| 摘要 |
1517668 Transistor amplifiers R H PETERSON 15 Dec 1976 [17 Dec 1975] 52362/76 Heading H3T [Also in Division G5] In order to simulate reed organ pipes electronically tone signals rich in harmonics, e.g. pulse signals of small mark/space ratio, are applied to a voltage controlled low pass filter which has a rapid roll off and whose cut-off frequency is made to increase progressively immediately after keying. In Fig. 5 keyswitches 44 enable tone generators 60-68 which may comprise oscillators plus envelope controlling gates (not shown). The output of the generators is applied to stop filters 43-46 which simulate "flue" pipes such as diapason and 52-53 which simulate reed pipes such as the waldhorn. Operation of any key also applies voltage to a line 76 to charge a capacitor 80c, 82c associated with voltage controlled filters 52, 53 whereby the filter frequency increases as the capacitor charges. The filters (Fig. 7) comprise RC networks 114-120, 122-136 with feedback from emitter followers to sharpen the knee of the characteristic and the resistor 114, 116, 122. 124 shunted by light dependent resistors 138-144 illuminated by a lamp 146 fed by the voltage on the capacitor 80c, 82c to vary the frequency.
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