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RE: Service manual/schematic for Quad ESL-988 + modding tips?

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In Reply to: RE: Service manual/schematic for Quad ESL-988 + modding tips? posted by kentaja on September 16, 2012 at 09:33:58

Do you mean 670 V between the secondaries before the resistor "bridge"?
What do you think about this: http://www.keith-snook.info/Loud-Speakers/QUAD-ESL63/QUAD-ESL63.html
Here the cap is referred to as C14. Any other thoughts about doubling the 3R3 and the other suggestions in the article?

Edits: 09/16/12

Follow Ups:

RE: Service manual/schematic for Quad ESL-988 + modding tips? - kentaja 13:11:48 09/16/12 (4)
Yes the voltage should ideally be 670V before the resistor bridge. Measure across the yellow secondary wires that attach to the PCB.
There are two 3R3 resistors in parallel so the resistance is actually 1R65. Two resistors were used to increase power handling and keep the resistors small. A single 10watt 1R65 would be sufficient. I would recommend that the stock value be maintained. If one has an amp with variable output impedance the value can be changed or the resistors may be eliminated. Not many amps with variable output impedance. C14 is the coupling capacitor for the transformers. On the 98 PCB this cap is marked C26. The value is 1.5uF/100V.

I have seen the article before.
The problem he notes in the panel is not an issue. This is simply the conductive coating on the membrane. Sometimes they can be a bit sloppy when applying the conductive coating but this does not affect panel performance in any way. I have seen far worse!
Removing the RC network filter is an old tweak that started in the ESL-63 days. Some like the sound this way I don't. It changes the entire balance of the speaker and moves it in the wrong direction IMO. If someone prefers the speaker that way that is OK but I like the performance of the speaker with the RC network in place even with just the stock components.
As Rob Flain pointed out the 1.5 ohm resistor of the filter provides a load for the amplifier if the speaker should go into protect mode. If the speaker should clamp without the resistor in place the amplifier will see a dead short. This momentary short may not present a problem with a tube amp or solid state amp with an appropriate protection circuit but why take the chance?
I do think removing FS2 is a good idea. It provides little practical protection and does degrade performance. It was implemented late in the production of the ESL-63 and carried over to the current speakers. I routinely eliminate FS2 with late production ESL-63 and all new production speakers. I don't use FS2 on the new ESL-63 boards that I produce. I have never had any reports of problems with FS2 out of the circuit.
I have produced new delay line assemblies for the speaker including better caps, Teflon in this case. Testing is under way and several units are in the field for evaluation.
As great as the Quad sounds stock careful tweaking makes them even better. PJW knew what he was doing, everything is there for a reason and I believe maintaining the overall circuit values, etc., produces the best results.

Edits: 09/16/12 09/16/12 09/16/12
- RE: Service manual/schematic for Quad ESL-988 + modding tips? - Zombie 23:27:16 09/17/12 (2)
  Would be interesting to get a reminder when the tests are evaluated.
  - RE: Service manual/schematic for Quad ESL-988 + modding tips? - kentaja 07:47:48 09/18/12 (1)
    Drop me a private email in a month and I will be happy to share the results.
    - RE: Service manual/schematic for Quad ESL-988 + modding tips? - Zombie 01:21:31 08/23/19 (0)
      Hello! How did the test go? A long time has passed :)
- RE: Service manual/schematic for Quad ESL-988 + modding tips? - kentaja 19:26:13 09/16/12 (0)
  A follow up. I read the article again and the comments about the panels catching fire is rather silly. I suppose in theory it is possible but highly unlikely I would say virtually impossible.
  
  I have done experiments defeating the sniffer circuit and let the panels spark away. Thousands of cycles of sparking. Have they ever caught on fire? Nope. Of course the panel looks like Swiss cheese afterwards!
  
  Is there a scenario where the Mylar might ignite and catch on fire? Yes. I produced a panel that dropped the surface resistance well below what would be acceptable for stable performance. In this experiment the Mylar did catch on fire. Talk about cool! Took several seconds for the Mylar to completely burn away. There was no damage to the stator assembly it was easily rebuilt and the panel worked fine again.
  
  What can happen without FS2 in place is someone uses a very small wattage amp and just clips the snot out of thing. How can someone listen to it that way? Can't they hear the amplifier clipping? What will happen when abused this why is the R1, R2 resistors will fry burning the PCB and making quite a mess but this take perhaps 10-15 minutes of constant continuous clipping. The board is a charred mess and has to be replaced. But I seriously doubt the speaker is going to catch on fire.
  
  I have never seen another electrostat that the maker is concerned with the speaker catching on fire and adds protection circuits to stop such a thing. This is really grasping at straws.
  
  If someone clips an amp in this fashion and continues to pound on the speaker and abuse the thing in this way they deserve the damage that is caused and the repair bill that will follow. I see no reason to degrade speaker performance to stop this kind of abuse.

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