Microphone amplifier with low power transistors. Active microphone amplifier. Complete The End Millenium Amplifier Circuit

It is no secret that knowledge (in the broad sense) is a subjective image of reality. In a narrower sense, knowledge is interpreted as the possession of a certain objective(verified) information that allows you to solve a specific problem.
How objective your image of reality?
Try to analyze how much of your knowledge has been gained true by, i.e. either from your direct experience or as a result of your thinking based on fundamental truths and scientifically based concepts.
This will be the immutable thing that you can rely on when choosing equipment. The remaining approximately 80-99% of all other people’s para-quasi-anti-false-pseudo-as-if knowledge obtained from fabricated articles, abundantly supplied with stunningly beautiful pictures, six-figure price tags and extremely subjective utterances of experts - singles, I suggest you immediately forget.
But remember forever that Scientific explanations are aimed at consciousness. And advertising of all sorts of expensive audiophile things affects the subconscious. It works much more effectively; it is difficult for a person to go against his faith. In general, people, take care of your head!
In fact, almost everything we think his knowledge is gleaned from what came to hand or directly into the ears from the ether. From a young age, in the most primitive way, we become victims of marketing, the flock of professional and well-paid “gurus”. We were told a lot about the intricacies of the sound of this or that cable, about the various influences of interference from the network, about errors when reading laser disks, jitter......about a great variety of processes that must influence the sound.

We now know exactly what should influence! But what are these influences? in numerical terms, and most importantly, can we hear it?! Somehow we were not informed about this.
Let me remind you that influences with similar results add up as the root of the sum of squares. 5% and 1% will not give 6%, but only 5.099%. In other words, when analyzing any influences, you need to know at least order their smallness. Otherwise, we are simply doomed to be Don Quixotes! The Adepts of the Secret Knowledge came up with a lot of horror stories and windmills...

I am not against esotericism and even some superstitions, because (like all of us in this world) I do not have a comprehensive picture! On the contrary, I try to find a rational grain in everything; however, there are some things I know very well.

So, Horror Stories, sorry, our typical misconceptions

Fallacy of Delusions, №000
About the “deadness” and “boringness” of uncolored sound
There is a common belief that precision equipment quickly becomes boring with its monotonous and idealized sound.
This would certainly be the case if recording studios always produced equally “sterile” and “standard” sound. Certainly, there is no standard sound! All musicians, without exception, strive to give the sound “their own,” preferably an easily recognizable style and coloring; many of them use only their favorite gadgets, worn to holes, the position of the knobs on which is kept in the strictest confidence and is not shown even to their wives! Sound engineers are not far behind them, because no one wants to be an inconspicuous robot.
But alas, there are always those who want to claim that all the efforts of the above people are a waste of time without their wonderful “warm” sound! It is not clear why they decided that the sound was initially “cold”.
Really, you shouldn’t exchange the great variety and individuality of possible sounds for a single sound, even if it’s pleasant to the ear!

Misconception #00
About the "flaws" of sound engineering
It is often written that the high resolution of the equipment allows you to hear a lot of what you hear not worth it, for example, flaws in sound engineering or the creaking of chairs in a concert hall; and that instead of music it turns out to be an anatomy lesson.
As they say, if you are afraid of wolves, don’t go into the forest... From my own experience, I can say that I am not very pleased to hear the shortcomings of a recording, but not to hear its advantages is doubly unpleasant!!!
Advantages but very different things happen, for example, in some moments I really enjoy the strong distortions and other features from the same Alana Parsonsa, although some would call them disgusting. And his remastered 24-bit recordings are actually something, these features form a wonderful sound canvas and begin to live their own lives. And it is especially important that the chips reach your ears “as is”, because the colored ones also in yours equipment they have a chance to become just garbage.
What sounds like garbage on low-quality equipment often turns out to be very lively, stylish and unusual sound events. And it is useless to argue whether these are really flaws or whether they were specially written this way for beauty.
Well, if we get tired of all this, we can always listen to MP3 bitrate 64 or net radio, we certainly won’t hear any mistakes from the sound engineer, everything is clear, we can distinguish zero from one!

