— QUAD ESL63 Loudspeaker Problem leads to Modification —

In May 1996 I purchased a black pair of ESL63 loudspeakers from QUAD and as my wife often reminds me they cost much more than I should have spent on Hi-Fi and take up a lot of space — Within 6 months they developed an intermittent fault where the frequency response of one side "changed" and the otherwise excellent stereo image appeared to shift around and in my room it appeared as if one speaker was being raised and lowered !

The speakers were sent back to QUAD which cost a lot in postage although they did return them for free — The fault was attributed to the HT power supply which they replaced under warranty — When you have a pair of ESL63s and friends interested in Hi-Fi you find they get borrowed a lot and by 1997 when we moved housed they were looking "a bit tired" with torn grille cloth and the same intermittent fault was back again

The ESL63 boxes which had been stored in the garage were not in a good condition so in August 1997 I arranged to take them personally to Huntingdon — QUAD service manager Rob Flain said that the service department would again look at the fault and could restore them to as new condition for only 40GBP per speaker plus any parts required and would ship them to my new address in new boxes — Excellent I thought

QUAD "looked" for the fault and — although I pointed out a clear foreign object in the area of the problem — they returned the speakers to my new address with new cloth grilles and boxes and charged me almost 300GBP — They found no fault and as I listened to them for several months they appeared okay

Due to decorating the new home and having a new job the ESL63s were put back in their boxes and — because I had borrowed a pair of Tannoy SRM10s for a while and my LS3/5A mods plus other speakers coming and going including 2 pairs of QUAD 11s — they were only used occasionally up to 2008 when after being used for a few months they showed signs of the intermittent fault once again

QUAD ESL63 Loudspeaker diapragm fault
In September 2008 the problem became very persistent so I contacted QUAD now IAG and again spoke to Rob Flain and arranged to send my speakers to their new workshop in Huntingdon along with a letter with pictures of the "foreign object" in the centre panel and copies of my previous letters

IAG service department said they could not fault the speakers and as you can see from the picture apart from the "metallic" object at top right the panels and dust covers look brand new

This time I insisted they at least soak test the speaker I had photographed and marked and this they did for several days — I then got a call from Rob Flain who said the panel was "fluttering" and should be changed and this I agreed to as they would discount the parts

View from other side of panel — It looks like some surface coating has come free of the membrane and it had been like this from new

My ESL63 speakers were returned and when I called to ask about the problem with the faulty panel and if I could have it back I was told that no one had looked at it and it had been "thrown in the skip" as soon as removed

I was a bit disappointed that IAG do not analyse such odd problems and feed back information into the design or production process but then they have not had in house design since the mid 90s and their production is in China

But — as I thought at the time — at least I had a pair of ESLs that have been "fully" checked and should last for some time to come

QUAD Loudspeaker ESL63 problem
Unfortunately in January 2009 the original 1996 problem came back yet again so I contacted Rob Flain at IAG service who suggested that I should return them — I was now becoming very frustrated with this persistent problem and decided to look into it myself — IAG said they had checked all the panels and power supplies which I trusted so what else could be the cause of the problem ?

Looking over the schematic 2209—2—63 supplied to me by QUAD in 1997 as the correct issue for my speakers there are a number of possible causes:

The 2 transformers L14 and L15 would be tricky to test so were initially ignored

I had never liked the idea of the 220µF input capacitor C25 and why the 1.5Ω resistor R15 ?

Triac T1 is provided to clamp the input if the HT arcs as detected by an aerial wire into Tr3

Polyswitch fuse FS2 operates if T1 operates or if subjected to continued high level input

The protection diode array D26 to D37 could be the cause and is easily disconnected but IAG would have seen that

There's the delay line where I would like to see high voltage poly Cs in place of the ceramics C1 to C13

Then I noticed a 1.5µF 100V capacitor behind R1 and R2 but could not find it on the schematic

I called Rob Flain at IAG and asked about the capacitor which was not on the schematic I had been given and the conversation led to the fact that the service department were using the same issue schematic — Some days later I received in the post a photo copy of an updated schematic 2209—4—63 and a note from Rob Flain explaining some questions I had asked:

"I think the resistor capacitor combination has more than one effective use.

At low frequencies it makes a 1.5 ohm series resistor thus slightly reducing output below about (guessing) 3kHz. This is most likely matches partly the effect of the capacitors in the terminating resistors of the delay line that make the whole voltage appear across all the elements for LF.

The 1.5 ohm also protects the amplifier if the spark detector kicks in and crowbars the transformers, at least the polyswitch has time to heat up and save the day."

