Connecting a dynamic microphone to a computer.
The microphone input of sound cards is intended for connecting electret (a type of condenser) microphones. A condenser microphone has a built-in amplifier and therefore the output signal is quite strong.
Fig. 1 Diagram of a condenser microphone.
In most cases, electret microphones have worse performance than dynamic microphones. If you need high-quality sound recording, it makes sense to use a higher quality (compared to what is installed, for example, in headsets) dynamic microphone, which could have remained from the times of the USSR, for example from a tape recorder, or the microphone came from a DVD set with karaoke. The photo shows several examples of dynamic microphones.
Fig.2 Dynamic microphone from DVD player with karaoke.
Fig.3 Dynamic microphone Octave MD-47. Year of manufacture 1972. Wonderful sound.
Fig.4 Dynamic microphone. DEMSH-1A capsule.
Fig.5 Stylish retro headset with a dynamic microphone.
Connected to the microphone input sound card dynamic microphone, it is not possible to get a normal signal level, at least if you do not shout into this microphone. Strengthening is needed.
Unlike dynamic microphones, all condenser microphones require power from an amplifier. To operate the amplifier built into the condenser microphone, approximately 3 volts of power is supplied to the middle contact - Vbias (in Fig. 8 - +V). The amplifier circuit for a dynamic microphone is similar to the built-in amplifier for a condenser microphone.
Fig. 7 Amplifier circuit for a dynamic microphone.
Fig.8 Microphone plug.
Part values vary widely.
Transistor V1 n-p-n type. For example S945, KT315B, KT3102. Resistor R1 is within 47..100 kOhm, it is advisable to install a trimmer and bring the transistor to the optimal mode, and then measure the resistance of the trim resistor and set a constant of a similar value. Although the circuit will work immediately with any transistor and resistor with a rating within these limits. Capacitors C1, C2 from 10 μF to 100 μF, optimally 47 μF at 10 V. Resistor R2 1..4.7 kOhm
It is advisable to place the circuit in the microphone body itself, as close as possible to the capsule, in order to avoid amplification of noise that can penetrate the cable. If the microphone is to be used for its previous purpose or the ability to connect different dynamic microphones is needed, then the circuit can be mounted in a separate shielded case with a jack for connecting microphones and a cable for connecting to a sound card.
Microphones are used to convert the energy of sound vibrations into alternating electrical voltage. According to the classification, acoustic microphones are divided into two large groups:
High-resistance (capacitor, electret, piezoelectric);
Low resistance (electrodynamic, electromagnetic, carbon).
Microphones of the first group can be conventionally represented as equivalent
variable capacitors, and microphones of the second group - in the form of inductors with moving magnets or in the form of variable resistors.
Among high-impedance microphones, electret microphones are more affordable. Their parameters are normalized in standard range audio frequencies, which has the popular name “two by twenty” (20 Hz ... 20 kHz). Other features: high sensitivity, wide bandwidth, narrow radiation pattern, low distortion, low level noise
There are two- and three-terminal electret microphones (Fig. 3.37, a, b). To make it easier to identify the wires coming out of the microphone, they are deliberately made multi-colored, for example, white, red, blue.
Fig, 3.37. Internal circuits of electret microphones: a) two communication wires; b) three communication wires.
Despite the transistors inside the microphone, it is short-sighted to send the signal from it directly to the MK input. Requires preliminary audio amplifier. In this case, it makes no difference whether the amplifier is built into the MK ADC channel or whether it is a separate external unit assembled on transistors or microcircuits.
Electret microphones are similar to piezo vibration sensors, but unlike the latter they have a linear transmission and wider frequency response. This allows you to process without distortion sound signals human speech, which, in fact, is the direct purpose of the microphone.
