Electronic drum. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Musician

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The design of an electronic musical instrument is proposed, which makes it possible to simulate playing various percussion instruments from a bass drum to cymbals. The dimensions of the device allow you to carry it in a briefcase. By connecting headphones to the output of the "drum", you can work out the playing technique without fear of disturbing your neighbors. The timbre, decay rate and other characteristics of the instrument's sound can be adjusted over a wide range.

An electronic percussion musical instrument is assembled according to the scheme shown in fig. 1.

(click to enlarge)

Hitting a drum stick - a short press on the SB1 button - switches the trigger from the elements DD1.1 and DD1.2. serving to suppress the bounce of the button contacts.

As is known, the sound spectrum of a percussion instrument contains damped harmonic and noise components. The first is formed by a node consisting of an inverter DD1.3. operational amplifier DA1 and related elements. At the moment of "impact" a high logic level pulse from the output 10 DD1.3 through the differentiating circuit C2R9. diode VD1. resistive divider R12R13 is fed to the input of the damped oscillation generator at the op-amp DA1. The latter is the equivalent of a high Q resonant circuit.

The frequency of the oscillations excited by the pulse depends on the ratings of the capacitors C5-C8. The following values ​​are recommended depending on the type of instrument being simulated:

Selecting the timbre of the sound, the frequency is regulated within certain limits by a variable resistor R10. The quality factor of the circuit and the damping time of oscillations (after-sound) are changed by a variable resistor R21.

Reverse-biased emitter junction of transistor VT1. operating in the avalanche breakdown mode, serves as a noise signal generator. Its amplifier is assembled on transistors VT2 and VT3. Next, the noise enters the input of the op-amp DA2 through the emitter junction of the phototransistor, which is part of the optocoupler U1. The gain of the stage on the op-amp is inversely proportional to the resistance of this transition, and it, in turn, depends on the illumination of the base of the phototransistor, created by the LED of the optocoupler. Thus, controlling the current flowing through the LED. you can change the amplitude of the noise at the output of DA2.

When the SB 1 button is pressed, the logic level at the output 11 of the DD1.4 element is high. Capacitor C3 is charged through resistors R7. R8 and diode VD2. Current through optocoupler LED U1. included in the emitter circuit of the transistor VT4. is growing. The amplitude of the noise at the output of the op-amp DA2 increases. After releasing the button, capacitor C3 is discharged through resistors R14 and R15. the current through the LED drops, the amplitude of the noise decreases. Variable resistors R7 and R15 regulate the rate of rise (attack) and fall of noise, respectively. The capacitance of the capacitor C4 is selected, achieving the desired tone.

The components of the "drum" signal are summed at the input of the op-amp DA3. Variable resistors R23 and R26 adjust their volume. With switches SA1 and SA2, one or both signals can be turned off.

All fixed resistors of the device are MLT-0.125 or others with a rated power of at least 0.125 W. Variable resistors - any non-wire, suitable in size. Film capacitors of the K5-K8 series are used as C72-C78. Oxide capacitors C3. C9. C10 -K50-35 or imported. The remaining capacitors can be ceramic group H90. Transistors - any low-power p-pn structures. As an op-amp DA1-DA3, you can use the K140UD7, K153UD2 and other microcircuits, taking into account the purpose of their conclusions and with the correction circuits required according to the reference data. Instead of the K56TLA7 microcircuit, its functional counterparts from the 564. K176, 164 series are suitable.

A possible design of the mechanical part of the "drum" is shown in fig. 2. Its base is a square or trapezoidal wooden case 5 in plan. A plywood plate 6 is fixed in it with screws 7, and the fastening should not be rigid. The free edge of the plate 7 is clamped between the limiter 10 and the pusher of the microswitch 9. The latter should work when the drumstick hits the plate 7. To prevent the drumstick from hitting the plywood too hard, thin rubber is glued onto the plate 7.

Wire harness 8 contacts microswitch 9 connected to socket 4, which is used to connect the "drum"

to the electronic part of the device. The type of socket does not matter, but the number of contacts is at least three. Suitable, for example, SG3 or SG5. With the help of bushing 2 and screw 3, the structure is fixed in a position convenient for the performer on a metal stand 1.

On the basis of the considered device, it is possible to manufacture an entire drum set by adding the required number of sound formation channels similar to those considered above. If the output signals of all channels are fed to point S, the output of the op-amp DA3 will be the sum of the sounds of the instruments. The initial noise signal for them can also be common. His. as shown in the diagram, they are removed from the emitter of the transistor VT3.

Author: V. Utkin, Zlatoust, Chelyabinsk Region

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