US3609202A

US3609202A - Electronic organ gating system

Info

Publication number: US3609202A
Application number: US541380A
Authority: US
Inventors: Alfred J Bissonette; Walter Munch Jr
Original assignee: DH Baldwin Co
Current assignee: BPO ACQUISITION CORP; Baldwin Piano and Organ Co; DH Baldwin Co
Priority date: 1966-04-08
Filing date: 1966-04-08
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28

Abstract

A gating system for electronic music, wherein a pair of gates is employed to gate each tone signal, the gates being in cascade for each tone signal, and each pair of gates utilizing a common first gate directly connected to a tone signal generator, followed by two parallel gates, one proceeding to a 4'' bus and one to an 8'' foot bus.

Description

United States Patent Alfred J. Bissonette Terrace Park, Ohio; Walter Munch, Jr., Covington, K 541,380

Apr. 8, 1966 Sept. 28, 197 l D. H. Baldwin Comapny Cincinnati, Ohio Inventors Appl. No. Filed Patented Assignee ELECTRONIC ORGAN GATING SYSTEM 12 Claims, 5 Drawing Figs.

US. Cl 84/1.0l, 84/113, 84/1.24, 84/1.26

Int. Cl Gl0h 1/00 Field of Search 307/244,

256, 259,239, 253; 84/1.0l, 1.12, 1.04, 1.1 1, 1.17,l.19,1.21-l.23,l.26,1.06, 1.07,1.13; 328/102,101

[56] References Cited UNITED STATES PATENTS 2,618,753 11/1952 Van Mierlo 307/259 X 3,176,060 3/1965 Bissonette et al 84/1.01 3,408,449 10/1968 Tinker 84/1 .11 3,509,263 4/1970 Cordry 84/1.13

Primary ExaminerMilton O. Hirshfield Assistant Examiner-Ulysses Weldon Att0meysW. H. Breunig and Hurvitz and Rose ABSTRACT: A gating system for electronic music, wherein a pair of gates is employed to gate each tone signal, the gates being in cascade for each tone signal, and each pair of gates utilizing a common first gate directly connected to a tone signal generator, followed by two parallel gates, one proceeding to a 4' bus and one to an 8' foot bus.

PATENTEusfiPza 12m SHEET 2 BF 2 FIGA E "C I I0 BY fiuuam ELECTRONIC ORGAN GATING SYSTEM This application pertains to electronic musical instruments and, in particular, concerns a improved keying system for electronic organs and the like.

Prior art systems have in many cases employed variable-resistance key switches which prevent key clicks in keying circuits for electronic organs. Also, in accordance with the teachings of the above-mentioned Munch and Scherer patent, diode gates have also been employed using a direct-contact switch and a diode keying circuit for accomplishing the desired onset to the musical tones. In keying circuits such as the latter of the systems mentioned above, if several gates are employed for keying a common-frequency signal to a number of different circuits, difficulty is sometimes developed with feed-through by virtue of the inherent capacitance of the diodes.

Essentially, when a single oscillator is to be passed via multiple gates to plural loads, each of the gates in its nonconductive condition passes some of the output to the oscillator and for two, three or more such gates the oscillator may provide audible output at a sufficient level to be disturbing to the sensitive ear, because each gate contributes some feed-through signal.

In accordance with the present invention, a diode additional to those in the gates is provided in association with each oscillator, but not each gate. The additional diode pertaining to an oscillator is gated on when any gate associated with that oscillator is gated on. While the oscillator output is not being gated through leakage therefrom is thus reduced. When the oscillator output is being gated through, any leakage therefrom which may eitist is audibly lost in the intentionally gated through tone.

Therefore, it is a primary object of this invention to provide a low cost keying system of improved performance for an electronic musical instrument.

Another important object of the invention is to obviate the use of variable'resistance key switches in keying circuits for electronic organs.

