High quality computer microphone. Connecting a dynamic microphone to a computer How to connect an electret microphone to a transceiver
This document collects wiring diagrams and information on how the power supply of electret microphones is built. The document is written for people who can read simple electrical circuits.
- Introduction
- Introduction to electret microphones
- Basic power supply circuits for electret microphones
- Sound cards and electret microphones
- plug-in power
- Phantom power in professional audio
- T-powering
- Other useful information
1. Introduction
Most types of microphones require power to work, usually condenser microphones, as well as microphones similar to them in principle of operation. The power supply is necessary for the operation of the internal preamplifier and polarization of the membranes of the microphone capsule. If there is no built-in power source (battery, accumulator) in the microphone, voltage is supplied to the microphone through the same wires as the signal from the microphone to the preamplifier.
There are times when a microphone is mistaken for a broken one just because they do not know about the need to apply phantom power to it or insert a battery.
2. Introduction to electret microphones
Electret microphones have the best price/quality ratio. These microphones can be very sensitive, quite durable, extremely compact, and also have low power consumption. Electret microphones are widely used, due to their compact size they are often built into finished products, while maintaining high performance. According to some estimates, an electret microphone is used in 90% of cases, which, given the above, is more than justified. Most lavalier microphones, microphones used in amateur video cameras, and microphones used in conjunction with computer sound cards are electret microphones.
Electret microphones are similar to condenser microphones in that they convert mechanical vibrations into an electrical signal. Condenser microphones convert mechanical vibrations into a change in the capacitance of a capacitor, obtained by applying voltage to the membranes of the microphone capsule. A change in capacitance, in turn, leads to a change in the voltage across the plates in proportion to the sound waves. While a condenser microphone capsule needs an external (phantom) power supply, an electret microphone capsule diaphragm has its own charge of several volts. He needs power for the built-in buffer preamplifier, and not for membrane polarization.
A typical electret microphone capsule (Fig.01) has two pins (sometimes three) for connection to a 1-9 volt current source and, as a rule, draws less than 0.5 mA. This power is used to power a miniature buffer preamp built into the microphone capsule to match the high impedance of the microphone and the connected cable. It should be remembered that the cable has its own capacitance, and at frequencies above 1 kHz, its resistance can reach several tens of kOhm.
The load resistor determines the capsule resistance, and is designed to match the low noise preamplifier. This is usually 1-10kΩ. The lower limit is determined by the voltage noise of the amplifier, while the upper limit is determined by the current noise of the amplifier. In most cases, a voltage of 1.5-5V is applied to the microphone through a resistor of several kOhm.
Due to the fact that the electret microphone incorporates a buffer preamplifier that adds its own noise to the useful signal, it determines the signal-to-noise ratio (usually around 94dB), which is equivalent to an acoustic signal-to-noise ratio of 20-30dB.
Electret microphones require a bias voltage for the built-in buffer preamp. This voltage must be stabilized, not contain ripples, otherwise they will go to the output as part of a useful signal.
3. Basic power supply circuits for electret microphones
3.1 Circuit diagram
Figure 02 shows the main power supply circuit of an electret microphone, it should be referred to when considering the connection of any electret microphone. The output resistance is determined by resistors R1 and R2. In practice, the output resistance can be taken as R2.
3.2 Powering the electret microphone from a battery (accumulator)
This circuit (Fig.04) can be used in conjunction with consumer tape recorders and sound cards, originally designed to work with dynamic microphones. When you assemble this circuit inside the microphone housing (or in a small outer box), your electret microphone will find universal use.When building this circuit, it will be useful to add a switch to turn off the battery when the microphone is not in use. It should be noted that the output level of this microphone is much higher than that obtained with a dynamic microphone, so it is necessary to control the gain at the input of the sound card (amplifier/mixing console/tape recorder, etc.). If this is not done, a high input level may result in overmodulation. The output impedance of this circuit is in the region of 2 kΩ, so it is not recommended to use an overly long microphone cable. Otherwise, it may work as a low-pass filter (a few meters won't have much effect).
3.3 The simplest power supply circuit for an electret microphone
In most cases it is acceptable to use one/two 1.5V batteries (depending on the microphone used) to power the microphone. The battery is connected in series with the microphone (Fig.05). This circuit works as long as the DC current from the battery does not adversely affect the preamplifier. It happens, but not always. Normally, the preamplifier works only as an AC amplifier, and the constant of the component does not have any effect on it.
