Preamplifier, what is the function and principle of preamplifier

Preamplifier, what is the function and principle of the preamplifier?

Preamplifier

Note: I saw a post asking about the preamplifier, and I was tempted to post the information I collected for your reference:

In the sound system, the function of the pre-amplifier is not complicated. It is only responsible for switching the signal source, processing the signal and controlling the volume. This is the last processing procedure before the music information enters the post-amplifier. Its connection position is between the signal source equipment and the post-amplifier, so the role played by the pre-amplifier is to organize and adjust the signal.

Preamplifiers can be simple or complex in design.

A simple preamplifier only needs to have signal source input, signal source selection, and volume control. In other words, a simple preamplifier only needs a signal source switching switch and a volume potentiometer, plus a chassis and input and output terminals.

Complex preamplifiers have many functions: designers can add a buffer circuit to each input in the signal source to isolate the buffer interface between the preamplifier and the signal source; after the signal passes through the switch, it enters a huge circuit structure in the most complex and rigorous way, including buffering, equalization, adjustment and other steps, and finally passes through another buffer circuit to reduce the impedance before connecting to the output terminal. Of course, this design can use simple ICs or a large number of transistor structure circuits. If you want to use vacuum tubes, of course you can fill the chassis with vacuum tubes, plus additional designs such as battery power supply. As long as it has the function of a preamplifier, there is no limit.

Simple or complex? The design and materials of a preamplifier are like the ingredients in a chef's hand. They can be combined, prepared and cooked in different ways to create different flavors. Electronic designers are also like chefs. They can use any electronic materials, design and cook in any way they want, and design and manufacture a preamplifier. The sound quality of the playback can be very different. I remember that in the 1980s and 1990s, Burmester had an 808, and later Mark Levinson's Cello released a Pallet Suit, which became a model of complex preamplifiers.

Cello Suite by Mark Levinson

I will not talk about simple passive pre-amplifiers or exaggerated and complex full-function pre-amplifiers here (in fact, I translated an article about Counterpoint's phono preamplifier more than ten years ago, which shared 17 vacuum tubes and was extremely exaggerated and complex). We will focus on the basic structure that a standard pre-amplifier should have.

The pre-amplifier is also called the "pre-amplifier". The amplification ratio is usually set to 10 times, so it is also called the "10x amplifier". People simply call it the "pre-amplifier".

It is a must-have for any equipment. The preamplifier only uses signal lines for input and output. The input terminals used by preamplifiers on the market are mostly single-ended RCA terminals or balanced XLR terminals, except for the early models of Mark Levinson that use Lemo terminals. This three-pin plug is exactly the same as the "AES/EBU" balanced terminal used by digital converters. Please pay attention to the difference in the name. XLR, balanced terminal, and Canon terminal refer to the plug itself, while "AES/EBU" refers to the format of digital transmission; if you see an XLR terminal on the preamplifier and say "my preamplifier has an AES/EBU plug", it will be a joke. Some European equipment occasionally uses special input and output terminals. Linn and Naim have used multi-hole DIN plugs. Like balanced terminals, they have the function of grounding the negative terminal first. Therefore, if the power is not turned off, the signal line can be directly unplugged without causing noise. Users who use single-ended RCA terminals must not try it rashly.

After the signal enters the preamplifier from the input and output terminals, the signal is guided to the switch using a circuit board or an isolated signal line. The switch is responsible for switching the input source. By using several switches together, you can also control the type of recording output source, so that you can listen to music while recording music from another source. After the signal passes through the switch, it enters the left and right channel balance control potentiometer. The balance potentiometer used in the audio system is a special MN type. This potentiometer has a special design. When it is rotated to the left, the volume of the left channel remains unchanged, but the right channel gradually decreases with the angle. When the knob is turned to the far left, the right channel happens to have no sound; similarly, when it is rotated to the right, the volume of the left channel gradually decreases, thereby achieving the purpose of controlling the volume of the left and right channels. Under normal use, there is no need to adjust the left and right balance, so some preamplifiers gradually omit this design, or hide the left and right balance potentiometers in the corner of the chassis, anyway, it is not often used.

After passing through the balance potentiometer, the signal then enters the volume potentiometer. The volume potentiometer also uses a dedicated A-type potentiometer, which is manufactured according to logarithmic characteristics, so that the angle of the knob rotation can increase linearly with the ear's perception. What angle should the volume potentiometer be turned to for normal use? There is no definite answer, it depends on the total gain of the overall equipment. For speakers with high efficiency and high gain of the rear stage, the amplification factor required by the front stage must be reduced, and the sound will be loud even if the volume is turned up a little bit; on the contrary, the single-gain front stage has only one-time amplification, so it is often not loud enough even if the volume is turned to the bottom. Normally, the knob position is normal from the 9 o'clock position to the 12 o'clock position, and it is also the most convenient to turn.