It is a further object of the invention to provide an economical double diode gating system for tones of electronic organs, in which one diode gate normally isolates a tone source as to all possible utilization circuits while another gates through that tone source to a specific utilization circuit, so that when a tone source is not being utilized at all it is doubly isolated from all utilization circuits.

It is another object of the invention to provide a novel diode gating circuit employing two gates in cascade which are both rendered selectively conductive and nonconductive in response to a single control voltage applied via a single control lead.

It is still another object of the present invention to provide a gating circuit for tone signals, employing two cascaded gates, one of which is a shunting gate and the other of which is a series gate, in which both gates are selectively rendered conductive and nonconductive in response to a single gating voltage applied via a single lead.

It is still another object of the present invention to provide a novel gating circuit for musical tones, in which two single diodes are employed in each gating system, one of which passes tone from a tone source for utilization in a plurality of utilization circuits, and the other of which selects a particular utilization circuit.

These and other objects, which will be obvious to one skilled in the art upon reading these specifications, are accomplished by the exemplary embodiments described herein.

Reference is made to the accompanying drawings, in which:

FIG. 1 is a block diagram of an organ gating system according to the invention;

FIG. 2 is a schematic circuit diagram of a portion of the system of FIG. 1;

FIG. 3 is a schematic circuit diagram of a modification of the circuit of FIG. 2;

FIG. 4 is a schematic circuit diagram of a modification of the gating circuitry of FIG. 1, capable of inclusion in the system of FIG. 1 in substitution of the gating circuit there employed; and

FIG. 5 is a schematic circuit diagram of a modification of the system of FIG. 4.

Briefly describing one preferred embodiment of the present invention, each tone generator of an organ is connected in series with a first gate, which is normally maintained nonconductive. The first gate proceeds to several parallel second gates, which are rendered conductive individually at will on closure of key switches, which selectively apply DC on gating voltage to the gates. Any one of the parallel second gates which is rendered conductive conveys its DC gating voltage to its associated first gate, rendering the latter conductive of the tone signal. Accordingly, each tone generator provides a tone to a load via a first gate, and any one of several second gates, the latter being in parallel with each other, but all in series with the first gate. When any one of the several second gates is rendered conductive, the first gate is thus also rendered conductive. Feedthrough from the generator to its ultimate load, a loudspeaker, is thereby minimized when all the associated second gates are nonconductive. When any of the second gates is rendered conductive, so that the associated tone is heard, some fcedthrough via the others of the second gates occurs, but is permissible since it is superposed on a tone having a compatible tone spectrum, or identical frequencies.

A bypass impedance is connected to ground from each first gate, but not, unless desired, from the second gates. The bypass impedance has small impedance to ground for signal, relative to the nonconductive feed-through impedance of the first gate, but relatively large impedance ground for signal, relative to the conductive impedance of the first gate. Isolation at the first gate is thus enhanced, which minimizes total feedthrough with a minimum number of bypass impedances to ground, i.e. one for each tone source of an organ system rather than one for each gate. In FIG. 1, source C C,, C,, and C, represent selected exemplary sources from a rank of generators covering the usual several octaves of an electronic organ, C and C being an octave apart, and C, and C, being an octave apart. They are shown having a common connection to a circuit 10 which provides a grounded return path for the tone signals from an output system to be described. Tone signals from the sources mentioned are shown as passing to

diodes

2, 4, 6 and 8, respectively, and thence to points ll, l2, l4 and 16, respectively, from which are shown two keying circuit paths for each source, comprising, in the case of the signal from source C,, one path consisting of series back-to-back diodes l8 and 20, with a common resistor 22 having a terminal connected to their junction, and a tone-envelope-shaping capacitor 24, connecting the other terminal of resistor 22 to ground. The gate comprising the

elements

18, 20 and 22 is made effective by the key switch 26, passing direct current from a source 28 to the gate via a charging resistor 30, when key switch 26 is closed. The rate of buildup of the signal will be determined primarily by the time constant of the resistor 30 and capacitor 24. Upon opening of switch 26, the decay envelope will be determined principally by the time constant of the resistance 22 and capacitor 24. Signal derived through the gate just mentioned may be collected in an 8' collector 32, the output of which may be passed through a tone color filter 34 by closure of the stop switch 36, or through another filter 38 through a stop switch 40. The outputs of

filters

34, 38 may pass to an output system comprised of the usual amplifier 40 and loudspeaker system 42. As is well known in the art addi tional filter circuits and stop switches may be used, if so desired.

