GB1294996A - - Google Patents

Abstract

1294996 Transistor tone gating circuits MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 19 Jan 1970 [18 Jan 1969 (2)] 2576/70 Heading H3T [Also in Division G5] A signal selecting system is so arranged that, however, many switches 20-24 are closed, provided that switch 80 is also closed, one only of the gates 6-10 is opened to pass a signal to the output from the corresponding control terminal 152-156. Switches 20-24 are connected to the keyboard of an electronic musical instrument and depression of pedal 81 ensures that the tone corresponding to either the highest or lowest frequency is passed to the output if frequency generators f1-f5 are in progressive order. Transistors 29a-33a are normally conductive, but when any of keys 20-24 are closed, as well as key 80, the transistor corresponding to the uppermost key, and all those between it and the resistor 79 are cut off, and of the normally non-conductive transistors 29b-33b only the one whose emitter is connected to the base of the uppermost non-conducting transistor 29a-33a conducts, producing a switching voltage fed via one of diodes 39-43 to open one of the gates 152-156. Supply 96 is provided to make the switching action more reliable. The gate circuit, Fig. 3 (not shown), includes 3 transistors (128-130) for 4<SP>1</SP> , 8<SP>1</SP> , 16<SP>1</SP> tones, with separate inputs and outputs, and with bases connected together and to the control input (153). The input signal also charges capacitor (105) via a resistor (134b) giving a rise time to the gate, and the capacitor discharges via a series chain of resistors (134a, 134b) and transistor (110) whose base is connected to a variable supply to give controlled sustaining of tones transmitted through the gate. Whenever any one or more keys 20-24 are depressed, the current increase in resistor 82 gives rise to a signal which when amplified and differentiated triggers a monostable multivibrator 92, 98 to open transistor 100 for a short time, thus saturating transistor (110), Fig. 3 (not shown), and switching off all gates. When any key 20-24 is released, negative going pulses are fed via one of diodes 44-48 to a similar circuit to cause transistor 28 to be switched off for a short time interval, thus clearing the circuit. The switch 80 may be in series with the transistor 28. The switching may be performed by contacts. The signal from the output is fed via tone colour circuits (11), and amplifier (12) to a loud-speaker (13), Fig. 1 (not shown).