Misconception #3.1
I repeat, there are no amplifiers without feedback at all; for example, in the emitter (source, cathode) follower circuit, in which 99.5% of all output stages are assembled, there is 100% local current feedback. Simply put, local feedback is an integral property of any amplifier stage, and talking about its harmfulness is simply stupid.

It's time to figure out how the general OS differs from the local one.
1. In both cases, part of the voltage (current) from the output of the amplifier is supplied in antiphase to its input.

2. In both cases, similar circuit solutions are used, usually the only difference is in the resistor values, which determine the depth of the local OS.

3. The local OS linearizes the amplification stage, but only up to a certain limit, about 0.05 – 0.2% total harmonic distortion. Limitations are imposed by the physical properties of the active elements. General environmental protection is free from this fundamental limitation.

4. The phase shift in a circuit without OOOS is completely harmless, since it cannot exceed 90 degrees for each stage, and the stability condition is satisfied automatically. In a circuit with an OOOS, consisting of several stages, this phase shift “accumulates”, and this is the only limitation on the depth of the OOOS. .

And, if you believe the esotericists, the sound is “killed” only by the general operating system, but not by the local one, which makes it possible to localize the problem precisely in the phase shift.
It is interesting that the phase shift in an amplifier is a virtual concept in a sense and for audio frequencies is in no way related to the delay in signal propagation in time, from which In fact The quality of the LLC's work depends very much. Latency equivalent to a 90 degree phase shift at 20kHz – approx. 12 µsec, and no, not even the slowest amplifier has such a delay. For comparison, in ES6.2 the delay from input to output is 60 nsec, i.e. 200 times less. Accordingly, the general environmental protection system in it works in exactly the same way as any local one.

So, the general OOS is no fundamentally different from the local one, with the exception of the number of cascades covered, and the phase shift that “accumulates”. The difference completely disappears, if you build an amplifier so that the phase shift from input to output in the audio frequency band is small.

But let's return to the quality of amplifiers without OOS.
With input stage everything is fine, the nonlinearities it introduces are small, since the amplitude of the input and output signals is small.
With voltage amplification stage everything is not so great anymore, its gain is usually quite high, and the output amplitude is comparable to the supply voltage, and nonlinear capacitances and the nonlinear dependence of gain and output resistance on voltage are fully affected. The distortions introduced by this cascade are 0.05 – 0.5%, and contrary to popular belief, they do not depend very much on the amplifier architecture.
Fully (supposedly) balanced amplifiers perform almost as well as any other.This happens for the reason that the main contribution is made by only two transistors (in the diagram below Q4 and Q7), but in good amplifiers they Always two, regardless of whether the amplifier is "balanced" or not. In addition, completely complementary transistors simply do not exist; the capacitance and curvature of transistors of different structures differ significantly due to technological reasons.
The figure below shows the results of modeling a “symmetrical” and once sensational amplifier without OOS “ The end Millennium » , the diagram is taken from here, simple and beautiful.

From the simulation results it is easy to see that the distortion of the End Millennium amplifier without load ( and even without an output stage!!!) approximately 0.07% THD and 0.1% IMD. As a trick, a cascade, even a carefully tuned one, will add (as will be shown below) about the same amount, but the trick is that as a result of multiplying the distortion spectra, the final spectrum will contain a lot of harmonics and intermodulations of a high order. Apparently, this same garbage is declared to be of “unique” quality.
It is unclear what 0.0017% THD the authors claimed. Quite a bold statement even for a good amplifier with OOOS. The error is almost 50 times, however! But, thanks to the authors, now we know which numbers they consider “reference”.