Actuated concurrently by switch 26 is a second gate circuit comprising a charging resistor 46 for the envelope-shaping capacitor 48, connected through series resistor 50 to the diode portion of the gate, which is composed of series connected back-to-back diodes 52 and $4. This gate is connected to the collector 56 and to a tone color system comprised of

filters

58 and 60, actuable by

stop switches

62 and 64.

Filters

58 and 60 in turn pass signal to the output system comprised of amplifier 40 and loudspeaker system 42. The signal for the gate comprised of

diodes

52 and 54 derives from the source C by way of diode 6 and point 14.

The circuits just described show how signals may be concurrently derived from two separate sources. On the other hand, more than one tone signal from the same source, such as C,, may be derived concurrently, for example, by way of switch 26 and a switch 66 which supplies direct current to resistor 68 from source 28. The keying voltage is supplied gradually to the capacitor 70 through the resistor 68 and is applied to the gate composed of

diodes

72 and 74 by way of resistor 76. The signal appears in the collector 32 and may be heard in the output system, as desired, by a closure of stop switches, such as 36 and 40.

Thus, it will be seen that the diode 6 is common to two key ing circuits, one comprised of

diodes

52 and 54 and the other of

diodes

72 and 74, and conducts when either of the keying circuits is conductive.

In accordance with the teachings of the aforementioned Munch and Scherer patent, a bypass impedance 78, which may be composed of a parallel combination of resistance and capacitance, (as in FIG. 2) is indicated generally at 78 for each signal path. This impedance is related to the other impedances of each circuit such that when, for example, the gate connected to the point 14 is nonconductive, the bypass impedance of 78 is relatively low with respect to the nonconductive impedance of the gate, but when the gate is conductive, the impedance of 78 is high with respect to the conductive impedance of the gate. Thus, it will be seen that a diode such as 6, and an associated shunt impedance 78, provide extra isolation and reduction of feed-through for both the gates comprised of

diodes

72 and 74 and of the

diodes

52 and 54.

It will be obvious, in accordance with the teachings of this invention, that additional gates may be connected to a point such as 14, as desired, the diode 6 acting as isolation for them also. Similar switching and gating circuits are shown for sources C,, C and C,, but it is not believed necessary to detail their operation. It will be obvious that it will be similar to that of the gate and keying circuits described.

In order to maintain the proper impedance relationships in the circuit, load or coupling resistors are shown at 80 and 82.

The circuit element 78 is illustrated in FIG. 1 as an impedance. The function of impedance 78 is to provide a low bypass impedance when the gate is nonconductive, relative to the gate impedance, but to provide a relatively high impedance relative to gate impedance when the gate is conductive.

The impedance 78 may take various forms, one of which is the parallel RC network of FIG. 2 and another of which is the capacitance 77 of FIG. 3, embodied in impedance 78'. The network of FIG. 2 is useful in enabling application of a bias, C to diode 8, which is not feasible in the circuit of FIG. 3. In either case the impedance values for the several gates must be properly selected, for the different frequencies of the several tone sources, to perform the required function in each case.

In the gating system of FIG. 4, a source 100 of musical tone signals, represented as square waves, but which may be sinusoidal or sawtooth in form, is connected from ground to a first gating point 101, via a resistance 102. A diode 103 is connected between point 101 and ground, its anode being at ground. A negative bias voltage source 104 is connected to point 101 through a resistance 105. The bias voltage is sufficiently high to render diode 103 conductive, for all values of the tone signal.

