be used for its designed winding voltages (in our case 6V).

So, lets say we use a crossover frequency of 400Hz.
The highest voltage we can apply to our 6V winding will be 48V because 400Hz/50Hz=8 so 8*6V= 48V.

Typically an amplifier that can produce 48V is quite a large amplifier up into the 288 watt range for an 8 ohm rating.

Can our transformer handle this?

The Antek AN-0206 is rated at 25 watts at 50hz and we are doubling are input voltage 3 times.
Every time we double it our VA rating goes up by 2^2 or 4!!
Therefore (4^3times)*25watts= 1600watts!!!

The transformer core would definite be able to handle our 288watt amplifier much less a 100watt one with no problem.

This is providing that the winding's have a thick enough gauge of wire to handle the current.
This should not be much of issue since you plan on using 4 of them and the 6V winding's will be all paralleled together.

Much less than tolerating any SPL's at above 20V to 30V into the step-up transformers with a large panel for an example.

I hope this helps !!!

jer

Last edited by geraldfryjr; 26th November 2013 at 04:17 PM.
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Old 27th November 2013, 06:47 AM   #14
golfnut is offline golfnut  New Zealand
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Default more transformer info

Hi BuyDIY
Because ESLs are voltage driven and draw little current, the power rating of the transformer is not really relevant for ESL applications. From an ESL perspective, the only specs that are important are the step-up ratio, secondary voltage rating, and mains frequency. Equally important are the transformer properties that are not in the spec sheets: leakage inductance and winding capacitance.

Step-up ratio: interpretation is obvious.

Secondary voltage rating and mains frequency: as Jer has explained, the voltage rating is proportional to frequency. So a transformer with secondaries rated for 6Vrms at 50 Hz, can be used at 12 V rms at 100 Hz, etc. If you exceed the voltage on the winding, the transformer core will saturate presenting a low impedance to the amplifier, resulting in high currents and distortion – possibly a dead amp if it’s not protected.

Leakage inductance: comes about from imperfect coupling between two transformer windings on the same core. One or other of the windings will be incompletely coupled to the other and it will appear, from an electronic point of view, to have an extra inductance in series with the winding. This is the leakage inductance, L. Typical values are a few millihenries on the high-voltage side.

Winding capacitance: comes about from three effects (i) capacitance between adjacent turns of the same winding, (ii) capacitance between one of the windings and the transformer core, and (ii) capacitance between the turns of different windings. When you use just two transformers on an ESL in the usual push-pull arrangement, the various capacitances can be treated as a single winding capacitance, C. Typical values are many tens of picofarads, perhaps a few hundred picofarads. The resonant frequency of the transformer is given by fo=1/(2.Pi.sqrt(L.C)) – typically 50 kHz to 130 kHz for toroids. This is the ‘unloaded’ resonant frequency.

When you use the transformer with the ESL, you have to add the ESL capacitance (500pf to 2000 pF) to the winding capacitance. This is the loaded resonant frequency, can easily drop below 20 kHz. The loaded resonant frequency is a good measure of the bandwidth of the transformer-ESL system. You can see why a small leakage inductance is desirable – however, there are compromises – see later). Low inductance is necessary if you want high-step up ratios, higher voltage ratings, lower operating frequencies, or any combination of these.

When you use multiple transformers in an ESL by connecting the high-voltage windings in series and the low voltage windings in parallel. Two things happen: Firstly, the leakage inductances add in series (as Jer surmised). This bit is simple. The way the capacitances behave is more complicated. The capacitances within one winding and between the core and secondary winding appear to add in series (so that capacitance gets smaller.) At the same time all of the capacitances between the two windings add in parallel, so that part gets bigger.

As a result you can connect two or three transformers together without changing the unloaded resonant frequency very much. After that, the resonant frequency falls in proportion to the square root of the number of toroids, but with care you can use up to 8 or 10 toroidal transformers to form a single ‘compound transformer’.

There is a practical upper limit to the VA ratings of the transformers used in ESLs; If you keep the leakage inductance too low with large transformers, the bandwidth of the system becomes limited by the series resistance in the windings.

Also if you have too high a step-up ratio (say 200 for arguments sake), then any inductance in the amplifier output (zero to 10 microhenry depending on design) or the speaker leads (about 1 microhenry), is transformed to the ESL side. If it is 10 microhenry on the low voltage side, then the equivalent inductance on the high voltage side is 10 uH x 200^2 = 400 mH, which is too high.