If you don't know the correct polarity of the battery, try plugging it in both directions. In the vast majority of cases, reverse polarity at low voltage will not cause any damage to the microphone capsule.
4. Sound cards and electret microphones
This section discusses options for supplying power to microphones from sound cards.
4.1 Sound Blaster variant
Sound Blaster sound cards (SB16, AWE32, SB32, AWE64) from Creative Labs use 3.5mm stereo jacks to connect electret microphones. The pinout of the jack is shown in Figure 06.Creative Labs lists the specs on their website. which a microphone connected to Sound Blaster sound cards must have:
- Input type: unbalanced (single-ended), low-impedance
- Sensitivity: about -20dBV (100mV)
- Input impedance: 600-1500 ohm
- Connector: 3.5mm stereo jack
- Pinout: Figure 07
 |
| Fig.07 - Connector pinout from Creative Labs website |
 |
| Fig.08 - Microphone input of the Sound Blaster sound card |
4.2 Other options for connecting a microphone to a sound card
Sound cards from other models/manufacturers may use the method discussed above, or may have their own version. Sound cards that use a 3.5mm mono jack connector for connecting microphones usually have a jumper that allows you to power up or turn off the microphone if necessary. If the jumper is in the position at which voltage is applied to the microphone (usually +5V through a 2-10kΩ resistor), then this voltage is supplied through the same wire as the signal from the microphone to the sound card (Fig.09).
The sound card inputs in this case have a sensitivity of about 10mV.
This connection is also used on Compaq computers that come with a Compaq Business Audio sound card (the Sound Blaster microphone works well with the Compaq Deskpro XE560). Offset voltage measured at Compaq output, 2.43V. Short circuit current 0.34mA. This suggests that the bias voltage is applied through a resistor of about 7kΩ. The 3.5mm jack ring is not used and is not attached to anything. Compaq's user manual says that this mic input is only used to connect a phantom-powered electret microphone, such as one supplied by Compaq itself. According to Compac, this method of power supply is called phantom power, but this term should not be confused with what is used in professional audio equipment. According to the declared technical characteristics, the input impedance of the microphone is 1kOhm, and the maximum allowable input signal level is 0.013V.
4.3 Applying bias voltage to a three-wire electret microphone capsule from a sound card
This circuit (Fig. 10) is suitable for connecting a three-wire electret microphone capsule to a Sound Blaster sound card that supports bias voltage (HC) supply to an electret microphone.
4.4 Applying bias voltage to a two-wire electret microphone capsule from a sound card
This circuit (Fig. 11) is suitable for pairing a two-wire electret capsule with a sound card (Sound Blaster) that supports bias voltage. |
| Fig.12 - The simplest circuit that works with SB16 |
4.5 Powering electret microphones with 3.5 mm mono jack from SB16
The power supply circuit shown below (Figure 13) can be used with microphones that are biased on the same wire as the audio signal.4.6 Connecting the handset microphone to the sound card
According to some news articles on comp.sys.ibm.pc.soundcard.tech, the floor circuit can be used to connect an electret handset capsule to a Sound Blaster sound card. First of all, you need to make sure that the microphone in the selected tube is electret. If this is the case, then you need to disconnect the tube, open it and find the plus of the microphone capsule. After that, the capsule is connected as shown in the figure above (Fig. 13). If you want to use the handset's RJ11 jack, the microphone is connected to the wires of the outer pair. Different handsets have different output levels and some may not be strong enough for use with a Sound Blaster.If you want to use the speaker of the handset, then connect it to the Tip and insert it into the sound card. Before doing this, make sure that it has a resistance of more than 8 ohms, otherwise the amplifier at the output of the sound card may burn out.
4.7 Powering the multimedia microphone from an external source
The basic idea of powering a multimedia (MM) microphone is shown below (Fig. 14).
The general power supply circuit of a computer microphone designed to work with Sound Blaster and other similar sound cards is shown in the figure below (Fig. 15):
 |
| Fig.15 - General power supply circuit of a computer microphone |
Note 2: Typically, the supply voltage of microphones connected to a sound card is about 5 volts, supplied through a 2.2kΩ resistor. Microphone capsules are not normally susceptible to 3 to 9 volts DC, and will work (although the level of voltage applied may affect the output voltage of the microphone).
