| 摘要 |
PURPOSE:To detect the intermusic accurately, by adjusting a height of a light shield plate provided between a light emitting element and a photodetector forming an intermusic sensor so as to make the amount of photodetection of a tone arm almost equal at up/down position. CONSTITUTION:The light emitting element 1 and the photodetector 2 are sectioned at a slight shield plate 6 and they are contained in a holder 4. In determining the relation of each position as shown in Figure, the following relation is established; x=(W+w)h1/ (2h2-h1)], where W is the width of the element 1, w is the thickness of the plate 6, h1 is the height of the plate 6 from the photodetecting plane, and h2 is the height of the photodetection plane to a record disc. The x is proportional to the photodetection area and to the amount of photodetection accordingly. An output V of the photodetector 2 is V=Kx, where K is a proportional constant. The x is increased with the increased h2 and although the photodetection area is increased, the distance between the elements 1 and 2 is increased to decrease the amount of the photodetection. Thus, in selecting the h2 to a suitable value, the amount of photodetection of the photodetector 2 is made almost constant at a certain range of the h1. Thus, the h1 at up/down position of the tone arm is kept within the said range. Then, the intermusic detection level is made constant and the circuit is simplified. |
