Planar Speaker Asylum Welcome! Need support, you got it. Or share your ideas and experiences.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Planar Speaker Asylum ]

---

[ Alert Moderator ]

---

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

Posted by kentaja (M) on September 16, 2012 at 13:11:48

In Reply to: RE: Service manual/schematic for Quad ESL-988 + modding tips? posted by Zombie on September 16, 2012 at 10:52:12:

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

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---