In part II of the LS3/5a essay I will share some thoughts about choosing the right amplifier as also illuminate some of the specific construction details.
The KEF T50 tweeter
Looking at the tweeter of a LS3/5a is somewhat strange….after we fought with the velcro fixed Tygan grill of the speaker we will see a strange looking (tea strainer) cover and there is no tweeter visible. But beliefe me – it is there….;-))) First lets talk about the grills….the frequency response of the LS3/5a is measured and constructed with the grills in place – so it is NOT recommended to get rid of them – as the speaker construction behind the grilles is everything else than beautiful it is also a good fashion statement to let the grills where they belong. The same has to be said about the tweeter cover….I once I read in an internet article, that it is necessary to get rid of them to achieve more treble energy – the opposite is true…. The vented covers raise the sensitivity of the tweeter instead of dampening the latter!!!! The KEF T50 is made out of Mylar foil……it is the same material chosen by the microphone manufacturers for their capsule membrane and…..yes – it is the same material our beloved Quad “membranes” are made of. It was not so common at the end of the 60ties (last century) to use synthetic materials for speaker development – so KEF stood out as one of the first manufacturers who thought about new materials. The T50 was nearly 10 years a sort of reference in its segment – a lot of different speaker designs were made around this legendary tweeter. This little gem is able to reproduce frequencies above 40Khz – something which is also not too common in our modern days. With the implementation of the LS3/5a dividing network the speaker features a slight raise toward the highest treble. It is the opposite of what we will find with the Quad ESL 57 which has a frequency roll off starting at 15 Khz which takes care of a slightly rolled off highest treble performance. The LS3/5a renders the treble in a completely different way. If we enjoy to use moving coil carts with a slight emphasis in the region of 15 – 20Khz (high frequency rise typical for most moving coils) with the Quad ESL 57, we will be more satisfied using the LS3/5a with cartridges which domesticate such behaviour. In other words – a top notch Lyra, like the Etna SL is a dream to use together with the Quad ESL 57, in contrast to that the LS3/5a loves cartridges like the Koetsu Urushi Wajima for example. As we are now aware of this special character of the LS3/5a in the treble department – we must avoid any gear – be it an amplifier, preamplifier or source component which has a somewhat tilted up treble performance….
The T50 is surrounded by a thick felt square which prevents the sound waves to become diffracted at the enclosure and the surface of the speaker. That is important as we already discussed in part I of this essay the tremendous omnidirectionality the LS3/5a has to offer.
The tweeter is electrically secured by a resistor in front of the latter (15 Ohm model) – this thing can get really, really hot – and sometimes – if you disassemble a LS3/5a, you will see some burnt damping foam around the position of this resistor. It can happen that those things are burnt – if you are lucky, it is just the resistor and not the whole tweeter…. A blown tweeter will resulting in buying two new (old) ones, because those tweeters were matched as a pair. And if you buy two new ones it is a good idea to measure their resistance (of the functioning one) because as you can read in part I – different tweeters (electrically) could be used with different tabs of the autoformers…..so you have to search for a replacement pair which fits the technical specs of that particular pair originally used in your specific speaker to get the same treble response once adjusted at the crossover board.
The KEF B110 woofer
The B110 is a legend – it was one of the first speaker chassis made completely with a high damped synthetic material. KEF was searching for a lightweight as also robust material with a very good inner damping. They designed a completely new material to achieve that – and called it Bextrene! The very first B110 chassis had a membrane surrounding made of neoprene – later KEF opted for a rubber surrounding which was more consistent and easier to manufacture. If you look at the B110 woofer of any original LS3/5a, you will observe that it is mounted from the backside, which is totally uncommon in speaker design. If we want to achieve a time aligned behaviour of both speaker systems we would opt normally for the opposite, than mounting the bass chassis behind the plane of the tweeter. The LS3/5a crossover addressed that specific mounting position so that we will hear an astonishing phase coherency between the two speaker systems. In fact the crossover point is located around 3Khz so it is chosen in a very critical frequency region were our ear is very, very sensitive (Fletcher / Munson curve), but we will not detect any phase anomalies while listening to a proper installed LS3/5a. The B110 is a long throw woofer system to compensate for its small surface and size. Do not be afraid if you once observe the woofer moving while you are listening to some deep and strong bass impulses – what you see is normal;-))))…..If you overdo it, you will hear a loud Pock Pock sound, which is the voice coil former that knocks at the inner side of the magnet….so it is time to decrease your listening level.
The B110 gives us in the LS3/5a an amazing midrange performance – you can characterise the LS3/5a as a full range speaker with a tweeter on top….The whole important midrange spectrum is covered only by the B110! The woofers are also matched as a pair in our beloved mini monitor – so if one is defective – you are in for a very, very long search! If your B110 looks dirty – please be advised that it is not a good idea to use any liquid to clean the damn thing. Bextrene reacts not too good if it is mated with windex cleaner or pure water…so let the thing like it is – get rid of the dust and thats it!