4.8 Connecting a multimedia microphone to a regular microphone input
+5V can be generated from the larger one using a voltage regulator such as the 7805. Alternatively, three 1.5V batteries can be used in series, or one 4.5V can be used. It should be turned on as shown in the figure above (Fig. 16).
4.9 Plug-in power
Many small camcorders and recorders use a 3.5mm stereo mic plug to connect stereo microphones. Some devices are designed for microphones with an external power supply, while others supply power through the same connector that carries the audio signal. Devices that provide power to capsules through the mic input refer to this input as "Plug-in power".
For devices that use a plug-in power connection for electret microphones, the diagram is shown below (Fig. 17):
Plug-in power microphone connection technology from the point of view of the circuitry of the recording device (Fig. 18):
 |
| Fig.18 - Plug-in power connector circuitry |
Notes
The buffer preamplifier of an electret microphone is also just a preamplifier, a voltage converter, a repeater, a field effect transistor, an impedance matcher.
It's been in my head for a long time. Gathering his strength, he began to search for amplifier circuits. Most of the circuits I've looked at that I didn't like. I wanted to assemble it easier, better and smaller (for a laptop, because the built-in one was made, apparently, just for show - the quality is bad). And after a short search, a microphone signal amplifier circuit with phantom power was found and tested. Phantom power (this is when power and information is transmitted over a single wire) is a huge plus of this scheme, because it saves us from third-party power supplies and the problems associated with them. For example: if we feed the amplifier from a simple battery, then sooner or later it will sit down, which will lead to the inoperability of the circuit at the moment; if we power it from a battery, then sooner or later it will have to be charged, which will also lead to some difficulties and unnecessary movements; if we feed from a power supply unit, then there are two minuses here, which, in my opinion, discard the option of using it - these are wires (to power our PA) and interference. You can get rid of interference in many ways (put a stabilizer, all kinds of filters, etc.), but it’s not so easy to get rid of wires (it’s possible, however, to transfer energy at a distance, but why fence a whole complex of devices to power some then a microphone amplifier?) In addition, this reduces the practicality of the device. Let's move on to the diagram:
Variant amplifier circuit for a dynamic microphone
The circuit is distinguished by its super-simplicity and mega-repeatability, in the circuit there are two resistors (R1, 2), two capacitors (C2, 3), a 3.5 plug (J1), one electret microphone and a transistor. Capacitor C3 works as a microphone filter. The capacitance C2 should not be neglected, that is, it is not necessary to set either more or less than the nominal value indicated in the circuit, otherwise this will entail a lot of interference. Transistor T1 set domestic kt3102
. To reduce the size of the device, I used an SMD transistor marked "1Ks". If you don't know how to solder at all, go ahead to the forum.
When replacing T1, there were no special changes in quality. All other parts are also in SMD cases, including capacitor C3. The whole board turned out to be quite small, although you can make it even smaller using the LUT printed circuit board manufacturing technology. But I also managed with a simple half-millimeter permanent marker. Etched the board in ferric chloride in 5 minutes. The result is such a microphone amplifier board, which is attached to the 3.5 plug.
All this fits well inside the casing from the plug. If you also do this, then I advise you to make the board as small as possible, since it deformed the casing for me and changed its shape. It is desirable to wash the board with a solvent or acetone. The result is such a useful device, with good sensitivity:
Before connecting the microphone to the computer, check all the contacts and see if there is +5v power at the microphone input (and it should be), in order to avoid comments like: “I assembled it exactly as in the circuit, but it doesn’t work!”. This can be done like this: connect a new plug to the microphone jack and measure the voltage with a voltmeter between ground (large tap) and two short solder taps. Just in case, try not to short the plug pins together when you measure the voltage. What will happen then, I do not know and do not want to check. My microphone amplifier has been working for 3 months, I am completely satisfied with the quality and sensitivity. Collect and unsubscribe on the forum about your results, questions, and maybe even about the modifications of the body, circuit and methods for their manufacture. was with you BFG5000, good luck!
Discuss the article ELECTRET MICROPHONE AMPLIFIER
This article is written based on the experience of manufacturing more than two hundred of these adapters. The scheme was taken as a basis from an article from the Radiodesign magazine No. 18, p. 52 (Fig. 1).
