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Introduction

The idea to build an ESL came to me after refurbishing my Quad ESL 57's. Since Quad ceased manufacturing the panels and I needed a new treble unit I started looking for alternatives on the net. Lucky for me I soon found the site of Sheldon D. Stokes, SDS labs. He has an excellent section on the Quad ESL 55 where he is so kind to share his knowledge on refurbishing the ESL 55 with the rest of the world. He can also rebuild the Quads for you at very moderate prices. With the help of his site and a lot of E-mails to him I managed to rebuild my Quads. They sound great now.

As the rebuilding of the Quad panels was relatively easy I wondered if it would be possible to build a set of my own. I started looking on the net again and found some sites that were of interest. Two of them were the site of Mark Rehorst, How to make Electrostatic Loudspeakers and the site of Neil McKean, Electrostatic Loudspeaker Design. These sites convinced me that it was possible to build an ESL myself. Then I found a book in Dutch 'Elektrostatische Luidsprekers' written by E. Fikier. In this book Eddy Fikier gives three designs for an ESL, a full range panel stator ESL ( ESL 240) a full range wire stator ESL(ESL 175) and a hybrid wire stator ESL (ESL 150H).

I started to look for materials and found it to be very difficult to find perforated metal sheets at reasonable price. Exit ESL 240. As I wanted to build an ESL I didn't like the idea of building a hybrid so I said the ESL 150H good-bye as well. That left me with the ESL 175. I started reading about it, made some drawing on how to construct them, changed some of the measurements of the initial design, bought the materials and started.

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ESL's in general

An ESL is a relatively simple device. It consist of five major parts.

  • The Stators
  • The diaphragm
  • The spacers
  • The audio transformer
  • The high voltage power supply

For a more elaborate introduction I refer to the sites mentioned above. If you don't know at all how ESL's work you really should read those sites first.

Description of the ESL 175

Type: Full range Wire Stator ESL
Initial designer: E. Fikier (full credits for the design go to E. Fikier but since I changed some of his specifications I think its more appropriate to say initial design)
Dimensions:
ESL size: 1600 x 260 x 80 mm
HV power supply: 7500 V
Audio transformer: 1:50
Amplifier power: min 40 W
Sensitivity: 82 (88) dB (1/W/1 m) with an audio transformer 1:50 (1:150)
Freq. response: 60 Hz...20 kHz (audio transformer 1:50); 40 Hz...20 kHz (audio transformer 1:150)

For an exact description of the ESL 175 I have to refer to the book of E. Fikier.

Building of the stators

One important advice: It is not difficult to build ESL's but you have to work carefully !!. Don't rush, time is on your hand. No one is putting a gun to your head, its not work, although it feels like that sometimes. Keep your working space clean, it will save you a lot of time. I learned the hard way.

The frames

The frames for the stators are made of MDF (18 mm). Each frames consists of two layers of MDF overlapping each other in order to get a solid construction. I made the outer layer of the frame 15 mm smaller then the underlying frame so that the outer dimensions are the same but the inner dimensions become bigger. In the bigger rectangle I can put the frame with the grill cloth. This is a cosmetic change from the original design.

In order to be able to wind the wires on the frame you have to place nails on top and at the bottom of the frame. In my first set I nailed the nails (diameter 2 mm) after constructing the frame. With the first nail I got a split in the MDF. I forgot that you have to drill holes before nailing the nails. Now I had to drill over two hundred hole in a ready frame. This is not a good idea. So for the second set I drilled the holes and nailed the nails before putting it al together. I also adjusted the original design a bit by make the frame parts in which the nails are placed 10 mm smaller so that the nails and the glue wouldn't stick out of the frame after finishing them.

In my first set I used about a thousand screws and glue to fix it al together. In my second set I used no screws at all. I only used glue and lots of wood clamps. In order to do this as accurately as possible I made a mould from MDF in order to get the four frame half's (two stators) as equal as possible.This works much better and saved me about a ton of filler. After finishing gluing the MDF together I checked it for straightness, I had to sand some unevenness away but I talking tenths of mm now.

