Sample and hold circuit for an electric organ

Claim 2

An electric organ, comprising a resistance, an array of keys of said organ, means responsive to actuation of selected keys of said array of keys for grounding selected parts of said resistance, said resistance having a preselected variable voltage ungrounded point of reference, means including a feedback circuit for maintaining the voltage of said preselected point of reference constant when any of said keys is actuated by feeding back current through said resistance in amplitude sufficient to maintain said voltage of said preselected point of reference constant, said feedback circuit includIng a storage capacitor shunt connected to ground at a location between said point of reference and a load point, a feedback resistance connected between said load point and said point of reference, and a voltage tone signal oscillator responsive to the voltage of said load point.

Claim 3

The combination according to claim 1, wherein is included a voltage comparator having a fixed reference input voltage and a variable input voltage terminal, means connecting said variable input voltage terminal to said point of reference, said voltage comparator having an output terminal connected to control voltage across said storage capacitor.

Claim 4

The combination according to claim 2, wherein is included an auxiliary feedback loop connected between said voltage comparator output terminal and said point of reference, said auxiliary feedback loop including current sources for supplying current to and draining current from said point of reference.

Claim 5

The combination according to claim 3, wherein is included means responsive to the voltage at said point of reference for supplying current to and draining current from said storage capacitor.

Claim 6

An electric organ, comprising an array of key switches, an adjustable resistance, means responsive to said key switches for adjusting the value of said adjustable resistance, amplifying means having its input connected to a preselected point of said resistance and having an output point, a resistive feedback loop extending from said output point to said preselected point, a source of reference voltage, means for developing an input error signal for said amplifier as the difference of said reference voltage and the voltage of said preselected point, a voltage controlled tone signal source connected to said output point, and means for acoustically transducing the signal output of said tone signal source.

Claim 7

An electric organ, comprising an array of key switches, an adjustable resistance, means responsive to said key switches for adjusting the value of said adjustable resistance, amplifying means having its input connected to a preselected point of said resistance and having an output point, a resistive feedback loop extending from said output point to said preselected point, a source of reference voltage, means for developing an input error signal for said amplifier as the difference of said reference voltage and the voltage of said preselected point, a voltage controlled tone signal source connected to said output point, and means for acoustically transducing the signal output of said tone signal source.

Claim 8

The combination according to claim 5, wherein said amplifier includes a capacitive memory for sustaining the output of said amplifier.

Claim 9

An electric organ having a keyboard, a string of series connected resistances, means respnsive to selective actuation of keys of said keyboard for connecting to a point of reference potential selected junctions of said resistances, whereby said string of resistances has a total resistance which is a function of location of that selective junction which is farthest removed from said point of reference potential, a source of reference voltage, and means for injecting current into said string of resistances of magnitude selected to cause the voltage across said string of resistances substantially to equal the voltage of said source of reference voltage for any selective actuations of said keys, a voltage controlled tone signal oscillator operative to generate a tone frequency as a function of a control voltage, means responsive to said means for injecting current for applying said control voltage to said voltage controlled oscillator, wherein is provided a voltage comparator for comparing said reference voltage with said voltage across said string of resistances, said voltage comparator having an output terminal, means responsive to the voltage at said output terminal for controlling said means for injecting current.

Claim 10

An electric organ having a keyboard, a string of series connected resistances, means respnsive to selective actuation of keys of said keyboard for connecting to a point of reference potential selected junctions of said resistances, whereby said string of resistances has a total resistance which is a function of location of that selective junction which is farthest removed from said point of reference potential, a source of reference voltage, and means for injecting current into said string of resistances of magnitude selected to cause the voltage across said string of resistances substantially to equal the voltage of said source of reference voltage for any selective actuations of said keys, a voltage controlled tone signal oscillator operative to generate a tone frequency as a function of a control voltage, means responsive to said means for injecting current for applying said control voltage to said voltage controlled oscillator, wherein is provided a voltage comparator for comparing said reference voltage with said voltage across said string of resistances, said voltage comparator having an output terminal, means responsive to the voltage at said output terminal for controlling said means for injecting current.

Claim 11

The combination according to claim 7, wherein said last means includes a feedback path connected between said output terminal of said voltage comparator and said string of resistances.

Claim 12

The combination according to claim 9, wherein said last means includes a further feedback circuit directly responsive to said control voltage for feeding back voltage to said string of resistances.

Claim 13

The combination according to claim 9 including a storage capacitor having a charge responsive to said voltage of said output terminal of said voltage comparator, and means for controlling the rate of change of said charge in response to a change of current flow into said string of resistances.