The elements indicated in the diagram are not very critical; the RFC choke can be omitted. Initially, this scheme was made in a small neat box, which constantly clung to something and soon became very annoying. After that, the idea of manufacturing an adapter arose, which did not differ much from the proprietary connector. Many different options have been tested. Your attention is given to the final version.
We take a standard 8-pin connector and disassemble it, as shown in Fig. 2.
All conclusions, with the exception of No. 7, are shortened as much as possible. The remaining output is a common microphone wire for transceivers of all models. We increase the diameter of the hole in the end of the connector to 7.2 mm with a file (I turn it on a lathe, but it also turns out pretty quickly with a file).
Next, we take a connector for a 3.5 mm audio plug, cut it off, as shown in Fig. 3 (the length of the remaining screwed part is 10-11 mm). To improve contact, the center conductors are bent and soldered together, and the body lead is shortened. We solder conductors to the conclusions, preferably in fluoroplastic insulation.
For insulation, a heat shrink tube is put on and heated in any way. We wind the trimmed 11 mm rest of the case. We make and put on a gasket with a cut-out hole, depending on the diameter of the body with a heat-shrinkable tube, from any insulating material - fluoroplastic, textolite, but the simplest option is from a plastic bottle.
And this is what the finished board looks like (Fig. 4). Two conductors pass through the hole in the center, and a recess along the edge of the board serves for soldering to the remaining pin 7 on the microphone plug.
The build process goes like this:
1. Unscrew the semi-ring at the end of the microphone plug, insert the audio connector, clamp the bracket and cut off the insulating gasket around the perimeter. Thus, two parts of the manufactured adapter are isolated and the braid of the microphone cable will not have contact with the transceiver case;
2. We take two fluoroplastic wires 1 cm long and solder them -
ICOM - to pins 1 and 2
KENWOOD - to pins 1 and 5
YAESU - to pins 2 and 8 (before making an adapter to a transceiver of this model, check for voltage at pin 2).
We pass the conductors through the holes in the board and solder them to the corresponding points, and the board itself is attached to pin 7 (the microphone body) at the recessed point;
3. We solder the conductors from the adui connector to the board;
4. A heat shrink tube is put on the board and heated to prevent accidental contacts of the board with the wall of the connector housing;
5. We collect the connector, screw the fixing screw.
Assembly steps can be seen in Figure 5.
This is what the adapter looks like on my ICOM 756 PRO 3 (Fig. 6).
Any constructive wishes and suggestions will be greatly appreciated.
My address: [email protected] tel. 8-067-167-34-50 or 8-05662-2-22-23
Yuri Primak, UT7EL
It just so happened that KENWOOD (unlike ICOM), following a long tradition, completes its shortwave transceivers with dynamic microphones. As a result, the microphone input is primarily designed for their connection. Switching to an electret microphone requires a small upgrade, and this will require a constant voltage source, and the refinement itself will entail the addition of several elements. It's good that KENWOOD provided for the presence of a low-voltage direct voltage source, the so-called. phantom power, and brought it to the 5th pin of the microphone connector (round, 8-pin).
Someone will say - "I also have a problem ...". However, quite often I come across on-air conversations on this topic, and the question is “How to connect?” is still relevant. Someone read something somewhere, talked to someone, told something to someone, and conversations about “THIS” are constantly going on.
I would like to focus on the following. Connecting, as you understand, is not at all difficult, there are several options. Let's use the simplest and most typical connection scheme. It is fairly well known and contains only a few details. And yet…
Many of those with whom I had a chance to talk complained - they say, the + 8V source, which “sits” on the 5th pin of the microphone connector in KENWOOD transceivers, has long burned out, and they cannot use this method.
Indeed, this source is very weak, in the user manual it is written about it that its load capacity is no more than YumA. In addition, he is without protection - the slightest short circuit and ... thanks for the company. I myself for a long time avoided turning on an electret microphone in this way. Until now, most often, I use external power, and ... battery. But this does not mean that you should abandon this connection method.
Somehow it was necessary to connect a Taiwanese telephone headset to the TS-570. Without hesitation, I soldered a circuit on SMD elements on a tiny handkerchief - it took up very little space. And in order to exclude a short circuit of the + 8V bus, I turned on a tiny LED in series, one of those that glow brightly with a weak forward current, something about 1mA. Try shorting the microphone input with tweezers and it will immediately light up.