After finishing I got a rectangle with outer dimensions 260 x 1600 and inner dimensions 160 x 1500. In the frame I glued every 150 mm PVC-pipes (16 mm diameter, exact 160 mm long) I used the mould and spacers made from MDF to get the exact distances between the pipes. I used Poly-urethane two components glue to glue the pipes in the frame. I put pieces of paper in the mould so that the glue wouldn't stick to the mould. This works pretty good. I checked the frame after gluing the pipes and some of them stuck out a bit. I waited for about an hour an a half so that the glue was hardened but not to hard to adjust these pipes. I used a big piece of flat and clean MDF to put the pipes in their exact place. It is very important that the pipes lay in the exact same line as the frame.The frames and the pipes are made to support the wires wires that are glued to the top and bottom of the frame and to each pipe. Below the drawings I made for the construction of the stators. You can click on them to enlarge them.

construction1 construction2
construction3 construction4
construction6 construction5
construction7 construction8
construction9

The stator wires

For the wires I used installation wire (outer diameter 1.77mm, 0.75 mm2). This comes in rolls of a 100 meters. I messed up completely with the first few rolls. After having wound a few meters on the frame the roll was completely gone and I was left with a ball of string that I had to spend hours on to get it right again. I did this not one time but several times. At last I found the answer by putting the roll in a box just as big as the roll and with a hole in the cover. I put the wire through the hole and that works perfect.

On the ready frame the wires are wound around the nails up and down the frame. In the first set I got the distance between the wires totally wrong. The distance between the wires was much to big (about 3 mm) which resulted in about 25 wires for one stator. E. Fikier is a bit unclear on that point but after rereading and some thinking I got it right for the second set. I now have 46 wires on one stator and I think I can put them even closer together.

With first set I found out that the frame would bend after putting the wires on them. Of course I found out to late that the frame hadn't bend uniformly because the bending gets worse after placing more and more wires. This resulted in wires with different tensions. With the second set I clamped the frame firmly to my work bench so that it wouldn't bend. After winding the wires I released the frame. It still would bend but now uniformly so that the wire tension was uniform everywhere. The bending as such is no problem since the to frame as fixed together in the end and then the straight each other out.

After winding the wires I got to the part of gluing the wires to the PVC-pipes. There are twelve pipes times 46 wires times two stators times two ESL's. That is a lot of gluing. I experimented for some time, cursed a bit, in fact I cursed a lot but eventually found a good way to do it. I placed the wires in their exact position and put painters tape over them. Where the wires lay on the PVC-pipe I left a small gap of about 1 mm between the pieces of tape. With a stopping knife I pressed the Poly-urethane glue in the gap, not to much, just enough to fill the gap. Then I left it for about an hour and a half to let the glue harden a bit. Then I removed the tape. The good part was that the glue wasn't totally hardened and that I could push back the few pieces that stuck out. The result was a very clean and even glue line. It is very important not to pull off the tape too soon because this result in hundreds of points of glue sticking out above the wires. When that happens its disaster day, believe me, I now.

The Spacers

After finishing the stators so far I glued the spacers on them. I used 4 mm and 2mm plexi glass (30 mm width). This works just fine. I bought in the measurements I needed so that saved me some work. You can buy sheets as well but the price difference isn't big. It cost about $25,- for one set of ESL's.. For the first as well as for the second set I used Poly-urethane glue to glue the spacers to the frame. That was a big mistake. The glue is perfect, in fact it is to perfect. There is no way to remove the spacers. When I tried I ended up putting my work next to the garbage because when removing spacers I also removed half of the MDF. The glue is to strong. For my next set I will use another glue, one that can be removed if necessary.

