Hardman Studio Wurlitzer Masthead

The Evolution of Pipe Organ Relays

This chapter of our Wurlitzer story will answer one of the more frequently asked questions heard from guests attending our theater organ concerts: "What is the computer for?" It seems incongruous to have a beautifully restored 90 year old musical instrument being controlled by a modern digital computer.  Here is some background information to help answer the question, and to explain why I chose a computer-based relay to run our Wurlitzer.

First of all, removing, packing, transporting, restoring and installing a 1920's "state of the art" organ control system is an expensive and time consuming labor of love. While I respect those who would choose to preserve Wurlitzer's original electro-pneumatic relay for authenticity, I wanted to take advantage of today's "state of the art" relay hardware, with its inherent reliability, superior functionality, and extraordinary flexibility.

So what follows is a non-technical explanation intended for the casual reader describing what an organ relay is, what it does, why it is necessary, and even a little about how it works. You can start reading with a brief historical perspective of organ control systems, or jump directly to the last section describing computer-based relays and the Uniflex 3000 relay I chose to manage our Wurlitzer here in Great Falls.

Tracker Action Organs
Tracker Action

The earliest pipe organs used a direct mechanical linkage to connect the motion of a key to a valve located under the base of the associated pipe. When a key is depressed, this linkage pulls the connected valve open, allowing wind to enter the toe of the pipe causing it to sound.

Some organists appreciate the keyboard feel of a tracker instrument because of the tactile feedback experienced when keys are pressed hard enough to overcome the wind pressure holding the valves closed.
Pipe Organ All Mechanical Tracker Action Pipe Organ Mechanical Tracker Action
To build a grander ensemble, an organist will add sounds from other sets (ranks) of pipes. This adds to the complexity of a tracker mechanism, and it also requires more finger pressure from additional pipe valves forced open against wind pressure. As larger instruments were built, growing mechanical issues tended to limit the number of ranks that could be comfortably played. The problem only gets worse when pipes from other keyboards are selectively coupled mechanically to the keyboard being played by the organist, requiring even greater finger pressure on the keys, making it all but impossible to build large instruments. Additionally, a tracker console is a permanent integral part of the organ case because the mechanical linkages between keys and pipe valves prevent their separation.

Incorporating a Relay
To overcome these limitations, relays that remotely control the opening of the pipe valves using pneumatic, direct electric, or electro-pneumatic actions have for the most part replaced mechanical tracker actions, especially in larger instruments. The relay enables the organist to play more pipes simultaneously without exceeding comfortable key pressures. Keyboards can be connected to these relays by pneumatic tubing and/or electric wiring. Additionally, the keyboard console does not have to be an integral part of the organ case, and can be located at a distance from the pipes. Console mobility can be achieved by connecting the console and pipes electrically.

Tubular Pneumatic Actions
Many early relays used all pneumatic actions to open the pipe valves. Small air valves were operated by each key on the console keyboard that allow air pressure to enter tubing that went to pneumatic bellows that opened a valve for each associated pipe. The advantage of this type of action is that it allows separation of the console and the remote pipes.  One disadvantage is the time lag introduced by the long tubes before the pipe valves respond to key changes. Another is the greater time and expense to install many fragile metal tubes between console and windchests. The bulky tubing is quite soft and easily kinked or squashed if not handled very carefully. This type of action was often used for larger scale louder pipes using higher wind pressures.
Tubular Pneumatic Pipe Organ Valve Action 

Direct Electric Actions
Wicks Direct Electric Organ Pipe ValveAs the knowledge and practical application of electricity evolved, a new kind of organ control evolved using electrically operated valves instead of direct mechanical linkages to their respective pipes. Direct Electric Actions are inherently simple, very reliable and have achieved modest success in low wind pressure instruments; however they have not found much acceptance as replacements in high pressure theater organs.

Wurlitzer Pneumatic Pilot Valve ActionElectro-Pneumatic Actions  (E-P)  
The name Electro-Pneumatic refers to the combination of an electrically controlled pilot valve to control a powerful pneumatic bellows which forces a hinged pallet valve open admiting wind to the toe of a pipe.