After the signal passes through the volume potentiometer, it directly enters the amplifier circuit. The amplifier circuit can be complex or simple, and the design forms vary. After the output of the amplifier circuit, some pre-stages will be designed with a mute relay to control the output of the pre-stage signal. After passing through the mute switch, it is directly connected to the output terminal.

The operating structure of the preamplifier is: input → signal switching → left and right balance → volume control → amplifier circuit → mute switch → output.

The difference between active and passive

The meaning of "active" is that active components are used in the circuit. An active preamplifier is an active preamplifier, which must be plugged in to work. Is there a preamplifier that does not need to be plugged in? Yes, this is a passive preamplifier.

From the perspective of circuit architecture, the passive preamplifier actually omits the "amplification circuit" process. After the signal is input, it passes through the signal switching switch, enters the balance control (or this function is omitted), and then uses a volume potentiometer to control the volume, and finally outputs directly. From the perspective of volume control, it can only attenuate but not amplify. From the perspective of impedance matching, it cannot play the role of buffering. Therefore, the passive preamplifier is the most economical and direct preamplifier. First Sound is one of the most famous passive preamplifiers. It only consists of a switching switch and a volume controller. Since there are no active components, the S/N ratio is quite high. Jeff Roland's Synergy is also a model of Chuchu.

Active preamplifiers have amplifier circuits that can amplify the input signal and then output it, so the gain is absolutely sufficient; passive preamplifiers will never be able to achieve the task of amplification unless they use a passive booster to increase the output voltage. From the perspective of buffering and impedance matching, active preamplifiers have active components for signal amplification, so they can convert the signal source with higher impedance characteristics into a signal output with lower impedance, which is easy to drive the rear stage circuit. This is also a requirement that passive preamplifiers cannot match. Passive preamplifiers can only attenuate at best. When the volume is turned up, it is equivalent to the signal source directly entering the rear stage, and there is no buffering effect. If a booster is used to amplify the voltage, the result after amplification must also follow the physical principle of mass and energy being constant, and the output impedance is increased. Therefore, almost no passive preamplifier is willing to use a booster for voltage amplification, and at most a volume potentiometer is used to control the volume.

Since passive pre-amplifiers have so many shortcomings, why is it necessary for them to exist?

Because the passive preamplifier has no amplification circuit, its signal path is direct, and it can output the signal of the source equipment directly to the post-amplifier in the shortest path. This is the original intention of people using passive preamplifiers. Since no active components are used, there are no problems such as distortion, sound coloration, noise, phase drift, etc., and because of the use of mechanical switches, there is no limit on the gain-bandwidth product of the passive preamplifier. A normally designed passive preamplifier can transmit signals of several MHz, especially the noise and S/N ratio specifications, which are almost unmatched by any active preamplifier. Each has its own advantages and disadvantages! As long as the preamplifier is suitable for your system, there is nothing wrong with it.

Vacuum tube preamplifier

According to the history of the development of electronic materials, the earliest electronic component invented was the vacuum tube. Several decades later, semiconductors were invented. Germanium crystals were the first to appear on the market, and then silicon components dominated the market. When the technology for manufacturing silicon crystal clusters matured, integrated circuits (ICs) appeared. Therefore, the process of using active components in the preamplifier has progressed along with the development of semiconductor components. The earliest preamplifiers all used vacuum tube designs. Starting from the power supply part, after the transformer outputs the AC voltage, the diode is used for tube rectification and tube voltage regulation. The rectification and voltage regulation characteristics of the vacuum tube are not ideal, so the sound of the early vacuum tube preamplifier is generally not ideal. There is a hissing noise in the hum, the S/N ratio is not high, and the bandwidth is not enough. However, for the time, this is already a good product!

Electronic components have been continuously improved, and the circuit level of amplifiers has gradually improved. After the invention of semiconductors, semiconductors replaced some vacuum tubes. The vacuum tube rectification and tube voltage stabilization, which were inefficient and poorly functioning, were gradually replaced by semiconductor components. Semiconductors with small size and stable operation have produced stable power supplies, and the performance of pre-amplifiers has also been greatly improved. Background noise has been greatly reduced, the S/N ratio has been improved immediately, the hum has disappeared, and listening to music has begun to enter a higher level of enjoyment.

