Sensitive microphone for computer. Sensitive microphone for a computer What can you do with a microphone
In this article I will tell you how to make a microphone, because a truly sensitive microphone can only be made with your own hands, or more precisely, by remaking a standard microphone. Of course, many can argue with this statement, but not those who took this issue seriously. Very often, people spend a huge amount of time setting up their microphone and choosing the best combination of the PC sound card and the microphone itself. In addition, if you have a laptop, then in most cases the sound systems in such computers also leave much to be desired. Well, let's get down to business.
How to make your own microphone
In the design of the microphone unit we will use elements of electronics that have already served their useful life. Take an electret microphone from any old tape recorder or tape recorder. If you don’t have one at home, then a microphone from a mobile phone will do. You can even use two microphones at once, this will allow you to significantly expand the directionality of the sound. The signal from the microphone or microphones must be amplified by a low-noise transistor type VT1, then the signal will be sent to an operational amplifier type DA1. The output of this amplifier can be connected both to regular headphones and further fed to processing or recording devices (for example, a laptop or desktop computer). We will power the amplifier from the battery of an old mobile phone. They (mobile phone batteries) are good because the battery life of a microphone from such a battery will be tens of hours. And to charge the battery, use any USB port on your computer. Now about the amplifier. It is quite possible to leave it plugged into the port all the time, since the charging current in this case will be very small. The cable with the USB connector can be taken from the mouse. At the amplifier output, it is best to use a 3.5 mm jack - the same as for headphones from the player. The volume control from the headphones is also suitable, and the remaining parts, for example, the SA1 power switch, must be made from any small-sized ones.
DIY microphone: finishing touches
Now we place the microphone components on a small board made of fiberglass. Next, glue a small piece of foam rubber onto the battery, and then lay the board on top. Now we tighten it all up well with electrical tape and try on the regulator handle. After this, to eliminate interference and interference, we place our structure in a tin screen, soldering it to the common wire. Please note that the microphone or microphones must be secured in a piece of soft but dense material. Then we cut out a niche in a piece of foam rubber and insert the entire block into it, and pull a fabric cover over it on top. By the way, it is quite possible to use foam rubber that is used for car washing. Well, that's almost all - all that remains is to make the slots for the plug, as well as the volume control and switch. I note that such a microphone will be much better than any factory products, excluding, of course, professional equipment. But the fact is that for such equipment you will have to pay more than tens of thousands of rubles, and the cost of our product is a maximum of a thousand, given that we assembled it almost entirely from old parts. So, if you are not involved in professional recording and you need a microphone for your own personal purposes, then this homemade design will come in handy.
A few words about electret microphones.
Currently, electret microphones have almost completely replaced microphones of other designs. This is due to the fact that at a relatively low price, they have a smooth frequency response, light weight and high reliability. When it comes to miniature microphones, then they simply have no equal.
1. Insulator.
2. A metal ring, but with a film stretched over it.
3. The base, which is also one of the microphone plates.
4. Film, also known as another microphone plate.
5. Microphone leads.
An electret microphone is a capacitor, one of the plates of which is made of a very thin polyethylene film, which is stretched over a ring. The polyethylene film is irradiated with a beam of electrons that penetrate to a shallow depth, thereby creating a space charge that can persist for a long time.
This type of dielectric is called an electret, which is why the microphone is called “Electret”.
A very thin layer of metal is also sprayed onto the film, which is used as one of the electrodes. The other electrode is a metal cylinder, the flat surface of which is located at a short distance from the film.
Film vibrations caused by acoustic waves create an electric current between the electrodes. Since this current is extremely small, and the output impedance of such a microphone can reach gigaohms, it is extremely difficult to transmit the signal generated by the microphone through wires without significant distortion. Therefore, to match the high impedance of the microphone with the relatively low input impedance of the amplifier, a matching stage is used, made on a unipolar (field-effect) transistor, which is structurally located in the housing of the microphone capsule.
Mic – electret microphone.
VT1 – field effect transistor.
R1 – matching stage load.
R2 – microphone power ballast resistor.
C1 – decoupling capacitor.
The capsule body (shown in the diagram with a dotted line) is made of metal, which shields the microphone and matching stage from external electric fields.