Hope this is helpful
Rod
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Old 27th November 2013, 09:04 AM   #15
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If you want full or higher power at 300-400Hz you need 0,1mm(or even thinner) core material and not the standerd 0,3mm. Only short time overload is possible.

Quote:
Originally Posted by geraldfryjr View Post
Yes, I think that they would work alright.

Keep in mind the above info that Golfnut has provided.

Even though my cores are rated at 200watts each it seems that I do get better THD performance at the lower frequency's just before the saturation point than I did when testing the AS-1206.
But, only very slightly.
I will have more on this at a later time.

As long as your crossover is above 300Hz/360Hz for any size you won't have any issues about this.

I found that I have gotten better results (for the amplifier) from using from using 4 cores with the 120v winding's on each core rather than 2 cores with its 120v winding in series.

This actually gives you a lesser amount of leak inductance than you would with using just 2 cores total.

I am not sure but it also seems logical that the transfomer's capacitance's are effectively in series as well.
When using separate cores this would suggest that it would lower the overall capacitance reflected through the transformation ratio as well.
More on this later too!

The reasoning is that when you have the two separate cores 120v winding's in series you simply add the two leakage inductance's together ( Hence~ Leakage inductance will be 2X ).

Where as if the two winding's are on the same core they share what is called mutual inductance, and, the leakage inductance is goes up as a square of the multiple of the number of turns.

Hence~ If you double the number of turns then the inductance is 4 times that of a single amount of turns if the winding turns are on the same core.

This hold true for the winding's actual inductance as well as the leakage inductance.

So for just one half of the setup, if you use 2 cores then your leakage inductance will be say 2, and, For one core with its two winding in series, it will be twice that at 4, for an example.

The trick is to keep your leakage inductance as low as you can as especially with larger panels (Larger capacitance).

The effect of leakage inductance and the total capacitance (Panel plus the Transformer) determines the resonate frequency of the transformer system.
You want this above the audio band if possible, else it can be dampened using a resistor on the primary side.

This resonance causes a very high peak in the response of the system at this resonate frequency, and, a very low impedance for the amp if it has to produce energy for it.
Literally a shorting action for the amplifier.
You don't want this to happen!!!

I ran into this action in my study (as documented) as it created havoc for my setup from crossover distortions (because the amp could not supply enough current) also the transformer going into (a Tesla action of operation) oscillation and generating High RF Voltages as well.

This caused resistors that I was using to burn up that should not have and a few cheapy DMM's that I was using for measurements rendered burnt and useless as well.

All because of the RF that was generated when the amp could not switch fast enough leaving the transformer ringing at will.

Now to the main part of your question,

Every time you double the input frequency you can double the input voltage into any winding for what ever voltage it is rated at.
This effectively quadruples the power (VA rating) that can be transferred through the core without it going into saturation.

Being that they are designed for 50Hz/60Hz we will use 50Hz for our example because it is the lowest frequency that can be used for its designed winding voltages (in our case 6V).

So, lets say we use a crossover frequency of 400Hz.
The highest voltage we can apply to our 6V winding will be 48V because 400Hz/50Hz=8 so 8*6V= 48V.

Typically an amplifier that can produce 48V is quite a large amplifier up into the 288 watt range for an 8 ohm rating.

Can our transformer handle this?

The Antek AN-0206 is rated at 25 watts at 50hz and we are doubling are input voltage 3 times.
Every time we double it our VA rating goes up by 2^2 or 4!!
Therefore (4^3times)*25watts= 1600watts!!!

The transformer core would definite be able to handle our 288watt amplifier much less a 100watt one with no problem.


This is providing that the winding's have a thick enough gauge of wire to handle the current.
This should not be much of issue since you plan on using 4 of them and the 6V winding's will be all paralleled together.

Much less than tolerating any SPL's at above 20V to 30V into the step-up transformers with a large panel for an example.

I hope this helps !!!

jer
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Old 21st December 2013, 11:27 PM   #16
BuyDIY is offline BuyDIY  United States
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Well..... Charlie is right. Finding a transformer in the US, with a single primary and secondary, is next to ZERO.
I think I might go ahead and order the toroids Charlie suggested.

Vigortronix Toroidal Transformer 230V Single Primary 50VA 0-6V 0-6V | Rapid Online

Does anyone see any issues with the above toroids?