The variety of electret microphones is huge, but inexpensive models of multimedia headsets contain, as a rule, low-voltage microphones with a power supply of 1.5...5V. Professional ones are powered by +48V phantom power supply.
In this case, the choice of a limiting resistor of great fundamental importance does not matter. I use this rule: I choose a resistor based on the supply voltage. For each volt of supply from 7500 m to 1 kOhm. With a supply voltage of 8V, the total resistor will be in the range of 6.2 ... 7.5 kOhm (taking into account the voltage drop across the LED).
The output voltage (peak) of some electret microphones, even at a relatively low-impedance load, can reach several volts, especially when close to the speaker. By putting a small variable resistor, you can select the desired level. And, if it is combined with a switch, even better. It is desirable to turn it on exactly as indicated in the diagram, after the constant capacitor, and not before it. The point is that a dynamic microphone coil is connected to the microphone input of the transceiver, closing the DC component to the screen (AGND).
For the most part, the microphone connector of cheap telephone headsets (multimedia) from different manufacturers is a minijack (3.5″). And there is a very specific way to unsolder them. In turn, the desoldering of the reciprocal connector can be done “for yourself”. This is exactly what I ran into when I first turned on my headset. Having unsoldered, the reciprocal connector for a homemade microphone, everything, as it should be, worked. Actually, I did not even imagine that someday I would see the glow of the limiting LED. An, no, I stuck the headset, the LED lit up. I, to put it mildly, already "fucked up".
It turned out that the factory wiring of this headset was done in a way that I did not expect. A glowing LED told me that the microphone input had landed “on the ground” and there was nothing to count on the signal - I had to figure out what was the matter! It turned out that the middle contact of the connector of this headset closed with the screen of the connecting wire, and in my reciprocal connector it was in parallel with the central contact (apparently, a factory defect). I had to bring it in line - everything was restored and earned. It would seem, nothing special, but I had to tinker.
And further. You have connected an unknown microphone. The connector pinout is correct and the LED is on. This means that this microphone is either faulty (short circuit), or dynamic, the coil of which closed the phantom power circuit to ground (for direct current, it has little resistance).
The 1000pF capacitor must be soldered directly to the pins of the microphone jack. Try to assemble the circuit as compactly as possible without long connecting wires.
Almost all headsets that are designed to work with a PC have such “pathetic” characteristics that if you try to use a microphone from such a headset for sound recording or the same karaoke, you will get nothing but disappointment. There is only one reason for this - all such microphones are designed for speech transmission and have a very narrow frequency range. This not only reduces the cost of the design itself, but also contributes to speech intelligibility, which is the main requirement of the headset.
Attempts to connect a conventional dynamic or electret microphone usually end in failure - the level from such a microphone is clearly not enough to "build up" the sound card. Additionally, ignorance of the input circuit of sound cards affects and incorrect connection of a dynamic microphone ends the matter. Assemble a microphone amplifier and connect it “wisely”? It would be nice, but it's much easier to use the IEC-3 microphone, which was at one time widely used in wearable equipment and is still quite common today. But of course, you will have to connect “by mind”.
This electret microphone has fairly high characteristics (frequency range, for example, lies in the range of 50 - 15,000 Hz) and, most importantly, it has a built-in source follower assembled on a field-effect transistor, which not only matches the high resistance of the microphone with the amplifier, but it also has more than enough output level for any sound card. The only drawback, perhaps, is that the microphone needs power. But its current consumption is so small that two AA batteries connected in series will last for many months of continuous operation. Let's take a look at the internal circuit of the microphone, which is located in an aluminum cup, and think about how to connect it to a computer:
The gray color indicates an aluminum cup, which is a screen and is connected to the common wire of the circuit. As I said, such a microphone requires external power, and minus 3-5 V must be applied to the resistor (red wire), and plus to the blue one. From white we will remove a useful signal.
Now let's take a look at the computer's microphone input circuit:
It turns out that the signal should be sent only to the very tip of the connector, marked in green, and the sound card itself supplies +5 V to the red one through a resistor. This is done to power the headset pre-amps, if used. We will not use this voltage for two reasons: firstly, we need a different polarity, and if we simply “turn over” the wires, then the microphone will “receive” a lot. Secondly, the PC power supply is pulsed and the interference at these five volts will be decent. The use of galvanic cells in terms of interference is ideal - pure "permanence" without the slightest ripple. So, the complete scheme for connecting our microphone to a computer will look like this.