Claim 14

An electric organ, comprising an array of key switches, an adjacent resistance, means responsive to seLective actuation of said key switches for adjusting the value of said adjustable resistance as a function of the selective actuation of said key switches, a voltage comparator having a reference input terminal and a variable input terminal, means applying a fixed voltage to said reference input terminal, means connecting a point of variable resistance to said varaible input terminal, said voltage comparator having an output terminal, a loop having a first section extending from said output terminal to a load terminal and a second section extending from said load terminal to said variable input terminal, said loop being arranged to tend to maintain the voltage at said variable input terminal equal to the voltage at said reference input terminal for any selective actuations of said keys, a voltage controlled tone signal oscillator connected to said load terminal, and means for acoustically transducting the signal output of said tone signal oscillator.

Claim 15

An electric organ, comprising an array of key switches, an adjacent resistance, means responsive to seLective actuation of said key switches for adjusting the value of said adjustable resistance as a function of the selective actuation of said key switches, a voltage comparator having a reference input terminal and a variable input terminal, means applying a fixed voltage to said reference input terminal, means connecting a point of variable resistance to said varaible input terminal, said voltage comparator having an output terminal, a loop having a first section extending from said output terminal to a load terminal and a second section extending from said load terminal to said variable input terminal, said loop being arranged to tend to maintain the voltage at said variable input terminal equal to the voltage at said reference input terminal for any selective actuations of said keys, a voltage controlled tone signal oscillator connected to said load terminal, and means for acoustically transducting the signal output of said tone signal oscillator.

Claim 16

The combination according to claim 11, wherein said first section includes a storage capacitor connected between a point of said first section and a point of reference potential, and an amplifier extending from said storage capacitor to said load terminal.

Claim 17

The combination according to claim 12, wherein said adjustable resistance is a series of resistances connected in series, and wherein said key switches are respectively connected between the junctions of said series of resistances and a point of reference potential.

Claim 18

The combination according to claim 13, wherein said points of reference potential are ground.

Claim 19

The combination according to claim 13, wherein are provided four two terminal current sources, I1, I2, I3, I4, means connecting said current sources I1, I3 in series with each other, means connecting said current sources I2I4 in series with each other and in parallel with said current sources I1, I3, means connecting said adjustable resistances to the junction of said current sources I1I3, means connecting the junction of said current sources I2) I4 to said storage capacitor, means connecting the output terminal of said voltage comparator jointly to the unjoined terminals of all said current sources, said current sources I1 and I3 providing current flow in series with each other in the same sense and said current sources I2 and I4 providing current flow in series with each other in the same sense, and said current sources being responsive to the voltage at said junctions for controlling the relative amplitudes of current flowing through said current sources.

Claim 20

An electric organ, comprising a series connected array of resistances connected to a reference point, key switches for at will connecting junctions of said resistances to ground, a comparison circuit responsive to the voltage of said reference point and to a fixed reference voltage for generating an error signal, a memory capacitor, current charge and discharge means responsive to said error signal for respectively increasing and decreasing the charge in said capacitor, an output terminal, means respnsive to the voltage across said capacitor for applying an amplified version of said voltage across said capacitor to said output terminal, a resistive feedback circuit extending from said output terminal to said reference point, a voltage controlled tone signal oscillator conected to said output terminal and responsive to the voltage of said output terminal to generate tone frequency signals of variable frequency, and means for acoustically transducing said tone frequency signals.

Claim 21

An electric organ, comprising a series connected array of resistances connected to a reference point, key switches for at will connecting junctions of said resistances to ground, a comparison circuit responsive to the voltage of said reference point and to a fixed reference voltage for generating an error signal, a memory capacitor, current charge and discharge means responsive to said error signal for respectively increasing and decreasing the charge in said capacitor, an output terminal, means respnsive to the voltage across said capacitor for applying an amplified version of said voltage across said capacitor to said output terminal, a resistive feedback circuit extending from said output terminal to said reference point, a voltage controlled tone signal oscillator conected to said output terminal and responsive to the voltage of said output terminal to generate tone frequency signals of variable frequency, and means for acoustically transducing said tone frequency signals.

Claim 22

The combination according to claim 16, wherein is included means responsive to opening of all said key switches for disabling said means for respectively increasing and decreasing said charge in said capacitor.

Claim 23

The combination according to claim 17, wherein is included means for controlling the rate of change of charge of said capacitor by said current increasing and decreasing means in response to opening or closure of any of said key switches.