So far, most vacuum tube amplifiers are still based on semiconductor voltage stabilization. In fact, for sound, vacuum tubes are indeed irreplaceable good components. Although they are large in size, they have their own unique and irreplaceable tone. Warmth and mellowness are common characteristics of tube machines. Audio Research and Sonic Frontiers, which insist on using vacuum tube amplification, almost all of their preamplifiers are designed with vacuum tubes, but it is undeniable that their designers still prefer to use semiconductors for rectification and voltage stabilization. The circuit architecture of vacuum tubes was developed as early as 20 years ago. Differential, cascade, push-pull, and phase inversion all appeared in early vacuum tube preamplifiers. To achieve the same goal using the same components, there are only a few ways. Therefore, for modern vacuum tube designers, circuit innovation is no longer a goal to pursue. Providing a stable and clean power supply for the vacuum tube circuit and matching it with high-quality passive materials can make the vacuum tube work well. Finally, the sound can be adjusted by matching the parts.

Some vacuum tube preamplifiers have very complex circuits, while others only use one vacuum tube. What is the difference? Does the more tubes there are, the better the sound will be? Of course, the answer is not necessarily. The most vacuum tubes used in the preamplifier is probably the Sonic Frontiers Line 3, which is Sonic Frontiers' most advanced preamplifier, using 12 vacuum tubes at once; and there are also many vacuum tube preamplifiers that only use one dual triode for amplification, such as the Audio Research LS-2. The number of vacuum tubes used in the preamplifier certainly does not mean that the sound will definitely be good. If you plan and design with a rigorous attitude, otherwise the sound coloration and distortion of the vacuum tube will be difficult to deal with before the sound is turned on. When designers plan high-end equipment, they must consider the distribution of circuit architecture and its price level. Even if they design different levels of products with the same concept, the sound of the high-priced ones will definitely be better than the models under their own brand. There is no absolute relationship between the number of vacuum tubes used and the sound. Designers just design the equipment more complete and rigorous to win the trust of consumers.

The pinnacle of vacuum tube preamplifiers, Audio Research's SP-11 many years ago and the recently popular Sonic Frontiers Line 3. Sonic Frontiers likes to use precision semiconductor voltage stabilization, combined with vacuum tube amplification, the sound has both the transparency of crystal machines and the thickness of tube machines.

Hybrid vacuum tube preamplifier

Hybrid preamplifiers were popular for a while, and Luxman first launched a hybrid circuit with vacuum tubes and transistors. The main purpose of the development of hybrid preamplifiers is to combine the advantages of semiconductors and vacuum tubes to form a popular design.

When semiconductor components were maturely used in audio circuits, vacuum tubes seemed to have lost their original status. No one was interested in the bulky vacuum tubes, and audio equipment continued to flaunt all-semiconductor and all-transistor designs. However, the manufacturing and circuit composition of early semiconductors inevitably made the sound hard, cold, and even noisy. So some audio fans began to look back for the taste of tubes. It turns out that
audio fans need not only excellent characteristics, but more importantly, the musicality of the playback sound.
Are vacuum tubes more musical?

This is of course impossible to prove, but it was an indisputable fact at the time. Luxman was the first to put vacuum tubes into transistor circuits, letting them be responsible for the first-stage amplification, and "influencing" the sound of transistors through the unique tone of vacuum tubes. After Audio Research launched a semiconductor preamplifier that was not well received, it also reviewed the reasons why vacuum tubes were popular. Sound is actually the focus of audio fans; technology is just a gimmick.

Audio Research thought that FET and vacuum tubes are both high-input impedance components, but FET has a bandwidth that vacuum tubes cannot achieve. However, the early FET sounded cold, while vacuum tubes were full of warmth. Why not combine the strengths of both? So Audio Research used FET input and added a 6922 vacuum tube in the output section. This is the popular LS-2 gallstone hybrid preamplifier.

The successful launch of LS-2 has indeed opened a successful path for hybrid preamplifier design. There are still many hybrid preamplifiers on the market. They have the characteristics of high frequency bandwidth and S/N ratio is the same as that of crystal machines. Users can also change tubes and adjust the sound by themselves. Anyway, as long as the sound is good, different paths lead to the same destination. Audio Research likes to use semiconductor and vacuum tube hybrid designs. After opening the inside, you can find vacuum tubes, transistors, and ICs on the circuit board.

Transistor front stage

The transistor front stage is certainly not limited to field effect transistors (FET) or bipolar junction transistors (BJT). The development of transistors is for better specifications. Therefore, when transistor manufacturing technology gradually matures, the materials used in audio also develop in the direction of full transistors. Although the circuit architecture of transistors and vacuum tubes is similar, they are very different. Transistors are small in size and can be used in large quantities in circuit boards with limited space, so the circuit design can be more rigorous and precise. Different transistors have different characteristics, and appropriate matching can create excellent results.