The listening height should be adjusted so that your ear is located virtually between the tweeter and woofer position – if you sit too low, you might detect some strange phase anomalies, if the position is to high, the sensational imaging abilities would suffer seriously.
As I explained in part I – every manufacturer of the 15 Ohm Ls3/5a made its own crossover. Most of the very early models used autoformers which were wound in house by the specific manufacturer. Later on the British company Drake delivered all licensees with their autoformer model leaving out Spendor – they used their own stuff till the 15 Ohm era was at its end. All LS3/5a crossovers share a distinct complexity. If you are a proper High End freak – and peek inside of such a dividing network – most of us would say – that cannot work – nor will it sound good….but the reality shows us every time we listen to these little speakers, that the BBC did an amazing job – the LS3/5a is one if the most important speaker designs of all time – and this is not my humble opinion only….
The parts of the finest LS3/5a 15 Ohm incarnations used throughout the circuit were top class in those years…..do not mess with them! I know that it is easy to find monster High End foil capacitors in the audio accessory shops today – but I can assure you – every moded version does loose its magic – and at the end you have destroyed an original! Let the things like they are – watch out for strongly used parts and try to replace them with the same type once used in your speaker (one of the reasons why in the strong far east scene they collect also parts of the LS3/5a…..). If you disassemble a LS3/5a you will aware of how complicated the whole thing was built. If you change the order of some washers or forget some of the rubber O rings, the little diva will not be air tight anymore….
Everything which is present and mounted in a certain way is not an option, it is very, very important – there is no place for tuning work or trying to better the performance other than using a better position in your room or better equipment to drive the little diva.
The classic LS3/5a has an impedance of 15 Ohm which is totally unusual today. The maximum power these speakers will handle is around 25 – 30 stable watt. If we buy a little transistor amplifier which is able to produce 50 watt at 8 Ohm – the same amp will deliver 25 watt at 15 Ohm…keep that in mind. A transistor amp which works near its clipping is the best way to destroy any speaker – so you have to search for something a little bit beefier than 50 watt….the impedance figure of the LS3/5a is not so much loved by transistor electronic.
The opposite is the case if we discuss 15 Ohm impedance together with a tube amplifier. Our tube amp might have output transformer taps which are made for 16 Ohm…. To understand the advantage of a high impedance speaker mated with a tube amp I have to explain things a little bit more. The outputstage of our tube amp has naturally a high impedance, it varies a little bit from tube type to tube type – but generally it is a high impedance figure. The output transformer is used to adjust for the high tube output impedance to be matched to the low speaker impedance. If we use a 4 Ohm speaker a lot more windings are necessary to achieve that as with a high impedance speaker, as the LS3/5a is. Finally a high impedance speaker design is a very good match for any given tube amplifier as also OTL (output transformerless) designs!
As the LS3/5a is not very sensitive, you might think it is not a good idea to pair the speakers with low powered tube amps – but the opposite is true. The high impedance of the speaker compensates for its restricted sensitivity! A LS3/5a is not a good match for a SET amp like a 300B or even more so a 2A3 – both have too little power to drive the speaker to sufficient sound pressure levels, but a 6L6 GC push pull design or an EL 34 amplifier – may it configured in triode mode or as a penthode works like a charm. Keep in mind the little box is very, very accurate to the source – so if you think of something cheap and mediocre – the whole system will sound accordingly….If you opt for a transistor amplifier there are also great models out there which have a legendary status. The Naim chrome bumper amp range comes to mind or legendary class a amps from Britain (Sugden, Musical Fidelity A 1000) or the US (ML or Cello) as also the amazing Lavardin of our days. The latter is one of the most musical transistor amps that can drive a LS3/5a! But if we have the chance to listen to one of the rare 15 Ohm specimen today I would opt for a nice tube amp!