The capsule of an electret microphone is usually called a device in the housing of which not only the electret microphone itself is located, but also a matching stage on a field-effect transistor.
As can be seen from the diagram, power is required to power the matching stage. This power is supplied to the input of the microphone amplifier directly from the circuitry of this very amplifier.
To find out whether a particular microphone amplifier is suitable for connecting an electret microphone, just connect a multimeter to the input jack. If you are aiming for 2-3 Volts, then the amplifier can be paired with an electret microphone. Most microphone amplifiers used in built-in and separate computer audio cards are designed to work with electret microphones.
What will you need to make a microphone?
1. Electret microphone capsule. You can, of course, buy it on the radio market for 20-30 cents, but even better, take it out of some broken Chinese radio or the same telephone set that has been lying around in the closet for a long time. Typically, an electret microphone capsule with a diameter of 10mm is installed there. The larger the diameter of the capsule, the wider the low frequency range, which makes the voice softer and more natural.
2. A piece of thin shielded wire. I suggest choosing a thin wire for purely aesthetic reasons. It is more difficult to find than a medium or thick wire, but we are making a miniature microphone.
3. Jack type plug (Jack) 3.5mm.
4. Two gram syringe.
5. A small paper clip for attaching the microphone to clothing.
6. A piece of thick foam rubber for making a windproof cap.
Let's start making the microphone.
We cut off part of the syringe body, from the side where the needle is attached, somewhere near the 1 gram mark using a knife with replaceable blades.
Remove markings from the surface of the syringe body with acetone.
We process the cut edge with fine sandpaper.
Note. The housing for the microphone can be made even shorter, but then it will be awkward to hold in your hand if necessary, and the windproof cap will hold worse. In addition, the additional space in the microphone body allows for a simple but effective knot-type cord attachment.
We insert the shielded cable into the hole for the needle and tie it in a knot.
We solder the microphone capsule so that the braid of the shielded wire is connected to the body.
We insert the microphone capsule into the body and snap the place on the body that once served to attach the needle into the claw of the office clip.
1 - “Hot” wire.
2 - Cable braid.
On the other side of the cable we solder the plug. Pinout (pinout), as in the picture. It is not difficult to notice that the left and right channels are connected together.
Well, finally, we make a windproof cap (nozzle) from foam rubber.
We cut off a suitable block of foam rubber with a sharp knife.
We cut out a cylindrical recess with some sharply sharpened tube.
For such work I use sections from broken telescopic antennas. These sections are thin-walled brass tubes that can be easily sharpened with a sharp scalpel by rotating the tip of the latter along the inner surface of the tube.
We cut off everything unnecessary to get something similar to a sphere.
This is what happened.
And this is how you can use it.
To assemble the sensitive microphone circuit we will need:
1. Transistor BC547 or KT3102, you can try KT315.2. Resistors R1 and R2 with a nominal value of 1 kOhm. To increase the sensitivity of R1 for the capsule, rated from 0.5 - 10 kOhm.
4. Disc ceramic capacitor with a nominal value of 100-300 pF. It can be omitted if initially there are no “spikes” or excitations of the amplifier.
5. Electrolytic capacitor 5-100 µF (6.3 -16 V).
First of all, let's determine the polarity of connecting the microphone capsule. This is done simply: the minus is always connected to the body. Then we assemble the circuit, either by surface mounting or on a mini-board. The entire sensitivity of the preamplifier will depend on the gain of the transistor and the selected resistor R1. Usually the amplifier is assembled and works immediately; its sensitivity should be sufficient with a reserve.
The recording was made using a capsule without a preamplifier circuit.
The recording was made on a capsule from a pre-amplifier circuit.
The difference is visible to the naked eye. Now you don’t have to hang a microphone around your neck and shout into it. You can easily put it on the table and speak without any extra effort. Well, if the sensitivity turns out to be too high, then you can always reduce it without any problems using the settings in the operating system.
It’s very difficult to get by without a computer microphone these days; without it you can’t use voice search, and you won’t be able to chat with a friend via video call. However, not all computers have built-in microphones, and moreover, they often do not have very good sensitivity. You can solve this problem quite simply - assemble the microphone yourself.