If you sort electret microphones produced in CIS countries in order of improving their parameters, you will get the following row: MD-38, MD-59,
MK-5A, MKE-3, MKE-5B, MKE-19, MK-120, KMK-51. The operating frequency range is from 20…50 Hz to 15…20 kHz, the unevenness of the amplitude-frequency response is 4… 12 dB, sensitivity at a frequency of 1 kHz is 0.63… 10 mV/Pa.
In Fig. 3.38, a, b shows diagrams of direct connection of electret microphones to MK. In Fig. 3.39, a...k shows circuits with transistor amplifiers, and in Fig. 3.40, a...p - with amplifiers on microcircuits.
Rice. 3.38. Schemes for direct connection of electret microphones to MK:
a) direct connection of microphone VM1 to MK is possible if the ADC channel has an internal signal amplifier with a coefficient of at least 100. Filter R2, C/ reduces low-frequency background from ripples of the +5 V supply voltage;
b) connecting a stereo microphone VMI to a two-channel ADC MK, which has an internal amplifier. Resistors R3 limit the current through the MK diodes when strong blows on the microphone body or on the piezo plate itself.
c) the VTI transistor must have the highest possible gain (coefficient hjy^)’,
d) resistor R3 selects the voltage on the collector of transistor VT1, close to half the supply (to symmetrically limit the signal from microphone VM 1)\
e) chain /?/, C1 reduces the amplitude of network ripples from the +5 V power supply, and therefore the unwanted “rumble” with a frequency of 50/100 Hz is reduced. Here and henceforth, the letters “c”, “b”, “k” will indicate the color of the microphone wires “blue”, “white”, “red”;
e) simplified connection of a three-pin BMI microphone. The absence of a resistor in the emitter of the VTI transistor reduces the input resistance of the stage;
g) remote “two-terminal microphone” with phantom power for transistors VTI, VT2 through resistor R5. Resistor R1 selects the voltage +2.4…+2.6 V at the emitter of transistor VT2. The analog comparator MK records moments when the signal from the microphone is greater than a certain threshold, which is set by resistor R7\0
h) the transistor operates in cutoff mode, due to which sinusoidal sound signals from the VMI microphone become rectangular pulses;
i) connecting a three-pin VMI microphone using a two-wire circuit. Microphone VM1 and resistor R1 can be swapped. Resistor R2 selects the voltage at the MK input, close to half the power;
j) a resistor is used to select the voltage at the input of the MK, close to +1.5 V.
a) transformer isolation allows you to move elements VM1, DAI, GBJ, T1 to long distance, in this case, the MK input should be protected with Schottky diodes. The current consumption of the DA chip is ultra-low, which allows you to avoid placing a switch in the GB1\ battery circuit
Rice. 3.40. Diagrams for connecting electret microphones to M K through amplifiers to
microcircuits (continuation):
b) amplifier for microphone “light music”. Resistor R4 sets the response threshold of the analog comparator MK within 0…+3 V;
c) “electronic sound level meter”. The positive output of the analog comparator MK receives a smoothed voltage proportional to the average signal level from microphone VM1. A “saw” is programmatically generated at the negative output of the analog comparator;
d) resistor R3 regulates the symmetry of the signal, and resistor R5 regulates the gain of the op-amp DAL. The detected signal (elements VDI, VD2, SZ, C4) is supplied to the input of the MK. The average sound level is measured by an internal ADC;
e) non-standard use of the “LED” microcircuit Z) / l / from Panasonic. Possible replacements are LB1423N, LB1433N (Sanyo), BA6137 (ROHM). Switch ZL1 sets sensitivity in five gradations on a logarithmic scale: -10; -5; 0; +3; +6 dB;
e) the gain of the op-amp cascade Z)/4/ depends on the ratio of the resistances of resistors R4, R5. Frequency response in the region low frequencies determined by capacitor C/;
g) the gain of the op-amp cascade Z)/l / is given by the ratio of the resistances of resistors R5, R6. The symmetry of the signal limitation depends on the ratio of resistors R3, R7\
h) microphone amplifier with continuously adjustable sound level using resistor R5\
i) two-stage amplifier with distributed gain: Ku= 100 (DAI.I), Ku= 5 (DAI.2). The divider on resistors R4, /?5 sets the bias, which is slightly less than half the supply. This is due to the fact that the DA / op amp does not have a “rail-to-rail” characteristic;