The development of transistor circuits still comes from the vacuum tube architecture. Differential is the most commonly used amplification method. Single differential, double differential, current source, Darlington, cascade and other circuit techniques can be constructed step by step like a puzzle according to the designer's preferences. The simplest transistor amplifier circuit is single-ended amplification, which directly amplifies with one or two transistors; complex architectures can also be used to build high towers meticulously and rigorously. Mark Levinson, Cello Encore, Palette, Krell, Thershold and other companies are the companies that like to use a large number of transistors to manufacture equipment. They use transistors with several characteristics:

1. There are so many of them that two can be used, and one will never be enough.
2. Bipolar transistors are preferred. Although FET has better performance in terms of characteristics, it may be a habit and preference, and a pre-stage is almost entirely bipolar transistors from beginning to end.
3. They are very particular about power supply. The voltage stabilization circuit based on transistors can actually achieve very good performance. The DC power supply made with low-noise parts has noise characteristics comparable to batteries. But perfection is even more perfect. Designers such as Mark Levinson and Cello are fond of multi-level voltage stabilization. After the power is output from the transformer, it is rectified by diodes and then stabilized by capacitors. The fun starts here. Using precise transistor voltage stabilization circuits, voltage stabilization is repeated after voltage stabilization. Two or three consecutive series voltage stabilizations make it impossible for power ripples to occur.

In recent years, these manufacturers who like to design preamplifiers with transistors have also begun to try to add FET and IC designs. The circuit structure is still extremely complex, but the sound has a very high degree of transparency and resolution, with so many details that it is scary, but there is no trace of the jerky expression of the old transistors. It can be seen that the absolute performance of the sound cannot be inferred based on the circuit structure and material type. In the past, people always said that the sound of FET is clearer, the sound of MOSFET has the flavor of vacuum tubes, and the transistor is jerky and inflexible. Now these statements are completely incorrect. Manufacturers such as Mark Levinson, Krell and Cello love to use a large number of transistors to stack circuits. When you open the chassis, you will see that it is full of resistors and transistors.

Some people say that 6DJ8 is a vacuum tube designed for audio, so NE5534 should be the first IC designed specifically for audio. In 1981, when IC design was not yet developed, Philips' subsidiary launched the NE5534 IC, claiming that it was specially designed for audio purposes. Its features include bipolar crystal differential input and low impedance output, which is suitable for use in pre-stage circuits. NE5534 is an operational amplifier OPAMP, which condenses the amplifier circuit into an eight-pin IC. As long as a few resistors and capacitors are added to prevent oscillation, the amplifier circuit required in the pre-amplifier can be formed. The news really made a sensation in the industry. The amplifier circuit that originally required a large number of parts could be replaced by an IC, which made the designers dumbfounded. However, at that time, everyone generally did not believe in the sound of IC, and always thought that its characteristics were very poor and the sound was not ideal. Therefore, no one was willing to use OPAMP as the main amplification component of the pre-stage, except for MBL 6010.

The characteristics of early OPAMPs are indeed quite unsatisfactory. They have low slew rates, poor noise characteristics, and different degrees of compensation correction must be given according to different circuits. However, the performance of modern ICs is not the same as that of Japanese ones. Modern OPAMPs designed specifically for audio have the advantages of high input impedance like FETs and vacuum tubes (with input impedance of several megohms, which is actually higher than FETs), and also have the advantages of low output impedance of BJT (which can be reduced to tens of ohms, which is also lower than small signal transistors). Its slew rate is as high as thousands of V/μs, and the output midpoint voltage is unmeasurably low. It can be directly connected to the next stage without adding cross-connect capacitors. Its bandwidth is even more amazing. It is no problem to directly amplify RF signals. It is low-priced and has super strong characteristics. It has long become an essential amplifier component for audio design.

Although modern OPAMPs have excellent characteristics, they are still small in size. Designers think that if a preamplifier is composed of only a few OPAMPs, can it sell for a lot of money? Therefore, the development of IC preamplifiers is not about sound, but whether it can be sold at a high price. There is definitely no preamplifier in the world that is luckier than the MBL 6010. A preamplifier only uses a dozen NE5534 OPAMPs, but its price is as high as more than 600,000 yuan. The Germans are really good at it. Both MBL 6010 and McIntosh C100 use NE 5534 as the main amplification component. The difference is that the circuit of mbl 6010 is quite simple, while McIntosh C100 uses a large number of OPAMPs to build a two-story work.

This is a new trend in the development of preamplifiers, but due to the difficulty in technology research and development, there are not many manufacturers that can design digital preamplifiers. Digital preamplifiers mean that both control and amplification are performed in a digital way. In terms of the functions of preamplifiers, it is indeed not so troublesome and complicated, but trying new things is always the driving force of development. How does a digital preamplifier work? After the analog signal is input into the preamplifier, the internal A/D conversion is used to convert the analog signal into a digital signal. Then, according to the size data of the volume controller, the DSP is used for calculation. Then, the digital data after calculation is converted into an analog signal using the technology of the digital-to-analog converter, and then output to the post-amplifier. Isn't it a waste of effort to go around in circles like this? However, Accuphase believes that the purpose of their launch of the DC-300 is to announce that they have the highly completed C-290V analog preamplifier. In order to respond to the advent of the digital age, the launch of a digital preamplifier with a complex processing program is the beginning of the next challenge.

