U.S. patent number 3,707,594 [Application Number 05/121,387] was granted by the patent office on 1972-12-26 for automatic rhythm sound producing device adapted for use with keyboard musical instruments.
This patent grant is currently assigned to Nippon Gakki Seizo Kabushiki Kaisha. Invention is credited to Kiyoshi Ichikawa.
United States Patent |
3,707,594 |
Ichikawa |
December 26, 1972 |
AUTOMATIC RHYTHM SOUND PRODUCING DEVICE ADAPTED FOR USE WITH
KEYBOARD MUSICAL INSTRUMENTS
Abstract
An automatic rhythm sound producing device built in a keyboard
musical instrument capable of playing ordinary tones of the melody,
chord or bass, or combinations thereof upon selective depression of
a plurality of keys arranged in the order of musical notes. The
device includes a combination pulse generator which comprises a
clock pulse generator followed by a frequency dividing counter
chain to generate combination pulses, and having a resetting
arrangement. The outputs from the combination pulse generator are
supplied to a timing pulse encoder so as to cause outputs of the
various stages of the counter chain to appear on the output lines
of the encoder as a train of selected timing pulses which represent
desired rhythm patterns. The outputs from the encoder are supplied
to individual rhythm sound generators to produce rhythm sounds
according to the selected rhythm patterns for an automatic rhythm
performance. A trigger generator is provided to detect a depression
of a key and upon detection to start the normally reset counter
chain, thereby initiating the automatic rhythm performance.
Inventors: |
Ichikawa; Kiyoshi (Hamakita,
JA) |
Assignee: |
Nippon Gakki Seizo Kabushiki
Kaisha (Hamamatou-shi, Shizuoka-ken, JA)
|
Family
ID: |
26356788 |
Appl.
No.: |
05/121,387 |
Filed: |
March 5, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Mar 10, 1970 [JA] |
|
|
45/22708 |
Mar 10, 1970 [JA] |
|
|
45/19911 |
|
Current U.S.
Class: |
84/713;
84/DIG.12; 84/667; 984/351 |
Current CPC
Class: |
G10H
1/40 (20130101); Y10S 84/12 (20130101); G10H
2230/321 (20130101); G10H 2210/391 (20130101); G10H
2230/265 (20130101) |
Current International
Class: |
G10H
1/40 (20060101); G10f 001/00 () |
Field of
Search: |
;84/1.01,1.03,1.24,DIG.12 ;307/220,222,223 ;331/51 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Weldon; U.
Claims
What I claim is:
1. An automatic rhythm sound producing device adapted for use with
a keyboard musical instrument which includes a first playing
section having--a plurality of keys arranged in the order of
musical notes for playing tones of a melody and those of an
accompaniment upon selective depression of said keys, said first
playing section being separate from said automatic rhythm sound
producing device, said automatic rhythm sound producing device
comprising:
a clock pulse generator for generating a repetitive frequency
signal corresponding to a multiple of the basic rhythm
frequency;
a frequency dividing counter chain including a plurality of counter
stages and coupled with the clock pulse generator for counting down
to submultiples of the frequency of signals generated from said
clock pulse generator and including a resetting means for
maintaining said counter chain normally inoperative;
a timing pulse encoder connected to the stages of said counter
chain for producing a plurality of rhythm pattern signals each
being comprised of a preset different combination of output signals
from said clock generator;
a plurality of rhythm sound generators supplied with said
respective rhythm pattern signals for producing a preset rhythm
sound corresponding to a rhythm pattern selected from the output
rhythm pattern signals of said encoder; and
circuit means coupled to said first playing section to generate a
trigger pulse upon detection of the depression of a key in the
keyboard of said separate first playing section, and connected to
said counter chain through the said resetting means to initiate the
operation of said counter chain responsive to said detection of the
depression of a key in said first playing section, thereby
automatically initiating generation of rhythm sounds.
2. The automatic rhythm sound producing device according to claim 1
wherein said circuit means for triggering said counter chain
includes a bistable multivibrator having two active circuit
elements, means coupling a predetermined tone signal produced upon
selective depression of the keys to the input terminal of one of
said elements to bring it to a nonconductive state and to bring the
other element to a conductive state, and means coupling the output
terminal of said other element with each stage of said counter
chain to enable said counter chain.
