Frequently Asked Questions


Who are you ?

Hello. My name is Andrew King. I was brought into this world in the late 1960's. In a past life I was a Giant Panda.

Do you do this speaker repair as a business ?

NO. I have a full time job working for a multinational telecoms company. It pays the bills.

Why do you do this speaker repair ?

After finishing my time at University I found myself with a few months spare before I started my new job. Most people in this situation would take some time off and perhaps do some travel. Not me. I helped out a friend of mine making valve amplifiers. This was the first time I heard a pair of ESL 57's. This was a revelation. This caused my interest in ESL's and its why this website is here. I just had to find out how they worked. Once I did this I then found out that I could repair them if I had to. When Quad UK stopped servicing them many other people needed repair work which I am able to do.

Do you supply speakers ?

No. You have to find these yourself. If they have problems thats where I can help you.

Do you sell new parts ?

Some, Yes. I can make the high voltage power supplies and the clamp circuits (to limit damage to the treble panels). Other than that I don't supply any new parts.

You seem to know a lot about Quad ESL's. Where did you get all this information ?

I started by buying a pair for myself. These were inevitably faulty. It all started from there. Everything I now know came from either working on them myself or other sources (mostly the internet).

So what previous experience do you have ?

First and foremost I am an engineer. I did a Mechanical Engineering Apprenticeship mostly to find out how things work and how things are made. This is mostly why I am interested in the Quad ESL. I don't know much about electronics except what I have picked up along the way. I know a little bit about computing having done a degree in Software Engineering. I currently work for a multinational telecoms company working on current switching technologies and future IP based telephony.

What have I learnt working on the ESL 57 ?

Generally speaking, every time I work on a pair of ESL's it amazes me how something that was made in the way the ESL's are made could sound so good. Sure if you want boom boxes these aren't for you. If you want to hear the sound of Howlin' Wolf being prompted by his recording engineer as he is singing Back Door Wolf then get a pair of ESL's (this actually happens - listen to the track and you will hear his recording engineer reminding him what the lyrics are before he sings them - at first I thought it was print through on the tape but it isn't). It also reminds me how little we have progressed in the last 50 years. Think about it. What genuine technological advances can you think of ? CD ? DAB ? Tape Cassette ? DVD ? Every year we get the latest and greatest products from faceless Japanese companies being driven by corporate marketing which knows we all want something better than what they have got next door. Well, I am here to tell you that just 'cause somethings 40 odd years old doesn't mean its design and performance shouldn't be ignored.

Do I work on the ESL 63's ?

Not if I can help it. I will look at the 63's and so long as its something simple (like a faulty power supply or blown component) I will try to fix it. Otherwise I would suggest contacting Quad directly as they still service the 63.

I think my ESL's are low on output. How can I check ?

Well you would need to use an SPL meter and get a known output level from an amplifier. I never do this. I find that measuring the high voltage in the speaker tells me a great deal. You can think of the high voltage like blood. If your blood pressure is normal thats fine but if its low what could cause it ? One of two things. Either you have a weak heart or you severed a major artery. In the ESL this analogy maps to your power supply being low or you have some panels whose insulation has failed. One way to check for insulation problems is to play some music through them and unplug each speaker from the mains. If the sound level drops off quickly then you have an insulation problem.

My speakers make a clicking noise all the time. Is it a problem ?

Probably not. The ESL was first made in 1957 and last made in 1980 which means that any ESL is at least 20 odd years old. Over this time the inside of the speaker will have got very dusty, some bits may have corroded and in extreme cases animals may have urinated on them (yes, it happens). The clicking you are hearing is a spark jumping from somewhere that has high voltage to somewhere else that has lower voltage. The easiest way to determine if this is affecting your speaker is firstly listen to the speaker with music playing through it. Does it sound OK ? Secondly you will need to measure the high voltage. I use my electrostatic voltmeter but a high voltage probe does the same thing.

What amplifiers do you recommend ?

First thng to say about aby ESL's is that they are a different load on the amplifier when compared to normal speakers. Normal speakers draw current from an amp - they are a resistive load. You have a coil in a magnetic field so you are essentially driving a resistor (albeit one that changes resistance with frequency AKA impedance). Electrostatics do not present a load of any kind. Although some loss across the audio transformer and crossover will happen the audio signal eventually ends up on two large surfaces which has a diaphragm in between them. These surfaces dont connect to anything else and so therefore they dont draw any current from the amplifier. But large flat surfaces are essentially capacitors. ESL's therefore present a capacitive load which also changes with frequency. This capacitive load is awful. At times the load seen by the amps drops to 1ohm or less. This is like almost shorting the outputs of your amplifier. Most transistor amplifiers hate this. Those little bits of silicon just complain, overheat and go pop. You could put a resistor in series with the speaker but that will just reduce the output of the speaker. This is why I always recommend valve amps to drive ESL's. Now before all those pre-conceptions about valve amps start coming into your head I will put you straight. Valve amps are reliable, they can sound dynamic, fluid, open, detailed - about the only area of concern is small children and hot glass. The most important thing to look for when getting a valve amp is what output tubes does it have. Single ended amps like the ones that use 300b output tubes are probably best avoided due to their low power output. Push pull amps that use EL34 output tubes are the best compromise as far as power and cost are concerned. For a sweeter but less powerful amplifier go for EL84's. It then comes down to which one you like the sound of.


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