Van de Graaff generator
Other electrostatic machines like the Wimshurst machine or Bonetti machine work similarly to the Van De Graaff; charge is transported by moving plates, disks, or cylinders to a high voltage electrode. For these generators, however, corona discharge from exposed metal parts at high potentials and poorer insulation result in smaller voltages. In an electrostatic generator, the rate of charge transported (current) to the high-voltage electrode is very small. After the machine is started, the voltage on the terminal electrode increases until the leakage current from the electrode equals the rate of charge transport. Therefore, leakage from the terminal determines the maximum voltage attainable. In the Van de Graaff generator, the belt allows the transport of charge into the interior of a large hollow spherical electrode. This is the ideal shape to minimize leakage and corona discharge, so the Van de Graaff generator can produce the greatest voltage. This is why the Van de Graaff design has been used for all electrostatic particle accelerators. In general, the larger the diameter and the smoother the sphere is, the higher the voltage that can be achieved.
Stop action magnet
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.