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Old 6th November 2007, 09:58 PM   #21
Kontra is offline Kontra  Russian Federation
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Question direct-coupled amplifer?

I read here 1 year
I have built the panel the sizes of 1000 mm * 700ėė
Backlash of 5 mm + 5 mm
Coverage of stators - teflon
The film - mylar 8 micron is covered with graphite and from above pool nylon
Tried to use the transformer. It was not pleasant to me.
Whether who has the amplifier on tube without the transformer on an exit?
Direct-coupled the amplifier.
If for whom such is - tell more in detail.
Whether who uses the amplifier of class D direct-coupled?
Whether who knows about the transformer of impedances?
I ask to excuse for my the poor English. My basic language - Russian.
Andre from Russia
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Old 7th November 2007, 05:31 AM   #22
Calvin is offline Calvin  Germany
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Hi Andre,

To make sure I understood You right:
- Your panel is of size 1000x700m and has a membrane-to-stator distance of 5mm?
-- If so, 5mm (+-5mm=10mm stator-stator) is far too much!
Reduce the distance to less than 2.5mm (e.g. +-2.5mm=5mm).
The distance is far too great to get acceptable results!

- Teflon is not the best material as insulator for ESL-stators!
-- It has a too high value in resistivity and a too low value in dielectric constant. Materials like PVC, Nylon, Polyurethane, Acrylics are better.

- Do You mix graphite and Nylon as coating for the membrane?
-- My experiences with graphite were rather disappointing, though some readers report successful usage of the stuff. I havenīt tried the Nylon and will not, because to my taste it adds to much mass and there are too many negative reports on that material (some people tried hard to get a working emulsion, but failed constantely). I prefer easier to handle materials which are not poisonous or smelly and that can be tuned in resistivity and -if needed- can be coated on a second or third time, and that can be brushed on or sprayed.

Using a transformer as coupling device between amp and ESL is the easiest way. and I recommend this way for every beginner!
But to function correctly the transformer needs to fullfill strikt requirements. You canīt just use any transformer simply because it has 2 or 3 windings on!

To get an idea what transformation-factor would be needed I calculate or measure the capacitance of the panel and calculate the impedance value at 20kHz. Now I take the square root of this impedance value. This value equals the transformation factor of the transformer. Connecting the transformer with the calculated value means that this results in an impedance of 1Ohm@20kHz (theoretically, in practise itīll be more). This is the lowest value Iīd recommend.
Now estimate how much drive voltage Your panel can take. Assuming ~2kV/mm as flashover treshold for air, a panel with 10mm stator-stator distance would need 20kVpp=7kVrms. A typical amp will push out about 20Vrms to 35Vrms. So we need a transformer with an transformation factor of 200 to 350 here!!!

A panel of 1000x7000x10mm has a calculated capacitance of just 620pF. This translates to ~12.8kOhm@20kHz. Taking the square root we get a transformation factor of 113. This is just half of what is needed.

It is much easier to reach the high voltages needed in an ESL with an transformer than with a direct coupled amplifier. Only small headphones could be driven directly by connecting the panel to the Anodes of the output tubes. Larger panels need higher voltages, so that a specially designed amplifier is needed that works with plate voltages of 2kV-5kV. Still these amps are more suited to drive hybrid-ESL-panels rather than FullRange-ESL-panels.

At this time direct coupled D-amps are ot of range. There are no such fast output devices (in solid state) that can withstand such high voltages and besides the switching transients would be a great problem (interference with radio). I havenīt seen a direct coupled high voltage tube class-d amp yet.

So Andre, if I understood Your infos about Your panelīs dimension right, I can only suggest You to rebuild the panel using much less distance between the stators. If (as example) You use a distance of 3mm (+-1.5mm) the panel would show a capacitance of ~2nF. That translates to an impedance value of 3.85kOhm@20kHz.
Square rooting gives a value of 62.
A pair of standard toroidal power transformers of ~100VA rating and 230V/6V (6V-winding connected in parallel, 230V-windings connected in series) will result in a transformer with an factor of ~1:65 to 1:70 (depending on the losses of the trannies)

The panel will be able to take a signal voltage of 6kVpp = 2.1kVrms before flashovers occur.

The amplifier will have to supply up to 32Vrms (just slightly more than 100W@8Ohms). As an example a UCD180 could be of interest here!
The panel would be useful above ~200Hz and should be augmented with a subwoofer! This hybrid ESL will yield very high SPLs (~120dB@4m should be realistic!) with low distortion (most of the distortion will be produced by the transformers) without demanding excessive power!

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Old 7th November 2007, 04:16 PM   #23
Kontra is offline Kontra  Russian Federation
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Default ansver for Calvin

You right:
in my panel distance a membrane to stators - 5 mm and distance stator to stator - 10 mm
Teflon I use as a covering of metal (steel thickness of 1 mm R3V4) instead of a paint thickness of a covering of 10 micron
I apply teflon to apply a variable voltage between plates stators in size 8Kvolt - 10 Kvolt and a voltage I submit on a film 12Kvolt constant
The big distance between plates stators is made that the film at moving on frequency 40 herz did not touch stators at me there is no in the panel of crosspieces (supports) I made the low-frequency panel. That the full range I sounded has made 2 small panels of 500 mm * 300 mm that they radiated high and average frequencies
I Tested the panel with the special DIY transformer. At my handmade transformer the secondary winding is divided{shared} into 6 parts to reduce capacitanse between windings. To receive the necessary variable voltage I has connected such 2 special transformers. Initial windings in parallel and secondary it is consecutive. Thus the secondary winding of my common transformer will consist of 12 parts. A material of the core - special amorphous steel. Not crystal structure of metal
Whether means your text, what you did not do{make} never lamp direct-drive amplifer?
To be as much as possible understood I is compelled to write shortly and primitively. Therefore not diplomatic. But it is not rough. I polite.
Again I want to ask - whether who did{made} the amplifier with an anodi voltage 15 Kvolt?
About coating:
First I have rubred with graphite a film, have washed off surpluses isopropanol spirit, have then measured resistance. Measured a current between two copper coins as the "fathers founders" learned. Rehorst for example.
Then I have covered a graphite grid with liquid nylon (a solution in phenol)
Sorry for my pimguin and non diplomatic eng
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Old 9th November 2007, 08:46 PM   #24
Kontra is offline Kontra  Russian Federation
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Default tube direct dryve amplifer

Example DIY amplifer direct drive - made in China for ESL louspeakers
About the amplifier I similar to these also asked.
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