In the two-channel world, digital preamplifiers are indeed superfluous, but Accuphase has actually seen the future. The popularity of multi-channels is an inevitable trend. Multi-channels equal surround systems. Starting from the interpretation of the signal source, it must rely on highly calculated digital technology. Today, every surround processor must use digital design, using digital technology to decode the signal of each channel, and then amplify it in an analog way. Why not try to directly use full digital processing, convert the decoded sound data directly into output, and omit the pre-amplification part? In this way, a more direct effect can be achieved, which should be of substantial help in improving the sound quality.

In fact, the concept of digital pre-stage has appeared many years ago, but these digital pre-stages exist in digital-to-analog converters. Vimak DS-2000 should be the first digital-to-analog converter that integrates digital pre-stage. Let's not talk about the various designs of this digital-to-analog converter for now, but just explain the internal attached digital pre-stage. The digital pre-stage of Vimak DS-2000 is as follows: there is a high-bit DSP operator inside DS-2000, which oversamples the CD data by 128 times, and then directly rewrites the digital data according to the digital volume controller on the panel, thereby determining the output of the DAC chip. In other words, the signal output of DS-2000 is the direct output of the DAC chip, rather than the attenuation of the volume potentiometer. It provides the simplest path design and the most direct sound quality. Of course, the designer of Vimak is not small, and these digital technologies are not difficult for him. The lack of Vimak in the audio world has made many digital manufacturers feel relieved! The most famous digital pre-stage is Accuphase DC-300.

Single gain preamplifier

As mentioned at the beginning, active amplifiers have internal amplification circuits, and the general gain is 0 to 10 times, while passive preamplifiers use volume potentiometers for attenuation, and their maximum output is equal to the input. There is also an active preamplifier whose amplification ratio is the same as that of a passive preamplifier, which is a single-gain preamplifier.

The purpose of a single-gain preamplifier is to imagine the preamplifier as a buffer. In English, a 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 it out with low impedance output. Therefore, a single-gain preamplifier has the function of impedance conversion. There are not many single-gain preamplifiers 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 preamplifier launched by the domestic manufacturer AC and DC Studio is a specific representative of the single-gain preamplifier. This preamplifier uses twin field effect transistors as input and ZTX bipolar transistors as output. It has the characteristics of high input impedance and low output impedance. Due to the few parts, the S/N ratio is very high. When the volume is turned to the maximum, the ear is close to the tweeter and no hissing can be heard. The sound is transparent and untainted, and the details are presented naturally. It is an extremely cheap single-gain preamplifier with excellent sound quality.

Is the simpler the preamplifier circuit, the more ideal it is?

There is a lot of nonsense out there about preamplifiers, so it’s time to clear it up. In an ideal listening environment, the fewer components a signal path has, the more completely true and perfect the amplifier is likely to be. This is the simple is the best theory.

Every additional component adds a bit of distortion, with switches and volume controls being the main offenders, but many good recordings can be made with a little help up front to eliminate those harsh, tiring-sounding playback flaws.

This results in a situation where the tone controls provide fine-tuned, sensitive operation (in fact, many high-end preamplifiers use stepped resistor selectors instead of the usual potentiometers). When you audition an amplifier, try using only the bass and treble knobs to control the volume, and you will hear the difference. You should get relatively small changes. This phenomenon is not only common when listening to rock or pop music, even classical music listeners will often want to find a "left-hand down" knob that tapers off the treble to tame the natural top end of the recording.

The volume control, as hard as it tried, still couldn't get the amp to pump any louder -- making the bookshelf woofer sound like a Cerwin Vega monster. Remember that added distortion we mentioned? For the party, turning the knobs to both the bass and treble up, the whole thing got louder, but the distortion started to blow the speakers.

Best of both worlds? A preamp with a good volume control and a direct source output, or a "volume off" button to bypass it when needed. But beware, purists will even insist that simple is better.

Output and input impedance matching between the preamplifier and the postamplifier

Both preamplifiers and power amplifiers have output and input impedance specifications. Output impedance refers to the internal resistance of the preamplifier or power amplifier signal output, and the unit is ohm. The lower the output impedance, the lower the internal resistance of the amplifier and the stronger the driving ability. Similarly, input impedance refers to the impedance encountered by the preamplifier or power amplifier when the signal is input to the device, and the unit is also ohm. The higher the input impedance, the easier it is to drive the front-end equipment, and the influence of the load effect can also be reduced. Every amplifier has input impedance and output impedance. Generally speaking, the higher the input impedance Ri, the better, and the lower the output impedance Ro, the better. In the ideal impedance matching, the lower the output impedance of the preamplifier, the better, and the higher the input impedance of the power amplifier, the better, in order to avoid the influence of the load effect.
Usually, the input impedance of the power amplifier is better to be more than ten times higher than the output impedance of the preamplifier, so that the strength of the preamplifier can be fully exerted. This is just like the principle of a locomotive pulling a carriage. The same carriage will be pulled by locomotives of different horsepower with different ease. The locomotive with greater horsepower (lower output impedance) will naturally pull the lighter carriage (lower input impedance) with greater ease and joy.

