This chapter of our Wurlitzer story will answer one of
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
"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
the last section describing computer-based relays and the Uniflex
3000 relay I chose to manage our Wurlitzer here in Great Falls.
The earliest pipe organs used a direct mechanical linkage to connect
the motion of a key directly to a valve located under the toe of the
associated pipe. When a key is depressed, wind is admitted to the pipe
by opening the connected valve, causing the pipe to sound. Some
organists appreciate the keyboard feel of a tracker instrument because
tactile feedback experienced when keys are pressed hard enough to
overcome the wind pressure holding the valves closed.
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
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.
Many early relays used all pneumatic actions to open the pipe valves.
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. The
disadvantage is the time lag introduced by the long tubes before the
pipe valves respond to key changes. This type of action was often
used for larger scale louder pipes using higher wind
As 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.
Electro-Pneumatic Actions (E-P)
Electro-Pneumatic refers to
the combination of an
electrically controlled pilot valve to control a powerful
pneumatic bellows which then forces open a hinged
pallet valve that admits 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 a pilot valve under the associated pipe.
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.
swell shades to enclosed pipe chambers enables the organist to
impart dynamic expression to his music. Swell shades are the
acoustic equivalant of venetian blinds.
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
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 an organ seem
bigger than it really is by offering an enormous diversity of sound
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,
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
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
instruments have more pipes, more stop tabs, more couplers, more
keyboards, and for theater organs, lots of unification. This means many
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
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
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.
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
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
switch", 61 being the number of pipes in that rank. Some extended
ranks have 73, 85, or even 97 pipes to accommodate unification and
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
showing what an original installation Wurlitzer relay room looks like.
The original relay room for our Wurlitzer would have looked much the
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
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.
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 imposed by the most recent 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.
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.
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.
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 cannot be achieved by changing the
pipes' wind pressure since doing so alters their pitches. But
dynamic expression can
be accomplished by placing
into a pipe chamber with swell shades, 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
currently offer commercially successful electronic organ relays.
For our Wurlitzer here in Great Falls, I chose one made by
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.
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
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
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
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
control pilot lights. Boards located in the pipe chambers drive pipe
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.
The organ user interacts with the computer by viewing Uniflex's Run
Mode display. A touch screen capability is available to avoid the need
for a mouse.
clicking on the various buttons on the display, the user controls the
relay operation, e.g., start and stop the organ software, view an index
listing the organists who have stored personal stop combinations and
any recorded performance tracks.
The organ definition editor can be invoked to make and file changes to
the organ's Specification. A recording can be started and finished,
tracks can be named or renamed, and playlists can be created, played,
aborted. The tempo of playback can be adjusted, and to simulate the
time delay of hearing a distant pipe chamber in a large theater
environment, a variable time delay can be introduced between the
organist's playing, and hearing the resulting sound. Now dealing with
that 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
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!