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Old 21st June 2012, 02:41 PM   #241
AndrewT is offline AndrewT  Scotland
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Hi,
is post239 effectively telling us that a step up transformer driving a highly capacitive load needs to have the few turns of the primary next to the core?
Is it also saying that a thick insulating gap to the core minimises the transformer losses?
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Old 21st June 2012, 02:44 PM   #242
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If you have a esl panel with 2.8 nF capacitance between stators, and you drive this panel with a 1:175 step up transformer, then the minimum impedance that the amplifier will see is: (1/6.28x20000x0.0000000028) divided by (175x175) = 0.092 ohm!!

So if you will keep your amplifier in the comfort zone, the max step up must not be higher than 1:53 with your big panels....

Of course, You can put a resistance in series with the transformer for taming the high
resonance peak, but the value of this usally lies around 0.6-0.9 Ohm resulting in a good total minimum impedance of around 2 ohms when using 1:53 step up.

One more thing:There's no reason for building very big panels, as the acoustic impedance load on the membrane will be higher and dampen it's movements.
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Old 21st June 2012, 02:57 PM   #243
Legis is online now Legis  Finland
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Quote:
Originally Posted by JonasKarud View Post
If you have a esl panel with 2.8 nF capacitance between stators, and you drive this panel with a 1:175 step up transformer, then the minimum impedance that the amplifier will see is: (1/6.28x20000x0.0000000028) divided by (175x175) = 0.092 ohm!!

So if you will keep your amplifier in the comfort zone, the max step up must not be higher than 1:53 with your big panels....

Of course, You can put a resistance in series with the transformer for taming the high
resonance peak, but the value of this usally lies around 0.6-0.9 Ohm resulting in a good total minimum impedance of around 2 ohms when using 1:53 step up.

One more thing:There's no reason for building very big panels, as the acoustic impedance load on the membrane will be higher and dampen it's movements.
Hi, thanks for the clarification. Yes the impedance will be quite small, the driving amps are luckily quite big (24 power transistors, 120,000F, 1,5kV trafo and two massive convection elements per mono).

Big stats sound quite good. A line source is ideal when it's from floor to the ceiling. Also the width of the panel has to be something, if one wants to reproduce lower registers. Bass actually sounds very good from a panel, mine go to ~37Hz in my room if driven full range but I will limit the low end response because of the transformers, and handle the middle and low bass with dynamic woofers in dipole line arrays.
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Old 21st June 2012, 03:00 PM   #244
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Very Good,Legis, it sound just about right I don't for see an issues if the primary is bifilar.

But if it is all possible see if you can have them double up on the insulation layer to the secondary base as this will help tremendously,or as much as they can.
If they use 2 mil material then 10 layers should be good, as an example.


AndrewT, the thicker the insulation the less parasitic capacitance the winding will have.
Even though the core is not connected to anything it still acts like one of the plates of a capacitor and couples each individual turn to form the total residual capacitance of the winding.

I wanted to undo one of my cores and add a thicker layer of insulation to prove this,But I am just not up to dealing with trying to straighten out that much wire and then rewind it again.
At least until I can devise a simple torrid winding hoop of some sorts.


jer
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Old 21st June 2012, 03:06 PM   #245
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Ahh, Very good Point, Jonas, I didn't stop to calculate the actual impedance of such a large panel.
Most all of the designs that I have been working with have a capacitance of 1/3 to 1/4 or less of those of Legis's.

jer
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Old 21st June 2012, 03:20 PM   #246
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This maybe redundant, But here is a core that I have been considering on using,

Toroidal Core PN# 140

the also have some bigger ones as well !!!

But very affordable.

jer
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Old 21st June 2012, 08:27 PM   #247
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Yes, big panels certainly sounds good, but there seems to be an optimum panel widht for high output at low freqs, 8-10 inch for a single membrane, two stator panel and
12-13 inch for a double membrane, three stator panel.

This is my own findings from a long life of building electrostats (and still counting).....
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Old 21st June 2012, 09:26 PM   #248
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If it were me, I would consider using using 1 or even 3 of the center sections separated from the two end sections as just for the highs.
This would help greatly to reduce the load on the amp.

My little panels are just 3.25" wide and I get at least 45 to 60 degrees of horizontal dispersion for the highest frequency's.
I believe those large panels are already physically sectioned as such by the photos I have seen,so my comment may be irrelevant.

If the stator sections are physically separated from each other, This could easily be done with just a handful of resistors using a segmentation equalizing technique.
This would help with any lobing patterns that you might hear while walking around the room as well.

One of my next builds will be like that as I understand it works very well !!

I sure would like to have a listen to them !!!

Jer

Last edited by geraldfryjr; 21st June 2012 at 09:30 PM.
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Old 7th March 2013, 05:59 PM   #249
Legis is online now Legis  Finland
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Can I use regular toroidal transformer, with 1:8 step up ratio to drive basic dynamic tweeter load (16ohm compression driver + 200R series resistor). Is the bandwidth enough to reach ultra frequencies without much phase shift? Lets say the primary inductance is for example 166mH. If that kind of trafo is a low pass filter with that load, which kind of transformer should it be? Bifilar wound pri and sec, minimal primary turns...? Should I use a electrostatic shield or not between the pri and sec?

The reason if anyone is wondering, is that I will be current driving the compression drivers, the step up trafo is just to boost the output level back to almost normal. Just a side hobby besides electrostatic speakers.

Thanks!

Last edited by Legis; 7th March 2013 at 06:02 PM.
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Old 7th March 2013, 06:32 PM   #250
Legis is online now Legis  Finland
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Actually when I measure the two primaries in series, the inductance reads 166mH, but when the primaries are in parallel the inductance is vanishingly low 0,03mH. Secondary is unshorted in both cases. I quess this kind of primary inductance gives wide bandwidth?

The trafo has 2 x 50 primary turns on a 100VA core (~15-18cm2). If I remember correctly, the primaries are bifilarly wound.

Last edited by Legis; 7th March 2013 at 06:39 PM.
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