Because I decided to buy old Quad ESL 57 and rebuild it, I was surfing on the net and look at the various web pages. One among many kept my attention. This is story of Marc Schutte and his rebuild of this famous Quad speakers.
Quad ESL rebuild
Some years ago, i came across some Quad ESL57 electrostatic speakers. At the time, i took a quick look at them, saw that the high voltage power supply was broken, and put them into a corner for a while. A few months later, when looking for a schematic for a different project, i discovered that there is lots of information on them to be found on the internet, from general reviews to very detailed info on how to repair and rebuild these old speakers. One site in particular, Sheldon Stokes’s www.quadesl.com , is a very good source of information. So, i finally got around to taking the old ESL’s apart, and fixed the power supply, to give them a try.
How to convince my wife?
After listening to the ESL’s for a while, the conclusion was that these where indeed very good sounding speakers. Probably not for the deep bass loving people, nor for those with a very big living room, but for me, the sound is perfect. The only trouble was, when i telling my wife i wanted to put them in the living room, she said: “No way, these are the ugliest things i have ever seen!”. Now, as much as i love to disagree with her, i have to admit she’s right. The ESL57 may have been considered beautiful in the 1950’s and 60’s, but it looks butt ugly in a more modern environment. Also, because they are so close to the floor, you need very much space to create an acceptable listening position. So, it was obvious that if i was to get that ESL sound i wanted, the looks of these speakers had to undergo some drastic changes!
Modifying the ESL-57
During the initial repairs, i had already noticed that the Quad ESL exists of three separate panels, two for bass, one for mid and highs. After some measuring i quickly discovered that stacking the panels on top of each other, rather than side-by-side, would put the mid-high panel in exactly the right listening height. But would the sound of such a setup be just as good as the original? Of course, there was only one way to find out. So out came the panels, wiring and electronics of one of the speakers, and a test setup was made.
As you can see in the pictures, the panels are held together by nothing more than a wooden frame. The wiring, transformer and power supply are on the bench behind it. Needless to say this setup is for testing purposes only! The power supply for the panels puts out several kilovolts, which makes this very dangerous in a real-world situation. One of the complaints about the Quad ESL is about the directional radiation pattern. This makes it very important to make sure that the mid-high range panel is positioned at the right height for the listener. After some experimenting, the final test setup has the panels stacked directly on top of each other, with the bottom panel slightly facing up, and the top panel facing slightly down. This has the additional advantage of keeping the overall height as low as possible. Nevertheless, the finished speaker measures an impressive 205 centimeters in height, which is more than enough i think!
In the picture on the right you can clearly see the tilting of the top and bottom panel. An airtight seal around the panels prevents air leaking around the sides of the panels, this helps improve bass response greatly!
Putting it together
After determining the best possible setup for the panels, building a visually more pleasing (and safer) housing was the logical next step. The biggest challenge here is to make the speaker “cabinet” as rigid as possible, while maintaining a slender look. This is done by using a wooden base, on which the transformer is placed. The top part is bolted and glued onto the wooden base, with a hole in the middle for the wiring. Perforated sheet metal was used both to protect the ESL panels and for safety. The sheet metal also adds stiffness to the frame. It is bolted to the frame with lots of screws, to prevent resonance at certain frequencies.
The audio transformer has been repainted, and all wiring was redone with high voltage teflon cable. The high voltage supply is located behind the back of the lower bass panel. It is a good idea to test this power supply, and replace the caps in it, to increase reliability. For more details about this, take a look at Sheldon’s site, http://www.quadesl.com. He also has a schematic for mid-high panel overload protection. It fits under the audio transformer, and prevents the panel from arcing when too much power is applied. Next, the metal sheets are covered with black cloth, and extra wooden paneling is added to the sides and on top.
The end result can be seen in the following pictures:
The “new” ESL speakers are now in daily use for more than two years, and are still the best ESL speakers i have heard to date. The directional sound pattern is something i will have to live with, but as i usually am the only one listening, this is not too much of a problem.
The pictures on these pages are not intended to be a detailed building plan. If you feel inspired by this article, and want to attempt to make this modification yourself, be advised that this is not a beginners project! Sufficient electrical and woodworking skills are needed to successfully complete this project.
How to contact me
If you have any questions, feel free to e-mail me at firstname.lastname@example.org , and I’ll try to answer your questions as soon as i can.