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wolfiesn 10th April 2011 04:34 PM

Quad ESL57 - Treble reduced radically?
Hello all,

I have a pair of 57s: overall in excellent condition, and have been using them day in-day out for months with no problems.
Yesterday my cat (!) dislodged the pre-amp connection to my Quad 303: a very loud crackling noise ensued for a split second. I immediately disconnected the speaker connections and re-connected everything.
One speaker was completely unaffected; the other is now almost treble-less.
I stripped off the covers on the affected speaker, expecting to find signs of arcing on the treble panel, but it looks absolutely perfect - almost brand new! After examining visually all the electronics I failed to find any signs of damage (no exploded components anywhere)

What do you think the problem might be, and where should I go from here?

Thanks to all you experts in advance!


Fabien Lefebvre 11th April 2011 09:43 AM

By treble-less we can either understand:
1/ the treble panel has lost efficiency but the bass panels work as expected
2/ there is a loss of efficiency in the treble area, meaning both treble and bass panels have a problem
You can try to play a sine at 1kHz to decide on which option. If both speakers prove to be as efficient on this kind of signal then it is more a treble panel issue (or - less likely - audio transformer), otherwise the EHT module is root cause.
Next step, if EHT is identified as defect: switch the power supplies between the two speakers. Easy to do: 2 times 3 connections to un-solder. But take care to protect the dust convers using for example a simple sheet of paper. And see to it to let the speakers unplugged for few hours before opening the rear side.

lcsaszar 11th April 2011 02:30 PM

If the treble panel got a high energy transient, it might easily become shorted. An easy test is to connect a small neon bulb in series with the HT going to the centre pin of the treble panel. If it blinks or is permanently on, you most likely have a short. If not, look for a HT issue.

kavermei 11th April 2011 07:18 PM

If I were you, I would first check to make sure the problem is in the speakers. Do you have other speakers to test with? It might just be something has come loose inside the amp or preamp.

Best of luck!


SY 11th April 2011 08:01 PM

First things first- exchange the speaker wiring left-to-right. Does the problem stay on the same side or does it swap?

woodturner-fran 11th April 2011 08:23 PM

More likely to be your preamp.....

stokessd 11th April 2011 10:10 PM

You arc'ed your treble panel. Welcome to the club. It's rebuild time. There's a lot of choices on that front. Many of us do it and earn a few bucks on the side. I think I may be the first doing Quad ESL 57 and 63 rebuilds shortly after Quad stopped supporting the 57's in the early 90's.

Since you are on a DIY forum, I'd seriously take a look at the ER Audio rebuild kits:

Electrostatic Loudspeakers By ER Audio


wolfiesn 13th April 2011 03:22 PM

Quad 57 - reduced treble
Firstly let me thank you all for your replies!

However, I noticed something that changes things perhaps.

I re-powered the speakers and noticed two things:

1. The wiring had been replaced with a flat copper cable (brand unknown)
2. There was (in the vicinity of the treble centre panel) a series of coronal arc discharges upon powering up.

Again, no damage to any panel is evident.

I'm thinking I should re-wire the speakers, perhaps with a better insulated cable - any suggestions?
And, obviously, rebuild the EHT, as I'm beginning to believe this might be the culprit?

Again, any thoughts will be hugely appreciated!

Best again to everyone


lcsaszar 14th April 2011 02:26 PM


Originally Posted by wolfiesn (
1. The wiring had been replaced with a flat copper cable (brand unknown)
2. There was (in the vicinity of the treble centre panel) a series of coronal arc discharges upon powering up.

1. Have you checked the insulation? Does the edge of the cable touching anything, e.g. the perforated metal dust cover?
2. Discharge to the panel or to other part? Usually it can be traced visually or by smelling around :)
Rewiring (restoring the original wiring) is a good idea, anyway.

candersson 14th April 2011 07:42 PM

I did a search for ESL:s and just got this thread - and thought I'd drop a few lines here.

I have had a pair of -57 for a few years now and also managed to strip down a treble panel to fix some "minor" arching. It was fun but with lots of work assemble it back together.

Anyway, I created an HT-probe by using two resistors, one 1Gohm and one 1Mohm to make a voltage divider and then hook it up to a multimeter measuring voltage. If you have access to the resistors and good insulating tape, you can create it quite easily. Ok, it does not give an accurate reading, but you will get something like 4.5V for the 6kV bass panel voltage and about 1.2V for the 1.5kV treble panel voltage. Any severe arching or shorting paths will be seen as a drop in these voltage readings.

Of course, you can then test to disconnect the bass panel and remeasure. After that, disconnect the treble panel and take new readings. This way, you can find out the condition of each panel and the EHT itself.

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