3. The automatic rhythm sound producing device according to claim 1
wherein said circuit means for triggering said counter chain
comprises a DC power supply with one electrode thereof grounded; a
plurality of key switches connected to the other electrode of said
DC power supply for generating signals upon selective depression of
the corresponding keys; a rectifier for rectifying said generated
signals; a capacitor for receiving the rectified signal and being
charged responsive thereto; and an active circuit element having at
least three electrodes with a first electrode coupled to said
capacitor for supplying a signal corresponding to said charged
signal, with a second electrode coupled to each stage of said
counter chain to enable said counter chain through said element
only upon selective depression of the keys with a third electrode
coupled to the said DC power supply.
4. The automatic rhythm sound producing device according to claim 1
including a plurality of manual switches and wherein said keys are
arranged on several keyboards, the ends on one side of the keys on
each keyboard being jointly grounded, and the ends on the other
side of the keys on all the keyboards being jointly coupled with
said circuit means for triggering said binary counter chain through
corresponding manual switches.
5. The automatic rhythm sound producing device according to claim 1
wherein said circuit means to generate a trigger pulse further
includes selector switches for selectively detecting depressions of
keys in different keyboards.
6. The automatic rhythm sound producing device according to claim 1
wherein said clock pulse generator comprises an astable
multivibrator.
7. The automatic rhythm sound producing device according to claim 1
wherein said counter chain comprises a plurality of flip-flop
circuits connected in cascade, the first stage of which is coupled
with said clock pulse generator.
Description
BACKGROUND OF THE INVENTION
This invention relates to an automatic rhythm sound producing
device and more particularly to an automatic rhythm sound producing
device adapted for use with a keyboard electronic musical
instrument.
With respect to a keyboard electronic musical instrument, for
example, an electronic organ, there has recently been more
favorably accepted a type in which there is incorporated an
automatic rhythm sound producing device having a rhythm section for
playing the percussion sounds of the claves, cymbals, tom tom,
cowbell, or bass drum or the tones of the melody, chord or bass or
combinations thereof in exact timing with a rhythm pattern selected
from various rhythm tempos or patterns such as the march, rumba,
tango, samba, waltz and bossa nova.
FIG. 1 is a schematic circuit diagram of a conventional keyboard
electronic musical instrument in which there is incorporated the
aforementioned type of automatic rhythm sound producing device. The
main device of the musical instrument consists of an organ section
16 comprising keyboards 12 having a plurality of keys 11.sub.1,
11.sub.2 . . . 11.sub.n arranged in the order of musical notes;
keyers 13 associated with the keys 11.sub.n of the keyboards 12 and
provided with a plurality of keying switches operated upon
selective depression of the corresponding keys; tone generators 14
designed to enable to generate tone signals having pitches preset
for the respective keys and, upon selective operation of the keying
switches, produce the corresponding tone signals therefrom; and
tone coloring filters 15 so designed as to form musical sounds
having desired tone colors from the tone signals. On the other
hand, the automatic rhythm sound producing device consists of a
rhythm section 25 comprising a combination pulse generator 22
formed of a clock pulse generator followed by a frequency dividing
counter chain for selecting a desired rhythm pattern from among the
various types of rhythm patterns and actuated by a normally open
switch 21 manually closed at the start of a rhythm performance; a
timing pulse encoder 23 consisting of a proper logic circuit
including diodes in matrix arrangement so as to selectively form a
train of timing pulses corresponding to a desired rhythm pattern
from combination pulses supplied from the generator 22; and rhythm
sound generators 24 for generating rhythm sound signals being
triggered by the timing pulses. The resultant output signals from
the sections 16 and 25 are conducted through separate volume
controllers VR.sub.1 and VR.sub.2 respectively and one common
amplifier A ( which may be provided separately) to be reproduced
from a loud-speaker S (which may be provided separately).
However, where it is desired to play both the tones of the melody,
chord or bass or combinations thereof from the section 16 and the
rhythm sounds from the section 25, the conventional instrument
having an automatic rhythm sound producing device built therein in
the aforementioned manner has the drawbacks that there is not only
required a troublesome process of operating the start switch 21 for
rhythm sound performance in addition to selective depression of a
desired key on the keyboards 12 for musical scale tone performance,
but also there are presented appreciable difficulties in exactly
timing the initiation of rhythm sound performance with that of
musical tone performance.
