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metaldrumer 29th March 2013 01:36 AM

ESL hybrid
 
Hi! i have been planing to build an ESL design, and i've chosen to start with the "jazzman" design, because it's pretty well explained, and i've no experience with ESL, so, it's a pretty good starting point, but, i am really on a tight budget.

With the budget in mind, i was planing to buy this transformer:

Antek - AN-0506

but... it's been discontinued, and it has been replaced by this one:

Antek - AS-0506

how much will affect this change in the ESL?

Thanks!

geraldfryjr 29th March 2013 03:42 AM

I would suggest not to use the AS version or any shielded version of a transformer for ESL use.

1. The electrostatic shield adds capacitance to the transformer this helps to lower the impedance even more as seen by the amplifier at the higher frequency's, This is not good!

2. The insulation between the shield and the HV winding is inadequate for ESL use as it is just some Aluminium tape applied right on top of the HV winding around the circumference of the transformer with only one (maybe two in some spots) layers of 2mil mylar tape.

Upon a core saturation test of a AS-1206 this insulation had failed shorting about 7 or 8 turns of the top layered winding Shorting the transformer.
Luckily I was able to disassemble the transformer and repair the winding and continue to do more testing.
Although it is now modified from its original state I have the the same amount to LV winding turns on it using some speaker wire.

I will be posting some pictures of this later on tonight sometime here,

Testing Your Transformer and Using the Transformer Test Jig

As I get going I will be explaining what the parameters mean and explore someways to improve the transformers performance and different configurations.

jer :)

bolserst 29th March 2013 02:53 PM

Quote:

Originally Posted by geraldfryjr (Post 3432236)
I would suggest not to use the AS version or any shielded version of a transformer for ESL use....
2. The insulation between the shield and the HV winding is inadequate for ESL use as it is just some Aluminium tape applied right on top of the HV winding around the circumference of the transformer with only one (maybe two in some spots) layers of 2mil mylar tape.

Huh, I had not read the Antek description carefully. There are actually two shields on their AS transformers.

The one you mentioned, which is wrapped around the transformer after it is completely wound, has it's ends connected to form a shorted turn.
This is sometimes known as a "belly-band" shield and is used to stop the core and windings from radiating EMI to nearby ciruits.

The other shield is in between the primary and secondary windings to minimize interwinding capacitance.
This is referred to as a faraday shield. It must NOT form a shorted turn.

The farady shield in between the windings should be fine for ESL use since it was tested for 3500Vac. It will, however, probably increase the leakage inductance somewhat compared to the non-shielded version of the transformer just because it adds thickness between the primary and secondary. Will be interested to see what you get for leakage inductance measurements.

The outer "belly-band" should definitely be removed for ESL use and is evidently not that difficult to do based on your description.
So, maybe still useable for DIY with a little more effort.

metaldrumer 29th March 2013 06:11 PM

Thanks for the reply!


I'm sorry if this question is stupid... when you are referring to "HV winding" you are referring to the winding that's on the "outside" part of the transformer right? And what's needed to do with this transformer to be able to use with ESL it's remove the metal plate on the top (magnetic shield), and remove the mylar on the outside of the transformer? or the aluminum tape and the mylar thats between the HV winding and the LV winding?

Sorry if i bother you, i don't want to screw up anything haha :D

geraldfryjr 29th March 2013 08:55 PM

The HV Winding is on the inside closest to the core.
It is the 120V windings and remeber that we are using them in reverse now.
As what would be the Primary (120v) Winding is now the Secondary Winding in our use of the transformer.
I did finally post those pictures in the other link as I had promised and the removal of the shields is very straight forward and causes no damage to the transformer.

jer :)

waldtraut 30th March 2013 03:39 PM

So it's OK to use the AS-0506 or the AS-1206 as long as the modifications described herein are made, right? I'm looking to buy new Xfmrs...

geraldfryjr 30th March 2013 07:07 PM

7 Attachment(s)
I have not tested the 0506 myself.
But the 1206 doesn't measure too badly at all.

However it does exhibit a dip at about 10Khz in the FR when the 120V windings are tied in series.
I am not sure if this is caused by the limiting resistor in my test setup or how it will effect the system as a whole.
It seems that this dips corresponds to the peak in the impedance curve.
I will be looking at this a bit closer to verify it.
Posted is a picture showing these dips from the input/output ( I believe) of the transformer.
I forget what value of resistor I used. :(
The FR curve is flat when the 120V windings are open or in Parallel.
The Screen shot was done before I had the mishap and was measured in its stock form from the factory.
It was one of the very first measurements I did with it.

