US3022695A - Percussion circuit - Google Patents

Description

Feb. 27, 1962 R. E. WILLIAMS PERCUSSION CIRCUIT Filed April 1, 1959 R 255 Etfiitx @Q m w EE 9% \w w m Q aw W M E v m I w R a V B um E g Y QR WQQER. w f A mm .395 5E3 Q ww I I I Sa o 3% e M ew H a 4 N Qt MN P NE ATTORNEYS United States Patent PERCUSSiON CERCUIT Richard E. Williams, Box 556, Vienna, Va. Filed Apr. 1, 1959, Ser. No. 803,420 3 Qiairns. (Cl. 841.l8)

The present invention relates generally to systems for generating percussion effects in electronic organs, and more particularly to systems for generating percussion effects in photo-electric organs.

The present invention is applicable particularly to electric organs of the type employing photoelectric generators. In such systems one or more tone wheels may be employed, each tone wheel being provided with a plurality of recorded sound tracks, and each track preferably pertaining to one pitch or tone of the organ. The tone tracks are rotated with respect to a plurality of light sources on one side, and a photoelectric cell on the other side, each tone track modulating the light deriving from one or more of the light sources and the light being intercepted, after modulation, by the photoelectric cell, whereby the output circuit of the photoelectric cell includes electrical signals modulated in accordance with the recorded tones. The organ is played by depressing keys of one or more manuals, and depression of any key eiiects energization and consequent illumination of one or more of the lamps, and consequent generation of tones corresponding with the enrgized lamps. The present invention concerns itself with the introduction of percussive effects in such organs.

In accordance with a primary feature of the present invention a relatively high resistance is connected from an ungrounded end of each lamp to a common point, and a single relatively low resistance from the common point to ground. The lamps are all energized from a common voltage source, via individual key switches, so that closure of any switch energizes the associated lamp and also generates a small voltage across the low resistance. In effect, the several resistances constitute a logical OR matrix, which generates a signal in response to closure of any key. The relative sizes of the resistances provide isolation between lamps, and also the selection of values for the relatively large resistances assures that the lamps will not be robbed of any appreciahle current or voltage.

The voltage available across the relatively low resistance is applied via a high pass filter to the input of a voltage amplifier so arranged that one positive output pulse only is generated in response to energization of any lamp and one negative pulse only, in response to de-energization of any lamp, regardless of the energized condition of the remainder of the lamps. Across the output circuit of the amplifier is connected in series a gaseous discharge cell, for example, a two electrode neon cell and a condenser. The voltage applied on the neon cell in the absence of pulses is insufiicient to fire the cell, but the positive pulses are of sufilcient magnitude to ignite the cell, thereby connecting the condenser in series with a positive voltage source, and charging the condenser substantially instantaneously. A negative voltage source is connected in series with a high resistance to the junction of the condenser and the neon cell, so that the junction is normally maintained at the potential of the negative source, and so that when the condenser charge varies, as because the neon cell fires, the negative source tends nevertheless to recharge the condenser to the voltage of the negative source, but very slowly because of the interposition of the high resistance. A diode is connected with its anode at the junction of the condenser in the neon cell, and its cathode connected to ground, said diode acting as a clamping circuit for preventing the potential of the junction rising above 3,il22,595 Patented Feb. 27, 1962 ice ground level. Connected across the diode is a resistance and condenser in series, the constants of which are selected to absorb very rapid changes, which might otherwise give rise to clicks in the output of the system. The condenser is connected to the grid of a tone amplifier, to which isalso connected an input circuit deriving from that photoelectric cell or" the system which is subjected to tone modulated light. Both connections to the grid proceed via isolating resistances, so that interaction of the two input circuits is prevented. The output of the tone amplifier then proceeds via formant filters and an audio power amplifier to an electro-acoustic transducer.

Connected across the condenser is a switch, which constitutes, in its closed position, a short circuit around the condenser, preventing any change of voltage thereacross, and in its open condition permitting control of the voltage across the condenser. This switch constitutes a percussive stop and is controlled by means of a stop tab, in an actual organ.