Point 101 is connected in series with a double diode gate 106, comprised of

diodes

107 and 108 having their anodes back to back to form agating junction 109. The cathode of diode I08 proceeds to a resistance, as 80 of FIG. 1, which may be termed broadly a load, or coupling resistance.

Leads O then correspond with connections to other gates, i.e. may represent a 4' or 8' bus, as 56 or 32 of FIG. 1. The connections 0, are employed for gates which use a common gating voltage, whereas O indicates connections to other diodes which use the same pitch, by analogy to FIG. 1. Accordingly, the point 101 of FIG. 4 may correspond with points such as 16, 14, 12 or 11 of FIG. 1. The operation of the diode gate 106 is the same as has been described in FIG. I. The difference between the systems of FIG. 1 and FIG. 4 relates then to the substitution of shunt diode 103, for series diodes as 8, 6, etc. ofFIG. 1.

In FIG. 4, on closure of key-operated switch 110, positive gating voltage charges capacitance 24, via charging resistance 30, and the voltage across capacitance 24 is applied to gating point 109, rendering gate 106 conductive. At the same time, the positive gating voltage passes through diode 107 and is applied to junction point 101. The cathode of diode 103 then becomes biased positively, and the diode 103 thereupon becomes nonconductive of the tone signal to ground, but transmissive thereof to the gate 106 and output system.

Applying corresponding numerals of reference to corresponding parts of FIGS. 5 and 4, the diodes 107, 108 (FIG. 4) are dispensed with, and resistances 120, 121 substituted, providing a junction or gating point 109. To point 109 is connected the cathode of a single diode 122, the anode of which is grounded, and negative bias is applied to the anode of diode 122 from terminal 104 via resistance 105.

By virtue of its negative bias, diode 122 is normally conductive and provides a low impedance ground at point 109. By virtue of that same bias, diode 125, in series with tone source 100, is rendered nonconductive of tone signal, since its anode is coupled to point 109.

On application of positive bias voltage to point 109, by closure of switch 110, diode 122 becomes nonconductive and diode I25 conductive, rendering the entire gate transmissive to signal to the output system.

The general and overall system of FIG. I may employ the gating system indicated in FIG. I, or either of those illustrated in FIGS. 4 and 5. The impedance 78 may be employed in the system of FIG. 5, but is not required in the system of FIG. 4, since in that system diode 103 provides the required obviating action.

While we have described and illustrated one specific embodiment of our 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 is claimed is:

1. In an electronic music system,

a tone signal source,

a first diode gate connected in cascade with said tone signal source,

a load circuit connected in series with said diode gate,

a further diode gate connected to gate said tone signal from said tone signal source to said first diode gate,

said first and further diode gates being normally both nonconductive of said tone signal from said tone signal source to said load circuit,

a source of gating voltage,

keying means for at will connecting said source of gating voltage to said first diode gate,

said first diode gate being arranged to become conductive in response to application of said gating voltage thereto by said keying means,

means responsive to operation of said keying means for connecting said source of gating voltage to said first diode gate for concurrently applying said gating voltage to said further diode gate in such sense as to render said further diode gate conductive of said tone signal to said load circuit,

wherein said first diode gate includes a pair of back to back diodes, and

wherein said further diode is connected in shunt to said tone signal source, and

means for applying said voltage to the junction of said pair of back to back diodes.

2. In an electronic music system,

a tone signal source,

a first diode gate connected in cascade with said tone signal source, I

a load circuit connected in series with said diode gate,

a source of gating voltage,

wherein said first diode gate includes a pair of back to back diodes, and

wherein said further diode is connected in series with said tone signal source, and

means applying said voltage to the junction of said pair of back to back diodes.