Further, the prior art instrument generally so designed as to play
as many varieties of performance as possible by full working of
both hands and feet of a player has a disadvantage that when
additionally equipped with the afore-said rhythm section 25, then
the p ayer is obstructed in producing such varieties of performance
due to the required operation of the start switch 21.
It is, therefore, the object of the present invention to provide a
novel type of automatic rhythm sound producing device adapted for
use with a keyboard electronic musical instrument enabling the
automatically synchronous start of the rhythm sounds with the
ordinary melody tones or accompaniment sounds, thereby always
exactly timing the performance of rhythm sounds from the rhythm
section with that of musical tones from the organ section and
effecting performance in a far greater variety.
SUMMARY OF THE INVENTION
According to an aspect of this invention, there is provided an
automatic rhythm sound producing device incorporated in a keyboard
electronic musical instrument for playing the ordinary tones of the
melody, chord or bass or combinations thereof upon selective
depression of a plurality of keys arranged in the order of musical
notes, which device comprises a combination pulse generator formed
of a clock pulse generator followed by a frequency dividing counter
chain to generate combination pulses and having a resetting
arrangement. The outputs at various counter stages are supplied to
a timing pulse encoder to produce a train of selected timing pulses
representing desired rhythm patterns, and outputs from the encoder
are supplied to individual rhythm sound generators, to produce
rhythm sounds according to the selected rhythm patterns for an
automatic rhythm performance. A trigger generator is providied to
detect a depression of the key and upon detection to start the
normally reset counter chain thereby initiating the automatic
rhythm performance.
Further, this invention provides an automatic rhythm sound
producing device adapted for use with a keyboard electronic musical
instrument wherein there are provided normally open switches for
each of several key stages, for example, upper, lower and pedal
keyboards and those used in common to all the key stages, and all
key operation mechanisms are coupled with the combination pulse
generator through the switches, thereby enabling desired rhythm
sounds to be played either at the start of performance or at any
desired time during performance upon selective depression of the
keys of each or all key stages.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic circuit diagram of a prior art automatic
rhythm sound producing device used with a keyboard electronic
musical instrument;
FIG. 2 is a schematic circuit diagram of a keyboard electronic
musical instrument provided with an automatic rhythm sound
producing device according to an embodiment of this invention;
FIG. 3 represents a concrete circuit arrangement of the trigger
generator and combination pulse generator of FIG. 2;
FIG. 4 is a schematic circuit arrangement of an automatic rhythm
sound producing device according to another embodiment of the
invention adapted for use with a keyboard electronic musical
instrument;
FIG. 5 is a schematic circuit arrangement of an automatic rhythm
sound producing device according to still another embodiment of the
invention adapted for use with a keyboard electronic musical
instrument; and
FIG. 6 is an another schematic circuit arrangement of the main part
of connection between the keyboard and rhythm pattern generator
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 is a schematic circuit diagram of a keyboard electronic
musical instrument provided with an automatic rhythm sound
producing device according to an embodiment of this invention. The
organ section 36 of the instrument comprises several keyboards 32,
for example, upper, lower and pedal keyboards having a plurality of
keys 31.sub.1, 31.sub.2 . . . 31.sub.n arranged in the order of
musical notes; keyers 33 having a plurality of keying switches
provided for the respective keys 31.sub.1 to 31.sub.n on the
keyboards 32 to be actuated interlockingly with the corresponding
keys upon their selective depression; tone generators 34 designed
to generate tone signals having pitches preset for the individual
keys and, only upon depression of the corresponding keys, produce
tone signals therefrom; and tone coloring filters 35 for properly
adjusting the colors of tone signals generated so as to form the
ordinary musical tones of the melody, chord or bass or combinations
thereof. In addition to the above-mentioned organ section 36, the
instrument includes a rhythm section 37 enabling rhythm sounds such
as the desired percussion e.g. cymbals, maracas, drums, etc. sounds
and the ordinary tones of the chord or bass sounds or combinations
thereof to be played in exact timing with various tempos, for
example, the march, tango, samba, bossa nova and waltz. In this
case, the present invention is so designed as to enable both
musical tones from the organ section 36 and rhythm sounds from the
rhythm section 37 to be played upon selective depression of the
keys 31.sub.1 to 31.sub.n on the keyboards 32 using, as described
above, output signals from the filter 35 or keyer 33. Namely, the
present invention includes a trigger generator 38 which receives
outputs from the filter 35 or keyer 33 to energize a combination
pulse generator 39 as later described. FIG. 3 is a concrete circuit
arrangement of the generators 38 and 39. The trigger generator 38
comprises an amplifier section 38a having three cascade connected
transistors TR.sub.1, TR.sub.2 and TR.sub.3 to amplify tone signal
outputs from the filter 35 or keyer 33; a wave shaper 38b
consisting of a clipper 51 having two transistors TR.sub.4 and
TR.sub.5 cascade connected to the amplifier section 38a and a
differentiation circuit 52 having a capacitor C and a resistor R
connected to the output terminal of the clipper 51; and a bistable
multivibrator 38c having two transistors TR.sub.6 and TR.sub.7 so
arranged that the base of either of them is supplied with rectified
signals obtained by passing output differentiation signals from the
shaper 38b through a rectifier 53 using, for example, a diode D.