The Diaphragm

After gluing the spacers I started working on the diaphragm. I bought a piece of Formica which has an extremely flat surface. On this flat surface I rolled out a sheet of Mylar. I bought the Mylar from Roger Sanders who has two types of the stuff. One of them is especially made for heat shrinking and that's the one I used. I cut it in the right size which is about 150 mm bigger all around than the piece that will be the diaphragm when finished. I tensioned it with 40 mm package tape and tensioned in but not to much. Then I lined out the surface that had to become conductive and forgot to make the parts for the connections to the power supply the first time. Found that one out after gluing it of course. I started over and all went well. I taped off the parts that didn't need conductivity with masking tape, put some graphite on the Mylar and started rubbing. after ten minutes or so I got a nice even surface of graphite. Building the first set I forgot to clean the surface thoroughly which resulted in a hissing and sissing ESL. Then I remembered Sheldon D. Stokes. After rubbing in the graphite he removes as much as he can with (iso propyl?) alcohol. So I did and that worked perfect. I got a diaphragm with a very high resistance. This is the easy part of making a diaphragm. Then I glued the diaphragm to the stator after making the necessary contacts for the power supply with some aluminum tape. The gluing went very well. I used only very little Poly-urethane glue and put a ton of books on the stator. The next day a cut the stator loose from the diaphragm that stuck out of it and there I was. I heat shrunk the diaphragm very carefully and that went surprisingly good. Ten minutes later I was ready. I attached the wires for the power supply to the aluminum tape with glue that I mixed with graphite because I wasn't sure it was conductive. And that was it for the stators, they were ready to be hooked up to the power supply and the audio transformer. Almost...

I noticed that I had forgotten a little part of the diaphragm, there was a very small wrinkle in the upper left corner. barely noticeable but it had to go. I got the heatgun, started, said something to someone and burned a big hole in the diaphragm. After regaining conscience I stated removing the diaphragm and found what I already knew. The glue was an absolute hazard to remove. It can be done but it is a lot of work. By lack of an alternative I used it again but I have to find something else. This was no fun at all. But in the end I got a new diaphragm glued on the stator and ready to hook it up.

For joining my first set of stators together I clamped them firmly together and put holes trough both of them. Then I took nuts and bolts and bolded them firmly together. This works very well but isn't very pleasing to see as you can imagine. For the second set I used bolts with little teeth. I put them between the two layers of the front frame and made the necessary holes in the frames. By doing so the bolt wasn't visible on the front of the ESL and I still could make a very tight connection between the two stators. A great advantage is that they can be very easy disassembled. This worked very well. I unbolted them again and glued a piece of MDF (82 x 1886) perpendicular to the long sides of the front stator. Now the construction was very stiff and bending it would be very hard. I made these side panels longer than the actual stator in order to create room for the electronics. I finished the additional wood work and now I really was ready for the great test.

Building the Electronics

Maybe you wondered why I hadn't tested them directly after bolting them together. Well, I had to wait for the audio transformers to arrive. I ordered them via Roger Sanders and since he lives in the USA and I live in the Netherlands that took a while as well. I had zero experience in building electronics so I had to find someone who could me a power supply. Finally I found Jan Wennekers willing to build me one.At last it all arrived and the big day was there.

We were very curious especially since it was my first ESL and Jan's first power supply. Well, their was music and what we heard was good. No deformations, a very clear sound. But also no bass at all and only a very moderate volume. This was very pleasing and discouraging at the same time. It worked and it worked quite well, but it was in no way anywhere near my Quad ESL 55's. In retrospect that was maybe a bit to high a goal to aim at with my first product.

The Audio Transformer

I can be very short on this subject. I bought them via Roger Sanders. They have a turns ratio 1:50 and cost about $ 45,-.

The High Voltage Power Supply

As Jan had no equipment for measuring the high voltage power supply and he suspected that the supply couldn't deliver the necessary 7500 V I decided to start working from there to get the ESL's better. Jan had made the power supply on a small circuit board 60 x 160 mm full with holes. Around the holes there is a small ring off copper to solder the components on. Over here they are called 'Euro-circuit boards DIN 41612'. I suspected that the board would lose a lot of Voltage because the copper rings were very close together. The space between them was less then 1 mm. I bought a small drilling device and milled away all copper rings that weren't needed. This gave a considerable improvement. The ESL's sounded louder now and had a little more bass. But they were still very far from good.

I decided to build a completely new power supply. I got the description from the book of E. Fikier and encountered my first problem. How to make a circuit board. I surfed the net for a bit and found some sites with information on circuit boards. Making one myself would be a costly business. Luckily I found Robs Electrosoft (Now out of business 05-05-2001). Rob made me the boards for about $ 10,- a piece, all holes drilled and in perfect shape. I bought the components at Conrad and started soldering everything in the right place. I used the following components:

HV power supply

Above the layout of the circuit board. You can click on it to enlarge it.