3. In an electronic music system,

a tone signal source,

a first diode gate connected in cascade with said tone signal source,

a load circuit connected in series with said diode gate,

a source of gating voltage,

means responsive to operation of said keying means for connecting said source of gating voltage to said first diode gate for concurrently applying said further diode gate conductive of said tone signal to said load circuit,

wherein said first diode gate is a shunt diode gate and said further diode gate is connected in series between said tone signal source and said first diode gate.

4. The combination according to claim 2 wherein is further provided a passive impedance connected in shunt from a point intermediate said gates and a point of reference potential,

said impedance having a value small relative to the nonconductive impedance of said further diode gate but large relative to the conductive impedance of said further diode gate.

5. The combination according to claim 3 wherein is further provided a passive impedance connected in shunt from a point intermediate said gates and a point of reference potential,

6. The combination according to claim 3 wherein each of said diode gates includes only one solid-state diode.

7. A gating circuit, comprising,

a source of tone signal,

a load,

a normally nonconductive solid-state diode keying circuit,

a solid-state diode gate in cascade with and antecedent to said first normally nonconductive solid-state diode keying circuit,

a source of DC keying voltage,

said keying circuit being normally nonconductive of said tone signal to said load and being rendered conductive responsive to application thereto of said DC keying voltage,

means for at will applying said DC keying voltage to said solid-state diode keying circuit,

means normally biasing said gate to nonconductive condition, and

means responsive to application of said DC keying voltage to said keying circuit for further applying said DC keying voltage to bias said gate into conductive condition of said signal to said load,

wherein said solid-state diode keying circuit includes back to back diodes, and said gate includes a single solid-state diode.

8. A gating circuit, comprising,

a source of tone signal,

a load,

a normally nonconductive solid-state diode keying circuit,

a solid-state diode gate in cascade with an antecedent to said first normally nonconductive solid-state diode keying circuit,

a source of DC keying voltage,

means normally biasing said gate to nonconductive condition, and

herein said keying circuit is a shunt to said source of signal and said gate is connected in series between said source of signal and said load.

9. A gating circuit, comprising,

a source of tone signal,

a load,

a normally nonconductive solid-state diode keying circuit,

a source of DC keying voltage,

means normally biasing said gate to nonconductive condition, and

wherein said keying circuit is in series with said source of signal and said load, and said gate is in circuit shunting said source of signal.

10. A keying system for an electric organ, comprising a tone source,

a normally nonconductive first gate in cascade with said tone source,

at least two second gates connected in cascade with said first gate and in parallel with each other,

separate key-operated means for rendering said second gates selectively conductive,

means responsive to conductivity of either of said second gates for rendering said first gate conductive,

filter circuits connected in cascade with said second gates,

and

a speaker connected in cascade with said filter circuits,

wherein is further provided a bypass circuit to ground for said first gate,

said bypass circuit to ground having a low impedance relative to the leakage impedance of said first gate and a high impedance relative to the conductive impedance of said first gate, at any frequency of said tone source.

ll. In an electronic musical instrument,

a source of tone signal,

a gate nonnally nonconductive of said tone signal connected in cascade with said source of tone signal,

a first tone channel connected in cascade with said gate,

a second tone channel connected in cascade with said gate and in parallel with said first tone channel,

a first tone signal collector connected to said first tone,

channel,

a second tone signal collector connected to said second tone channel,

said tone channels including each a separate normally nonconductive keying device, and

means responsive to transferring of either of said keying devices to its conductive state for rendering said normally nonconductive gate conductive of said tone signal,

wherein is further provided a shut impedance connecting the junction of said gate and said tone channels to a point of reference potential,

said shunt impedance having an impedance value relatively small in comparison with the nonconductive impedance of said gate while nonconductive and relatively large in comparison with the conductive impedance of said gate, whereby said shunt impedance substantially attenuates feed-through of said signal from said source of tone signal to said tone channels only while said gate is nonconductive.