The emitter of the transistor TR.sub.7 is directly grounded,
whereas those of the remaining transistors TR.sub.1 to TR.sub.6 are
grounded through a normally open switch 54 closed by a player only
when there are to be played rhythm sounds from the section 37. On
the other hand, the combination pulse generator 39 comprises a
clock pulse generator 39a formed of an astable vibrator having, for
example, two transistors TR.sub.11 and TR.sub.12 and which
generates a clock pulse train which is a multiple of the basic
rhythm frequency of the device; and a binary counter chain 39b
formed of a plurality of flip-flop circuits FF.sub.1, FF.sub.2,
FF.sub.3 and FF.sub.4 of FIG. 3 (where there is shown in detail
only one of the circuits, the others being indicated in blocks)
cascade connected in turn to the clock pulse generator 39a, each of
the flip-flop circuits including two transistors TR.sub.13 and
TR.sub.14. In this case, the emitters of the two transistors
TR.sub.11 and TR.sub.12 constituting the clock pulse generator 39a
and the emitters of the corresponding ones included in each group
of the paired TR.sub.13 and TR.sub.14 of the cascade connected
flip-flop circuits constituting the binary counter chain 39b are
directly grounded, whereas the emitters of the remaining ones
included in each group of the transistors TR.sub.13 and TR.sub.14
are jointly connected to (as a resetting arrangement) the collector
of one transistor TR.sub.6 of the bistable multivibrator 38C.
Where, in the aforesaid circuit arrangement, there are not supplied
the aforementioned output signals from the filter 35 or keyer 33 to
the amplifier section 38a with the switch 54 closed, that is, where
there is not depressed any of the keys 31.sub.1 to 31.sub.n on the
keyboards 32, the other transistor TR.sub.7 of the bistable
mulitivibrator 38c becomes conductive, while the one transistor
TR.sub.6 remains nonconductive. For the purpose of the present
invention, the bistable multivibrator 38c is so designed in advance
as to reverse the above-mentioned condition only when it is
supplied with output signals from the filter 35 or keyer 33, that
is, to cause the other transistor TR.sub.7 to become inoperative
and the one transistor TR.sub.6 to be fired.
Where the aforesaid circuit arrangement is in a normal condition
where there is not depressed any of the keys 31.sub.1 to 31.sub.n
on the keyboards 32, the transistor TR.sub.7 is conductive and the
transistor TR.sub.6 thereof remains nonconductive. Accordingly, the
flip-flop circuits FF.sub.1 to FF.sub.4 constituting each two
halves designed in the same way and the binary counter chain 39b
remain deenergized. Upon selective depression of any of the keys
31.sub.1 to 31.sub.n, however, the binary multivibrator 38c
presents a reversed condition, that is, where the transistor
TR.sub.7 becomes nonconductive and the transistor TR.sub.6 is
energized. As a result, the emitters of the transistors
constituting each set halves of the flip-flop circuits included in
the binary counter chain 39b are grounded through the collector of
the short-circuited transistor TR.sub.6 to render the flip-flop
circuits energized. Thus the condition of the flip-flop circuits
FF.sub.1 to FF.sub.4 is reversed to cause combination pulses
consisting of binary outputs obtained by successive downward
frequency division of clock pulses from the generator 39a to be
drawn out of the output terminals 1-No. 1, 1-No. 2, 1-No. 3 and
1-No. 4 on the set halves of the flip-flop circuits FF.sub.1 to
FF.sub.4.
