quad versterker, quad luidspreker, revisie, ombouw, reparatie
Armand van Ommeren
Kerkstraat 56
4854 CG Bavel
The Netherlands
0161-432451
armand@quadrevisie.nl
KvK Breda 20064173



Inleiding
Ik ken Geoffry Horn van de vele bezoeken aan buitenlandse persconferenties en fabrieken en heb vele uren met hem doorgebracht, discussiërend over klank, muziek en muziekopnamen – een bijzondere collega en een zeer aimabel mens met veel gevoel voor humor. Helaas overleed hij een paar jaar geleden. In het boek “The Closest Approach” beschreef hij zijn vriendschap en samenwerking met Peter Walker. Daar het boek niet meer is te krijgen, hier zijn verhaal.

Armand van Ommeren




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Herinneringen - Geoffry Horn







Aan het woord is Geoffry Horn
"To avoid confusion with a firm of similar name, the SP Fidelity Sound System has changed its title to The Acoustical Manufactering Company. Larger works have been obtained at 33 Sutton Road London NW 10 where all communications should now be addressed."

This notice appeared in Wireless World of 2 April 1937, page 329, informing the wider world of a new company which was to make a significant contribution to the future of reproduced sound. It was perhaps rather ambitious at the time, for this was then a one-man company. Peter James Walker had started it almost on an impulse only the year before.

Our paths crossed a few years later in October 1947 at the first post-war National Radio Exhibition at Olympia. These shows had been an annual event before the war, popularly known as Radiolympia. Then they had mainly been displays of shiny cabinets, but so many service men and women had acquired knowledge and interest in radio and related subjects during the 1939 – 1945 war that this 1947 event had been given a more technical slant. After many setbacks, Peter's company flourished during the war and he had taken a stand in a far comer of Olympia, where we first met. It was a significant meeting because we had so much in common that we became firm friends thereafter.

Both of us had chosen the science stream at school. Both of us had built numerous high quality amplifiers starting with the famous Wireless World design of 1934 and had a great interest in loudspeakers fostered by acquaintance with that great pioneer, Paul Voigt. Both of us sensing forthcoming hostilities, we had elected not to join our fathers' successful businesses – his a wholesale hardware supplier, mine possibly the first wireless-only shop in the country.

I had become a Post Office telephone engineer (visions of rows of switchboard girls are dated; we had over 5,000 valves in my bit!). Peter had joined GEC but rapidly moved to a company specialising in Public Address installations, TRIX. This field looked promising so he left and, with a small funding from his father, started on his own by building amplifiers. He has told of picking a design from current literature, adding a few ideas of his own and buying metalwork and parts three at a time – later extended to six and then ten. He would lay the chassis out in a row on his workshop floor and then pass along the row adding piece parts at each transit. Final pass would be to bolt down the bits before taking each one to the bench for wiring. Soon Miss Dingwall, his fiancée, joined the enterprise, controlling the purse with the job of purchasing a set of valves as each order came in. These orders hopefully arose from Peter's visits to various wireless dealers who he would persuade to diversify into the public address field. This enterprise was supported by his evening efforts in a dance band on saxophone and piano!

The early years were a struggle but the onset of war brought increased demand for all forms of public address and further designs were pursued. Bigger premises in Lever St, ECI were rented but fell victim to the Luftwaffe in 1941. Some suitable premises out of I.ondon in Huntingdon became available and production was resumed there. The firm was by then winding its own transformers, etc. and – as the proud possessor of a coil winder – secured a contract to make IF coils for ‘The Ministry’. Local employees were taken on as more work came in and variety was welcomed in the form of ‘specials’ for factory Music While You Work Installations and the like.

Peter’s interest in loudspeakers had led to the successful design of models for both indoor and outdoor public address usage. They used drivers from Goodmans, which formed another useful contact. The indoor model was a clever labyrinth affair which used a partitioned cabinet to form a folded pipe, the back of the unit coupled to it in such a way that the quarter- and half-wave resonances of the cabinet largely cancelled the pipe anti-resonances, resulting in a respectable bass down to 35 Hz. This model, the SL15, was taken up by one of the cinema chains, who needed additional loudspeakers outside the screen area which was covered by decorative curtains, while the long-legged ladies sold one ice creams and the like from their trays during the interval.

Substantial orders such as these helped Peter to push on with ideas for high quality domestic reproduction, rightly reasoning that the post-war public would welcome music in the home and that the technical side might also appeal, He had already adapted one of his smaller PA designs with an additional input stage and controls for domestic use (the QA12P) and had a prototype domestic labyrinth loudspeaker (the CL2, or Concert Labyrinth). These he was showing to selected visitors at the exhibition.