12. In an electrical musical instrument,

a tone signal source,

a least two tone signal collectors,

a separate keying circuit connected in parallel between said tone signal source and each of said collectors,

a intermediate isolating gate connected between said tone signal source and said separate keying circuits,

said isolating gate and said keying circuits being normally nonconductive of said tone signal, and

means for at will rendering said keying circuits selectively conductive of said tone signal and for concurrently rendering said isolating gate conductive of said tone signal,

wherein is further provided an impedance shunting said tone signal to a point of reference potential and located intermediate said keying circuits and said isolating gate, said impedance having an impedance value selected effectively to bypass said tone signal only while said gate is nonconductive.

Claims

1. In an electronic music system, a tone signal source, a first diode gate connected in cascade with said tone signal source, a load circuit connected in series with said diode gate, a further diode gate connected to gate said tone signal from said tone signal source to said first diode gate, said first and further diode gates being normally both nonconductive of said tone signal from said tone signal source to said load circuit, a source of gating voltage, keying means for at will connecting said source of gating voltage to said first diode gate, said first diode gate being arranged to become conductive in response to application of said gating voltage thereto by said keying means, means responsive to operation of said keying means for connecting said source of gating voltage to said first diode gate for concurrently applying said gating voltage to said further diode gate in such sense as to render said further diode gate conductive of said tone signal to said load circuit, wherein said first diode gate includes a pair of back to back diodes, and wherein said further diode is connected in shunt to said tone signal source, and means for applying said voltage to the junction of said pair of back to back diodes.

2. In an electronic music system, a tone signal source, a first diode gate connected in cascade with said tone signal source, a load circuit connected in series with said diode gate, a further diode gate connected to gate said tone signal from said tone signal source to said first diode gate, said first and further diode gates being normally both nonconductive of said tone signal from said tone signal source to said load circuit, a source of gating voltage, keying means for at will connecting said source of gating voltage to said first diode gate, said first diode gate being arranged to become conductive in response to application of said gating voltage thereto by said keying means, means responsive to operation of said keying means for connecting said source of gating voltage to said first diode gate for concurrently applying said gating voltage to said further diode gate in such sense as to render said further diode gate conductive of said tone signal to said load circuit, wherein said first diode gate includes a pair of back to back diodes, and wherein said further diode is connected in series with said tone signal source, and means applying said voltage to the junction of said pair of back to back diodes.

3. In an electronic music system, a tone signal source, a first diode gate connected in cascade with said tone signal source, a load circuit connected in series with said diode gate, a further diode gate connected to gate said tone signal from said tone signal source to said first diode gate, said first and further diode gates being normally both nonconductive of said tone signal from said tone signal source to said load circuit, a source of gating voltage, keying means for at will connecting said source of gating voltage to said first diode gate, said first diode gate being arranged to become conductive in response to application of said gating voltage thereto by said keying means, means responsive to operation of said keying means for connecting said source of gating voltage to said first diode gate for concurrently applying said gating voltage to said further diode gate in such sense as to render said further diode gate conductive of said tone signal to said load circuit, wherein said first diode gate is a shunt diode gate and said further diode gate is connected in series between said tone signal sOurce and said first diode gate.

4. The combination according to claim 2 wherein is further provided a passive impedance connected in shunt from a point intermediate said gates and a point of reference potential, said impedance having a value small relative to the nonconductive impedance of said further diode gate but large relative to the conductive impedance of said further diode gate.

5. The combination according to claim 3 wherein is further provided a passive impedance connected in shunt from a point intermediate said gates and a point of reference potential, said impedance having a value small relative to the nonconductive impedance of said further diode gate but large relative to the conductive impedance of said further diode gate.

7. A gating circuit, comprising, a source of tone signal, a load, a normally nonconductive solid-state diode keying circuit, a solid-state diode gate in cascade with and antecedent to said first normally nonconductive solid-state diode keying circuit, a source of DC keying voltage, said keying circuit being normally nonconductive of said tone signal to said load and being rendered conductive responsive to application thereto of said DC keying voltage, means for at will applying said DC keying voltage to said solid-state diode keying circuit, means normally biasing said gate to nonconductive condition, and means responsive to application of said DC keying voltage to said keying circuit for further applying said DC keying voltage to bias said gate into conductive condition of said signal to said load, wherein said solid-state diode keying circuit includes back to back diodes, and said gate includes a single solid-state diode.

