Preamplifier refers to the circuit or electronic equipment between the signal source and the amplifier stage, which is designed to receive weak voltage signals from the signal source.
The preamplifier amplifies the noise as well as the useful signal. The low-noise preamplifier is a preamplifier that minimizes the noise figure of the circuit.
For weak signal detection instruments or equipment, preamplifier is one of the main components to introduce noise.
The noise figure of the whole detection system mainly depends on the noise figure of the preamplifier.The minimum signal that can be detected by the instrument also depends on the noise of the preamplifier.
The preamplifier is usually directly connected to the sensor detecting the signal. Only when the optimal source resistance of the amplifier is equal to the output resistance of the signal source can the noise figure of the circuit be minimized.[1]
Function of preamplifier
1 Improve the signal-to-noise ratio of the system (the front amplifier is close to the detector, the transmission line is short, the distributed capacitance Cs is reduced, and the signal-to-noise ratio is improved) 2. Reduce the relative influence of external interference (the signal is preliminarily amplified by the front amplifier) 3. Reasonable layout, easy to adjust and use (the front amplifier is non adjustable, and the main amplifier has large adjustment times and shaping constants) 4. Realize impedance conversion and matching (the front amplifier is designed as high input impedance and low output impedance)[2]
classification
Voltage sensitive preamplifier (voltage amplifier)
Charge sensitive preamplifier (current integrator with capacitor negative feedback) has stable output gain, low noise and good performance
Current sensitive preamplifier (current preamplifier, parallel feedback current amplifier)
Fast response, time information can be obtained.Long distance transmission is available.Narrow rise time and width of output pulse, suitable for high count rate measurement.
function
Announce
edit
Preamplifier
The preamplifier has two functions: one is to select the required sound source signal and amplify it to the rated level;The second is to carry out various sound quality control to beautify the sound.
form
Announce
edit
The basic components of the preamplifier are: sound source selection, input amplification, sound quality control and other circuits.
effect
Announce
edit
Preamplifier Description
The function of the sound source selection circuit is to select the desired sound source signal and send it to the rear stage, while closing other sound source channels.
inputamplifierIts function is to amplify the sound source signal to the rated level, usually about 1V.
The function of sound quality control is to makesoundThe frequency characteristics of the system can be controlled to achievehigh fidelitySound quality;Or according to the listener's preferences, modify and beautify the voice.
Differentiated application
Announce
edit
Power amplifierLine amplifierThe difference and application between and preamplifier
The input signal is amplified by the preamplifier, such as throughMicrophoneThe picked up sound signal, because it is weak, needs to be amplified to a certain level before reaching other levels.Usually the front end has a higherVoltageGain, small signal can be amplified to standard level.
The line amplifier is used for transmission. In order to reduce transmission attenuation and enable the receiver to get a strong enough signal, transmission shall be carried outelectric currentAmplification and promotion sometimes need to improve the voltage transmission. For example, constant voltage broadcasting uses this principle.
The power amplifier mainly amplifies the current, so as to promote the low resistancespeakerMake a sound.Of course, this example is based onaudio frequencyAs an example, if the radio frequency signal is used, it is somewhat different from this statement, but the meaning is similar, liketransmitterThe output is output toantennaOn.
Single gain front stage
It was mentioned at the beginning that the active amplifier has an amplification circuit inside, and the general gain is 0 to 10 times, while the passive front stage uses a volume potentiometer to attenuate, and its maximum output is equal to the input.There is also an active front stage whose magnification is the same as that of the passive front stage, which is a single gain front stage.
