DE1772626C3 - Switches for electronic musical instruments - Google Patents

Description

The r.rlindiing refers to a switch iur electronic musical instruments with a transistor whose base is connected to a pulse generator is. in the emitter branch of which a key switch lietien and a hold circuit Collector ^ m output signal is removable.

five switches of this type are described in ύύί USA. -Patent 3 141 ¹ JI ¹ ). Other electronic switches for operating musical instruments as a replacement for the mechanical switches previously used are also known from the '.'SA. Patents 2 4X6 20s and 3 247 30ft or the German Auslegeschrift I ISI 1) 30. The main shortcoming of all these known switches is that, even when the key switch is in the A1'S position, a small part of the applied pulse signal is via parasitic capacitances such as those between the collector and the base of a transistor. Means that the supplied pulse signals have a high proportion of harmonic components with a very high frequency. These leakage currents, which so far have received practically no attention and certainly not combated, ultimately lead to a sound generation even if the components of the electronic musical instrument assigned to the individual key switches are not to be played at at all. This naturally results in a disruptive falsification of the sound quality desired for playing the electronic musical instrument and can even result in the electronic musical instrument emitting sounds without it being played at all.

The invention is therefore based on the object of designing a switch of the type mentioned at the outset in such a way that that when the key sounder is in the OFF position, regardless of the frequency composition the supplied pulse signals can not mean any current through the entire switch.

This object is achieved in that between the pulse generator and the A diode is inserted into the base of the transistor.

In the case of the switch designed according to the invention, the pulse signals are fed to the transistor base via the diode, which in reverse direction when the key switch is in the OFF position is biased so that no harmonic components of the pulse signals are transmitted because the Diode has a high impedance at this point in time. In addition to the total avoidance that can be achieved in this way undesired leakage currents when the switch is switched off, the invention offers the further advantage that for the construction of the switch transistors with an emitter-base-pn-junction with relative Use lower breakdown voltage, since the pulse signals de, · Transistorbasii are not immediate but get there via the diode and this has a very high impedance while the key switch is in its OFF position.

For the further explanation of the invention, reference is now made to the drawing; in this shows

Fig. Fine circuit diagram for a conventional switch arrangement for electronic musical instruments,

Fig. 2Viπ Schahbild for a first embodiment of a switch arrangement according to the invention for electronic musical instruments and

3 shows a schematic diagram for a second embodiment a switch arrangement according to the invention for electronic musical instruments.

In Fig. 1 shows a conventional switch arrangement of the previous type, the reference number 1 denoting a tone generator. reference numeral 2 a transistor; reference numerals 5 and 6 bias resistors. reference numeral 7 denotes a load resistor and reference numeral 3 denotes an emitter resistor. In addition, a circuit 4 is provided for influencing the decay behavior of the output signal, which consists of a resistor 9 and a capacitor 10. With r V ₁ is a voltage source for the operation of the transistor 2 and with ' V., a voltage source which supplies the emitter of the transistor 2 with a reverse bias voltage. Numeral 3 denotes a key switch which can be closed by depressing the key. Reference number 11 denotes a resistor and reference number 12 denotes an output terminal. Usually there is a resistor between the tone generator 1 and the node 13, but this is not shown in FIG.

During operation, the emitter-base blocking layer of the transistor 2 is first ^{strongly biased in the reverse direction by the voltage source:} V. With the key switch 3 in its open position.

In this way, the transistor 2 remains non-conductive for this input signal voltage even when it is supplied with an input signal voltage £ 1 from the tone generator 1 , so that this input signal voltage £ 1 is essentially not passed on to the output source 12 . However, a weak leakage signal occurs at the output terminal 12. This leakage signal is likely arises from the fact that the input signal voltage £ _s passes through the junction capacitance 14 between the collector and the base of transistor 2 to the output terminal 12th

If the key switch 3 is then closed, the emitter-base junction of the transistor 2 is biased slightly in the forward direction, and the transistor 2 can take over its normal switch function and thus forward the input signal voltage E _s to the output terminal 12.

In the case of the switch arrangement described above, the collector-emitter path of the transistor is used 2 by opening or closing the key switch 3 non-conductive or conductive and capable compared to the output signal of the tone generator 1 ii! to act as a switch in the manner described above. Such a common switch arrangement has

■ yoke when installed in an electronic musical instrument, that like z. B. an electron organ

has the disadvantage that with

It is more likely that a tone signal \ :. n will be audible in tone generator 1 even if no 1.Vr keys are pressed, since the open-close ratio (ie the ratio S _tin 'S _llu ^ between ..:. .η voltage level S _{cln of} the output signal that occurs; ■, closed key switch 3 at the output. ■ mrac 12, to the voltage level -S ',,,,. leakage signal with open key switch 3 at egg •' seungsklemmc 12) too low is.

In addition, the node 13 of the

! generator 1 always has a signal voltage / ·, '. to-

iuhrt. the, as the emitter-base breakdown .iiinung of transistor 2 is not very large.