Rice. 3.40. Schemes for connecting electret microphones to MK through amplifiers on
microcircuits (continuation):
j) the capacitance of capacitor C4b in some circuits is increased to 10...47 μF (the improvement in parameters is tested experimentally);
k) the “left” half of the DAI op-amp amplifies the signal, and the “right” half is connected according to the voltage follower circuit. This solution is usually used when the MC is located at a considerable distance from the amplifier or it is necessary to branch the signal into several directions;
m) resistors R2, R4 switch the inverters of the DDI logic chip to amplification mode. Resistor R3 can be replaced with a capacitor with a capacity of 0.15 μF;
m) specialized chip DA1 (Motorola) responds only to audio signals of a person’s voice;
o) a plug inserted into socket XS1 automatically breaks the connection between capacitors C/ and C2, while the internal microphone VM1 is turned off, and an external audio signal is sent to the DAL/ input. Both amplifiers of the Z)/l/ chip have rail-to-rail output levels;
n) the resistor sets the symmetry of the signal limitation at pin 1 of the DA 1 microcircuit. The VTI transistor, together with the elements R5, SZ, performs the function of a detector.^
3.5.2. Electrodynamic microphones
The main design elements of electrodynamic microphones are an inductance coil, a diaphragm and a magnet. The microphone diaphragm, under the influence of sound vibrations, brings the magnet closer to/away from the coil, and therefore an alternating voltage appears in the latter. Everything is like in school experiments in physics.
The signal from an electrodynamic microphone is too weak, so an amplifier is usually installed to interface with the MK. Its input impedance may be low. Connecting wires from microphone to input amplifier it is necessary to shield or reduce the length to 10... 15 cm. To eliminate false alarms, it is recommended to wrap the capsule with foam rubber and not screw the microphone tightly to the wall of the case.
Typical parameters of electrodynamic microphones: winding resistance 680…2200 Ohm, maximum operating voltage 1.5…2 V, operating current 0.5 mA. An important practical consequence is electrodynamic microphones
easy to distinguish from electret (capacitor, piezoceramic) by the presence of ohmic resistance between the terminals. The exception to the rule is industrial microphone modules that contain a transistor or integrated amplifier inside the housing.
You can replace the electrodynamic microphone with an electret one through the adapter shown in Fig. 3.41. Capacitor C2 corrects the frequency response in the high frequency region. A divider on resistors R1 creates an operating voltage for the BML microphone. Capacitor C1 serves as a power supply filter.
Rice. 3.43. Diagrams for connecting dynamic speakers to the input MK:
A) transistor amplifier shock sensor using a BAI loudspeaker. Sensitivity is adjusted by resistors RI, R2. Capacitor C2 smooths out signal peaks. Capacitor C/ is necessary so that the base of transistor VT1 is not connected to the common wire through the low resistance of the speaker BAI;
b) the VTI transistor is a common base amplifier. Its feature is its low input impedance, which is in good agreement with the parameters of the BAI loudspeaker. Resistor RI sets the operating point of the transistor VTI (voltage at its collector) to obtain symmetrical or asymmetrical signal clipping. Resistor R3 regulates the threshold (sensitivity, gain);
c) the microphone function is performed by the BAI headset. It has a higher winding resistance than a low-impedance loudspeaker, which increases sensitivity and makes it easier to connect to the MCU. Resistor RI regulates the signal amplitude;
In Fig. 3.43, a...d shows diagrams for connecting dynamic speakers to the MK input as microphones.
d) part of the circuit intercom, in which the BAI loudspeaker alternates between microphone and speaker functions. The MK determines the “Reception/Transmission” state by the LOW/HIGH level on the input line ( High level from resistor R4, and LOW from and BAI). If the MK has an ADC with an internal amplifier, then you can “listen” to the conversation in the path. In addition, if the MK line is switched to output mode, then it can be used to generate various sound signals in the ULF (via R3, VD1, R2, C2).
