Abstract: A grand piano has a keyboard placed on a key bed, and the keyboard is covered with a fall board after completion of practice on the keyboard, wherein a recess is formed in the fall board in such a manner as to offer a clearance to fingers on the black keys so that, even if the pianist straightens his or her fingers on the land portion before moving them to other keys, the nails are never hit against the inner surface of the fall board.

Abstract: A grand piano has a keyboard placed on a key bed, and the keyboard is covered with a fall board after completion of practice on the keyboard, wherein a recess is formed in the fall board in such a manner as to offer a clearance to fingers on the black keys so that, even if the pianist straightens his or her fingers on the land portion before moving them to other keys, the nails are never hit against the inner surface of the fall board.

Abstract: An acoustic apparatus has a Helmholtz resonator having an open duct port and cavity and a vibrator disposed in the Helmholtz resonator. An opening portion of the open duct port is extended in a horn-like shape, so that the open duct port communicates with a port mounting surface with a smooth curvature. An air-flow diffusing body corresponding to the shape of the port opening portion is provided at the center of the extended port opening portion, so that an effective sectional area of the air-flow path defined by the opening portion and the diffusing body is substantially equal to a sectional area of the open duct port excluding the opening portion.

Abstract: To the respective drains of a pair of FET's which constitute an input stage differential amplifier circuit are cascade-connected a first transistor and a second transistor, respectively, whose bases are connected in common. To a pair of active elements of the next stage amplifier circuit is connected a detecting circuit for detecting the sum of the driving currents of these active elements. By the output of detection of the detecting circuit, the potential of the common base of the first and second transistors is controlled, so that the currents flowing through these first and second transistors are held constant, whereby the apparent load, for input signals, of the paired FET's is elevated.

Abstract: A transistor amplifier comprises an input stage circuit and an output stage circuit direct-coupled to the input stage circuit: the input stage including complimentary paired transistors having bases commonly connected to an input terminal and emitters AC-wise grounded and further connected to constant current sources, respectively; the output stage being a single-ended push-pull amplifier circuit including complimentary paired transistors having bases connected to collectors of the input stage transistors, respectively, and emitters commonly connected to an output terminal. This transistor amplifier has advantages that it is simple in arrangement and that both its DC and AC operations are highly stabilized against variations in the ambient temperature and in the voltages of operating power supplies.