Preamplifier

In another post about how to choose a preamplifier, L said: "This era is all about individuality!" Indeed, the most important thing in choosing a preamplifier is the personality of the preamplifier.

The most important thing for a preamplifier is that its frequency response range must be wide (5-35K Hz or more). The longer the high frequency is, the richer the harmonics, overtones, and aftertaste will be. If the high frequency is not outstanding, no matter how good the mid- and low-frequency is, I will not accept it, which will affect the listening experience. A good preamplifier must first balance the entire sound range, the dynamic range should not be too large or too small, and the sound resolution should be very good, so that the sound will be transparent, the sound field will be natural, the instrument isolation will be exquisite, and the size will be appropriate.

When I asked what to consider when choosing a preamplifier, I suddenly remembered the three preamplifiers I own. I bought all of them (of course, I didn't buy all three at the same time) when I couldn't make a choice and choose one that suited my idea. What a stupid method! ? If I am so stupid, am I still qualified to continue writing this article?

If you want a rich sound, the mid-low and bass are the most difficult to adjust. How to adjust them and what materials to use depends on your personal skills. The only solution I had back then was to buy a few preamplifiers (Restek's Vector, I like its wide frequency range and strong interpretation ability, the sound it plays back is serious, clear and detailed, I call it "Yan Shou"; the other one is called "Huan Fei" is Audiolabor's Klar, the sound it plays back is rich and delicate, flesh and blood, smooth and unyielding, I like Yang Yuhuan more than Zhao Feiyan like Emperor Minghuang of Tang, especially in cold winter weather, it brings me warmth; unlike Zhao Feiyan who is as cold as ice, I only play her when I am in a hot mood, the sound it plays back can often calm me down, and has a special effect of calming the mind and reducing dryness. In addition, I also have an ARC SP 11 Mk II, which is a special measure for listening to human voices. Due to the complicated connection, unlike my "Yan Shou" and "Huan Fei", one is connected to XLR and the other is connected to RCA plugs to input my Restek It is as convenient as an Exponent power amplifier. I only need to change Bal to Unbal on the button on the back panel of Exponent to choose "slim" or "fat".

This example shows that the preamplifier is directly related to the listener's preference. I listen to a wide variety of music, so I use multiple preamplifiers. Other audiophiles should choose according to the type of music they listen to. For those who like classical music, of course, the frequency response range must be wide (5-35K Hz or more); for those who listen to human voices, the requirements for sound pressure and frequency domain can be lower...

In short, the key is to listen more and listen in combination 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 pre-amplifier of the audio equipment can restore the speed, transients, dynamics, sound pressure and other factors more realistically, then you can sit down and listen to the music calmly, enter the beautiful realm of music, appreciate the connotation of music and be deeply moved.

Friends who play HiFi tend to focus on adjusting certain aspects and neglect the influence of other factors. In addition to proper matching of equipment, there must be a good listening environment, careful adjustment and use to achieve the goal, which will not be achieved overnight. I believe that most audiophiles understand these principles, but there are not many friends who can take into account the overall play. In terms of equipment use alone, many audiophiles are not very clear about the performance of their own equipment, and often attribute the poor sound to certain equipment due to improper use. As a result, "playing" HiFi has become constantly "changing" HiFi. In the small town where I live, there is such an audiophile friend who has only been playing audio for five or six years and has changed no less than six systems. I am talking about "sets", and I changed the whole set! Guess how he plays the preamplifier now? He now uses a CD Wadia 861 as the source (he used to play an LP turntable half a year ago, but he could not get good sound and sold or returned it to the agent). This machine can be directly connected to the power amplifier because it has a digital volume remote control. However, this audiophile probably admired the reputation or thought the digital sound of Wadia 861 was too heavy, so he connected an ARC Reference II preamplifier, and then connected it to a Pass power amplifier with an output of 600W on each side to drive a pair of Wilson WATT / Puppy 6. Money can be spent like this! ? Maybe he thought that this would make the sound like a vacuum tube!

The preamplifier can be said to be the control center of the entire system. Most people think that the preamplifier is just a piece of equipment used to control the volume and select the source. They often turn a blind eye to the buttons and facilities on the machine, and even don't bother to understand the purpose of each button. They are actually wasting their money and the designer's efforts, and not making good use of its performance.