The tone amplifier is, in the absence of control pulses, subjected to the voltage of the negative source, and has a gain characteristic such as to provide substantially Zero gain in response to that voltage applied to the control grid. Accordingly, the tone amplifier is normally cutoff. In response to an input pulse ofpositive polarity, the voltage across the condenser rises rapidly to ground potential, which increases the gain of the amplifier rapidly to substantially full gain. 0n cessation of the control pulse, the neon cell de-ignites, and the condenser in series therewith discharges through the high resistance to the potential of the negative source. The discharge occurs quite slowly, so that the gain of the amplifier is reduced with corresponding slowness to a condition of substantially zero gain.

The net effect is a rapid rise in gain and a slow decrease in gain of the tone amplifier in response to each depression of a key of the organ, regardless of the condition of the remaining keys; i.e., whether they are or are not depressed.

It is, accordingly, a primary object of the present invention to provide a novel system for introducing percussive e'liects in a photoelectric musical instrument.

It is a further object of the invention to provide a percussion circuit for photoelectric organs which shall be operated in response only to each energization of a lamp of a photoelectric organ, regardless of the condition of the remaining lamps, and not in response to deenergization.

It is another object of the invention to provide a percussive system which is entirely electronic, and which does not rely upon the use of relays or other mechanically moving elements.

Still another object of the invention resides in the provision of a percussive circuit for a musical instrument which is extremely simple, requires a minimum number of inexpensive parts, is positive in action, and requires no maintenance.

It is a further object of the present invention to provide a system for sensing the energization of any one or more of a plurality of lamps, regardless of the operative condition of the remaining lamps, and for generating a short control pulse in response to initiation of such energization.

A further object of the invention resides in the provi sion of a circuit for generating a control pulse in response to energization of any one of a plurality of loads powered from a common source via selective switches, without appreciably robbing the load of voltage or current.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of 3 one specific embodiment thereof, especially When taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 of the accompanying drawing is a schematic circuit diagram of a system according to the invention; and

FIGURE 2 illustrates certain wave forms occuring in the system.

Proceeding now more particularly to the accompanying drawing, the reference numeral 1 denotes a tone or pitch disc applicable to many types of photoelectric organs employing selective illumination of tone tracks by means of selectively energizable lamps.

The reference numeral 2 denotes a slit disc, containing a plurality of slits, one for each tone track, which serves to guide light from an array of lamps 3 to appropriate ones of the pitch or tone tracks 4 of the pitch disc 1. The pitch disc 1 is rotated at a predetermined rate by means of a motor 5, and the light deriving from the lamps 3, and modulated by the pitch disc 1, are all collected by means of a photoelectric cell 6. The output of the photoelectric cell is applied via a lead 7 and an isolating resistance 8 to the grid 9 of a tone amplifier stage 10. The stage It) comprises a triode 11, the anode 12 of which is in series with an anode load 13 and a 3+ terminal 14. The cathode 15 of the triode 11 is connected to ground via a bias circuit 16, comprising a voltage divider connected to a source of positive voltage, thus eliminating need for a by-pass condenser.

The output from the amplifier stage is taken at the anode 12, via a lead 18, and proceeds to formant filters 19, and thence to a power audio amplifier 2t} and an electro-acoustic transducer 21, all in cascade.

The lamps 3 are selectively controlled by means of key-operated switches 22, all of which are connected in parallel to a voltage source 23, which is capable of supplying the required current and voltage to the lamps 3. Accordingly, the lamps 3 will be selectively energized in accordance with the selected ones of the switches 22, depression of a key of an organ, for example, resulting in closure of a corresponding one of the switches 22.

In accordance with the present invention separate resistances 30 are connected from the lamp side of switches 22 to a common point 30a. From the latter to ground is connected a further resistance 3%. The value of each of resistances 34) may be, for example, 10K, while resistance 30b may have a value of 400 ohms and in any event resistances 3% are high and resistance 30b quite low.