Rob Flain, IAG Group Service Manager, IAG Group Service . . .

I see the 1.5Ω R15 protecting amplifiers from the T1 crowbar short and also from low frequency excursions at amplifier switch on and due to footfall where the impedance of the input transformers is almost a short circuit — Footfall occurs during record playback where low frequency excursions are produced by the cartridge as people walk across suspended floors near the turntable and I'm sure it was noticed as a problem during development of the ESL 63 as fuses in the QUAD 405 were blow

The capacitor C25 must simply be to maintain the input sensitivity in the audio range — It is difficult to model the effect of the R15 C25 combination because the input impedance is high and variable in the region up to 500Hz where the combination turns over — There is NO benefit fitting a ridiculously large 220µF polycap it is better to simply remove or by pass C25 — If I can get a good ICP microphone I will make some FFT anechoic measurements to show this is so

QUAD Loudspeaker ESL63 underside view
My first test was to bypass R15 and C25 and FS2 of each speaker by removing FS2 and wiring directly from the input to one pad where FS2 had been mounted — Pink wire in picture — also see correct schematic for my ESL63s marked up with the modifications

I also removed "half" of each parallel resistor R1 and R2 to restore some input impedance at low frequencies and T1 because it could operate and short the amplifier although I doubt it ever had operated

According to IAG the crowbar circuit with T1 is to prevent a fire if the panels arc — It is not to protect the speakers or the amplifier it is to prevent the amplifier providing enough energy to start and maintain a fire if the panel arcs — The HT is not switched off during arcing so it is assumed there is not enough energy there alone to cause a fire

ESL-57s did not have fire protection so it must be a perceived problem with the ESL-63 and most likely because the intended use is with much higher input powers — The ESL-57 was made at the time of the 15W QUAD II but I could not see my ESL-63 loudspeakers would catch fire so the changes above were made and used for months


Once again the persistent fault was back — I was tempted to next remove the diode clamp protection from each speaker but decided instead to remove the 1.5µF capacitors that IAG service had not been aware of — What I actually did was swap the capacitors because the one from the faulty speaker had a black patch on top

I think C14 was fitted following some Hi—Fi magazine test in 1989 that indicated the input impedance of the ESL63 peaked around 22kHz — Although this had no bearing on the frequency response it could possibly affect operation with some amplifiers — The impedance peak is very sharp and could have produced a high a.c. voltage across C14 which was only rated 100V at d.c.

Initial listening following the C14 swap was as before — I was really getting to like the ESL 63s with the R15 C25 and FS2 bypassed — The bass appeared deeper — probably due to the series resistance giving effective current drive but more importantly the response to transients was so much better — Then once again the persistent fault came back

But this time on the other speaker so it looked like one of the C14 capacitors was to blame — I was relieved but also very annoyed that it had taken 3 expensive returns to QUAD — IAG since new and then a further 7 months to find a faulty capacitor that perhaps need not have been fitted

I was so annoyed that I took the only action an enraged Englishman could take — I sat down and wrote a letter — enclosing the two C14 capacitors hoping that at least I would get an apology from IAG service department and that they would test them and review their use in the QUAD ESL63 Loudspeaker

Several months later I have been listening to the modified ESL-63s without C14s and would not put them back as supplied by QUAD because they are so much better and do not appear any less sensitive — Also after several months I had not received a reply from Rob Flain at IAG so I gave him a call

I asked Rob if he had received my letter and if he had shown the capacitors — that had cost me so much time and money — to the accountant who was the managing director of IAG Service — as I had asked — He had shown my letter and the capacitors to Tim Harris who just laughed and threw them in the bin saying "what does he expect these are years old"

Yes Mr Harris the faulty capacitor was "years old" but it had been faulty when fitted in 1996 since IAG took over QUAD and on 3 costly occasions the IAG service department could not locate the problem — Even when I asked about the capacitors I was told nobody knew why they were fitted to my speakers as they were not on the schematic drawing they used and nobody left in service fully understood how the designs worked

Despite the long drawn out issue with my speakers I would like to thank Rob Flain and his staff who I am sure could provide a much better service under different management and I realise the fault was an odd and intermittent one but the fact is — IAG Service is NO LONGER QUAD service even if some of the faces are still the same

If the ignorance and arrogance toward "years old" customers displayed by senior IAG managers like Mr Tim Harris propagates and if they continue simply buying in designs with little in house knowledge of how they really function then I guess they are just another "Me too" Hi-Fi manufacturer as indicated by the 77 series onward and their good value but mediocre quality box speakers — Certainly not the "Best of British" they once were

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"And though you're not my enemy ~ I like things like they used to be"