| 摘要 |
1,164,422. Electronic musical instruments. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 5 April, 1968 [8 April, 1967], No. 16538/68. Heading G5J. A circuit for imitating the touch of a percussive musical instrument is arranged so that the build-up time of the note from a tone generator G is made independent of the duration of actuation of the key T. The key is mechanically coupled to a magnet M which induces a voltage pulse in an inductance L on actuation of the key. This voltage pulse is used to charge up a capacitor C through a diode D, and is also fed to the base of a transistor Tr, causing it to conduct and so ground the base of transistor O which is thereby switched off and does not pass any signal from generator G. At the end of the pulse, transistor Tr is switched off and the voltage stored in capacitor C is fed through resistor R to the base of transistor O which is hence switched on and passes a signal from generator G to associate amplifying apparatus at a level depending on the voltage across the capacitor and hence the intensity of actuation of the key. Diode D 2 and capacitor C 2 prevent " bottoming " of transistor O if the key is depressed before the voltage across the capacitor C 1 has decayed to zero. Fig. 5 (not shown) illustrates a further embodiment in which the switching transistor Tr is arranged between the capacitor to be charged and the base of the transistor O and switches on after the capacitor has charged up to allow voltage from the capacitor to switch transistor O on. |