Output stage. The best and carefully built(including in class "A") has an output impedance of 0.05 - 0.2 Ohm and distortion on a large signal of the order of 0.05 - 0.2%, and up to 0.4% on a medium-small signal (). The resulting distortion (especially on a large and complex signal, where it will vary chaotically with frequency, since the load impedance is not constant and is not very similar to a resistor) can be up to 0.5%. This “accuracy” can be checked by any Chinese tester!

So, what can you count on when you become the owner of an amplifier with the proud inscription “amplifier without negative feedback”?

Misconception #4
About the need for long-term “warm-up” of equipment
I don’t see any practical point in long-term (more than half an hour) warming up devices that do not contain moving parts or parts with a very high heat capacity. Well, I don’t believe in the possibility of hyperfine states of matter in an ordinary transistor or capacitor!
The human hearing aid is another matter! It can and should be warmed up over the years, especially when it begins to hear new synthetic sounds. It takes time to convince yourself that something is good.
In addition, if a product “warms up” for a week, that is, there is a rapid drift of parameters, then in a month it can “grow old”, and in two months it can die.

Misconception #5
About the “unimportance” of harmonic distortion.
Harmonic distortion has always been considered one of the main characteristics of the sound amplification path. But, like everything in this world, their correct understanding has its own subtleties. One subtlety - with numerically equal Kg, amplifiers can sound completely different due to the different spectral composition of the harmonics. The second subtlety is the unevenness of Kg at different frequencies. Below shows that It is incorrect to talk about distortions by considering only harmonic distortions, without regard to intermodulation ones.
The fact is that the same nonlinearities in the amplifier path that give rise to harmonics absolutely inevitably give rise to intermodulation. And this is not a subject for discussion, it is a mathematically proven fact. In fact, harmonic distortion is just a special case of intermodulation distortion, when one of the test frequencies is missing. Intermodulation of high-frequency components also affects mid-frequencies, the zone of greatest hearing sensitivity, and Not masked by HF components. The hearing threshold at mid frequencies is around 0 dB, and it is important to keep intermodulation below this threshold. First-order intermodulations, at best, are equal to harmonics in amplitude, hence the clear requirement: the level of harmonic distortion at high frequencies of the entire path (this is especially difficult to achieve in a PA) should not exceed the audibility threshold at medium frequencies. Thus, for a sound pressure of, for example, 96 dB, the level of harmonic distortion at HF should not be more than 0.0016%. An amplifier with such low HF distortion demonstrates an unusually subtle, airy, weightless sound.
This, as they say, is an argument Behind little distortion.
Argument Against the fact that supposedly the distortions are quieter than the background noise of the room and are not audible.
The assumption that distortion below the noise level will not be noticed is, in my opinion, an unforgivable and incorrect simplification. For example, we can perfectly hear the quiet singing of birds outside the window, but if we take a microphone, record it, weigh it using an equalizer along the hearing sensitivity curve and try to find the signal peaks corresponding to the singing in the resulting noise picture of the room that is adequate from the point of view of hearing, then we won't see anything! This happened because the measured level of the noise track carries information about the integral value of the signal, roughly speaking it is the root of the sum of the squares of all frequencies, each of which is significantly smaller in amplitude. We would easily see it on a spectrogram, because birdsong is a narrow-band signal that exceeds noise in the observed frequency interval.
There are at least two more features of human hearing, which should not be ignored and “simplified”, and which helped us to hear the birds singing against the background of the rumbling of the refrigerator and the snoring of our flatmate. This is direction selectivity and the ability to “accumulate” information about a repeating signal that is sufficiently long in time. According to some researchers ( Stereophony . - Kovalgin Yu.A.), the first of them is 12-15 dB (!), information on the second, unfortunately, could not be found. I don’t want to overestimate it, just as I don’t want to ignore it, so let’s take something average, for example 6 dB.
The total is approximately 20 dB.
As a result, if we listen to music in a quiet room (20-30 dBA), we arrive at approximately the same numbers: intermodulation and harmonic distortion of the amplification path throughout the entire frequency band should be less than the audibility threshold, about 0.003% and 0.002%, respectively. Naturally, it is preferable to have a reserve, just to be sure.

