Audio signal keyer

Claim 2

An audio keyer comprising a first differential amplifier having one input terminal to be supplied with an audio signal to be keyed and another input terminal to be supplied with a DC reference potential and a control terminal; a keying voltage developing circuit including a key-operated charge-discharge element and connected to said control terminal of said first differential amplifier so as to control the bias of the amplifier to thereby develop a keyed audio output signal at one of the output terminals of the amplifier and develop a DC potential corresponding to said average potential at the other terminal; and a second differential amplifier having one input terminal connected directly to said one output terminal of the first differential amplifier and another input terminal connected directly to the other output terminal of the first differential amplifier and having one output terminal for deriving a difference signal between the two inputs such that a DC component superimposed on the keyed audio signal is eliminated.

Claim 3

The keyer according to claim 1, which comprises DC voltage divider means having dividing resistors for supplying predetermined potentials to said first differential amplifier and said charge-discharge element, respectively.

Claim 4

The keyer according to claim 1, in which said chargedischarge element is a capacitor.

Claim 5

The keyer according to claim 1, in which each of said first and second differential amplifiers includes a pair of transistors having emitters connected in common, bases connected with said two input terminals and collectors capable of deriving outputs.

Claim 6

The keyer according to claim 4, in which said common emitter of the first differential amplifier is connected through said control terminal to the charge-discharge element across which the potential charges depend on the action of a key-operated on-off switch.

Claim 7

The combination in an audio signal keyer comprising a first differential amplifier including an input resistor, a pair of transistors first one of which has a base supplied with an audio signal through the input resistor and a collector adapted to develop the supplied audio signal across a collector load resistor and second one of which has a base connected to a biaS resistor and a collector capable of developing a DC signal across another collector load resistor, emitters of both said transistors being connected through an emitter resistor; signal buildup time and decay time determining means including a key-operated on-off switch and a charge-discharge capacitor in parallel connection between a DC voltage line and the common emitter of the first differential amplifier and reisitors for determining charge-discharge timing with said capacitor; a second differential amplifier including paired third and fourth transistors having bases directly connected with the collectors of the first and second transistors of the first differential amplifier and emitters connected to each other, said third transistor having a collector connected to another collector load resistor for deriving a difference output signal; and power supply means including a DC voltage divider having three resistors for dividing said DC power voltage into predetermined potentials for the base bias voltage of the first differential amplifier transistors and the charge-discharge capacitor.

Claim 8

The combination in an audio signal keyer comprising a first differential amplifier including an input resistor, a pair of transistors first one of which has a base supplied with an audio signal through the input resistor and a collector adapted to develop the supplied audio signal across a collector load resistor and second one of which has a base connected to a biaS resistor and a collector capable of developing a DC signal across another collector load resistor, emitters of both said transistors being connected through an emitter resistor; signal buildup time and decay time determining means including a key-operated on-off switch and a charge-discharge capacitor in parallel connection between a DC voltage line and the common emitter of the first differential amplifier and reisitors for determining charge-discharge timing with said capacitor; a second differential amplifier including paired third and fourth transistors having bases directly connected with the collectors of the first and second transistors of the first differential amplifier and emitters connected to each other, said third transistor having a collector connected to another collector load resistor for deriving a difference output signal; and power supply means including a DC voltage divider having three resistors for dividing said DC power voltage into predetermined potentials for the base bias voltage of the first differential amplifier transistors and the charge-discharge capacitor.

Claim 9

The combination according to claim 6, in which the DC signal developed at the collector of the second transistor of the first differential amplifier is predetermined to be equal to an average voltage of audio signal developed at the collector of the first transistor by setting the base bias voltage of the second transistor in connection with the potential across the charge-discharge capacitor.

Claim 10

A keying system for an electronic musical instrument comprising a large number of keyers equal in number to that of playing keys, each keyer including a plurality of input terminals adapted to be supplied with tone signals; a plurality of first input transistors connected to said plurality of input terminals respectively at their bases for keying the tone signals at their collectors; a reference DC voltage generating transistor constituting first differential amplifiers with said plurality of transistors, the emitters of the amplifier transistors being connected in common; and a key-operated signal amplitude characteristic determining circuit having a charge-discharge capacitor and resistors and varying the potential at the capacitor depending upon on-off action of a key-operated switch, said capacitor being connected in series with the common emitter of the first differential amplifiers so that the emitter bias may be controlled by the potential variation of the capacitor, and second differential amplifiers provided in common for the whoe keyers and for deriving keyed output signals, said second amplifiers including a second plurality of input transistors equal in number to that of the input transistors of each keyer and the bases of said second input transistors being connected with respective collectors of said first input transistors of each keyer and a DC reference transistor constituting differential amplifier pairs with said second input transistors and the base of the said DC reference transistor is connected to the collector of the said reference DC voltage generating transistor in the first differential amplifiers, whereby keyed output tone signals derived from the second amplifiers are free from the DC component.

Claim 11

A keying system for an electronic musical instrument comprising a large number of keyers equal in number to that of playing keys, each keyer including a plurality of input terminals adapted to be supplied with tone signals; a plurality of first input transistors connected to said plurality of input terminals respectively at their bases for keying the tone signals at their collectors; a reference DC voltage generating transistor constituting first differential amplifiers with said plurality of transistors, the emitters of the amplifier transistors being connected in common; and a key-operated signal amplitude characteristic determining circuit having a charge-discharge capacitor and resistors and varying the potential at the capacitor depending upon on-off action of a key-operated switch, said capacitor being connected in series with the common emitter of the first differential amplifiers so that the emitter bias may be controlled by the potential variation of the capacitor, and second differential amplifiers provided in common for the whoe keyers and for deriving keyed output signals, said second amplifiers including a second plurality of input transistors equal in number to that of the input transistors of each keyer and the bases of said second input transistors being connected with respective collectors of said first input transistors of each keyer and a DC reference transistor constituting differential amplifier pairs with said second input transistors and the base of the said DC reference transistor is connected to the collector of the said reference DC voltage generating transistor in the first differential amplifiers, whereby keyed output tone signals derived from the second amplifiers are free from the DC component.