The purpose of the single gain front stage is to imagine the front stage as a buffer. In English, the buffer has the function of isolation and buffering, that is, it does not change the signal strength of the source equipment, but receives the signal with high input impedance and sends the signal with the concept of low impedance output. Therefore, the single gain front stage has the function of impedance conversion.There are not many single gain front stages on the market, the main reason is that the gain is often insufficient, and the volume is still not enough when it is turned to the maximum. The Encore front stage launched by the domestic manufacturer AC/DC Studio is a specific representative of the single gain front stage.This previous stage uses the twin field effecttransistorAs input, ZTX bipolar transistor is used as output, which has the characteristics of high input impedance and low output impedance. Since there are few parts, S/NBeachHigh, the volume is turned to the maximum, the ear is close to the treble unit, and no hiss can be heard. The timbre is transparent, and the details are natural. It is an extremely cheap single gain front stage with excellent sound quality.
Is the simpler the preamplifier circuit, the better?
There is a lot of nonsense about the pre amplifier, so it's time to clarify it.In an ideal listening environment, the less the number of components in the signal path design, the more perfect this amplifier may be.This is simply the best theory.
Each additional component will add one point of distortion, while the switch and volume control are the main criminals.But a lot of good recordings can achieve this. You need to do a favor on the front tone to eliminate the sharp voice and fatigue when playing back.
In this way, the situation arises: tone control provides precise and sensitive operation (in fact, many high-level preamplifiers use step basedresistanceSelector replaces the common potentiometer).When you listen to an amplifier, you might as well try: when you control the volume only with the bass and treble knobs attached to it, you will hear the corresponding difference.You should make relatively small changes.This phenomenon not only happens when listening to rock music or pop music, but also when listening to classical music, friends often want to find the right knob with "left hand down" decreasing on the treble to tame the natural top of recording.
The fader has tried its best, but still cannot make the amplifier output higher - make the bookcase typeloudspeaker boxThe bass unit sounds like the monster Cerwin Vega.Please remember the additional distortion we mentioned?To enjoy the dance, turn the knob to the position where both bass and treble are raised. The whole sound wave is raised, but the distortion has begun to blow and beat the horn.
Is it best to have both worlds together?It not only has a pre amplifier with good volume control, but also can directly output the sound source, or is equipped with a "volume evacuation" button, which can be bypassed when necessary.But pay attention to one thing, purists will even insist that the simpler the better.
Both the pre stage amplifier and the post stage amplifier have the specifications of output and input impedance. The output impedance represents the internal resistance of the signal output of the pre stage or post stage amplifier, and the unit isOhmsThe lower the output impedance, the lower the internal resistance and the stronger the driving ability of the amplifier.Similarly, the input impedance is the impedance of the pre amplifier or the post amplifier to the signal input equipment. The unit is also ohms.The higher the input impedance, the easier the front-end equipment can be pushed, and the impact of load effect can be reduced.Each amplifier has input impedance and output impedance. Generally speaking, the input impedance Ri increasesGaoyueWell, the lower the output impedance Ro, the better.Impedance matching ideally, the lower the output impedance of the former stage, the better, and the higher the input impedance of the latter stage, the better. This is to avoid the impact of load effects.
Usually, the input impedance of the back stage amplifier should be more than ten times higher than the output impedance of the front stage amplifier, so that the strength of the front stage can be maximized.This is like the same reason that locomotives pull carriages. The same carriages are pulled by locomotives of different horsepower, so the ease is naturally different. The higher the horsepower (the lower the output impedance) is, the lighter the weight (the higher the input impedance) is, the more relaxed and happy the locomotive will be.
Selection method
Announce
edit
Forum approach
In another post about how to choose a preamplifier, Version L said: "This era is about personality!" Indeed, the most important thing in selecting a preamplifier is the personality of the preamplifier.
The preamplifier attaches most importance to itsFrequency response rangeIt must be broad (above 5-35K Hz). The higher the frequency is, the richer the harmonics, overtones, and aftertastes will be. The higher the frequency is not excellent. No matter how good the medium and low frequencies are, I will not accept them, which affects the sense of hearing.For a good pre stage amplifier, first of all, the whole sound range should be balanced, the dynamic should not be too large or too small, and the sound resolution should be very good, so that the sound can be transparent, the sound field is natural, the instrument isolation is exquisite, and the size is appropriate.