Microphone preamp, also known as a pre-amplifier or amplifier for a microphone, is a type of amplifier whose purpose is to amplify a weak signal to a linear level (about 0.5-1.5 volts), that is, to an acceptable value at which conventional audio power amplifiers operate .

The input source of acoustic signals for a preamplifier is usually vinyl record pickups, microphones, and pickups of various musical instruments. Below are three circuits of microphone amplifiers on transistors, as well as a variant of a microphone amplifier on the 4558 chip. All of them can be easily assembled with your own hands.

Circuit of a simple microphone preamplifier using one transistor

This microphone preamplifier circuit works with both dynamic and electret microphones.

Dynamic microphones are similar in design to loudspeakers. The acoustic wave affects the membrane and the acoustic coil attached to it. When the membrane oscillates, an electric current is generated in a coil exposed to the magnetic field of a permanent magnet.

The operation of electret microphones is based on the ability of certain types of materials with increased dielectric constant (electrets) to change the surface charge under the influence of an acoustic wave. This type of microphone differs from dynamic microphones in its high input impedance.

When using an electret microphone, to bias the voltage on the microphone, it is necessary to set the resistance R1

Since this microphone amplifier circuit is for a dynamic microphone, when using an electrodynamic microphone, its resistance should be in the range from 200 to 600 Ohms. In this case, C1 must be set to 10 microfarads. If it is an electrolytic capacitor, then its positive terminal must be connected towards the transistor.

Power is supplied from the crown battery or from a stabilized power source. Although it is better to use a battery to eliminate noise. can be replaced with a domestic one. Electrolytic capacitors for a voltage of 16 volts. To prevent interference, connect the preamplifier to the signal source and to the amplifier input using a shielded wire. If further powerful sound amplification is needed, then you can assemble an amplifier on a microcircuit.

Microphone preamplifier with 2 transistors

The structure of any preamplifier greatly affects its noise characteristics. If we take into account the fact that the high-quality radio components used in the preamplifier circuit still lead to distortion (noise) to one degree or another, then it is obvious that the only way to get a more or less high-quality microphone amplifier is to reduce the number of radio components in the circuit. An example is the following two-stage preliminary circuit.

With this option, the number of decoupling capacitors is minimized, since the transistors are connected in a circuit with a common emitter. There is also a direct connection between the cascades. To stabilize the operating mode of the circuit when the external temperature and supply voltage change, a direct current feedback loop has been added to the circuit.

Preamplifier for electret microphone with three transistors

This is another option. The peculiarity of this microphone amplifier circuit is that power is supplied to the preamplifier circuit through the same conductor (phantom power) through which the input signal travels.

This microphone preamplifier is designed to work together with, for example, MKE-3. The supply voltage to the microphone goes through resistance R1. The audio signal from the microphone output is supplied to the VT1 base through capacitor C1. , consisting of resistances R2, R3, creates the necessary bias at the base of VT1 (approximately 0.6 V). The amplified signal from resistor R5, acting as a load, goes to the base of VT2 which is part of the emitter follower on VT2 and VT3.

Near the output connector, two additional elements are installed: load resistor R6, through which power is supplied, and separating capacitor SZ, which separates the output audio signal from the supply voltage.

Pre-microphone amplifier based on 4558 chip

The 4558 operational amplifier is manufactured by ROHM. It is characterized as a low power and low noise amplifier. This microcircuit is used in a microphone amplifier, audio amplifiers, active filters, and voltage-controlled generators. The 4558 chip has internal phase compensation, increased input voltage threshold, high gain and low noise. This op amp also has short circuit protection.

(140.5 Kb, downloads: 2,161)

This is a good option for building a microphone preamp on a chip. The microphone preamplifier circuit is characterized by high amplification quality, simplicity and does not require much wiring. This dynamic microphone amplifier also works well with electret microphones.