In addition to an electric pilot valve, Wurlitzer usually used a primary pneumatic to operate a much larger secondary pneumatic in order to develop sufficient force needed to open the pallet valve against high wind pressure. Wurlitzer's E-P valve trains are amazingly fast, and work very well for high pressure instruments like theater organs. When a key on the keyboard is depressed, a small switch positioned under the key is closed sending an electric current through a wire connected to an electric pilot valve under the associated pipe.

Unlike the elaborate mechanical linkages in a tracker action, electric wiring connects keys to pilot valves. Being flexible and easy to work with, wire is easily routed to distant valves, making installation much simpler and faster, and allowing the console to be physically separated from the pipes which can now be located in remote pipe chambers.

Perhaps the most significant distinguishing difference between a theater organ and a classical organ is that all theater organs make extensive use of unification.  Unification refers to an organ design concept by which any particular set of pipes can be played from any manual or pedal keyboard, and at any desired pitch relationship to the keys being played. Any number of stop tabs from any keyboard can play the same set of pipes simultaneously.

Unification offers the creative organist freedom to produce a vastly greater variety of sound combinations from an organ of given size than would be possible without unification. Unification lets a theater organ seem larger than it really is by offering the organist such an enormous diversity of sound timbres from a limited number of pipe voices (ranks).

Unification even allows the organist to incorporate different pitches within the same or different sets of pipes for inclusion in the combination he is playing. For example, a simple combination might include a Flute at both 8' and 4' pitches within the same rank. Depressing any one single key on the keyboard would cause these two flute pipes to play, one at 8' unison pitch, and one at 4', an octave higher. Adding a 16' Post Horn would cause a third pipe to sound, an octave below the note played on the keyboard. The notes in this example are all in octave relationships with one another. However, other pitch offsets can be used very effectively to add tone color to the music. For example, 5-1/3',  2-2/3',  1-3/5' are all found on our Wurlitzer. Pitch offsets and stop tab locations are defined in the organ's Specification.

All Wurlitzer theater organs make extensive use of unification. Unification requires that one electrically operated valve train be dedicated to each pipe in the instrument, allowing independent control of each and every pipe. The cost to add unification is far less than it would be to find space for, buy, install, and wind many more ranks of pipes.

Why a "Relay" Control System is Needed
Relays are needed to multiply the number of electrical circuits that can be independently energized, without causing unintentional back-feeding to other circuits. They also solved key switch contact burning due to arcing from excessive electric current, and the need for regular maintenance to keep these key contacts clean and reliable.

Larger instruments have more pipes, more stop tabs, more couplers, more keyboards, and for theater organs, lots of unification. This means many more circuits, all needing to be switched simultaneously, but independently from one another. With their mechanical limitations, tracker actions can't begin to keep up. Electro-Pneumatic relays don't suffer those limitations, but they have their own; the hardware that makes up an E-P relay takes up a lot of space. Although E-P relays can be expanded to accommodate additional sets of pipes, more unification, or even a new larger console, such future expansion comes at quite a cost in hardware, labor, space, and time.

Wurlitzer's E-P relay control systems are assembled from lots and lots of small mechanical relays. Unfortunately it takes a whole room full of relay cabinets and their related switch stacks to do the job for a larger instrument. But on the other hand, this reliable technology did work very well!

The close-up below is the left third of a standard Wurlitzer Note Relay Cabinet as pictured on the right. There is such a relay cabinet for each manual and pedal keyboard. Each row has a glass front dust cover for diagnostic viewing that also air-seals the interior of the cabinet which is under positive wind pressure. Wing nuts were used instead of screws to provide quick and easy access for switch contact cleaning and adjustment.
Wurlitzer Pipe Organ Relay Cabinet Section  Wurlitzer Note Relay Cabinet with Switch Stack Above
Pictured below is a close-up of two individual note relays of the type used in a Wurlitzer note relay cabinet. When a key or pedal on the console is pressed, the relay for the corresponding note is activated when voltage from the switch under the depressed key energizes the coil in a pilot valve located under the associated "pneumatic" (leather bellows). This causes the inside of the pneumatic to be exhausted to atmosphere by the wind pressure inside the relay cabinet.