When I put forward the issues that need to be considered when choosing a front-end amplifier, I suddenly remembered that I had three front-end amplifiers, which I simply bought when I couldn't make a choice and choose one that was in line with my own idea (of course, the three front-end amplifiers were not added at the same time).What a stupid way!?Since you are so stupid, you are qualified to continue writing this article?
To thinkAbundantIt is the most difficult to adjust the low and middle tones and bass of your voice. How to adjust them and what materials to use depend on your personal efforts.I had no choice but to purchase several former stage amplifiers (Restek's Vector). I like its wide frequency domain, strong interpretation ability, and careful, clear and detailed sound playback. I call it "Swallow Thin"; the other one is called "Huanfei"It's the Klar of Audiolabor. The sound it plays back is rich and delicate. It's flesh and blood, and it's slippery without leaving hands. I like it as Tang MinghuangYang YuhuanMore than Zhao Feiyan, especially in cold winter weather, it brings me warmth;Unlike Zhao Feiyan, who is as cold as ice, I use her to play when my mood is hot and dry. The sound played back can often calm my whole person and have a special effect of calming my nerves and reducing dryness.In addition, I also have an ARC SP 11 Mk II, which is a special measure for listening to the voice. Because of the complicated connection, it is not as convenient as my "Swallow Thin" and "Ring Fertilizer", one of which is connected to the XLR, and the other is connected to the RCA plug to input my Restek Exponent rear amplifier. I just need to change Bal to Unbal on the button on the Exponent backplane, and then I can choose "Swallow Thin" or "Ring Fertilizer".
This example shows that the preference of the preamplifier for the listener is directly related. I listen to a wide range of music types and properties, so I use many. Other audiophiles, of course, should choose according to the type of music they listen to.If you like classical music, of course, the frequency response range must be wide (above 5-35K Hz);The requirements of sound pressure and frequency domain mainly for listening to voice can be reduced
In short, the key is to listen more and listen together with the selected speakers. Only in this way can the sound played back be the sound you want to hear in the future.
If the front amplifier of the audio equipment can be more truly restored in such elements as speed, transient, dynamic and sound pressure, you can sit down calmly and listen to music, and enter the realm of beautiful music, deeply moved by the connotation of music.
The friends who play HiFi tend to focus on the adjustment of certain links, while neglecting the influence of other factors. In addition to proper matching, the equipment should also have a good listening environment. Only by careful adjustment and use, can the goal be achieved, and it will not be achieved overnight.It is believed that most enthusiasts understand these principles, but there are not many friends who can take into account the overall play.As far as the use of equipment is concerned, many enthusiasts are not very familiar with their own equipment performance. They often attribute the poor sound to some equipment because of improper use.As a result, "playing" HiFi becomes "changing" HiFi constantly.In the small town where I live, there is such a passionate friend who has only five or six years of experience in playing audio, and has changed no less than six systems.What I said was "set", instead of the whole set!Guess how he plays with the pre amplifier now?He is now playing CD Wadia 861 as the source (he played an LP turntable six months ago, and could not get a good sound, so he transferred or returned it to the agent). This machine can be directly connected to the rear amplifier, because it has been set with a digital volume remote control.However, this enthusiast probably admired or thought that Wadia 861 had a heavy digital sound. In addition, an ARC Reference II pre amplifier was connected, and then connected to a Pass power amplifier with output of 600W on each side to drive a pair of Wilson WATT/Puppy 6.Money can be spent like this!?Maybe he thinks it can turn the sound into a vacuum tube!
The front stage can be said to be the control center of the whole system.Most people think that the front stage is just an equipment used to control the volume and select the source of information. They often turn a blind eye to the buttons and facilities on the machine, and even bother to understand the purpose of each button. In fact, they are wasting their own money and the designer's efforts, and do not give full play to its performance.