With error-free assembly, the circuit does not require configuration and starts working immediately. The highest current consumption is 9 mA, and at rest the current consumption is around 3 mA.

For pop orchestras, school radio centers or intercoms, a pre-amplifier is often needed for a low-impedance microphone or a dynamic head used in the same role. Circuits of such amplifiers are offered by the magazine "Funkamater" (GDR).

The first, the simplest, is used when the microphone is located at a considerable distance from the main amplifier. The 7.5-12 V supply voltage is supplied to the preamplifier via an “audio” cable with a grounded braid. Transistors (V1 and V2) provide high signal amplification. Capacitor C2 eliminates self-excitation. The operating mode is set using trimming resistor R3 so that the collector V2 has “half” supply voltage. Current consumption = 1.5 mA.

The second amplifier is designed to work with high-quality equipment. With an increase in resistance R5 = 100 kΩ, the device gain is maximum (51 dB). Sensitivity 3-8 mV, optimal microphone impedance = 200 ohms. At the top point of R2 the voltage is = + 6 V, and at the collector V1 the voltage is approximately + 2 V.

Both amplifiers are assembled from small parts and placed in tin cases the size of a matchbox and grounded. The devices use low-power silicon transistors: V1 low-noise, for example KT312B, V2 - KT306, KT315, KT342 with any letter index. Magazine "M-K" No. 2, 1985

Non-standard microphone activation.

Placing a microphone amplifier in close proximity to the microphone reduces the shielding requirements of interconnecting wires and improves the signal-to-background ratio. However, this raises a new problem associated with powering the microphone; the built-in battery requires frequent replacement, and using an additional power cord is not always convenient.

The figure shows a diagram of a two-stage microphone amplifier whose power is supplied via a signal wire. In this case, you only need to add one resistor R4 to the main amplifier, which serves as a load for the microphone amplifier and an isolation capacitor C2.

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It is inexpensive, costs about 120 rubles.

And here is his diagram:

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Fig. 4 . Electrical circuit of a microphone amplifier.

More different microamplifiers on microcircuits

These amplifiers are used to amplify signals of low magnitude (0.2-2 mV). The input impedance of the microphone amplifier, which provides the maximum signal-to-noise ratio, is selected to be 3 times the internal impedance.

The circuit implementation of a microphone amplifier is quite simple when using an operational amplifier. The operational amplifier should be selected based on the minimum noise level applied to the input. Of the domestic operational amplifiers, the most suitable are the KM551UD2A (Uin noise = 1 μV) or K157UD2 (Uin noise = 1.6 μV). Among foreign operational amplifiers, we can recommend NE5532.

Input voltage 1 mV,
Nominal output voltage 100 mV,
Signal to noise ratio = 56 dB,
Operating frequency range Hz,
Harmonic distortion 0.05%

The operational amplifier is connected in an inverting amplifier circuit. The gain is determined by the ratio of resistors R1 / R2 and is equal to 100. When replacing the operational amplifier K157UD2 with KM551UD2A, the signal to noise ratio will increase to 60 dB.

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Figure 3 shows a diagram of a microphone amplifier with a balanced input, in which the functions of a transformer are performed by a differential amplifier based on the operational amplifier DA1.

A summator of two signals is assembled on DA2. The higher the degree of matching of resistors RЗ and R4, R6 and R7, R8 and R9, R10 and R12, R11 and R13, the higher the degree of matching of resistors RЗ and R4, R6 and R7, R8 and R9.

The microphone amplifier has the following parameters:
Nominal input voltage = 2 mV,
Nominal output voltage = 100 mV,
Signal-to-noise ratio 60 dB,
Harmonic distortion 0.5%,
Reproducible frequency range Hz,
Minimum load resistance = 10 kom.

The gain of the microphone amplifier depends on the position of switch S1.

When the switch is open, K = 50, when closed = 100.