Wurlitzer Pneumaticr Note Relay Close-up The shorting bar attached to the collapsing relay armature is pulled down touching all those contact wires on the associated switch blocks. This delivers voltage to the individual note playing circuits as represented by the many switch contact wires, one little wire switch contact for each rank of pipes accessible from that relay cabinet's keyboard.

Pictured below are two views of a Wurlitzer switch stack. Each of the clustered horizontal wood blocks switches a single rank of pipes on and off, one for each stop tab using that pipe rank. The switch blocks are generally 61 notes wide, one for each manual key or 32 for the pedal clavier. When a stop tab is turned on, its related switch block is made to rotate about 30 degrees around its horizontal axis causing all its contacts to touch the corresponding vertical fixed contact strips, connecting keys to their corresponding pipe valves. The pneumatically operated control rods to rotate the switch blocks are on the back side, out of sight. In today's parlance, each switch block is a "61 pole single throw switch", 61 being the number of pipes in that rank. Some extended ranks have 73, 85, or even 97 pipes to accommodate unification and couplers.
Wurlitzer Pipe Organ Switch Stack  Closeup of 4 Wurlitzer Pipe Organ Rank Switches
It is surprising how much physical space is required to house all the relay cabinets needed to service two, three, or four manual keyboards of 61 notes each, one or two additional keyboard switch rails to enable second touch, a pedal clavier, many pistons and their combination action, pizzicato relay, couplers, and lots of stop tabs to take full advantage of unification. These relays can be seen in action in this short video showing what an original installation Wurlitzer relay room looks like while the organ is being played. The original relay room for our Wurlitzer would have looked much the same.

Wurlitzer's E-P relays were carefully designed and manufactured, and in spite of their apparent complexity, they proved to be remarkably reliable; but moving a relay or making changes to an organ's Specification are very difficult, costly and time consuming to accomplish. The job is made more difficult because the original copper wire's cotton insulation tends to break apart when disturbed, and won't meet today's fire codes either. It's a monumental task to replace all that wire.

Computer-Based Relays
The advent of solid state digital electronics, and particularly the microprocessor, offered new opportunities for flexible, highly efficient and very compact organ relay designs with essentially unlimited capacity to manage any organ in existence or even imagined. Since the switching requirements are accomplished in software, the size of the relay changes from a room full of hardware to a small computer and a few printed circuit boards the size of your two hands.

A computer-based control system repeatedly scans each key on each keyboard to determine which notes are being played, and scans each stop tab and piston to determine which pipe voices are to be played, and at what pitches. Scanning happens so frequently that the result can be thought of as providing an instantaneous look at the entire console all at once. Each of the 846 console switches on our Wurlitzer is sampled at least 100 times per second to determine if the switch is open or closed - on or off. The control system scans again to determine if any key, pedal, stop tab, piston, or coupler has been activated or deactivated since the previous scan just 10 milliseconds earlier.

Syndyne Stop Action Magnet - SAM
Finally, to put it all together, the computer applies software programmed logic to figure out which pipes need to be played to satisfy all of the requirements and conditions imposed by the most recent console scan. It then sends signals to turn on, or turn off, the affected pipe valves and other electrically controlled devices. For example, stop tabs are flipped up or down as required when the computer briefly energizes their ON or OFF coils to comply with the demands of the combination action. A Syndyne brand Stop Action Magnet is shown here. The stop tab is mounted to the moving arm at the left.

Common Digital Relay Functions
Functions common to most computer-based organ Relays include support for a combination action, performance record and playback, expression control, pizzicato, piston sequencer, keyboard sostenuto, transposition, crescendo sequence, support for multiple consoles, MIDI devices, multiple memory levels for each organist, continuous self-testing, and diagnostic routines.