If anyone has other suggestions on where I could buy toroids I would like to hear them.
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Old 22nd December 2013, 03:59 PM   #17
Bazukaz is offline Bazukaz  Lithuania
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Hi,

Quote:
Originally Posted by esltransformer View Post
If you want full or higher power at 300-400Hz you need 0,1mm(or even thinner) core material and not the standerd 0,3mm. Only short time overload is possible.
Could you please explain why? Also, why an audio transformer would need to satisfy continuous max. power rating at those frequencies?

Regards,
Lukas.
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Old 22nd December 2013, 04:30 PM   #18
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Normal cores are made for 50-60Hz. At these frequencies the core loss is reasonable low (eddycurrents). For high frequencies you need thinner laminations, thats why amourphous core materials can be used at 20kHz and SiFe not or only with very high losses (heat).

We are just lucky that for audiofrequencies we normally don't need much power but if we do we should have a problem with the traditional iron cores.

http://www.sekels.com/vertragshaendl...anokristallin/



Quote:
Originally Posted by Bazukaz View Post
Hi,



Could you please explain why? Also, why an audio transformer would need to satisfy continuous max. power rating at those frequencies?

Regards,
Lukas.

Last edited by esltransformer; 22nd December 2013 at 04:32 PM.
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Old 22nd December 2013, 06:25 PM   #19
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Quote:
Originally Posted by BuyDIY View Post
Well..... Charlie is right. Finding a transformer in the US, with a single primary and secondary, is next to ZERO.
I think I might go ahead and order the toroids Charlie suggested.

Vigortronix Toroidal Transformer 230V Single Primary 50VA 0-6V 0-6V | Rapid Online

Does anyone see any issues with the above toroids?

If anyone has other suggestions on where I could buy toroids I would like to hear them.


Just a note, Beware of buying transformers from overseas as the shipping may be a lot more than what it is worth.

I know of one DIY'er that has ordered some and to my knowledge, He is still waiting to receive them and it has been a few months already.

Since they have not been tested you are better off just getting the Antek's as they have been tested and work well.
They are good for up to about 4kv to 4.5kv or so before I had one fail under very extreme conditions.

Using two of them will get you into the 9Kv range with a good amplifier and this is a lot of voltage for any panel.
If you are seeking more voltage output swing then use 4 of them.

I don't expect the oversea's one to perform any better, Although I have not had one to test either.
Since they are designed for 50/60Hz the core saturation characteristics will be the same.

Stay away from the shielded types as well, if you can.
If not it is very simple to unwind the LVwinding and remove the shield and put the LV winding back on as it is only about 20 to 30 turns or so.

I don't see any reason that these would not work well for what they cost at $11,

Antek - AN-0206

I will try to get some of these to test sometime soon.

Or if you chose to have a larger core this one is a good alternative for $18,

Antek - AN-1212

Rewinding the LV for 6v is a peice of cake, or, you can just add a new winding as it is on top with some wire, as I have done in my earlier transformer testing and experiments.

This will also allow you to be able to fine tune to higher transformation Ratio as well, providing that you also use a proper higher crossover frequency than 300Hz to avoid core saturation.
You can do this with any toroid core power transformer.

One of the things about using the higher power core is that they use a thicker gauge of wire for the winding's and this also makes them less prone to fusing a winding turn should a Flashover in the panel occur.


FWIW

jer
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Old 24th December 2013, 03:14 PM   #20
Bazukaz is offline Bazukaz  Lithuania
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Hi,

I have just inspected a quad ESL 63 core. Lamination thickness seems to be standard 0.3mm. Furthermore time-tested arrays of toroids show reasonably low distortion and no heating up with audio frequencies. Anyway difference between peak and average output of music is high and most energy is concentrated below about 300 Hz. What I wanted to say is that even typical 0.3mm SiFE material can be good enough for ESL step-ups. For a tube output trannie the story may be different due to higher source impedance.

Regards,
Lukas.

Quote:
Originally Posted by esltransformer View Post
Normal cores are made for 50-60Hz. At these frequencies the core loss is reasonable low (eddycurrents). For high frequencies you need thinner laminations, thats why amourphous core materials can be used at 20kHz and SiFe not or only with very high losses (heat).

We are just lucky that for audiofrequencies we normally don't need much power but if we do we should have a problem with the traditional iron cores.

Schnittbandkerne aus VITROPERM (nanokristallin)*: Sekels GmbH
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