The stop action magnet, usually abbreviated to SAM, is an electromagnetic device used for the control of pipe organs and virtual pipe organs, and forms part of the organ's combination action. On a classical organ the device may be referred to as a drawstop solenoid. The SAM can be considered an electrical relay, the difference being that the SAM also has a drawknob or a tab, which enables it to be operated manually as well as electrically.
The pipe organ is a musical instrument that produces sound by driving pressurized air through the organ pipes selected via a keyboard. Because each pipe produces a single pitch, the pipes are provided in sets called ranks, each of which has a common timbre and volume throughout the keyboard compass. Most organs have multiple ranks of pipes of differing timbre, pitch, and volume that the player can employ singly or in combination through the use of controls called stops.
A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
A SAM will have an armature which is operated by an electrically induced magnetic field and dependent on whether the SAM is being used with a drawknob or a tilting tablet on a classically voiced organ or with a flat tab on a theatre organ, the armature will move in either a linear fashion or with semi-circular movement, in a small defined arc. A drawknob or tab is attached to the armature to facilitate hand operation.
A theatre organ is a distinct type of pipe organ originally developed to provide music and sound effects to accompany silent films during the first 3 decades of the 20th century.
Each SAM consists of two coils of wire, wound on bobbins, which surround a single central, magnetically conductive pole piece or two separate pole pieces (determined by the designer) and will have one or more switching contacts or reed switches that are switched on or off by the movement of the armature. The switching contact is used to control which rank or ranks of pipes will sound when keys on a keyboard are depressed, although the actual 'rank switching' is often handled by a more complex electromagnetic or electronic relay system.
The reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by W. B. Ellwood. It consists of a pair of contacts on ferromagnetic metal reeds in a hermetically sealed glass envelope. The contacts may be normally open, closing when a magnetic field is present, or normally closed and opening when a magnetic field is applied. The switch may be actuated by a coil, making a reed relay, or by bringing a magnet near the switch. Once the magnet is pulled away from the switch, the reed switch will go back to its original position.
In mechanical operation using a SAM with a drawknob attached, a player will either pull the drawknob towards themselves to select an 'on' state, or push the drawknob away to select an 'off' state. The movement of the drawknob affects the state of the switch or reed contact. Similarly, with a SAM that utilises a tilting tablet, the player will tilt the tablet up or down by hand to operate it. With a theatre organ the tab attached to each SAM is raised or lowered by the player to operate the switch contact/s.
Whilst hand registering the organ is often carried out, this can only be used to facilitate small changes in the overall tonal colour, due to physical restrictions. i.e. The operator cannot operate more than one or two devices simultaneously, especially when using only one hand for registration, whilst playing keys with the other hand! This is where the true versatility of the SAM comes into play. By applying a low voltage electric current (usually between 12 and 30 volts at up to 0.5 ampere) to one or the other of a SAM's electromagnets (coils) the armature can be made to follow the same movement and thus operate its switching contact/s as if it had been actuated by a human operator. The advantage of electrical operation being that many SAMs can be electrically connected together and switched by the use of a single button (piston) depressed by the human player using only one finger. It can therefore be seen that operating many SAMs in simultaneous combination will have a far greater instantaneous effect on the sound of the organ (which is essential for tonal variety) than is achievable by the use of single SAMs. Furthermore, combinations of registration changes can be stored in electronic or electromechanical memory which forms part of the organ's combination action, for instant recall at the touch of a button (piston) and translated into electrical impulses used to operate multiple SAMs.
The ampere, often shortened to "amp", is the base unit of electric current in the International System of Units (SI). It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics.
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.
One further use of SAMs in multiples is to achieve instant cancellation of organ registrations either in banks or for the entire organ. Most organs will have a General Cancel button for the purpose of entire cancellation, whilst at least one style of pipe organ manufactured by the John Compton company in the 20th century uses an ingenious system known as Second Touch Cancel, where each SAM has an extra contact fitted which is operated by depressing any single SAM's tab past its normal 'on' position, and which serves to switch all associated SAMs in its department to the 'off' position.