The point 30a is connected via a bus, and via a coupling condenser 30c to the grid of a triode amplifier tube 32, this grid being connected to ground via a grid leak 33 in conventional fashion.

The grid leak 33 may be of high resistance and the condenser 30c sufficiently large that no difierentiation occurs. It is important to note that no differentiation takes place, because of the character of the coupling circuit employed. The triode 32 is anode-loaded by means of a resistance 34 and is supplied with anode voltage from a B+ terminal 35, in conventional fashion. The anode of the triode 32 is coupled via a coupling condenser 36 and a grid leak 37, constituting a differentiating network, to a grid of a further triode 38 which is in turn anode-loaded by an anode resistance 39 and supplied with anode voltage from the B+ terminal 35. In response to generation of a pulse at point 30a, a positive pulse appears at the anode of the triode 38. This occurs whenever one of the lamps 3 is energized, despite the then energized conditions of others of the lamps. Once the lamp has been energized, the voltage at point 30a becomes a steady voltage, which is not transferred to the triode 38 because of the presence of the series coupling condensers fade and 36.

It follows that in response to and concurrent with depression of any key of the electronic organ, a corresponding one of the switches 22 is closed, :1 correspond- 4. ing one of the lamps 3 is energized, a voltage rise occurs at point 30a, and a pulse of positive polarity appears at the anode of the triode 38. When the key is released, on the contrar', only a negative pulse appears at the anode of the triode 38, and while the key remains depressed, no change in voltage is detectable at this anode, from the no signal condition.

The anode of the triode 38 is connected via a neon cell 4% and a large condenser 41 back to ground at its cathode. The neon cell 46* and the voltages available thereto are so selected that steady voltage at the anode of the triode 38 is not sufilcient to fire the neon cell 4:). It follows that negative pulses at the anode of the triode 38 have no effect, but the circuitry is so arranged that positive pulses are sufficient to fire or ignite the neon cell 40, in effect closing the circuit for the condenser 41 and charging same toward the voltage of the anode 33. Connected across the condenser 41 is a diode 44, the cathode of which is grounded. it follows that the ungrounded terminal of the condenser 41 can never rise higher than ground potential, even when the neon cell 4% is ignited, the diode 44 constituting a clamping device.

Between the junction 43 of the neon cell 4% and the condenser 41 is connected an extremely high resistance 45, which is in turn connected in series with a negative voltage terminal 46. The diode 44 presents no conductive path to ground for a negative voltage at the tenninal 46. Accordingly, the normal condition of charge for the condenser 41 is that the ungrounded terminal of the condenser 41; i.e., the junction point 43, is at the negative voltage of the terminal 46. When the neon cell conducts, a high positive voltage is applied to the terminal 43, which in effect discharges the condenser 41, bringing the ungrounded terminal to ground potential, but being incapable of raising the potential of the ungrounded potential of the condenser 41 above ground because of the clamping diode 44. The anode of the diode 44 is connected to ground through a relatively high resistance 47 and a condenser 48, in series. The junction of the resistance 47 and the condcnser 48 is connected via an isolating resistance 4-9 to the grid 9 of the triode 11. The triode 11 is, accordingly, continually maintained at the voltage of the terminal 46, until such time as the neon cell 40 fires, raising the terminal 43 to ground potential, and correspondingly raising the potential of the grid 9 to ground potential. For ground potential condition of the triode 11, it has normal gain. When subjected to the negative voltage of the terminal 46, the amplifier stage 10 is inoperative, or at least operative at sufficiently low gain substantially to prevent amplification of signals applied to the stage 10 via the lead 7.

The switch 50 serves to short or open the condenser 48, according as the switch 50 is closed or opened. When closed, the percussive system is disabled, resistance 49 then constituting a grid bias resistance.