This article was written based on the experience of manufacturing more than two hundred of these adapters. The diagram was taken as a basis from an article from the magazine “Radiodesign” No. 18, p. 52 (Fig. 1).
The elements indicated in the diagram are not very critical; the RFC choke does not need to be installed. Initially, this circuit was made in a small, neat box, which constantly caught on something and soon became very annoying. After which the idea of making an adapter arose, which was not very different from the proprietary connector. Many different options have been tested. The final version is presented to your attention.
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 pin is the 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 grind it on a lathe, but it can also be done quite quickly with a file).
Next, take the connector for the 3.5 mm audio plug, cut it off as shown in Fig. 3 (the length of the remaining screw-on 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 terminals, preferably in fluoroplastic insulation.
For insulation, a heat-shrinkable tube is put on and heated in any way. We screw on the trimmed 11 mm remainder of the body. 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 polyethylene bottle.
And this is what the finished board looks like (Fig. 4). Two conductors pass through the hole in the center, and the notch along the edge of the board is used for soldering to the remaining pin 7 on the microphone plug.
The assembly process proceeds as follows:
1. Unscrew the half-ring at the end of the microphone plug, insert the audio connector, clamp the bracket and cut off the insulating pad around the perimeter. In this way, the two parts of the adapter being manufactured are isolated and the braid of the microphone cable will not have contact with the transceiver body;
2. 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 for the transceiver of this model, check the presence of 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 at the notch is attached to pin 7 (microphone body);
3. Solder the conductors from the audio connector to the board;
4. A heat-shrinkable tube is placed on the board and heated to prevent accidental contacts of the board with the wall of the connector housing;
5. Assemble the connector and tighten the fixing screw.
The assembly steps can be seen in Fig.5.
This is what the adapter looks like on my ICOM 756 PRO 3 (Fig. 6).
Any constructive wishes and suggestions will be welcomed with gratitude.
My address: [email protected] tel. 8-067-167-34-50 or 8-05662-2-22-23
Yuri Primak, UT7EL
It's been in my head for a long time. Having gathered my strength, I began to search for amplifier circuits. Most of the schemes I looked at I didn't like. I wanted to assemble it easier, better and smaller (for a laptop, because the built-in one was apparently made just for show - the quality is poor). 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 transmission are carried out over one wire) is a huge advantage of this circuit, because it saves us from third-party power sources and the problems associated with them. For example: if we power the amplifier from a simple battery, it will sooner or later run out, which will lead to the inoperability of the circuit this 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 power it from a power supply, then there are two disadvantages that, in my opinion, rule out the option of using it - these are wires (for powering our PA) and interference. You can get rid of interference in many ways (install a stabilizer, all sorts of filters, etc.), but getting rid of wires is not so easy (you can, however, transfer energy at a distance, but why fence off a whole complex of devices to power some a microphone amplifier?) In addition, this reduces the practicality of the device. Let's move on to the diagram:
Amplifier circuit option for a dynamic microphone
The circuit is distinguished by its super-simplicity and mega-repeatability; the circuit contains 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. Capacity C2 should not be neglected, that is, it should not be set more or less than the nominal value indicated in the diagram, otherwise this will entail a lot of interference. We install domestic transistor T1 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 to the forum.
When replacing T1 there were no significant changes in quality. All other parts are also in SMD cases, including capacitor C3. The entire board turned out to be quite small, although you can make it even smaller using manufacturing technology printed circuit boards LUT. But I made do with a simple half-millimeter permanent marker. I etched the board in ferric chloride in 5 minutes. The result is a microphone amplifier board that is attached to a 3.5 plug.
