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Leach & Overington
The Leach & Overington 89-Key Concert Organ
An 89-key mechanical organ designed, built and owned
by Dr. Andrew Leach and Mr. Tony Overington.
by Andrew Leach (030225 MMDigest)

leach_L&O_1.jpg (33 kb)

What started out as a fairly casual idea back in 1980 soon began to grow into a huge project.  It was some months later, after the introduction to the idea, that we were enjoying one too many pints of Sussex ale in a local hostelry and were discussing the idea further.  One of us said, "We won't just build a toy organ -- we'll build a proper one."

"Right," said the other, "proper it will be!"

And so began in earnest the plans for this mighty instrument.  Well, it seemed possible with our combined experiences of joinery and organ restoration.

We decided we would not be copying another maker's organ but, rather, it would be to our own ideas and design.  It had to be, first and foremost, musical and able to play a wide range of music -- not just a fair organ or a street organ or a dance organ, but a concert organ.

Many traditional ideas of mechanical organ building have been used in its construction, but also a lot of original ideas are used, often using more durable and efficient materials than would have been used 80 years ago.

The musical scale or arrangement of notes, upon which it is based required some considerable thought initially, but it was eventually decided that, of all the mechanical organs ever built, Mortier of Antwerp had probably developed the most musically successful scale, And so we based the organ on the 92-key Mortier scale which is fully chromatic in all four musical departments.  This also meant that we could obtain music fairly readily for it, with only minor alterations needed to the scale layout.

It was at about this stage that we met the late Peter Watts of Chipping Norton, who owned a 91-key Mortier organ, and the late Steve Clarke who worked for him arranging music.  A friendship grew up and over the years these two gentlemen gave us much help in designing the organ.  It was Steve Clarke who taught us much to do with specification and pipe scaling.  He arranged most of the music so far for the organ.

We spent the first two years experimenting with ideas and mechanisms in the workshop trying to get the right methods of doing things and also the right sounds from several test pipes.  It was often quite disheartening and sometimes we would just give up for a while to return a week later and crack it almost immediately! But gradually we learned (the hard way usually) and so various components started to pile up.

One of the most difficult tasks was to successfully make and voice violin pipes.  We had already decided that there were to be a substantial number of ranks of violins in order to create a rich sound on the melody section, but it was an almost impossible task for some considerable time to get this enormous section of pipe work correct.  It all suddenly fell into place one day and thereafter we were kept very busy voicing and finishing several hundred violin pipes for quite a few weeks.  From then on we were kept very busy building more and more pipes and wind chests.

Both our houses, workshops and garages were filling up with piles of components and both our wives were beginning to wonder when it would all end!  After many interruptions for more pressing things in life, a few years later the time had come to partially and temporarily put the various components together to see if it worked.

At this stage we had to build the main wind chest.  This is a considerably sized lump that sits in the middle of the instrument and weighs probably 300 kg or more.  It is 8 feet long, 3 feet wide and 1 foot deep.  It is in effect a giant relay and distribution box and is crucial for the correct functioning of the entire organ.  On an organ of this size we decided to be generous in its design with large main pallets and plenty of windway space.  Eventually enough space was found in one of the workshops to build a temporary frame and erect some of the chests and pipes.

It was to be at least a couple of years more before we had any music from it though, for the project had grown in size considerably from the first ideas and we had to purchase two specially made centrifugal blowers to power it.  One of these is a 3 hp motor providing wind at 10" water glass pressure at 450 cubic feet per minute, and the second takes 100 cubic feet of this to boost the wind to 20" water glass (wg) pressure with a 1 hp motor.

This latter blower is used to power the harmonic tubas.  These pipes were rescued in 1968 from the demolished Odeon cinema at Chadwell Heath in London and had been stored all these years for just such a project!  They were made by Compton.  Finally we had some music from the beast.  From then on we had many more pipes to make including some extraordinarily difficult carillon flutes; the smallest of these has a speaking length of just 3/4".

We also acquired an octave of 16-foot stopped Bourdon made by Wurlitzer; these came originally from the Empress ballroom in Blackpool.  They are heavily constructed with thick arched lips and are finely made.  To help balance these we had to build a rank of 8-foot open pipes of very large scale.  The low A of this rank has a scale of 5-3/16", a cut-up of 2-7/8" and is made of 3/4" thick timber.

These and their chests and also the 8-foot stopped pipes and chests are all made from tulip wood.  The pile of timber just for this section half filled one of the workshops.

The counter melody cello grave is of unusually large scale too, with the low C of this rank being about 87" long, and having a scale of 3-5/16", a cut up of 1-1/8" and is made of 7/16" thick timber.

leach_L&O_2.jpg (27 kb)
The weight of organ and vehicle combined is 8-1/2 tons (3860 kg].

The time came to look for a suitable vehicle into which we could build the organ, a task which seemed daunting at first.  We did consider building it onto a separate trailer but the practicalities of maneuvering such a vehicle ruled this out, and so it was fortunate that very soon a large Bedford TK with a Luton style body was advertised locally.  It was ideal and soon purchased.