  • 2 circuit board trafo's (220/12 V)
  • 27 capacitors 0.047 uf / 630 V
  • 27 diodes 1N4007 (1000 V)
  • 8 resistors 1 M Ohm

Soldering the board was easy, I had had to make sure that the solder was nice round shaped with no points sticking out. After an hour or two I finished the board. I soldered the connections to my first set of ESL's and the audio transformer. I turned the power and waited a while for the ESL's to charge up. I put a CD in the player and turned the volume knob.

The sound was much, much better now.. There was more bass, they sounded much louder and the sound itself was very clear. But they still were absolutely no match for the Quads.

By this time I had finished my second set of ESL's as well, the ones with the wires in the right amount. I hooked them up with the new power supply and again there was a great improvement compared to the first set. Again more bass and much more sound pressure. They still weren't loud compared to the Quads but the sound was quite good. I I decided to listen to them for a few days. I moved the Quads to another room. I listened to them for a few weeks and actually got used to them a bit. They lacked high sound pressures and bass but it is surprising how fast you get used to that. One day I moved the Quads back in. I shouldn't have done that. I had hoped that over the weeks my ESL's would have gotten better but they hadn't. Compared to the Quads the sound had absolutely no body. The sound was very clear and bright but it was very thin as well.

As I thought that I did the construction part of the ESL's reasonably well I decided to look at the power supply again. I had no way to measure the high Voltage output so I Bought a high Voltage probe. That an expensive device ($ 90,-) but very useful as well. With the help from MartinJan Dijkstra I managed to measure the high voltage output. The unit delivered 4200 V. That was about 3000 V short to the 7500 V I needed!. I contacted Roger Sanders and told him about my problems. He suspected that the capacitors weren't large enough . I build a new power supply with the following components:

  • 2 circuit board trafo's (220/12 V)
  • 27 capacitors 0.1 uf / 630 V
  • 27 diodes 1N5408 (1000 V)
  • 8 resistors 1 M Ohm

This resulted in a power supply that delivered 5200 V. I had read somewhere that I should cover the entire circuit board with acid free silicone lute in order to diminish internal losses. I bought a tube of the stuff and covered the whole board with it and make it look good as well I evened it out. To do this I put some liquid soap on my finger because this works very good with silicone lute. Unfortunately I forgot that liquid soap is also very conductive. Some of the soap must have found its way to the circuit board. The power supply now delivers only about 2700 V.

Recently I got information from several visitors on this topic . They had some good suggestions. I'll try them out in the near future and let you know how I'm doing. Roger Sanders describes a variable power supply in his book. Is there anybody out there how knows how to build such a device? If you have any suggestions on the power supply please let me know.

That's how far I got with my ESL's. The past months I didn't do much work on the ESL's as I was constructing this site. Now I am waiting a bit on for information from several visitors who are trying some new things with the power supply. One of them has bought a 15.000 V power supply that he is going to test in the near future. I hope he has success.

Update

A lot has happened since I wrote the article above. The Audio Circuit kept growing and took up all my time. However I went on improving my ESL's. With succes ! I made a good working power supply and tried various transformers. The use of other transformer gave a great improvement. I first used a old Final transformer. The result was a much better sound, a lot more bass and better overalll sound. Then I hooked up a the transformers of my Quad ESL 57's. The result was astounishing. Much and much better sound.

This was a turning point for me. I came to the conclusion that a great part of building ESL's has to do with electronics. And this is exactly the field in which I have absolutly no expertise. This combined with my pair of stacked Quad ESL 57's that are always in the back looking at my home brews made me decide to stop building ESL's.

Conclusion

Electronics in ESL's are fairly simply when you start out. Bringing your ESL's to level that they can compete with commercial designs is another issue. At this point understanding of electronics is essential.

Don't get me wrong, building the ESL's was a very pleasant experience and absolute fun to do. I wouldn't want to have missed it for the world. And if I didn't have the Quad ESL 57's I probably still would be building them despite the lack of knowlegde of electronics.

Greetings and happy building, Hans Zeeuwe