With future prospects looking favourable he had commissioned the construction of a small, purpose-built factory on an industrial estate in St Peter's Road, Huntingdon. (He always assured visitors that he wasn't the saint referred to.) This was now staffed and up and running and he was hoping to form an assessment of the future of music in the home at this show before laying out a lot of capital. As we were talking of this, Paul Voigt himself walked in.

I had not seen him for around three years (time wasted in the RAF) and he did not look well, informing us he was soon to undergo a major operation with a long recovery time and thereafter intended to go to Canada hoping to run his firm from there where supplies of wood for his loudspeakers would be freely available. One gathered that he had had a difficult time during the war but in discussion shared our belief that there would be a great future for what would inevitably become known as ‘hi-fi’. After he had left, Peter invited me to Huntingdon to see and listen to a couple of items he had in development if the domestic market took off; these turned out to be the first Quad Amplifier and Control Unit and the Corner Ribbon Loudspeaker.

Q.U.A.D. as an acronym first appeared in the publicity standing for Quality Unit Ampifier Domestic, but I remain unclear which came first! The full stops, however, soon disappeared and the word ‘Quad’ rapidly spread from the one amplifier to the firm and its products. The first Control Unit – or pre-amplifier – introduced the cast alloy panel and the flush secondary controls which are retained to this day. It could be mounted through a panel in any suitable item of furniture and could lend itself to the modem lifestyles then becoming popular. Primarily intended for the playing of records, then only in 78 rpm format, it pioneered a sophisticated filter system for distortion reduction as well as bass and treble tone controls to balance deficient loudspeakers and listening rooms.

The accompanying power amplifier was a refinement of later PA versions which used a unique output transformer with independent sections for the cathode and anode loads of the KT66 valves. The twin pentode input and phase shift stage, too, were a lot cleverer than it was obvious – original Quad thinking was already to the fore. The Corner Ribbon Loudspeaker was equally novel; bass and midrange were handled by a 12in twin cone Goodmans unit in a double reflex arrangement, partly inherited from the CL2.

This scheme was, to my knowledge, the first of a type subsequently favoured some 30 years later under the title of Coupled Cavity. The ribbon device derived from readily available hugely powerful alloy magnets produced for wartime centimetric radar. The aluminium corrugated ribbon strip, about ½ in wide, was originally formed by passing it between the teeth of an old fashioned mangle. Shaped pole pieces were glued to the magnet and a short horn formed to direct the radiation to approximately equal that of the midrange and a 45 degree reflector behind the ribbon sent some energy up to the ceiling enlarging the apparent source.

The complete loudspeaker set new standards to my ears, particularly the ribbon which added at least an octave of extremely clean reproduction to the best then available, I already owned what since the 1930s had been considered the best, a Voigt Domestic Corner Horn; however I made moves to sell it and ordered a ribbon for delivery from the first production due in 1949. As I expected, the vast differences in sensitivity forced an amplifier redesign and I went from a single 65N7 (just over 1 W) to the usual pair of KT66s.

Round about this time my promotion in the Post Office meant no more ‘hands-on’, but instead pen-pushing in an office; this did not appeal. Coincidentally, the spread of television – in which my father had little interest – offered a lucrative expansion of his business. Investigation showed that certain firms, Dynatron and Murphy for example, were in the quality vision grade, and the market for quality music was growing rapidly. So father took a back seat; he was happy to do this, and having used his PA gear to become one of the first disc jockeys, having run. from the early 1940s on. over 350 dances in local village halls for the troops – latterly Gls. Nevertheless, he came into the business most days until he died at 82, doing odd jobs but never interfering. So I forfeited my Civil Service pension and became a retailer – and a leading Quad agent!

Understandably, Quad had been requested to provide a radio tuner to go with their amplifier and had produced a matching switched device with three medium wave and one long wave positions indicated by illuminated ‘lozenges’ in the lower half of the matching diecast panel. Frankly, it was a disaster. One supplied to a customer living on top of the Chiltern Hills found he could never avoid hearing several stations at once. Peter most honestly admitted that neither he nor his staff knew much about radio and were not very interested; so with the forthcoming Quad II on the stocks, he threw out a challenge – design me a better one!

A litre bottle of midnight oil produced a rather nice simple ‘superhet’ with an unusual form of variable selectivity which could give it local station quality. Fine, but putting it in a form where it matched the new Quad II was far more difficult. Quad liked the performance of the bare chassis prototype but getting castings milled out for the ¼ in thick perspex dial and fitting it was a nightmare. However, an old Post Office colleague was now running a small company making bits for the local car industry and he was a great help, producing support pillars batch of tuners tapped into the panel and pulleys for the cord driving the pointer etc.