The lorry had seen better days and so the decision was made to completely overhaul the entire vehicle, which included removing the old box body, stripping down the whole vehicle to the chassis and rebuilding the mechanics and cab and having a new purpose-built body fitted back onto the chassis.  A 9 kVA generator is fitted underneath, big enough to power the organ.  This all in one vehicle, which means it is relatively easy to move around.  Even so, the organ fills almost the entire lorry.  The weight of organ and vehicle combined is 8-1/2 tons (3860 kg].

When finished the main frame and case of the organ was constructed, a substantial construction which is bolted to the main chassis.  From then on all the many parts were fitted in, and something like three miles of various sized tubes were run in.  At last we were able to hear the organ as it would eventually sound.

The decorative front of the organ is based on architectural lines of the Georgian period.  The purists, however, will point out that the lower dental mouldings (which were in fact the moulded ends of the ceiling joists) are missing, this for a very good reason.

When the full size drawing for the top were completed it became very obvious that the fluted columns and mouldings and lower wainscotings had to be in the same proportions.  This would have denied access to the front of the organ when the front was closed and added considerable more weight to the vehicle.

It was therefore decided to leave out the lower dental mouldings and scale the lower front down, thus allowing access.  One point of interest: the top moulding is machined from solid 11-inch by 2-inch thick timber.  It took 45 minutes to set up the machine, and 6-1/2 minutes to machine the final job.  The guilding on the organ front is 22-carat gold leaf.

All the pipes stand on their own off-wind chests, 42 chests in total.  Violin Piano is on 2 chests, and Violin Forte is on 3 chests.  This was done to facilitate tuning but also it means that each rank receives its optimum wind supply.

The melody Harmonic Tuba is augmented with a rank of Open Flues an octave lower and a rank of Violins an octave lower in order to obtain the correct harmonic balance from this register.  (The reeds on their own were found to be extremely harsh).  The counter melody Harmonic Tuba is likewise augmented with a bridged Open Flue and a Stopped Flue.

Both the counter melody and bass Tuba chests are operated on an exhaust pneumatic system, because these pipes play on the higher 20" wg pressure and this overcomes the pressure differential problem between 10" wg action pressure and 20" wg pipe pressure.  The melody Harmonic Tuba, although also on 20" wg pressure, has smaller pallets and hence a conventional push rod system is used.

The 16-foot stopped Bourdon and 8-foot Open Principal are also operated on an exhaust pneumatic system due to the very large pallets in these chests.  The percussion has its own secondary relay system to allow the motors to work as fast as possible.  There are two single rise reservoirs, one supplying 10" wg pressure to the main organ and one supplying 20" wg pressure to the Tubas.  The register box is an air lock type on 20" wg.

The longest pneumatic signal from key frame to main chest and back to the pouch on the off chest is nearly 40 feet and there is no discernible delay in the speech of this pipe, the lowest A on the 16-foot Bourdon.

Various types of timber are used, a lot of the pipes being made from Siberian archangel pine, with the fronts from Douglas fir.  Some pipes have been made from reclaimed old church organ pipe timber, over 100 years old, which is extremely dry and ideal for this purpose.  The large 8-foot open Principal, the 8-foot stopped Bourdon, and their chests and the counter melody and bass Tuba chests, are all made from tulip wood.

Many of the soundboards and off-wind chests are made from sycamore and some from beech.  Only the best quality leathers have been used throughout the organ, with no 'seconds' used.  All valve push rods are made from stainless steel running in Delron bushes and will probably last forever.

The key frame has 89 keys, 88 of which are used to control all functions, with one spare key.  All the electrical controls are positioned above the key frame for ease of use.  All the pipe work in the centre case is operated from ventils incorporated in the main wind chest and the side case chests are operated from individual ventils by their respective chests.

The four big Tuba chests are operated by large exhaust pneumatic ventils which supply wind extremely quickly to these high pressure pipes.  Relays are used to operate the primary valves to these ventils.  It is only by adhering to these principles of separate off-wind chests, pneumatic relays and carefully calculated pallet sizes, that the organ plays so promptly and accurately.

It is thought to be the largest mechanical organ ever built in the UK entirely from scratch.  The cost to build it new today would, in my opinion, be in excess of 300,000 UK pounds.  It is a project that has stretched our imagination, our energy, our determination, our finances and our patience to the limit, and without the patience of our wives it would never have succeeded.  We think we have however succeeded in proving that such a thing can be done by amateurs.

A new professionally recorded CD of the Leach & Overington 89-key Concert Organ, Volume 2, is now available, featuring music arranged mainly by Jan Kees de Ruijter and Tom Meijer.  Titles on the CD include:  Buglers Holiday; Scott Joplin selection; New York, New York; Stomping at the Savoy; Crazy Party Mix; No Matter What; Pink Panther; Rhapsody in Blue; Mortier Boogie; Memories from Cats; The Caliph of Baghdad; Toselli Serenade; Second Waltz; West Side Story.

The new CD is available from me at

  Leach & Overington,
  4 Daniels Cottages, Newpound, Wisborough Green,
  West Sussex RH14 0AX  England.

Price is 10.00 UKP plus 1.50 p&p (UK mainland).  Overseas postage will be more and will have to be determined at time of request, depending on country.  Cheques made payable to Leach & Overington in UK pounds Sterling, please.

Andrew Leach
23 Feb 2003 21:02:56 -0000

Organ Specification
Organ Scale

25 February 2003

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