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Microphone preamplifier

From Wikipedia, the free encyclopedia

The term microphone preamplifier can either refer to the electronic circuitry within a microphone, or to a separate device or circuit that the microphone is connected to. In either instance, the purpose of the microphone preamplifier is the same.

A microphone preamplifier is a sound engineering device that prepares a microphone signal to be processed by other equipment. Microphone signals are often too weak to be transmitted to units such as mixing consoles and recording devices with adequate quality. Preamplifiers increase a microphone signal to line level (i.e. the level of signal strength required by such devices) by providing stable gain while preventing induced noise that would otherwise distort the signal.[1] For additional discussion of signal level, see Gain stage.

A microphone preamplifier is colloquially called a microphone preamp, mic preamp, preamp (not to be confused with a control amplifier in high-fidelity reproduction equipment), mic pre and pre.

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  • ✪ Tone and volume control + microphone preamplifier
  • ✪ Do You Need a $100 Pre Amp in your Home Recording Studio?
  • ✪ Which Mic Preamp Should I Buy?


Construyasuvideorockola Tone and volume control + independent microphone preamplifier Next we teach to build a circuit, which very well complements your stereo amplifier, improving sound and performance. A great advantage of this circuit, is that we can place the volume control, up to 30 meters away from the amplifier, without any noise being introduced. This makes it ideal for video jukebox, making it easier to control them. Also, the microphone input, allows to convert your video jukebox, into a karaoke. Materials The materials for this project are pretty economical and easy to get. In the description of the video, you will find the link to the article, in which you can download a PDF file, with the PCB, electric diagram, bill of materials, and everything necessary to carry out this project. Construction We will begin by placing all the resistors. The resistor terminals are bend with the help of a tweezers. They must remain straight, and of the same length. Then, the resistor is introduced into its corresponding place, taking care that it reaches the bottom, and is perfectly placed. With this same technique, we must place all other resistors Remember to use the component mask as a guide. After verifying that all the resistors are in their correct place, they are weld. Remember that the correct welding technique is done by joining, soldering iron, weld, and piece to be welded, at the same time. The welds should be round, and perfectly surround each terminal. Now we must cut all the leftovers of the resistor terminals. For this we can use a nail clipper. Leftovers are collected, as they will be recycled. These wires are stored, then used as jumpers. It is measured over the card, the length of the bridge to be made, is bent one end of the wire, Is measured again And bend the other end, at the exact distance, so that the jumper enters the holes in the card. The jumper is placed in its respective place. In the same way, we build and place the other jumpers, which go in the printed circuit board. We proceed to weld all the jumpers. The excess are cut. We weld two missing points for soldering And we cut. We already have correctly placed all the resistors and jumpers. The polyester and ceramic capacitors, have no polarity. We place the capacitors in their respective places. We place the polyester capacitors, that are responsible for setting the frequencies, which operates the tone control. Doing this work, we realized that we were missing one of the jumpers. We will place it later. We weld the capacitors. Now, place the 8-pin socket in the correct position. And weld it to the PCB. Then place the 16 pins socket. Check the position in the component mask. And weld the socket. The electrolytic capacitors do have polarity. Check at the time of placing them, that the strip that determines the negative pole, match the drawing, in the component mask. And weld the capacitors. Now place the LM7812 regulator. See close attention to polarity. Place the molex connector of the signal input, And the signal output connector, which will go to the amplifier. To the power connector, is removed the middle pin, And put it in place. We place the diode bridge, leaving it slightly raised from the PCB. See close attention to polarity. Place the potentiometer that controls the microphone volume, The Microphone Jack, The Jack for remote volume control, The volume potentiometer, The potentiometer that controls the high frequencies, The potentiometer that controls the low frequencies, And the power indicator LED. Now insert the 741 integrated circuit. Check the position on the component mask. In the same way, place the TA 76 30 integrated circuit. We already have our tone and volume control with independent microphone preamplifier. Using a toothbrush and thinner, we proceed to wash the PCB very well, on the tracks side. The idea is to remove grease and all metal particles and solder, which can generate short circuits. With a piece of toilet paper, it dries very well the PCB And finish cleaning with a dry brush. The PCB should be clean and shiny. Measurements With the multimeter on the continuity scale the AC power input is measured. There should be no impedance or continuity. Now, we feed the circuit with a transformer between 12 and 15 volts AC, and a minimum of 300 milliamperes. Always! The first time the preamplifier is turned on the series circuit should be used, with a bulb of between 5 and 10 watts Connect to the public network And if everything is correct, the LED turn on. Measure the voltage already rectified by the diode bridge and the 1000 microfarad capacitor There should be approximately 18 Volts DC. Now place the black tip on the bridge negative pole, and the red tip, on the pin 1 of the regulator. There should be the same 18 Volts DC. Then, measure the regulator output and there should be 12 volts approximately. To measure the voltage entering the 741 IC place the black tip on pin 3, and the red tip on pin 7. Should measure 6 volts, which is half the regulator voltage. Now, with the black tip on pin 3 and the red tip on pin 4, is measured minus 6 volts DC. The voltage must be symmetrical. You can also check the total voltage, on the jumper marked with +12 volts. Connections. For signal input, we constructed a cable with a double female RCA connector, one piece of shielded stereo cable and a 2.54mm 3-pin molex female connector. The signal output cable, has in the same connector of 3 pins, 3 wires; Left signal, ground and right signal. And it connects to the amplifier, bifurcated, in independent connectors, to send each signal to each mono stage of the amplifier, thus keeping the stereo sound. Our tone control with microphone preamplifier is ready to be used. In the following videos you can see how to do remote volume control for this project, And a 400 watts stereo amplifier, with which the sound test was performed. Now listen to the live sound test. Hi Guys! Now listen to the sound test, of our voltage controlled tones control With additional microphone input We are going to amplify it With our 400W stereo amplifier. Let's listen. The volume control Now listen to the low frequencies Now the high frequencies And the combination of both frequencies Now let's listen to the microphone input Hello Hello Here have the microphone input All right! The interesting You can mix it up With the music to do karaoke Let's see There have the mix of the microphone with the music All right! We hope that this project will please everyone You will find it on your website Remember to give Like And if they do not like Please comment to be able to continue improving Greetings to all We invite you to subscribe to our youtube channel Go to the tool Botton And check the box, send me updates Join us on Facebook And follow us on twitter Visit our website