Combination Action
While in performance, it is difficult and time consuming for an organist to change many stops all at once to effect a big change in the sound being produced by the instrument. A combination action stores many pre-programmed combinations of stop tabs which are assigned to a particular piston (momentary push button switch) typically located under each manual keyboard. A unique combination of stop tabs is saved by pressing a target piston while holding the "Combination Set" button. The organist can now recall that sound combination at will by pressing the assigned piston.

Performance Record and Playback
There are many reasons to record a piece of music. An organist can more objectively evaluate his performance by listening to his recording, or he might learn by listening to another organist's recorded performance. To make an audio CD, for example, the organist can record a few takes to the computer, and keep the best one. When it's time to bring in the microphones for the acoustical recording, the computer plays back the selected digital recordings, which replay the organ pipes in what is truly a perfect recreation of the original hand-played performance.

Dynamic Expression
In a pipe organ, dynamic expression cannot be achieved by changing the pipes' wind pressure since doing so alters their musical pitches. But dynamic expression can be accomplished by placing the organ into a closed pipe chamber with a window-like opening covered with swell shades which are the acoustical equivalent of venetian blinds. From the remote console the organist can vary the degree of swell shade opening to add dynamic expression to his music. In our Wurlitzer, the computer can specify which swell shade blades are to be used as well as their specific location, and sequence of opening. For example, when we are alone, Mildred and I enjoy listening to music recorded previously during concert performances here; but it can get pretty loud without a sound absorbing audience present, so we can reset the swell shades to limit sound levels for more comfortable listening.

Setting Up a Computer Relay
Several manufacturers currently offer commercially successful electronic organ relays. For our Wurlitzer here in Great Falls, I chose one made by Uniflex Relay Systems. The Uniflex 3000 software loads onto any PC and uses proprietary interactive editing software to initially establish and then maintain all the necessary parameters to define or model the target instrument in software. Initial programming takes some time, but after that, changes to the organ Specification can be made very easily and quickly at a video terminal, once the programming concepts are learned and understood. Here are a few snippets of some of the basic definitions created for our Wurlitzer. This is the first step in building the computer Definition File for the instrument.

Uniflex Editor

The Uniflex software performs all the basic functions needed to run the organ and play the pipes according to the constantly changing needs of the organist. It provides an advanced multi-track Uniflex Microprocessor Controlled Interface Board record/play capability, and a complete capture action combination function. Any number of organists can customize their own unique individual organ definitions and piston settings, and save them for future use.

One microprocessor controlled interface card is mounted in the console and one is between our two pipe chambers. They communicate with the computer via a single Cat-5 Ethernet cable with standard RJ-45 modular connectors. A wireless network can also be used to avoid having to install wire in difficult locations.

The two microprocessor-controlled interfaces communicate with input boards and output boards, which both look about the same. Input Boards are  located in the console and scan all the console switches like keys, stop tabs, and pistons. Output Boards are mounted in the console to drive stop tab electro-magnets which change the position of stop tabs and the Uniflex I-O BoardUniflex control pilot lights. Boards located in the pipe chambers drive pipe valves, and electrically controlled devices such as power supplies, and the blower. Cards handle 128 inputs or 128 outputs. With common grounding of system hardware, only a single wire connects each console switch to an Input Card pin, and each electrically driven device has a wire connecting it to an Output Card pin.

Uniflex Relay User Control Panel The organ user interacts with Uniflex using the Run Mode Display. A touch screen capability is available to avoid the need for a mouse. By clicking on the various buttons on the display, the user controls the relay operation, e.g., start and stop the organ playing, view an index listing the organists who have stored personal stop combinations and their recorded performance tracks. A recording can be started and finished, tracks can be named or renamed, and playlists can be created, played, and aborted during playback. For practice purposes, a variable time delay can be intentionally introduced to simulate the time it takes to hear sound coming from distant pipe chambers in a large theater. Now dealing with significant time delay takes a little practice!

So there are the basics of organ control relays, and some reasons why I chose a computer relay for our Wurlitzer. For those wanting to take a deeper look, a more comprehensive technical survey of organ control technology can be found at the website of our friends in the Cinema Organ Society in the UK.

Your suggestions, comments, and questions are always welcome, and so are your visits to Great Falls to listen and play the Wurlitzer!
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