Eventually we had a fully working prototype. Having visited us a number of times Peter knew we had a small manufacturing area producing odd pieces of apparatus for the University laboratories. I don’t know how we got involved in this but it employed a clever young man and a girl who was a wizard at wiring. His next request was: could we make a batch of tuners?

We settled on an initial 25 but ‘squad’, as our chap called them, wanted dozens more. Egli in Switzerland wanted a version with dials for the long wave stations sent over their telephone wires; Smith in Canada did not want long waves but must have a 10 kHz whistle filter. Eventually we settled for assembling, wiring and testing the chassis while Quad themselves took over the mechanical assembly, having found a local company to make the bits. I have no idea how many we made but two more girls arrived and every couple of weeks I would head for Huntingdon with a van load.

In 1951 a young chap named John Walker (no relation) joined Quad as an engineer but soon transferred to management and effectively ran the firm, freeing Peter to work in his laboratory in the front offices, which is where I usually joined him on my visits. He always had a lab assistant and the first I recall was a young chap named Derek who subsequently left to join Pye Ltd. Where he developed the Mozart amplifiers. If you are a circuit person you will realise that it is half a Quad II.

One of Peter’s useful acquaintances was David (DNT) Williamson of amplifier fame, whose circuit and description in 1947 Wireless World was copied by the thousand. He was at the Marconi/Osram valve labs at the time and one suspects that Graham Woodville, then lab boss, provided a lot of input as he did for many other famous designs in those early days. Williamson was contacted by an American importer who offered to finance a batch of amplifiers plus a generous fee for an accompanying Certificate of Authenticity signed by Williamson himself. He had no manufacturing facilities and asked Quad to make them and poor Derek was struggling with the final design or these monsters. I know not how many they made but I know Peter looked down on this design as hopelessly ‘over the top’.

Around this time the BBC began to have serious thoughts about VHF broadcasting. They had a 7m transmitter in Broadcasting House from the 1930s, so knew quite a bit about propagation at those frequencies even before the pre-war television service from Alexandra Palace. What was in doubt was whether or not the system should use Frequency Modulation which the Americans had adopted. Accordingly, they set up a small transmitter operating in the 90 MHz band using alternatly AM and FM.

My business partner, Philip Tandy, had held an Amateur Transmitting Licence (G2DU) since his school days and was able to wind coils for almost any job straight off the cuff. We had no idea whether the weak test transmissions could reach us in Oxford but Philip set himself the task of finding out by modifying the receiver of an American airborne VHF set (SCR 522). Wireless World had run a series of articles about FM design during the war and this proved very useful. A cut-down TV aerial soon produced a signal, although a weak one, but the FM tests were listenable whereas the AM had serious background noise and car ignition crackles.

Peter heard all this on one of his visits and asked if we would work on a preliminary and very tentative design for a Quad FM tuner, perhaps making a few prototypes switchable between AM and FM. The BBC were now running separate AM and FM transmitters in tandem so it had to be tunable and nothing like it existed, However, we eventually produced a very much more sensitive design on a Quad control-unit-sized aluminium chassis with a small shaft protruding to tune it. The signal at Huntingdon was much weaker but it was usable on FM. A BBC visitor to Quad heard it and Peter took an order for three without asking us – we were not too pleased! In the end, we made six but it was never intended to be a production job. That came later.

I had made, from a Wireless World design, a rather nice wide-range audio oscillator. One day, I had a call from Peter asking if he could borrow it. As he had B&K test gear I was quick to ask why and it transpired that Goodmans were about to make a range of vibration testers. (These are like moving coil loudspeakers with a small platform instead of a cone.) They had called on Quad to make a suitable Very Low Frequency Power Oscillator to drive them. This ended up as a joint-venture design, including styling the enclosures, with an output of about 30 W down to 5 Hz. (The output transformer was vast.) Goodmans later extended their range to a 1 kW version which was a bit beyond Quad but they still used the Quad oscillator to drive it.

There was another major project to now occupy Peter’s time; the electronic organ later named The Gregorian. For some years a small keyboard and rack of oscillators had stood in a passage and Peter would run a scale in passing, saying he was checking them for drift for a friend. The friend turned out to be The Davies Organ Company, this resulted in a lot of fun during my visits!

During one of these I found the lab to be even more untidy than usual; there were several Quad II power amps glowing happily fed from one of the FM tuners and a funny looking contraption on the bench. This appeared to be perforated zinc pieces culled from an old meat safe making a package about 6in square and held together by a selection of elastic bands. In response to my query as to what it might be Peter replied, ‘Put it to your ear but be careful – there are 400 volts on it.. It was, of course, the first tentative experiment in electrostatic loudspeaker research.

