Patent GB-747963-A (GB)
Title: Improvements in or relating to electrical musical instruments
Inventor: BIERL RICHARD
IPC: G10H1/057
Filed: 1952-06-06
Abstract: 747,963. Electrophonic organs. HOHNER. AKT.-GES., M. June 6, 1952 [June 8, 1951; - June 8, 1951; Feb. 29, 1952], No. 14370/52. Class 88(2) A touch responsive keyboard instrument is arranged so that attack and intensity on the one hand and delay on the other are independently controlled. Key - switches control the charging and discharging current of a group of condensers which in turn control the gain of an amplifier. Amplifier. Fig. 16. Condensers 146, 147, 148 control the gain of pentodes 143, 144 connected in push-pull. The condensers are normally connected to a negative source 153a over back contacts 28 of the keys. When a key 154a is pressed, the negative source is disconnected and the frequency corresponding to the key is fed to the amplifier input 137 under the control of a key contact not shown. When the key closes the first two contacts 22, the condensers are connected to the screen grids of the pentodes. When the third control 22 is closed, the condensers begin to charge from a positive source 152a and the amplifier gain increases at a rate controlled by an adjustable resistor 152. When the key is released, the condenser discharges to the negative source 153a and the gain decreases at a rate controlled by an adjustable resistor 154. The oscillations cease abruptly when the key is fully released. Key switches. In one arrangement, Fig. 2, a lever 34 carrying balanced weights 35, 36 is pivoted at 33 to a member 16 secured to a key 31 and is free to rotate within limits set by stops 39. When the key is depressed, contacts 17, 18 are closed to provide oscillation of the appropriate frequency at the amplifier input and two contacts 28, normally interconnected by a metallic plate 37, are opened. The kinetic energy of the lever when it strikes contacts 22 determines whether two or three of the contacts are closed before they turn the lever anticlockwise against an adjustable stop 41. The note ceases when contacts 17, 18 open. To provide a continuous note the stop 41 is, adjusted so that the contacts 22 are all held closed whilst the key is down. In a modification, Fig. 5, three springs 53 corresponding to springs 22 in Fig. 2, normally rest against an in-' sulating strip 54. When the key is depressed, a slotted member 47 engages the springs and holds two of them at a higher level than the third so that the weight 59a connects two of them before contacting the third. The oscillations start when the weight 59 is lowered and contact 58 withdraws an insulating pin 58a to permit contacts 56, 57 to close. The condenser is disconnected from the negative source when contact is broken between spring 58 and weight 59. The spring contacts 56, 57, 58 may be replaced by an arrangement shown in Fig. 7. A nose 41a carried by the member 46 first closes contacts 60, 61 to start the oscillation. Further movement causes an insulating pin 62 on contact 60 to push a pair of side-by-side contact springs 63' away from a shorting contact 63a. In the arrangement shown in Fig. II, twocontacts 83 and a contact 84 are controlled by a grooved extension 81 carried by the key so that a metallic plate 87 first engages contacts 83 and later contact 86. Contacts 79 start the oscillation and an insulating pin 79a breaks a connection between contact 89 and member 86 to disconnect the negative source from the condenser. The key switches may be arranged in cascade so that a second key is ineffective until a first key is released. The oscillations may be generated electronically crby vibrating reeds, strings.