Take the simplest preamplifier as an example. It usually only has the function of selecting the signal source and controlling the volume. But don't underestimate it. In fact, the quality of the sound is closely related to whether the preamplifier is operated correctly and adjusted. Putting aside the adjustment, controlling the volume knob can be said to be an art. The volume is enough to affect the quality of the sound of the entire system. In the small town where I live, there is another audiophile friend who likes to appreciate the sound of drums. When entertaining guests, he always plays 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 the natural sound of a good recording must be good. What's worse is that he thinks louder sounds better, so he listens to symphonies or single instruments at the same volume. As a result, you hear Teresa Teng's voice as loud as a bell, her petite body becomes as majestic as Yao Ming, the size of the violin expands to a double cello, the high notes of the guitar sound like a harpsichord, and the bass part sounds like a drum. When you frown and feel depressed, he still tells you how powerful his system's dynamics are, how the singers are full of energy, and how many recording details there are, which can make you angry to death!

Why do these friends listen to music in this way? It is simply because they rarely go to concerts, authentic live concerts. When they have heard the symphony orchestra playing in the same concert hall, the volume of a single instrument, and the sound of a real instrument, they will understand what is the ratio of sound, and then they can understand the loudness of the volume of a single instrument. In addition to listening to live, another way to understand the sound and volume of instruments is to listen to some real people playing without an amplifier system. Then when you listen to those canned music on CDs, you will not adjust the volume without any rules, which will not only distort the sound, deform the instruments, and hurt your ears, but also damage your hearing!

The highest skill of volume control is to make your audio equipment achieve the best performance, and to restore the volume of the band, solo instrument, and real singing to its original flavor! It is the 1:1 volume of HiFi, the same proportion of volume and the same size of stereo sound field, as if the entire symphony orchestra is performing live in the listening room at home! Audiophiles think: as long as they bring the most expensive equipment in the world home, they can achieve such a scene. In fact, it is not as simple as he imagined, and there is a lot of knowledge involved.

How to choose the right preamplifier

Translator's note: This is an article that I just started translating in the past two days. The purpose is to meet the requests of netizens in the forum. It will be posted in sections. I hope everyone will wait patiently.

When I asked what to consider when choosing a preamplifier, I suddenly remembered the three preamplifiers I own. I bought all of them (of course, I didn't buy all three at the same time) when I couldn't make a choice and choose one that suited my idea. What a stupid method! ? If I am so stupid, am I still qualified to continue writing this article?

The goal of adding a preamplifier is to achieve synergy between your source(s) and the amplifier. Any time you have a chance to audition multiple preamps connected in your system, you can't tell which one sounds better than another. The reason is that the better sounding one is usually more or less expensive, or that preamplifier has a lot more work done in its circuit design.

When choosing the ideal preamplifier, you must be clear about two things:

A. The output voltage of your audio source (most CD players are 2 volts)
B. The input sensitivity of your amplifier (most amplifiers are around 1 volt)

You need to know if the output level of your CD drive or other source is less than or greater than 2 volts. You also need to know if the input sensitivity of your power amplifier is less than or greater than 1 volt on the same note. Once you know these voltages, you can make a good choice of the correct preamplifier.

First, let’s understand what the two nouns represent.

The output voltage of your source is a fixed level that does not change, unless your source has a "variable output". This 2 volt signal (the music) drives the input stage of the power amplifier, or drives the preamplifier, which in turn drives the input of the preamplifier or the input stage of the power amplifier.

The input sensitivity of an amplifier, in simple terms, refers to how many volts the signal level is sent to the power amplifier. Any voltage exceeding this number will cause your power amplifier to try to use more power than it actually has, resulting in it being overloaded and causing what is known as "clipping".

So in all cases, a preamplifier is of course used to control the voltage from the sound source. When the preamp volume is turned to the left, you can measure that there is only zero volts output, and the power amplifier is therefore silent. When you turn the volume knob to the right to increase the output voltage, your power amplifier can drive the speakers to produce sound. The ideal operating range on the volume control should be between 1/4 and 3/4 to the right, which is the normal position for listening levels (in fact, when it exceeds the 1/2 position to the right, distortion already exists). This means that the preamplifier will never add any voltage to the input signal, that is, "gain". Under what circumstances does the preamplifier need to set "gain"? There are two reasons why you may want to increase the gain of the preamplifier:

A. When the power amplifier needs more than 1 volt to reach full power output.
B. When your audio source has less than 2 volt output.

Some power amplifiers require 5 volts to reach full power, and amplifiers are usually designed to reach full power at 2 volts. Occasionally, we see an amplifier that only requires 1/2 volt to reach full power.