Scheme
The circuit is extremely simple, containing only two resistors, two capacitors, a transistor and an electret microphone capsule. The transistor can be used in almost any low-power n-p-n structure, for example, KT3102, BC547, BC337. An electret microphone can be obtained, for example, from a broken headset or handset, or you can buy it at a radio parts store. The sensitivity of the microphone will greatly depend on this element, so it is advisable to take several and check which one is best suited. The advantage of this circuit is that it uses phantom power. Those. The sound signal is transmitted through the same wires as the power supply. If you take a voltmeter and measure the voltage at the microphone input of your computer, it will be about 3-4 volts. When connecting the microphone circuit, this voltage should drop to a level of 0.6-0.7 volts, thus, an external power source will not be needed and there will be no extra wires at the workplace.
Circuit assembly
The circuit contains a minimum of parts, so it can be assembled by hanging installation. But, sticking to tradition, I etched a miniature printed circuit board. You can even draw paths with a marker or nail polish. A few photos of the process:
Download the board:
(downloads: 206)
A microphone capsule is soldered on one end of the board, and a shielded wire on the other. Please note that the wire must have a shield, otherwise the microphone will produce terrible noise. The braid of the wire is soldered to the negative, and the two inner cores are connected and soldered to the output of the circuit. It is imperative to maintain the polarity of the microphone capsule, otherwise the circuit will not work. One of its outputs goes to minus, and the second to plus. Determining the polarity is very simple - you need to ring the terminals with the metal body of the capsule. The terminal that connects to the housing is negative.
Microphone assembly
For ease of use, a board with soldered parts must be placed in a suitable housing. Because Since the board has a narrow, elongated shape, you can use an ordinary ballpoint pen as a body. To do this, you need to remove the writing rod from it and check whether the board is the right width. If the circuit is assembled by hanging installation, then it can be given any shape and there will be no problems with capacity. In addition to a pen, any elongated object will work well, be it a marker or a simple plastic tube.You will need
- - shielded audio cable;
- - high-impedance earphone;
- - low-impedance science recorder (can be from a voice recorder or player);
- - radio broadcast speaker;
- - sound transformer;
- - soldering iron;
- - rosin;
- - tin;
- - electrical tape;
Instructions
The microphone can be made from a high-impedance earphone, which is used in headphones. To do this, connect it using a shielded cable to the corresponding connector of the amplifier or mixing console. This microphone is quite suitable for broadcasting or recording speech. But the quality will be insufficient for recording or amplifying a piece of music. If you want a high-quality wideband microphone, make it from a broadcast speaker.
Take the radio broadcast speaker and open its case. Inside, in addition to the speaker itself, you will also see an output speaker and a transformer, as well as a variable resistance resistor. You don't need the resistor now, so unsolder it from the circuit and remove it from the case. Connect the speaker to the transformer directly.
Unsolder the plug and wire from the high-resistance winding of the transformer and in their place connect the shielded wire with the appropriate connector for inclusion to the microphone jack of the recording or amplifying device.
This microphone could be improved somewhat. For example, you can screen it. Cover the inner surface of the broadcast speaker housing with foil or foil paper. You can use, for example, foil from cigarette packs. Make electrical contact between this shield and the audio cable's braided shield, for example using a screw and a terminal strip. This will get rid of interference from external electromagnetic fields.
The sound quality of such a microphone can also be improved. Connect a custom RC filter in series with the high-resistance winding of the transformer. This filter consists of a 510 pF capacitor and a 1 mOhm variable resistor connected in parallel. Attach the resistor to the front panel of the radio in the place of the previously removed volume control. Solder the filter and connect it to the amplifier, select the filter resistance for the best sound quality.
In a circuit with a matching transformer, you can use any low-impedance speaker, as well as the output transformer from any tube receiver. Instead of a speaker, you can use low-impedance headphones, including those from a telephone or player. If you take a miniature earphone from a player, then the entire structure can be made portable by placing the earphone itself in a metal tube and designing it as a cord microphone. In this case, place the step-up transformer in close proximity to the amplifier. All connections in this design are made with shielded wire.