Take the simplest front stage as an example. It usually only has the function of selecting the source and controlling the loudness and loudness, but you should not underestimate it. In fact, the sound quality is closely related to whether the front stage is operated correctly and adjusted.Setting aside the adjustment, the volume control knob (Volume) can be said to be an art. The volume is enough to affect the sound of the whole system.In the small town where I live, there is another friend who has a fever. He likes to enjoy the sound of drums. He treats guests with continuous drums. The volume knob is usually turned to 12.00 o 'clock or 13.00 o' clock. Who can stand it.No matter what music he listens to, he listens to it at the same volume, thinking that natural sounds that are well recorded are necessarily pleasant.What's more, he thought loud was good, so whether listening to symphony or playing a single instrument, he used the same volume to listen, and you heardTeresa TengHer voice sounds like a bell, and her petite body becomes likeYao MingMagnificent, the volume of the violin is expanded to a double cello, and his treble is like a clavichord, and the bass is like a drum.When you hear the frown and feel bored, he also tells you how dynamic his system is, how popular the singer is, and how many recording details are, which can make you half mad!
Why do these friends listen to music like this?Just because they don't go to concerts, orthodox live concerts.When he has heard the symphony orchestra playing in the same concert hall, the volume of a single instrument when playing, and the sound of a real instrument, he will understand what is called the sound proportion, so that he can understand the loudness of the volume of a single instrument when playing.In addition to listening to the scene, the other way to understand the sound and volume of musical instruments is to listen to some live performances without loudspeaker system.Then when you listen to canned music on CDs again, you will not adjust the volume without rules. Not only will the sound be distorted, the instrument be deformed, the ear suffer, but also the hearing may be damaged!
The highest skill of volume control is to make your own audio equipment achieve the best performance, and to restore the volume of bands, solo instruments, and real people when singing!The volume of HiFi is 1:1, the volume of the same proportion and the stereo sound field of the same size, as if the entire symphony orchestra were playing live in the listening room at home!Enthusiasts think that as long as the most expensive equipment in the world is brought home, we can achieve this kind of scenery.In fact, it is not as simple as he imagined, and there is much knowledge in it.
Translation methods
Translator's Note: This is an article that has just been translated in the past two days. The purpose is to meet the requirements of netizens in the forum. It will be posted in sections. I hope you will wait patiently.
When I put forward the issues that need to be considered when choosing a front-end amplifier, I suddenly remembered that I had three front-end amplifiers, which I simply bought when I couldn't make a choice and choose one that was in line with my own idea (of course, the three front-end amplifiers were not added at the same time).What a stupid way!?Since you are so stupid, you are qualified to continue writing this article?
The goal of adding a preamplifier is to achieve synergy between your sound source (s) and the amplifier.Whenever you have a chance to listen to multiple preamplifiers connected to your system, you can't tell which one has a better sound than the other.The reason is that the sound is good and the price is more or less high, or the circuit design of the pre amplifier has done a lot of work.
When choosing the ideal preamplifier, you must be clear about two things
A. Your sound source output voltage (maxOptical driveIs 2 volts);
B. The input sensitivity of your amplifier (most amplifiers are around 1 volt)
Whether your CD drive or other audio sourceOutput levelLess than or more than 2 volts, you must know.If the input sensitivity of your power amplifier is less than or greater than 1 V on the same note, you should also know.Once you know these voltages, you can choose the right preamplifier.
Related concepts
Announce
edit
Sound source output voltage
(output voltage of your source) The sound source output voltage is a fixed level that will not change unless your sound source has a "variable output".This 2-volt signal (music) drives the input stage of the power amplifier or the pre amplifier, which in turn drives the input of the pre amplifier or the input stage of the power amplifier.
Input sensitivity of amplifier
（input sensitivity of an amplifier）
In short, the input sensitivity of the amplifier means how many volts of the level signal is transmitted to thepowerAmplifier goes.Any voltage exceeding this amount will cause your power amplifier to try to use more power than it actually has, resulting in overload and so-called "clipping".