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An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix. Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in devices such as electric motors, generators, inductors, electromagnets, transformers, and sensor coils. Either an electric current is passed through the wire of the coil to generate a magnetic field, or conversely an external time-varying magnetic field through the interior of the coil generates an EMF (voltage) in the conductor.
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A mercury switch is an electrical switch that opens and closes a circuit when a small amount of the liquid metal mercury connects metal electrodes to close the circuit. There are several different basic designs but they all share the common design strength of non-eroding switch contacts.
A DC motor is any of a class of rotary electrical machines that converts direct current electrical energy into mechanical energy. The most common types rely on the forces produced by magnetic fields. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current flow in part of the motor.
In electrical controls, a stepping switch or stepping relay, also known as a uniselector, is an electromechanical device that switches an input signal path to one of several possible output paths, directed by a train of electrical pulses.
A manual is a musical keyboard designed to be played with the hands, on an instrument such as a pipe organ, harpsichord, clavichord, electronic organ, or synthesizer. The term "manual" is used with regard to any hand keyboard on these instruments to distinguish it from the pedalboard, which is a keyboard that the organist plays with their feet. It is proper to use "manual" rather than "keyboard", then, when referring to the hand keyboards on any instrument that has a pedalboard.
A soldering gun is an approximately pistol-shaped, electrically powered tool for soldering metals using tin-based solder to achieve a strong mechanical bond with good electrical contact. The tool has a trigger-style switch so it can be easily operated with one hand. The body of the tool contains a transformer with a primary winding connected to mains electricity when the trigger is pressed, and a single-turn secondary winding of thick copper with very low resistance. A soldering tip, made of a loop of thinner copper wire, is secured to the end of the transformer secondary by screws, completing the secondary circuit. When the primary of the transformer is energized, several hundred amperes of current flow through the secondary and very rapidly heat the copper tip. Since the tip has a much higher resistance than the rest of the tubular copper winding, the tip gets very hot while the remainder of the secondary warms much less. A tap on the primary winding is often used to power a pilot lamp which illuminates the workpiece.
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The universal motor is a type of electric motor that can operate on either AC or DC power and uses an electromagnet as its stator to create its magnetic field. It is a commutated series-wound motor where the stator's field coils are connected in series with the rotor windings through a commutator. It is often referred to as an AC series motor. The universal motor is very similar to a DC series motor in construction, but is modified slightly to allow the motor to operate properly on AC power. This type of electric motor can operate well on AC because the current in both the field coils and the armature will alternate synchronously with the supply. Hence the resulting mechanical force will occur in a consistent direction of rotation, independent of the direction of applied voltage, but determined by the commutator and polarity of the field coils.
A contactor is an electrically-controlled switch used for switching an electrical power circuit. A contactor is typically controlled by a circuit, which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch.
The electro-pneumatic action is a control system for pipe organs, whereby air pressure, controlled by an electric current and operated by the keys of an organ console, opens and closes valves within wind chests, allowing the pipes to speak. This system also allows the console to be physically detached from the organ itself. The only connection was via an electrical cable from the console to the relay, with some early organ consoles utilizing a separate wind supply to operate combination pistons.
A dynamo is an electrical generator that creates direct current using a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter. Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices is effective and usually economical.
The pipe organ is played from an area called the console or keydesk, which holds the manuals (keyboards), pedals, and stop controls. In electric-action organs, the console is often movable. This allows for greater flexibility in placement of the console for various activities. Some very large organs, such as the van den Heuvel organ at the Church of St. Eustache in Paris, have more than one console, enabling the organ to be played from several locations depending on the nature of the performance.
A magnetic starter is an electromagnetically operated switch which provides a safe method for starting an electric motor with a large load. Magnetic starters also provide under-voltage and overload protection and an automatic cutoff in the event of a power failure.
Registration is the technique of choosing and combining the stops of a pipe organ in order to produce a particular sound. Registration can also refer to a particular combination of stops, which may be recalled through combination action. The registration chosen for a particular piece will be determined by a number of factors, including the composer's indications, the time and place in which the piece was composed, the organ the piece is played upon, and the acoustic in which the organ resides.
A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, although it is usually considered distinct from most other alternators, which use field coils rather than permanent magnets.