I am in the process of remeasuring it for about the 24th time and documenting my measurements and how I got them.
It has been a slow process as I want to be sure that I am getting consistent results and repeatability to verify my range of values.

I have posted some preliminary Impedance curves here for you to take a look at,

http://www.diyaudio.com/forums/plana...ml#post3404300

These curves were made with the secondary winding's (120V) left open and not connected.
Connecting them in parallel there is no change in the curve.

Connecting them in series will cut the high frequency impedance approximately in half as this doubles up on the secondary capacitance.
The addition of the capacitance from the ESL'panel will drop this part of the curve even more depending on the capacitance value of your panel.

On the low frequency side of things the impedance is quite low and the value of inductance of the primary winding (6V) determines this.
As I get going I will explore some ways that may to help improve this.

Removing the shields is very easy to do and doesn't effect the quality of the device as it is.

It is unfortunate that I damaged my part before I got to get a really good handle on what these shields were doing to my measurements.
But, I can just as easily add them back on once I get some base measurments with the basic core as it is now.

I was using my CrownDC300a at full power (115Vp-p) using test tones when it failed.
This is a very heavy test situation and most likely will never see this kind of abuse using your average amplifier playing music.
And even less likely using two or more cores.

The second picture shows the dip as well as THD from the output of the secondary at 40Vrms in to the primary of the transformer.
This is a extreme test and I am not sure how accurate the THD figures are as I later found out the the Realtek ALC892 on my motherboard is not very good at all by just using a standard loop back test.

The third picture shows the FFT of the output of the transformer at full power at 2400Hz this includes the amp of course.
At lower levels the THD is very low and much much more lower than this.
I will have more on this later as calibration is very critical for a very accurate result of the THD figures.
At normal levels in many cases I could not find any more added distortions that had any significance above about 600Hz to 1Khz or so and it got better as the frequency got higher.
I will take a closer and more refined look at this later.

Even as they are it is still much lower than most dynamic drivers at this very high voltage level !!

The last four pictures show the input and output voltages at the onset of core saturation.
They were at full power just before any flat topping of clipping from the amplifier at 330Hz, 304Hz, 270Hz and 240Hz.

I didn't get any screenshots of the primary currents and that was the next set of tests that I was doing when the transformer failed.
Thus I was watching the currents when I connected the electrostatic shield and had forgot to disconnected it when I started a sweep tests as it was in the saturation range when it failed.

Just for the record the primary currents did rise considerably when I connected the shield.
By as much as 30% to 50% or so but that is all I have on that for now.
This is solid indication that the shield adds unneeded capacitance to the transformer for ESL use.

All of these test were made with no extra capacitance added and was with only the transformers self capacitance.

FWIW


jer :)

esltransformer 3rd April 2013 10:32 AM

information about transformers
 
I was wondering if it was possible to get good information about Antek transformers. I mean easy to understand measurements.
I give an example of what i like to see. Look at the pictures of an Audiostatic transformer i made (just the 1:150 transformer, no mirrordrive or filters C or R)

So i like to see what happens with a different load en what the saturation will be at frequency X. The impedance curve is really important for me, i don't like to use expensive amplifiers because a transformer or transformer/esl combination is not proper designed.

http://www.freebits.nl/images/743AS_frequency.jpg
http://www.freebits.nl/images/700AS_impedance.jpghttp://www.freebits.nl/images/244AS_saturation.jpg

tyu 3rd April 2013 01:34 PM

Thanks for the work an info on the 1206... Jer.......an on all other info you give us!
An the cool ESL site.....were you are the Global Moderator....

esltransformer 3rd April 2013 05:43 PM

I forgot to tell that not every transformer has identical frequency response for the both phases.
I measured a Sowter1:60 transformer (without load)

I am curious to see what the Anteks do for the 2 secondary windings (115+115V).

http://www.freebits.nl/images/329sowter_freq.jpg


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