Technical details

The output voltage on a dynamic microphone may be very low, typically in the 1 to 100 microvolt range. A microphone preamplifier increases that level by up to 70 dB, to anywhere up to 10 volts. This stronger signal is used to drive equalization circuitry within an audio mixer, to drive external audio effects, and to sum with other signals to create an audio mix for audio recording or for live sound.


In addition to providing gain for the microphone signal, a microphone preamplifier as found in a sound mixer or as a discrete component typically also provides power to the microphone in the form of Phantom power.

In use

A microphone is a transducer and as such is the source of much of the coloration of an audio mix. Most audio engineers would assert that a microphone preamplifier also affects the sound quality of an audio mix. A preamplifier might load the microphone with low impedance, forcing the microphone to work harder and so change its tone quality. A preamplifier might add coloration by adding a different characteristic than the audio mixer's built-in preamplifiers. Some microphones, for example condensers, must be used in conjunction with an impedance matching preamplifier to function properly.

Some preamplifiers exist as one part of a channel strip, which can include other kinds of audio recording devices such as compressors, equalization (EQ), noise gates, and enhancers.


  1. ^ Ballou, 1987, pp. 506–507.
  • Ballou, Glen; Gene Patronis; Mahlon Burkhard (1987). "Amplifiers". Handbook for Sound Engineers: The New Audio Cyclopedia. Indianapolis, Indiana: Howard W. Sams & Co. ISBN 0-672-21983-2.
This page was last edited on 3 December 2018, at 10:02
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