11 Break through the emitter barrier layer

■ J) Il.

With the invention, these disadvantages of the borrowed switch arrangement are now to be eliminated. at One embodiment of the invention is shown in FIGS !) jsiszvvcig of the transistor an asymmetrical construction ament. such as a diode, inserted, with Mitij being provided, which are synchronous / u the open "the closed state of a switch, such as a key switch, the diode a voltage in reverse direction or in forward direction. feed direction. In this way, the diode turns on when the key switch is in its ! ■ in a lien state represents a high impedance, whereby a signal applied to the anode of the diode is only greatly attenuated to the base of the transistor got. Such a signal weakness then leads to an increase in the open-ended \ gain and reduce the difficulties associated with emitter-junction breakdowns.

In Fig. 2 such a first embodiment of the invention is illustrated, wherein the reference number 21 a tone generator which generates a square-wave output signal, the reference number 32 a pn junction diode connected to the tone generator 21, the reference number 22 an npn transistor, the base of which is the output signal of the tone generator 21 is fed through the diode 32, and the reference number 27 denotes a load resistor, one end of which is connected to a positive voltage source -t- K, and the other end of which is connected on the one hand to the collector of the transistor 22 and on the other hand to an output terminal 33 . Reference number 24 denotes a circuit for generating ¹ an envelope curve, which circuit consists of a resistor 28 and a capacitor 29 and is connected to the emitter of the transistor 22 via an emitter resistor 31. The reference number 23 denotes a key switch connected to the emitter of the transistor 22 via resistors 30 and 31 for controlling the voltage states for the transistor 22 and for the diode 32. The reference numbers 25 and 26 denote bias resistors for the transistor 22, and with f K ₄ denotes a voltage source for operating the circuit 24 for envelope curve formation and for biasing the diode 32 in the reverse direction via the resistor 25 and a further resistor 28 when the key switch 23 is open.

Next, the mode of operation of the switch arrangement or the hold circuit described above will be discussed. Initially, when the key switch 23 is open, the diode 32 is supplied by the voltage source r K ₄ via the resistors 25 and 28. whose positive potential is selected to be greater than the peak value of the input signal voltage, biased in the reverse direction. The capacitor 29 is also charged to approximately the voltage ■ K, and the potential at the node 35 is also essentially equal to ¹ K ₁ . The potential - K ₁ is selected to be equal to the potential - K ₁ or less. This means that the transistor 22 is biased in such a way that it operates in the residual low range or in the vicinity thereof when the current is low and that its gain becomes essentially zero. Ap the node 34 connected to the base of the transistor 22 arrives at a signal that is damped by the high impedance of the reverse biased diode 32, since the impedance between the node 34 and the ground potential or the reference potential is smaller than the Reverse impedance / of the diode 32. The signal attenuated in this way cannot cause a breakdown of the emitter junction of the transistor 22 on the one hand, and on the other hand, unlike in the usual circuit, can essentially not be passed on to the output terminal 33.

If the key switch 23 is then closed, so the potential at the node 35 becomes within a short period of time that of the product of the capacitance of the capacitor 29 and the value of the resistor 28 very much small resistance 30 depends, equal to the earth potential. At that moment the diode becomes 32 forward biased, and the operating point of transistor 22 is ir. its active area, so that the transistor 22 begins to operate as an amplifier with a predetermined gain and the output of the tone generator 21 is supplied to the output terminal 33. Since the diode 32 is like mentioned above is biased in the forward direction. it does not stand in such a signal transmission in any way Way against.

Next, the key switch 23 is returned to its open state. At this point in time, the potential at the node 35 does not return immediately to its initial value of essentially f K ₄ . Rather, this potential at the node 35 decreases only gradually and in accordance with the charging characteristic of the capacitor 29, which essentially depends on the time constant RC from the value R of the resistor 28 and the capacitance C of the capacitor 29. As soon as the potential at the node 35 finally reaches the value + K ₄ again, both the diode 32 and the transistor 22 are again in their original bias state, thus preventing the output signal of the tone generator 21 from being passed on to the output terminal 33.

The transistor 22 does not return to its original position immediately when the key switch 23 is opened.

normal preload condition. This means that the bias condition for transistor 22 is at ÖITncn of the key switch 23 gradually changes from the state impressed on it when the switch 23 is closed is changed to the steady state with the switch 23 open, so that at the output terminal 33 still provides an output signal for a predetermined period of time even when the switch 23 is open is available. The amplitude of the output signal thus maintained increases substantially exponentially with the time constant of the element 24, which is decisive for the envelope curve formation, see above that a so-called envelope curve is formed in the output signal. Such an envelope in the Signal is designed to produce a natural sound in any electronic musical instrument of great importance, which is why, as mentioned above, a combination of a key switch with an electronic amplifier element and a circuit for the envelope curve formation in place operated by a key switch alone.

