Quad ESL Article


This information was graciously provided to me by:

Massimo de Majo
Copenhagen
Denmark
Massimo_de_Majo@mermaid.dk

Hl-FI NEWS & RECORD REVIEW NOVEMBER 1993

The Essential ESL

by Chris Beeching

This easy DIY service proves you can extend the life of your old Quad Electrostatics


Between 1957 and 1985, some 54,000 Quad Electrostatic loudspeakers were produced.

Although it has limitations, and was criticised for being bass light, expensive and difficult to drive, the ELS is still revered today.

In sonic terms, there is little to compare with an electrostatic for sheer transparency, effortlessness and ease of listening. One of the most surprising things on first hearing is that, no matter how near to, or far from the speaker you sit, the apparent volume of the sound doesn't change. With some boxloudspeakers, the nearer you get, the louder the sound becomes.

The criticism of 'lacking bass' is also easily allayed. Two fundamental factors affect how much bass the speaker is able to radiate compared with conventional box speakers. The first is that the ELS's impedance rises as frequency increases (unlike many modem designs, where impedance falls as frequency rises), thus the amplifier is asked to work into a smaller (more difficult) load at the lower frequency end. The second, somewhat less directly related reason, is that when the ELS was developed turntable manufacture was of a high standard for the era, but many examples had a fair degree of rumble. Because very low frequencies require large cone or diaphragm excursions, a steep roll-off filter was incorporated into the Quad 22 preamp in order to protect the bass panels .

A further 'minus' point was the height of the legs. No-one knew how much of an effect loudspeaker placement had on the ultimate sound spectrum produced by a speaker in the mid-to-late 1950s. With more investigation of things like room modes, phase responses and all the modern jargon connected with installing a speaker for best effect, we are now much better informed as to how to get improved performance from a modest box or panel. Had those short legs been extended to about 14in (35,5 cm), the ELS's performance would have improved considerably. They also seem to work best with high mass stands or stands which are very rigid.

With the advent of the transistor amplifier in the mid 1960s, Quad was forced to devise a protection circuit to limit voltage to the treble panel; it had become clear that some over-zealous listeners had pushed the speaker beyond its intended operating limits with disastrous consequences.

Now the audiophile fraternity seems to be polarising either towards high-power systems with highly inefficient speakers, or towards low-power systems with efficient speakers. A 'difficult' load in its infancy, the ELS is now quite respectably efficient compared with many current designs, and modem (and older) valve gear will produce astounding results.

However, the problem arises, as it does with all older equipment, of deterioration of components over time. Capacitors go down, resistors decay and often go high, and age begins to get at both the panels and the connecting cables.

Add to that a continued existence in a warm, dry environment and, if they've never been serviced, a horrific accumulation of dust in the insides - the fall-off in performance this combination will inflict is astonishing. All is not lost, however. As you will see, servicing the ELS is a relatively straightforward matter, and can be done in a day with some care and attention.

SERVICING

Before you start dismantling, make sure your speakers have been disconnected from the mains for a good while. Quad recommends at least two hours, but I would suggest overnight as a minimum. Some components can pass on a hefty belt if you choose to place two fingers on their contacts.

Removing the grilles is quite simple: unscrew the three screws securing the side bars to the main frame. Put these to one side, noting which was fitted where. The front grille is removed once the nine small screws have been removed from under the front edge. There is also an earth connection held by a nut bolt small tag. Release the grille, but leave the nut and bolt attached to the tag to save losing them. Once the small screws are undone, gently pull the bottom of the grille upwards and away from the speaker, and ease the top rolled-over edge from the rear of the speaker frame.

The rear grille is removed even more simply by undoing the screws and carefully lifting away. Any small dents in the front grille can now be pushed out carefully, restoring it to its former shape.

As far as the interior is concerned, dust is the most difficult menace to remove, but it is also wise to replace the crossover (and other) components and wiring with modem highperformance substitutes. Dust is most easily removed with a lowpower vacuum and soft brush. Never use a high-power vacuum, or seal the nozzle against the dust cover, as damage will result.

Because of the nature of the speaker, the treble and bass panels attract dust which adheres remarkably well to the dust covers over the panels. Years of accumulation are not easily removed, although the loose dust will eome away quite readily. For the 'ground in' deposits, a slightly damped J-Cloth is very effective, and will soon clean the surfaces. Be wary of detergents which may damage the dust covers.

Having cleaned the panels, and vacuumed the internals, it is now possible to identify and replace the wiring and components.

The first items to be replaced are the speaker connections. This is fairly straightforward, but requires the temporary removal of the input transforrner; make sure it is well supported, and does not strain the other connections or wiring.

Carefully unsolder the original speaker terminals, and fit a pair of Michells (or similar). While the unit is 'free', you can also replace the set of resistors and capacitors which make up the crossover network and filter/protection circuit. Using quality resistors and capacitors will make quite substantial improvements, but more of that later.

