Pipe Organ Logic - Key Switching System

The ‘Tracker’ Pipe Organ.

A ‘Tracker’ organ typically uses lengths of wood strips called ‘Trackers’, along with various other devices which include Stickers, Levers, Squares and Rollers to name a few.* This system has not changed in any radical degree over many centuries, however in recent times the use of material other than wood, and leather have been introduced, such as aluminium tubing, Nylon or other plastics.

In the tracker organ, the pallet is opened enough for the pipe to be in full speech very early in the key travel. It is the first 2 to 3 mm of travel of the front edge of the key, about 20% of the total key travel. However, in many electronic organs, both analogue and digital this is not the case. A very popular make of manuals for electronic/digital organs, which uses synthetic rubber ‘bubbles’ to both simulate the ‘pluck’ of the tracker system and to make the electrical contact, does both of these functions at the bottom of the key travel, not at the top, as it should be to mimic the tracker pipe organ!

Electronic/Digital Organs.

Various types of ‘switches’ have been used; gold plated wire on wire, leaf spring, optical and more recently Hall Effect solid state devices. So far almost none of these have strictly followed the tracker organ model of switching at the top of the key action, in a realistic way. The Pipe Organ Logic keying system, using Hall Effect sensors, allows this classic model to be replicated, along with realistic ‘pluck’. This system, combined with the latest ‘velocity sensing’ sample sets now makes it possible to build a digital organ of the highest standard, emulating all aspects of the Tracker organ.

Not everyone is interested in such realistic emulation of the tracker organ. For example, if your interest is mainly in the Wurlitzer style pipe organ then pluck and touch response is not of any importance as the theatre organ has always had ‘electric action’, that is the keys are either On or Off. Even so, the key switch should ‘close’, in no more than 3 mm of key travel. However, as we will cover later, the POL Hall Effect system can also produce Second Touch switching, without the addition of multiple switching devices to each key.


As mentioned above, in the tracker key system, full pipe speech is typically attained in the first 15 – 20% movement of the total key travel. In a key switch system that emulates this we should expect the ‘switching’ to take place over much the same proportion of key travel. At the same time, the ‘pluck’ effect should also be felt in the very beginning of the key travel, much less than 15%.

When we compare a tracker pipe organ with an electric action, or electro-pneumatic action, here again there are differences. The tracker system is ‘instantaneous’. There may be in some cases a very small amount of ‘dead’ movement in a badly adjusted tracker organ, but ideally the key begins the process of opening the pallet without any delay. In the electric action pipe organ there is inherent delay due to the time it takes for the magnetic field to build up in the coils of the ‘magnets’, the solenoid devices that pull the pallet open, there is significantly longer delay in electro-pneumatic organs. The same applies to the release of the key. Again, there is the delay due to the time it takes for the field around the coil to collapse or pneumatic ‘motors’ to return to the rest position. As a result the firing point is typically set a little deeper than in a tracker organ. None of these effects occur in the tracker system. It is instantaneously responsive to the player’s fingers on the keys.

In contrast to this it is very apparent that Organ Touch is very different to Piano Touch. The piano is a percussive instrument and its ‘action’ requires a certain minimum level of energy to be applied to the keys in order to produce a sound, any additional energy results in a louder sound and because of the nature of the sound producer, a struck string, also a change in the timbre. None of this applies to the pipe organ. As a result the playing method and ‘touch’ is quite different. Piano keys are ‘struck’ where as organ keys are ‘pressed’.

The Solution.

The switching system used in Manuals and Pedal keys of organs running on pipe organ emulation software, such as Hauptwerk, should make serious attempt to mimic the pipe organ. In the pipe organ world the Gold Standard is the Tracker or mechanical method of controlling the pallet valve under the pipes. In recent times, Both Optical and Magnetic types of switching have been used; however the Pipe Organ Logic system, using Hall Effect sensors, has advantages over the optical sensor system. Firstly the Hall Effect sensors used are of very low profile, around 0.5 millimetres in height. In addition, the POL system uses a single HE sensor which is used to give either velocity data or to give a second output for use as Second Touch in the theatre style organ. If need it can give both!

As soon as magnetic switching is mentioned, some will raise the issue of hysteresis, this is the difference in the physical position of the key to produce the ‘On’ signal and the ‘Off’ signal. This is a significant problem when magnetic reed switches are used for manual switching, it is not a problem of practical significance for pedalboard switching but certainly is in manual switching. There is a very wide range of Hall Effect sensors available today, but if the correct type is used with magnets of suitable ‘power’ the hysteresis becomes so small that it is of no practical significance, about 0.2 to 0.3 mm!

In addition, it must be noted that the installation of the POL key switching system also provides key-by-key regulation adjustment, so that each and every key ‘fires’ at the same place in the vertical movement of every key. Such adjustments are also found in the top quality keyboards of European organ builders, even in mechanical switching systems. This adjustment makes it possible even out the smallest of manufacturing dimensional variations in either metal frame or wood keys, regardless of the covering material. In addition, the POL H.E. system automatically compensates for wear and compression in felts. Every time the organ is switched on the system does a quick check of the ‘at rest’ position of every key and adjusts so that every key will ‘fire’ at the same physical position.


In summary, the Pipe Organ Logic manual keying systems, using Hall Effect sensors, gives the very highest quality of response, regulation and touch. It makes possible the manufacture of a digital organ to the high standards of the best ‘teaching’ institution tracker pipe organs, when matched with the Hauptwerk organ simulation software.

* Wikipedia

  • Trackers – trackers are the portions of the action used to make a pulling motion. Trackers can be used over long distances. They are thin strips of wood, roughly 10 mm wide and 2 mm thick. Although flexible, at rest they hold their shape. Playing a note pulls on the end nearer to the keyboard, so they are in tension while the note is playing. The term comes from the Latin verb "trahere", to draw (in the sense of "pull"); cf. modern English tractor.

  • Stickers — used for a pushing motion; often paired with trackers. Their length is limited by the material, though most of the time, capping off at about 250 mm.

  • Levers — levers are used to transfer from a tracker (pulling) to a sticker (pushing), or a general change of direction, or both.

  • Backfalls — backfalls are used for motion over a small or short distance where trackers and stickers would be otherwise illogical to use. As a natural result, the motion also changes direction.

  • Squares — a specific type of lever commonly used in organs which is at a right angle. Squares can also come in a "T" shape and form.

  • Rollers — Wooden shafts that rotate. Used for parallel direction in vertical or horizontal motion. They have small levers on each end, like cranks.

  • Roller board — location upon which rollers are attached (Note: rollers are often used densely in one section of the action and so are often closely associated with the roller board.)

  • Stops — knobs that indirectly control the flow of air over certain ranks of pipes. They are activated with a pulling motion by hand, and deactivated (or stopped) by pushing them shut.

  • Trundle — Trundles are used as a substitute for levers in the action associated with the Stops and Slider boards.