Referring again to FIG. 2, a timing pulse encoder or rhythm pattern
generator 40 consists of a logic circuit including for example, the
known diode matrix having a plurality of input and output
terminals. When combination pulses from the output terminals 1-No.
1 to 1-No. 4 on the set halves and the output terminals 0-No. 1,
0-No. 2, 0-No. 3 and 0-No. 4 on the reset halves of the flip-flop
circuits are supplied to the corresponding input terminals in a
preset combination by the player, then there is produced from the
predetermined output terminals a train of timing pulses or rhythm
pattern pulses exactly timed with the rhythm tempos selected from
among those representing, for example, the rumba, march, tango,
samba, waltz and bossa nova. The train of timing pulses thus
selectively obtained from the encoder 40 is supplied to a plurality
of rhythm sound generators 41 so arranged as to selectively
generate the aforesaid varieties of percussion sounds so as to
selectively excite the predetermined one of the rhythm sound
generators 41 preset by the player. Thus depression of any of the
keys on the keyboards 32 causes the desired tones of the melody,
chord or bass or combination thereof from the organ section 36 with
the well-timed start of the rhythm sounds from the rhythm section
37.
The automatic rhythm sound producing device arranged as described
above according to the present invention for use with a keyboard
electronic musical instrument not only enables the performance of
musical tones from the section 36 to be exactly timed with that of
rhythm sounds from the section 37, but also the player to be free
from the necessity of operating the start switch for the rhythm
section as has been the case with the prior art device and
consequently allowing him to carry out performance in as many
varieties as possible by fully working his hands and feet.
It will be noted that the concrete circuit arrangement associated
with the combination pulse generator 39, timing pulse encoder 40
and rhythm sound generators 41 of FIG. 2 are shown in detail in
FIG. 1 and the description thereof set forth in "Automatic Rhythm
Device" invented by Richard H. Campbell, Jr., U.S. Pat. No.
3,358,068 (Ser. No. 378,365).
Referring to FIG. 3, a variable resistor VR included in the clock
pulse generator 39a is intended properly to regulate the repetitive
period of clock pulses produced thereby. If, in FIG. 3, there is
provided a switch 55 shown in dotted lines between the vacant
contact 54s of the switch 54 and the collector of the one
transistor TR.sub.6 of the bistable multivibrator 38c connected in
common to the emitters of the transistors constituting the each set
halves of the flip-flop circuits FF.sub.1 to FF.sub.4, then it will
be possible to start and stop a rhythm performance manually by a
player as in the prior art device, by closing the switch 55 with
the switch 54 being turned on the contact 54s.
FIG. 4 is a schematic circuit diagram of an automatic rhythm sound
producing device according to another embodiment of this invention
adapted for use with a keyboard electronic musical instrument.
Where the instrument is provided with several keyboards arranged,
for example, in three stages, that is, upper, lower and pedal
keyboards 61, 62 and 63 the key switches 61.sub.1 to 61.sub.n,
62.sub.1 to 62.sub.n and 63.sub.1 to 63.sub.n fitted to the
keyboards 61, 62 and 63 respectively are jointly connected at one
end to be grounded and at the other end to the base of the other
transistor TR.sub.7 of a bistable multivibrator 381c having the
same arrangement as that of FIG. 3 through separate rhythm start
selector switches 64, 65 and 66 for the three respective keyboards
61, 62 and 63 and a common rhythm start selector switch 67 to all
of them. The same parts of FIG. 4 as those of FIG. 3 are denoted by
the same numerals and description thereof is omitted. The automatic
rhythm sound producing device of FIG. 4 arranged as described above
enables desired rhythm sounds not only to be automatically obtained
as in the preceding embodiment but also to be started selectively
in response to the selected keyboard during performance upon
depression of those keys corresponding to the selectively closed
ones of the selector switches 64 to 67. For example, with the
switch 66 along closed and the remaining switches 64, 65 and 67
left open, when the first measure of a tone is played by
selectively depressing the keys 61.sub.1 to 61.sub.n and 62.sub.1
to 62.sub.n on the upper and lower keyboards 61 and 62 with both
hands of a player and thereafter at the start of the second measure
there are selectively depressed the keys 63.sub.1 to 63.sub.n on
the pedal keyboard 63 with the player's feet, then it will be
possible to start an automatic rhythm performance at the beginning
of the second measure, being triggered by the pedal
performance.