A tube advice
With a tube amplifier we have the possibility to voice the amp to our liking – and if we listen to a LS3/5a using tube electronics it is time to praise the legendary Mullard MC1 ECC83. This is one of the oldest European ECC83 type of tubes and it sounds so damn fantastic with the legendary British speakers, if I did not know it better, I would guess they were constructed for each other. The Mullard MC1 features the one of a kind wrinkled glass surface as it also has a square getter construction and long narrow grey plates. To spot an original MC 1 we have to observe the lower segment of the tube – we will find there an etched code with the type MC1 and a number which should start with a capital B for the Blackburn production plant. The MC1 is not the only long plates Mullard ECC83 – the successor was named F92 and has also an amazing sound. To mate the Mullard MC1 with the proper ECC82 Mullard (phase inverter / preamplifier) things get a little bit exotic. The holy grail of all Mullard ECC82 is the military version of their ECC82 called CV 491 – and this is it….A Mullard CV 491 Long Plate together with its stablemate the MC1 is truly amazing. These tubes have a one of a kind bass gestalt. Full and tight as also very, very colourful – the dynamic abilities of the deepest octaves are astonishing. The midrange is reference class with a slight emphasis in the lower midband – which brings vocals in their three dimensional gestalt right in front of our speakers. The presence is somewhat defensive and opens up nicely towards the treble and air – I would call that a classic tube sound. The stage a Mullard is able to render is big and bolt – in this parameter it is one of the best tubes I know. I use them both in My Air Tight ATC2 HQ preamplifier together with a GEC CV 4005 rectifier and this preamp drives the ATM4 which I already described in my essay about the 6L6 GC – both amplifiers are mated with two Chartwell I and the performance is stunning!
Keep in mind that all the old long plates Mullard sound completely different than the short plates incarnation made from 1960 onwards. The short plates – especially the I63 type is very smooth and even rolled off in the treble department which cannot be said about the long plates Mullard tubes of the ECC83 and ECC82 family. The downside of choosing these legendary British made signal tubes is their rarity and the high prices we have to pay today. But think about it in a different way….if you spent €600,- on a power cable or a signal cable the benefit would be much, much smaller as if you opt for such an outstanding electron tube!!!! These legendary Mullard long plates types are unmatched till today – no modern construction comes even close!
Quad ESL 57 versus LS3/5a
If you like the sound of a Quad ESL 57 but you cannot place it in your room – than the LS3/5a is the closest thing to the original Quad in existence. It does not sound the same (of course not) – but the most important aspects of the reproduced music is cut from the same cloth. The LS3/5a can reproduce deeper frequencies with more impact if we position them in front of the long wall of our listening room (reed part 1 of this essay), the Quad on the other hand delivers its deepest frequencies with more accuracy and authority. Both are very, very fast reacting speaker systems, but the Quad is able to reproduce the leading edge in a fashion no other speaker can muster (unless we use also a ribbon or electrostatic construction). The LS3/5a can beam the sound into the room with an amazing omnidirectionality while the Quad is very much restricted in this discipline. If you want to listen to your favourite music with your family or friends and not alone, the LS3/5a is the better option, because you can enjoy their beautiful performance also if you are not located near the sweet spot. Both speakers are able to deliver an astonishing resolution – but they do it in a different way. The LS3/5a is able to reproduce the treble and air section of the reproduced music in a nearly unlimited style, the Quads do not have that outstanding treble performance, instead of that, they are able to deliver the smallest shades of colour as also a tremendous amount of micro dynamic variations without having such an unlimited high frequency performance. Some people opt for a super tweeter in conjunction with the ESL 57 to get exactly that kind of “unlimited” treble performance – but till now I am not aware of any solution which does not destroy the tremendous rightness this speaker has to offer.
The LS3/5a can play a little bit louder than the original Quad ESL but we cannot speak about a real grown performance showing macro dynamic shades – far from that. That brings us to the biggest disadvantage both speaker systems share….the maximum sound pressure level and the rendering of really big dynamic swings. Both speakers will deliver an undistorted signal up to 100 – 104db (in 1m) – and both are rather insensitive – the figures are nearly equal. If you can live with this restriction you will be payed off by so many seldom found qualities in the whole speaker market today, that it is my strongest advice to listen to one of them – maybe it will be your last pair of speakers……
Both constructions do not change their frequency coherence while played with varying volumes – so you are able to enjoy your favourite music in some intimate nighttime listening session in its full glory. If you are a mixing or mastering engineer this characteristic is highly appreciated and seldom found in any speaker design. The Quad shows even a miraculous feature, because it does not change its loudness proportional (logarithmic function) to the various listening distances – which I never detected with any other speaker system. What makes both constructions very special is the ability to get the complete midrange right. The Quad is in this regard a little bit more unforgiving, If there is any colouration in this frequency section present the electrostatic speakers will show you that in such a clear distinction, that you are amazed and sometimes shocked. Both speaker systems are able to render a soundstage you never will forget, the LS3/5a does that in a more bolt fashion, while the Quad has a more analytical gestalt with a tremendous pin point accuracy. The LS3/5a might be a little more spectacular if you do not listen carefully – maybe that is also achieved by the crazy discrepancy between the acoustic performance and the physical size of the little box.
To mate a LS3/5a with a sub woofer is not a good idea – I never heared till today any implementation of a separate woofer which lets the masterful voicing of the little gem intact. No sub can react in such a fast way as the little Bextrene B100 chassis can do – so you get heavy phase anomalies in the upper bass – which will destroy a good portion of what a LS3/5a is all about.