Quad ESL57 - Treble reduced radically?

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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!


Nick
 
Hello,
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.
 
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.
 
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


Sheldon
 
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


NS
 
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.
 
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.

esl57m6.jpg
 
You cannot be certain the fault is in the speakers until you have eliminated everything else. Your first test should be to swap the speakers from one channel to the other and see if the perceived lack of treble follows the swap.If it does then the fault lies in the speaker.If the fault stays in the same channel regardless of whether you swap or not, clearly identifies the problem as in the amp/pre-amp area.
It is absolutely pointless in trying to fix a problem (in the speaker) if the problem actually isn't there! The above test will confirm the above.
 
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.


The arc discharges you observed is your evidence of panel damage. How can you say that no damage is evident when you can't see inside the panels? I'll bet you that if you split that treble panel open, you'll have a nice arc through the diaphragm that has blackened and melted both stators in that region. Look for darkness in one of the stator holes in that region. The outside of the treble panel is not the "business end", it's what's going on inside that matters.


Sheldon
 
I agree with sheldon, it sounds like your treble panel has a short circuit. You can actually measure this. Unsolder the brown and blue wires from the bottom of the step-up transformer (remember which goes where). Measure the resistance between the two brown wires and between the two blue wires. One of them will probably read a low value (they should read open circuit).
If you find no short there hook up a capacitance meter. Between the brown wires you should measure something like 160-180 pF and between the blue something around 300 pF.
 
Too many unknowns here. Were the discharges inside the treble panel, behind the covers? Were the arcs seen from the "flat copper wire" to some other point near the treble panel?

I think - sort out the wiring with good HT leads, check the HT supply and then try the speakers. This is really easy to do. Dismounting a panel or order a new one might not be the first to go for.

Of course, switching the speaker wires from right to left speaker and left to right speaker, would be my first try, as was mentioned earlier.
 
There is no reliable test without opening the speaker, but what you can do to find out "big problems" can be:

- Listen to all four bass panels (stereo set) at the same distance - say 4 inches away. They should sound equally loud regardless of panel and at which location on the panel you put your ear.

- Listen to the middle section, i e treble section and mid section. Since it will be very difficult to judge if there is a problem with the mid sections or treble section, you can be fooled to think the panel is ok, but it is not. Listen at various heights from bottom to top of the speaker. The sound should be equally loud from each position.

If there is a large difference in sound level when you move your ear around over a panel, you probably have a severe short-cut inside the panel. Typically, the bottom of the speaker is working while the upper top parts of the panels can be "dead". The other way around is not very likely since the panels have there connections at the bottom.

Also note that the active panel surface does not extend all the way up to the top of the grille - it typically ends two inches down. So, don't be alarmed if not the entire area has a good sound level.
 
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