Although not shown in FIG. 2, that embodiment should preferably
include in the organ section such selector switches 64 through 67
as shown in FIG. 4 before connecting to the trigger generator
38.
FIG. 5 is a schematic block circuit diagram of an automatic rhythm
sound producing device according to still another embodiment of
this invention adapted for use with a keyboard electronic musical
instrument. The embodiment of FIG. 5 enables the ordinary tones of
the melody and those of the chord or those of the bass adapted for
the chord or combinations thereof to be played upon selective
depression of several of the keys 71.sub.1 to 71.sub.n arranged on
keyboards 72 in the order of musical notes in exact timing with a
desired rhythm pattern selected from among a plurality of rhythm
tempos or rhythm patterns. The tones of a desired chord consisting
of a combination of several tone signals of the prescribed pitches
obtained from a tone generator 73 upon selective depression of
several keys on the keyboard 72 are conducted to a chord detector
74. This chord detector 74 is formed of, for example, a matrix
circuit having a plurality of input terminals energized upon
selective depression of the keys 71.sub.1 to 71.sub.n and is so
designed as to detect the kind of chord thus supplied as well as to
draw out the base tones adapted for the detected chord from the
tone generator 73.
The tones of the chord and bass thus detected are temporarily
memorized in the corresponding chord memory 75 and bass memory 76.
A rhythm pattern generator 77 has substantially the same
arrangement as the aforementioned timing pulse encoder including
the bistable multivibrator 38c and produces a desired rhythm
pattern preset by the player upon selective depression of the keys
71.sub.1 to 71.sub.n. The rhythm pattern generator 77 regulates the
actuation of switches 78 and 79 cascade connected to the chord and
bass memories 75 and 76 respectively according to the generated
timing of an output rhythm pattern from the generator 77. The
automatic rhythm sound producing device of FIG. 5 having the
aforesaid arrangement generates the tones of the melody and the
tones of the chord or those of the bass adapted therefor or
combinations thereof exactly timed with the rhythm pattern all at
the same time.
FIG. 6 illustrates a concrete circuit arrangement of the other
section for triggering the binary counter chain upon selective
depression of the keys without using a start switch for a rhythm
performance as is the case with the conventional device. According
to the embodiment of FIG. 6, the aforementioned bistable
multivibrator 38c is substituted by, for example, a field effect
transistor TR.sub.20 to perform an equivalent function to that of
the multivibrator 38c. Either of the electrodes of a DC supply
source 81, for example, the negative electrode is grounded and the
other of the electrodes, for example, the positive electrode
thereof, is connected in common to one terminal of each of normally
open key switches 82.sub.1 to 82.sub.n selectively closed upon
selective depression of the keys. The other terminal of each of the
switches 82.sub.1 to 82.sub.n is grounded through a resistor
R.sub.1 and connected through a diode 83, the diode being connected
in the forward direction for the current from DC supply source 81,
and resistor R.sub.2, the diode 83 and the resistor R.sub.2 being
connected in series, to a non-grounded side of a grounded capacitor
C.sub.1, which in turn is connected to the gate electrode of the
transistor TR.sub.20 whose source electrode is grounded and whose
drain electrode is connected to a + B supply source through a load
resistor RL. The non-grounded side of the capacitor C.sub.1 is
coupled to ground through a normally open switch 84. According to
the circuit of the aforementioned arrangement, where one of the
keys is selectively depressed with the switch 84 left open and the
corresponding one of the switches 82.sub.1 to 82.sub.n is closed,
then a D.C. current from the DC supply source 81 is charged into
the capacitor C.sub.1 through the forward biased diode 83. The
charged voltage is supplied to the gate electrode of the transistor
TR.sub.20 to bring it from a non-conducting to a conducting state.
As a result, the voltage of the drain electrode of the transistor
TR.sub.20 is reduced substantially to a ground level, performing an
essentially equivalent action to that of the aforementioned
bistable multivibrator 38c. Even after the depressed key is
released to open the corresponding key switch, the charge in the
capacitor C.sub.1 is kept as it has been, being prevented from
discharging by the now backward biased diode 83 and infinitely
large impedance of the gate electrode of the transistor TR.sub.20,
and as a result the automatic rhythm performance is kept on.
When the switch 84 is closed, the voltage supplied to the capacitor
C.sub.1 is rapidly discharged therethrough to stop the automatic
rhythm performance.
* * * * *