The cause of the increase in the open / closed ratio can be stated as follows: the capacitance between the electrodes of the diode 32 and the impedance between the node 34 and the grounding point act as a kind of high-pass filter when the diode is blocked, so that the lower harmonics see corresponding components in the rectangular output of the Tongencrators 22 are filtered away while the higher harmonics pass through this filter. The higher harmonic components of the tone generator signal that are let through in this way then into a further high-pass filter from the collector-spacer capacitance of the transistor 22 and the impedance between the output terminal 33 and the ground point filtered again, before they reach output terminal 33. In this way appears at the output terminal 33 only a small portion of the output signal of the, consisting of extremely high harmonics Tone generator 21. However, such a signal consisting of high harmonic components has itself then, if it is amplified in subsequent switching stages, none for operating a loudspeaker adequate performance. Plus, the human ear is even when the speaker is through such a signal should be set in motion for these higher harmonic components of the original Sound signal not sensitive.

As mentioned above, essentially no lower harmonic or audio-frequency components of the signal occur at the node 34, and even these very weak audio-frequency components are further attenuated as they pass through the collector-boundary layer capacitance. As a result, the voltage level becomes S ₁₁₁₁ . of the leakage signal occurring at output terminal 33 is very low, and the open-close ratio (S _eitt / S _off ) increases. One of the aims of the invention is thus achieved.

If one now sets the embodiment of the invention dealt with in the preceding description accordingly Fig. 2 of the drawing, it can be seen that a satisfactory operation of such Arrangement is possible if one considers the individual components and voltages in the from the following Table 1 as can be seen.

Table 1

Vertex of the rectangular
Output signal of the tone generator 21 K) V

Diode 32 1 S1473

Transistor 22 npn silicon

Transistor2SC45 £

Voltage source + K ₁ 12 V

Voltage source -f V _A 10 V

Resistance 25 20 kß

Resistance 26 80 ki2

is resistance 27 400 Ω

Resistance 28 50 kS2

Resistance 30 63 U

Resistance 31 3.2 kS2

Capacitor 29 50 ₍ iF

In the case of a circuit according to FIG. 2 with the parameters compiled in Table 1 above, the oven / closed ratio is in a range from 80 to 90 CQ for a signal frequency of 1 kHz. The signal level is measured with reference to Spitzc-Spitzc-Wcrt of the signal voltage. From this measurement the advantageous effect of the circuit according to FIG. 2 compared to the circuit according to FIG. 1 can be seen at the same time, since with this circuit an open-to-close ratio of about 50 dB can at best be achieved. The second embodiment of a switch arrangement according to the invention illustrated in FIG. 3 differs from the embodiment illustrated in FIG. 2 in that an electronic switch embodied in a collector circuit is used. In their basic mode of operation, however, the two switch arrangements are essentially the same.

In FIG. 3, the collector of a transistor 42 is earthed via a load resistor 47 and a tone generator 41 is connected as a signal source between earth and a diode 52 connected to the base of the transistor 42 at a node 54. With the emitter of the transistor 42 is via an emitter resistor 5! an envelope forming circuit 44 composed of a resistor 48 and a capacitor 49 is connected. A resistor 50 is inserted between a node 55 and an output terminal of a key switch 43, the other output terminal of _{which is connected to a potential source -K 5.} A bias resistor 45 is located between the nodes 54 and 55. The transmission of the output signal of the tone generator 41 to an output terminal 53 is controlled by the key switch 43. With such a switch arrangement, not only can the desired holding

create an effect, but you also come to a satisfactory open-close relationship and can significantly reduce the risk of emitter-junction breakdown.

In a practical example for a circuit according to FIG. 3 got a Satisfactory mode of operation with the parameters compiled in Table 2 below achieve.

3601

Tabclic 2

Clock value of the reverse output signal of the tone generator 41 10 V

Diode 52 J S1473

Transi ·. or 42 npn silicon

Transistor2SC458

Resistance 45 5k £ 2

Resistance 47 200 Ω

Resistance 48 4OkQ

Resistance 50 50 Ω

Capacitor 49 50 | iF

Voltage source -K, ...... 12 V

The exemplary embodiments described above for Schaller arrangements according to the invention contain bipolar transistors as amplification elements, namely npn transistors and, as asymmetrical components, diodes with a single pn junction, however, it will be obvious to those skilled in the art that unipolar transistors such as z. B. surface field effect transistors or others can use equivalent semiconductor components.

ίο In addition, there is a tone generator in the examples described and shown with a rectangular output signal as a signal source, but can take place which also easily uses a signal source with a sinusoidal output signal Find.

1 sheet of drawings

309646/208

3601

Claims (1)

Claim: Switch for electronic musical instruments with a transistor, the base of which is attached to a Pulse generator is connected. in its limiting branch a key switch and a hold circuit and an output signal can be taken from its collector. thereby ge ίο indicates that between the pulse generator (21; 41) and the base of the transistor (22: 42) a diode (32; 52) is inserted.