Therefore, in all cases, a pre amplifier is naturally used to control the voltage from the sound source.When the volume of the current stage amplifier is turned to the left as far as possible, you can calculate that there is only zero voltage output, so the power amplifier has no sound.When you turn the volume knob to the right to increase the output voltage, your power amplifier can drive the speaker to make sound.The ideal operating range of the volume control should be between 1/4 and 3/4 to the right, which is the normal position of the listening level (in fact, distortion already exists when exceeding the right 1/2 position).The preamplifier will never add any voltage to the input signal, that is, "gain gain".
When does the front amplifier need to be set with "gain"?There are two reasons why you might want the preamplifier to increase gain:
A. When the power amplifier needs more than 1 volt to reach full power output.
B. When your sound source is only less than 2 volts output.
Some power amplifiers require 5V input to achieve full power output. Generally, the amplifier is designed to achieve full power output when all are set at 2V input.Occasionally we will see that some kind of amplifier only needs 1/2 V input to reach full power output.
Some modified optical disk drives have an output level of less than 2 volts, and some digital to analog converter DACs have an output level of less than 2 volts.(Although most DACs have at least 2 volts or slightly higher, sometimes up to 5 volts.)
People who like vinyl records may sometimes find it difficult to find a 2-volt phonograph head and phonograph disc terminal attached to the output.I have seen that most of them are 1 volt.
If the sound source has only 1 V output level and the input sensitivity of the amplifier is only 2 V, an additional pre amplifier with gain must be set, otherwise the post amplifier cannot play back the sound pressure normally.Even if there is a pair of ultra efficient speakers and the listening requirements are only very soft, the music played back will lack the sense of dynamics and weight.
Once the decision is made to require gain or no gain, the selection range has been greatly narrowed.However, whether the gain is selected or not, the matching "impedance" must be considered.
All sound sources and amplifiers have something called "output impedance".Think of it as the driving ability of this machine to deal with difficult loads, such as connecting amplifiers with very long signal lines.
On the contrary, all amplifiers have something called "input impedance".Think of it as the level applied by the preamplifier or CD driver when the machine encounters.
The general rule is that the lower the output impedance, the easier it is to drive difficult loads.Similarly, the higher the input impedance, the easier it is to drive.It is better for the pre amplifier to drive an amplifier with an input impedance of 100000 Ω when the output impedance is lower than 1000 Ω.
The output impedance of optical disk drives on the market is usually quite low, but unfortunately, the output impedance of power amplifiers is usually between 10000 Ω and 500000 Ω, most of which are near 50 K Ω.
50 K Ω is a suitable load, and most sound sources and the front amplifier will not cause problems when driving.Unless it is a front-end amplifier with high output impedance, try to drive a 50K Ω amplifier with an extra long signal line.The result may often be either a low frequency response fading or a lack of dynamic sound, or both.Listeners certainly don't want the sound played back to sound thin, so try to use short signal lines.If the output impedance of the preamplifier is quite low, it doesn't matter. Even if the power amplifier is on the other side of the house, it still has a strong low-frequency response and a sense of weight, and there will be no fading.
Model
Announce
edit
Here are three pre amplifier models:
The top A model has many gains or no gains according to how to set the selector switch on the backplane;Or use a normal output impedance or a low output impedance.Only in this way can we be sure that it actually makes a unique or regular good sound.
Model B has no gain and low output impedance, which is ideal for most systems.
Model C has larger gain and higher input sensitivity, which caters to the sound source with lower output or the amplifier with higher output sensitivity, or both.
If the player's signal is just a CD player, and the power amplifier used in the audio system is equipped with a volume control potential, if the front amplifier is used or not, it is possible to select or not select the front amplifier.In fact, in most cases, it is recommended not to choose the preamplifier.