All this fits well inside the plug casing. If you do this too, I advise you to make the board as small as possible, since for me it deformed the casing and changed its shape. It is advisable to wash the board with solvent or acetone. The result was a useful device with good sensitivity:
Before connecting the microphone to the computer, check all the contacts and whether there is +5v power at the microphone input (and there should be), in order to avoid comments like: “I assembled it exactly as in the diagram, but it doesn’t work!” This can be done this way: connect a new plug to the microphone connector and measure the voltage with a voltmeter between ground (large tap) and two short solder taps. Just in case, try not to short-circuit the plug leads together when you measure the voltage. I don’t know what will happen then and I don’t want to check. My microphone amplifier has been working for 3 months now, and I am completely satisfied with the quality and sensitivity. Collect and post on the forum about your results, questions, and maybe even about modifications to the case, circuits and methods of their manufacture. I was with you BFG5000, Good luck!
Discuss the article ELECTRIC MICROPHONE AMPLIFIER
It just so happens that the KENWOOD company (unlike ICOM), observing a long-standing tradition, completes its shortwave transceivers 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 upgrade itself will entail the addition of several elements. It’s good that KENWOOD has provided for the presence of a low-voltage constant 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 have a problem too...”. 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 “IT” are ongoing.
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 standard circuit connections. 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 that the +8V source, which “sits” on the 5th pin of the microphone connector in KENWOOD transceivers, burned out long ago, 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. On top of everything else, he is unprotected - the slightest short circuit and... thanks for the company. Myself for a long time avoided turning on the electret microphone this way. Until now, most often, I use external power, and... battery power. But this does not mean that you should abandon this method of connection.
Somehow I needed to connect a Taiwanese telephone headset to the TS-570. Without hesitation, I soldered a circuit using SMD elements on a tiny handkerchief - it took up very little space. And in order to prevent a short circuit in the +8V bus, I turned on a tiny LED in series, one of those that glows brightly at a weak forward current, something around 1mA. Try shorting the microphone input with tweezers and it will immediately light up.
The variety of electret microphones is huge, but inexpensive models Multimedia headsets usually contain low-voltage microphones with a power supply of 1.5....5V. Professional ones are powered from a +48V phantom power supply.
In this case, the choice of limiting resistor is not of great fundamental importance. I use this rule: I choose a resistor based on the supply voltage. For each volt of supply from 7500m to 1kOhm. 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 located close to the speaker. By installing a small variable resistor, you can select the required level. And, if it is combined with a switch, even better. It is advisable to turn it on exactly as indicated in the diagram, after the constant capacitor, and not before it. The idea is that a dynamic microphone coil is connected to the microphone input of the transceiver, shorting the DC component to the screen (AGND).
In most cases, the microphone jack of cheap telephone headsets (multimedia) from different manufacturers is a minijack (3.5″). And there is a very specific way to wire them. In turn, the wiring of the mating connector can be done to suit your needs. This is exactly what I ran into the first time I turned on my headset. Having unsoldered, the mating connector under homemade microphone, everything worked as expected. Actually, I didn’t even imagine that I would ever see the glow of the limit LED. But no, I plugged in the headset and the LED lit up. To put it mildly, I was already “stuck up.”
It turned out that the factory wiring of this headset was done in a way that I had not expected. The glowing LED told me that the microphone input had gone “to ground” and there was nothing to rely on for a signal - I had to figure out what was going on! It turned out that the middle contact of the connector of this headset was closed with the screen of the connecting wire, and in my mating connector it was paralleled with central contact(apparently a manufacturing defect). I had to bring it into compliance - everything was restored and working. It would seem nothing special, but we had to tinker.
And further. You have connected an unknown microphone. The connector is wired correctly and the LED is on. This means that this microphone is either faulty (short circuit), or dynamic, the coil of which has closed the phantom power circuit to ground (by DC it has little resistance).
The 1000pF capacitor must be soldered directly to the microphone jack pins. Try to assemble the circuit as compactly as possible without long connecting wires.
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