acoustic telescope. Scheme, description

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acoustic telescope. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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When it is hard to see, a person takes binoculars. What if you can't hear well? How to make it so that it becomes well audible, say, the singing of birds in the distance?

In such cases, a device that not only amplifies weak sounds many times over, but also improves the signal-to-noise ratio, will help. This device, let's call it "acoustic telescope", should be quite portable.

Schematic diagram of the receiver and amplifier of weak audio signals is shown in fig. 1.

Rice. 1 (click to enlarge)

At its input there is a sensitive electret microphone BM1, the signal amplification is provided by the DA1 microcircuit, which has a very high voltage gain at a low level of intrinsic noise. To match the relatively low input impedance of such an amplifier with the high input impedance of the microphone, a matching stage was introduced on the transistor VT1, connected according to the emitter follower circuit. For listening, miniature phones are used, placed in the ears. They (BF1, BF2) are connected to a power amplifier based on a transistor VT2, which matches the output impedance of the microcircuit and the impedance of the headphones. The device is powered by a single galvanic cell GB1 with a voltage of 1,5 V, from which a current of about 6 ... 7 mA is consumed. In the role of a horn, at the bottom of which a microphone is placed, there can be a cylindrical or conical pipe with a diameter of 5 ... 6 cm and a length of about 30 cm. made of plastic with elongated bottoms.

On fig. 2 shows another homemade design, consisting of three sections sliding into one another, glued from thick cardboard. The inner section is attached with its end to a plastic box-case, where the BM1 microphone is installed. Inside the case are the parts of the amplifier, the source and the power switch. It is also advisable to provide a place for storing telephones, which are removed in the working position and connected to the amplifier with their standard cord. At the same time, if you are listening not to birds, but to a lecturer, you can put the device, say, on a table, with the input sound guide in the right direction, and your hands remain free to write notes.

acoustic telescope
Fig. 2

We take miniature components - resistors of the MLT-0,125 type, capacitors C1 - K10-17, C4 - KLS, the rest K53-1. For sound reproduction, use stereo telephones with a voice coil impedance of about 20 ohms. The power source will be a miniature, but capacious enough for our purpose, AAA size R03 galvanic cell.

By selecting the values of the resistors R2, R5, you can adjust the collector currents of the transistors to the values \u1b\u4bindicated in the diagram in Figure 0. It is also useful to vary the resistance of the resistor R10 (within 4 ... 10 kOhm), achieving the best sound in phones. The selection of the value of RXNUMX will be simplified if a XNUMX kΩ variable resistor is temporarily switched on in its place by connecting the slider output to one of the extreme outputs. The resistance value found empirically can be measured with an ohmmeter or estimated from the angle of rotation of the axis, if the "variable" is taken with a linear characteristic (type "A") of the change in resistance. The figure on the right shows the location of the pins of the used microcircuit relative to the "key" label.

Author: P.Yuriev

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