8. A gating circuit, comprising, a source of tone signal, a load, a normally nonconductive solid-state diode keying circuit, a solid-state diode gate in cascade with and antecedent to said first normally nonconductive solid-state diode keying circuit, a source of DC keying voltage, said keying circuit being normally nonconductive of said tone signal to said load and being rendered conductive responsive to application thereto of said DC keying voltage, means for at will applying said DC keying voltage to said solid-state diode keying circuit, means normally biasing said gate to nonconductive condition, and means responsive to application of said DC keying voltage to said keying circuit for further applying said DC keying voltage to bias said gate into conductive condition of said signal to said load, wherein said keying circuit is a shunt to said source of signal and said gate is connected in series between said source of signal and said load.

9. A gating circuit, comprising, a source of tone signal, a load, a normally nonconductive solid-state diode keying circuit, a solid-state diode gate in cascade with and antecedent to said first normally nonconductive solid-state diode keying circuit, a source of DC keying voltage, said keying circuit being normally nonconductive of said tone signal to said load and being rendered conductive responsive to application thereto of said DC keying voltage, means for at will applying said DC keying voltage to said solid-state diode keying circuit, means normally biasing said gate to nonconductive condition, and means responsive to application of said DC keying voltage to said keying circuit for further applying said DC keying voltage to bias said gate into conductive condition of said signal to said load, wherein said keying circuit is in series with said source of signal and said load, and said gate is in circuit shunting said source of signal.

10. A keying system for an electric organ, comprising a tone source, a normally nonconductive first gate iN cascade with said tone source, at least two second gates connected in cascade with said first gate and in parallel with each other, separate key-operated means for rendering said second gates selectively conductive, means responsive to conductivity of either of said second gates for rendering said first gate conductive, filter circuits connected in cascade with said second gates, and a speaker connected in cascade with said filter circuits, wherein is further provided a bypass circuit to ground for said first gate, said bypass circuit to ground having a low impedance relative to the leakage impedance of said first gate and a high impedance relative to the conductive impedance of said first gate, at any frequency of said tone source.

11. In an electronic musical instrument, a source of tone signal, a gate normally nonconductive of said tone signal connected in cascade with said source of tone signal, a first tone channel connected in cascade with said gate, a second tone channel connected in cascade with said gate and in parallel with said first tone channel, a first tone signal collector connected to said first tone channel, a second tone signal collector connected to said second tone channel, said tone channels including each a separate normally nonconductive keying device, and means responsive to transferring of either of said keying devices to its conductive state for rendering said normally nonconductive gate conductive of said tone signal, wherein is further provided a shunt impedance connecting the junction of said gate and said tone channels to a point of reference potential, said shunt impedance having an impedance value relatively small in comparison with the nonconductive impedance of said gate while nonconductive and relatively large in comparison with the conductive impedance of said gate, whereby said shunt impedance substantially attenuates feed-through of said signal from said source of tone signal to said tone channels only while said gate is nonconductive.

12. In an electrical musical instrument, a tone signal source, at least two tone signal collectors, a separate keying circuit connected in parallel between said tone signal source and each of said collectors, an intermediate isolating gate connected between said tone signal source and said separate keying circuits, said isolating gate and said keying circuits being normally nonconductive of said tone signal, and means for at will rendering said keying circuits selectively conductive of said tone signal and for concurrently rendering said isolating gate conductive of said tone signal, wherein is further provided an impedance shunting said tone signal to a point of reference potential and located intermediate said keying circuits and said isolating gate, said impedance having an impedance value selected effectively to bypass said tone signal only while said gate is nonconductive.