Although Quad's internal cabling was good enough in its time, not only will that have suffered deterioration, but more is now 'known' about cable directionality and other related effects. Rewiring the panels is relatively straightforward. However, one word of warning: the solder connection on the back of each panel is very fragile in relative terms. It is imperative that you do not allow the joint to get too hot, otherwise there is a danger of the dust cover starting to melt and allowing dust into the 'chamber' containing the plates and diaphragm. If this happens, the speaker will attract dust like it's going out of fashion, and performance will decline rapidly.

The best way that I have found is to use a very hot soldering iron, and use the bare minimum of high quality solder. To unsolder each panel lead, gently pull each cable, and carefully touch each connection with the minimum of pressure from a very hot soldering iron. As soon as the cable comes away from its connecting post, blow hard on the exposed post to dissipate the heat.

Soldering the new cable needs similar care; whatever you do, don't allows the hot iron to linger on the joint. As soon as the solder has melted, remove the iron and blow hard again. Although a repair kit is available from Quad for the covers, it is far better not to have to repair it in the first place.

A quick word on cables. The crossover unit is quite simple, much of the signal division taking place mechanically as a result of the performance of the panels themselves. However, by selecting a mixture of solid core and stranded cables, you can further tune the speaker to the sort of tonal balance you might prefer. My own preference is for solid core on the bass, and stranded silver for the treble panels, but that won't suit everybody by any means.

Insulation is also important when considering cables you'll get a much better sound if you use a cable with Teflon insulation.

Replacing the resistors in the crossover network is also relatively easy. The crossover is situated beneath the audio transfonner, into the back of which the Ieads from the amplifier are connected. Make sure that any Ieads from the audio transformer are not stretched during this process; support the transformer, making sure it won't stray into the bass panel otherwise substantial damage could result. Ensure that all replacements are at Ieast of 2W power handling, are suitable for use with high voltages, and of a similar value to the original.

There is little that can be done to the EHT unit and the rectifier; replacing the wiring with new is probably about the limit for most people. If it fails to work, then a new unit will be necessary anyway. However, it is possible, with a little judicious filework, to recut the 'mains in' socket hole to accommodate an IEC socket instead of the round 3-pin Bulgin more often found on the back panel.

Always replace one wire at a time, whether audio, HT, mains or whatever. If by chance you should get two wires the wrong way round, at best the speaker will not work, at worst the speaker will be completely ruined, so take extra care.

On reassembly, make sure that all connections are secure, none of the dust covers is perforated or tom, and that none of the wires will catch on a sharp solder tag, corner or metal bracket. Fasten down any long or trailing wires.

TESTING

Now connect the speaker to the mains, and switch on without an amplifier connected. Allow it a couple of minutes to warm up and voltages and new components to stabilise. Now place your ear close to each panel in turn. From the bass ones you should just hear a very faint hiss; from the treble, a higher pitched faint hiss. If that's the case, all is well, so far.

Plug in the speaker Ieads from the amp, switch on and play a familiar track. All things being equal, it should sound superb. Now tum the volume almost right down and do the 'ear against the grille' test again with the track playing. You should hear each panel individually. Lastly, play the track at your normal listening level and check that both speakers produce roughly equal volumes.

Some people have removed the acoustic matting on the rear grille claiming improved detailing and transparency. In a large room that may be true, but in my experience of medium-sized rooms, removing this matting tends only to allow more of the rearward sound to be reflected off the back wall with a consequent increase in time-smear effects, and ultimately a more confused presentation. My own preferred listening scenario would be with the speakers about five feet (1.5 m) apart with the outer edges about 2-3 feet (60-90 cm.) from the side wall, and slightly toed in. All the walls behind the plane of the speaker would be heavily curtained, with the rear curtain/wall some five feet (1.5 m) behind the speakers. I would also put the speakers up on MAF stands; these lift the speaker some 14in (35 cm) off the floor and really allow the speaker to sing.

If it was safe to do so, I would also remove the front grille; it colours the sound slightly, giving some instruments a metallic "dead metal" feel. Normally you wouldn't notice it, but once you've heard a pair with the front grilles off you will understand what I mean. However, if there is any danger of anything (including you) falling into the speaker with a grille off while it's running, DON'T DO IT.

If you have any doubts about your ELSs, and you don't feel confident or competent enough to rebuild a pair as above, let Quad do it for you. If the speakers haven't been touched for a while, you'll really hear the benefit of having them serviced. Apart from the actual woodwork itself, almost all the components are available from Quad as 'normal' stock. In fact, you could if you were feeling reckless, buy a pair of electrostatics as a 'kit of parts' and assemble them yourself on your own frame.

Below are some prices for the more expensive parts: A treble panel costs 70, a bass panel about 83, and a rectifier block around 26. These prices exclude carriage. The Audio transformer costs ;75, and the crossover resistors between 45 and 55 pence each. Most spares are still available with the exclusion of the main carcass. For further information, phone Quad on +44 - 480 52561.