The anode of the triode 11 is coupled back to the ungrounded terminal of capacitor 48 via a series connected capacitor C and resistance R. These elements, together with condenser 48 provide a low frequency degenerative feedback path for the triode 11, when the system is percussive, which is eliminated under normal conditions; i.e., when switch 59 is closed. This feedback greatly reduces low frequency thump during percussion, and in addition the condenser C provides a Miller run-down, increasing the capacity of the timing circuit for a given value of condenser 48.

The present system employs a single RC coupling circuit between the point Mia and the trigger tube 40; i.e., the triode 32 is directly coupled to the point 33a and the triode 38 is RC coupled to the triode 32, no coupling condenser being required between point 30a and triode 32. This presents an unobvious advantage, eliminating any necessity for fiip-lop circuits for assuring that percussive effects will occur on depressing a key only, and not on releasing a key.

The voltage at point 30a, in response to depression and raising of a key, is'essentially a square wave, 69, as at FIGURE 2, which is reversed in phase by triode 32. The single RC coupling circuit, comprised of capacitor 36 and resistance 37, is essentially a differentiating circuit, generating a negative pulse 61 at the initiation of the the phase reversed square wave 62 and a positive pulse 63 at the rise ofthe phase reversed square wave 62. The triode 38 introduces a further phase reversal, generating pulses 64 and 65 (line d of FIGURE 2). The trigger tube 40 fires in response to pulse 64 and not in response to pulse 65, and in response to firing of trigger tube 49 a percussive wave form is generated. Were two RC cascaded coupling circuits employed, as for example by providin'g a coupling capacitor in series with bus 31, both the rise and the fall of pulse 69 would give rise to a pair. of pulses of successively opposite polarities, as 66, '67, and 68, 69. The trigger tube 46 would accordingly fire in response to both the rise and the fall of the pulse 61.

Reviewing now the operation of the present system, as the keys of an electronic organ incorporating the system are manipulated, various ones of the switches 22 are selectively closed. Closure of any one of the switches 22 results in illumination of the corresponding one of the lamps 3, the light from which passes through the modulating pitch disc 1 to the photoelectric cell 6, resulting in generation of tonal signal which is applied to the tonal amplifier stage for further processing in the formant filters 19 and eventual amplification by means of the audio amplifier 20 to a sufiicient level for radiation as sound. The tonal amplifier stage 16 is, however, normally maintained inoperative or at sufiiciently low gain that transfer of signal therefrom does not occur, by reason of theapplication tothe grid 9 of the stage 10 of a negative voltage deriving from. the terminal 46. Whenever one of the lamps 3 is energized, a positive signal is generated at the point 30a, which is amplified by the cascaded triode tubes 36 and 38, but differentiated only once by RC circuits 36, 37, and appears at the anode of the tube 38 as a single high positive pulse. This high positive pulse fires the normally de-ignited neon cell 46, permitting passage of current into the condenser 41. The condenser 41 is normally maintained with its ungrounded terminal at a negative voltage deriving from the terminal 46. When the neon cell 40 ignites, the voltage of the ungrounded terminal condenser 41 rises to ground potential, being prevented from rising farther by the clamping diode 44. The resistance 47 and the condenser 48, in series, constitute a clock filter, which prevents extremely rapid application of voltage rise to the grid 9 of the triode-ll. The rise time is made sutficiently slow that audible clicks are avoided. When the pulse available at the anode of the triode 38 has terminated, because the illumination from the array of lamps 3 has attained a steady state, the condenser 41 proceeds to vary its charge so that its ungrounded terminal may re-attain the voltage of the terminal 46. This is a relatively slow process since the discharge must take place through the high resistance 45. Accordingly, there is generated a percussive tonal envelope which has a relatively rapid rise and a relatively slow decay.

The rise time may be adjusted by adjusting the resistance 47, while the decay-time may be adjusted by varying the value of the resistance 45.

Raising a previously depressed one of keys 22 has no effect on the percussive eifect generating system, since only a negative pulse is thereby generated at the anode of triode 32.

The function of the present invention, in a general sense, is then to effect percussive translation'of tones from the tone generator of a photoelectric organ, by generating a rapidly rising automatic volume control (AVC) voltage in response to and concurrent with actuation of any key, followed by a relatively slow decay of gain, to a no-gain condition, in the ensuing time.