This project was to dominate his life for about three years, researching materials, investigating electrical breakdown, studying the effects of temperature and humidity and trying to mate air displacement and domestic acceptability. Many experimental versions were made; the most impressive I ever heard was when he built another wall some distance from the existing, filled the space with fibreglass wedges and set electrostatic panels in the centre. Completely impractical, of course, but one of many experiments to deal with the rear radiation from the diaphragm; others were a fibre- glass tube with panels let into one side.

A breakthrough was the realisation that a dipole design could be both practical and domestically acceptable. The study became so intense that I for one feared for his health. I hesitated to visit, disrupting progress, but both his staff and his wife insisted because we always found much to laugh about and to quote Peggy; his wife, ‘You’ll stop him going up the wall.’

One memory is of us both rubbing black Cherry Blossom boot polish into plastic sheet to make experimental conducting diaphragm material. Williamson, who was now with Ferranti in Scotland, provided a base for computerised calculation work and many Quad staff were involved, producing tools for stamping out holes in the fixed plates, etc. What is remarkable is that none of this radical effort leaked out into the industry or the public domain. Everybody in the know kept quiet until it was decided to show an electrostatic panel working with a light behind it at the 1956 Audio Show in London.

That caused quite a stir. A corner version of twin bass panels with a curved centre panel for the remainder nearly reached production but cost was against it and an alternative free standing arrangement of three panels (which we now call the ‘57’) was the eventual choice. I believe the styling was due to Christopher Heal. Serial Number One was to be raffled at the 1957 Show and we bought a batch of tickets; one of them, down to the previously mentioned Philip Tandy, was the winner and as he was very musical it gave him great joy. Unfortunately he died some years ago and Quad ESL 57 Number One is now in my care. By now Derek had been replaced by John Collinson who, as an ex-naval radar man, did know a lot about radio. His first job was to design a new and much more advanced AM tuner, requested by overseas agents who required short wave coverage, better sensitivity and more bells and whistles. Although comparatively expensive, this tuner was an excellent performer, as good as anything on the domestic market. UK acceptance was limited by the BBC announcing its decision to commence FM broadcasting and construct a high power transmitter at Wrotham in Kent.

We had already done some preliminary work on a possible FM tuner design but it now became urgent. The outstanding problem was that of tuning drift due to heat in the rather cramped space of the Quad format. Low consumption valves helped but the answer eventually arrived at was to use physically long coils wound with copper tape, each with an iron dust core which could be slid in and out by a micrometer screw arrangement. Much experimentation was needed to make this work but, with the mechanical assistance of my ex-Post Office colleague, It was achieved.

Of course, such a precision mechanism is not cheap but it was found possible to produce it on automatic machinery if the quantity was great enough to warrant setting it up. Fortunately, this tuner ran for many years and was used professionally quite extensively by a number of broadcasting authorities. Quad were happy to accept our very early prototype which was tidied up most expertly by John Collinson, who added the neat centre-of-tuning device which had appeared in an American magazine. He later produced a bolt-on stereodecoder for it using transistors which were by then available.

The FM tuner was the last Quad product I was involved with but, early on, we had agreed to provide service on their public address range and these continued to arrive for many years. They were usually no problem to my chaps - blown capacitors, resistors gone high, that sort of thing. What was amusing was some of the modifications some dealers had carried out, including one old MB 32 painted bright orange! Quad were moving into the transistor age; John Collinson produced the Quad 50 indus- trial amplifier in the course of which he robbed Peter of one of his overfull ash trays and filled it with blown output transistors! Their first solid state domestic amplifier, the 303, used a clever circuit developed by the late Peter Baxandall, another great friend to both of us and one of the cleverest circuit men I have ever met. John Collinson left to run Wharfedale (where he developed the Isodynamic headphone) and Mike Albinson joined the firm. There followed the technically brilliant model 405 ‘current dumping’ design which won the Queens Award for Technological Achievement in 1975. We argued at length but I always preferred the sound of the older 303.

Meanwhile, Peter was deeply into the development of the next electrostatic, the ESL-63. This became another landmark and in modified form is still current. But Peter’s last design never reached production. It took the form of a globe about 18 or 20 in size with a flat at the front where an electrostatic ‘target’ appeared. Other electrostatic diaphragms were lined up behind it and actively driven by an internal amplifier. It was a tour de force and sounded indistinguishable from the ESL-63. However, tooling costs would have been forbidding; and the product was shelved. At which point, Peter finally retired.

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