In response to closure of any key, all the keys concurrently depressed give rise to tones having percussive efiects which are co-extensive with the percussive effect allocable to the last depressed key.

The entire percussion circuit may be readily disabled by means of a stop switch 50, which shorts out condenser 48 when closed.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. In a system for producing percussive effects in a photoelectric musical instrument of the type comprising an ensemble of key controlled electric light sources energizable selectively in response to actuation of said keys, photoelectric means for intercepting light from said light sources, a modulating device for modulating the light from each of said light sources according to a musical tone and a gain controllable audio amplifier and acoustic transducer system connected in cascade with said photoelectric cell, the combination of resistive matrix means for generating a pulse of predetermined character only in response to actuation of at least one of said keys, means normally maintaining said audio amplifier in substantially zero gain condition, and means responsive to said pulse of predetermined character for relatively rapidly increasing the gain of said amplifier and for thereafter decreasing the gain of said amplifier to substantially zero gain condition.

2. The combination according to claim 1, wherein is provided a normally non-conductive gaseous conduction device having two electrodes and a body of gas therebetween, means responsive to said pulse for efiecting a discharge between said electrodes, a condenser, means normally maintaining a predetermined voltage level across said condenser, means responsive to said discharge for transiently increasing said voltage across said condenser, a connection from said condenser to said amplifier for controlling the gain of said amplifier as a function of the said voltage across said condenser, and means continuously operative for slowly bringing the voltage of said condenser toward said predetermined voltage level.

3. The combination according to claim 2, wherein is provided selectively operable means for preventin transfer of the voltage of said condenser to said amplifier.

4. An electrical musical instrument comprising a plurality of electrical tone generators of a type requiring the application of a potential thereto to render them operative, each of said generators including an electric lamp for generating a light beam and a light beam modulating element, a keyboard comprising a plurality of playing keys, a source of potential, switches respectively operated by the keys and respectively connected to the electric lamps to render said tone generators operative, pulse producing electronic means operable in response to initiation of energization of any one of said lamps even though other lamps are energized at the time of said initiation, percussive tonal envelope means coupled to said electronic means and adapted to be momentarily energized by the pulses produced by said pulse producing electronic means, and an output system including at least one electroacoustic transducer coupled to the output of said percussive tonal envelope means, said pulse producing electronic means including a resistance matrix, said resistance matrix including a high resistance in parallel between each of said lamps and a common point, and a low resistance connected from said common point to a point of reference potential.

5. In combination, a plurality of loads, a source of i voltage, means for selectively energizing said loads from said source of voltage, said last means including a separate key operated switch in series between said source of voltage and each of said loads, a relatively large resistance connected between each junction of one of said switches and the load which is connected in series therewith and a common point, a relatively small resistance connected between said common point and a point of reference potential, and a high pass filter connected in cascade with said common point, whereby said high pass filter provides a short control pulse in response to closure of any one or more of said key operated switches.

6. The combination according to claim 5 wherein each of said loads is a lamp load.

7. In a percussion system for an electronic organ, a plurality of tone generating circuits, each of said tone generating circuits including an electrically energizable device responsive to a predetermining energizing voltage and drawing a predetermined energizing current, a source of DC. voltage, substantially impedanceless connections aoaae'os between said source of DC. voltage and all said devices in parallel, a common impedance, separate impedance means responsive to application of voltage from said source of DC. voltage to each of said devices for generating a control pulse in said common impedance, and means responsive to said control pulse for generating a percussive envelope.

8. The combination according to claim 7 wherein each of said separate means is a resistance connected in parallel with one of said devices and in series with said common impedance.

References Cited in the file of this patent UNITED STATES PATENTS 1,886,687 Jacobs Nov. 8, 1932 2,033,232 Eremeeff Mar. 10, 1936 2,301,871 Hanert Nov. 10, 1942 2,357,191 Hanert Aug. 29, 1944

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