Some modified CD players have output levels of less than 2 volts, and some DACs have output levels of less than 2 volts. (Although most DACs have at least 2 volts or slightly more, sometimes up to 5 volts.) For those who love vinyl records, it can sometimes be difficult to find a 2-volt cartridge and turntable terminal stage with an output. Most I have seen are 1 volt. If the sound source only has an output level of 1 volt, and the input sensitivity of the amplifier is only 2 volts, you must have an additional preamplifier with gain, otherwise the power amplifier will not be able to play back the sound pressure properly. Even with a pair of ultra-efficient speakers, the listening requirements are only very soft, but the music played back will lack dynamics and weight. Once you decide whether you need gain or no gain, you have greatly narrowed the range of choices. But whether you choose gain or no gain, you must consider matching "impedance".

All audio sources and amplifiers have something called "output impedance". Think of it as the unit's ability to drive a difficult load, such as a long signal line connected to the amplifier.
Conversely, all amplifiers have something called "input impedance". Think of it as the level the unit encounters from the preamplifier or CD player.

The general rule is that the lower the output impedance, the easier it is to drive a difficult load. Likewise, the higher the input impedance, the easier it is to drive. A preamp with an output impedance of less than 1000Ω is best suited to driving an amplifier with an input impedance of 100,000Ω. The output impedance of commercially available CD players is usually quite low, but unfortunately the output impedance of power amplifiers is usually between 10,000Ω and 500,000Ω, most of which are around 50KΩ. 50KΩ is a reasonable load and most audio sources and preamps will have no problem driving it. The only problem is trying to drive a 50KΩ amplifier with a high output impedance preamp with extra long signal cables. The result is often either a roll-off in the bass response or a lack of dynamics, or both. Listeners certainly don't want the playback to sound thin, so try to use short signal cables. If the preamp has a fairly low output impedance, then it doesn't matter, even if the power amplifier is on the other side of the house, the bass response will still be strong and heavy, and there will be no roll-off.

There are 3 preamp models:

The top-of-the-line A model has lots of gain or no gain, or a normal output impedance or a low output impedance, depending on how the selector switch on the back panel is set, making it possible to ensure that it actually sounds unique or consistently good.

Model B has no gain but has low output impedance, making it an ideal match for most systems.

Model C has more gain and higher input sensitivity, catering to lower output sources or higher output sensitivity amplifiers, or both.

Speaking of this, perhaps you might want to read another article: "Does the preamplifier help improve or hurt the sound?"

If the player's signal is only a CD player, and the power amplifier used in the sound system has a volume control level, it is possible to use or not use a pre-amplifier. In fact, in most cases, it is recommended not to use a pre-amplifier.

[Edit this paragraph] Preamplifier role
　　The role of the sound source selection circuit is to select the required sound source signal to send to the back stage, while closing other sound source channels. 　　The role of the input amplifier is to amplify the sound source signal to the rated level, usually about 1V. 　　The role of sound quality control is to control the frequency characteristics of the sound system to achieve high-fidelity sound quality; or to modify and beautify the sound according to the listener's preferences. 　　The difference and application of power amplifiers, line amplifiers and preamplifiers 　　The input signal is amplified by the preamplifier, such as the sound signal picked up by the microphone. Because it is relatively weak, it needs to be amplified to a certain level before it can be sent to other levels. Usually the preamplifier has a higher voltage gain and can amplify small signals to the standard level. The 　　line amplifier is used for transmission. In order to reduce the transmission attenuation and enable the receiver to obtain a strong enough signal, the current must be amplified and driven during transmission. Sometimes it is also necessary to increase the voltage transmission. For example, constant voltage broadcasting uses this principle. 　　The power amplifier mainly amplifies the current so that the low-impedance speaker can make a sound. Of course, this example is based on an audio example. If it is a radio frequency signal, it will be slightly different from this explanation, but the meaning is similar. For example, the output of the transmitter amplifier is output to the antenna. 　　Single-gain preamplifier 　　As mentioned at the beginning, the active amplifier has an internal amplification circuit, and the general gain is 0 to ten times, while the passive preamplifier uses a volume potentiometer to attenuate, and its maximum output is equal to the input. There is also an active preamplifier, whose amplification ratio is the same as that of the passive preamplifier, which is the single-gain preamplifier. 　　The purpose of the single-gain preamplifier is to imagine the preamplifier as a buffer. In English, Buffer has the function of isolation and buffering, that is, it does not change the signal strength of the source equipment, but receives it with high input impedance and sends it out with the concept of low impedance output. Therefore, the single-gain preamplifier has the function of impedance conversion. There are not many single-gain preamplifiers 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 preamplifier launched by the domestic manufacturer AC and DC Studio is a specific representative of the single-gain preamplifier. This preamplifier uses twin field effect transistors as input and ZTX bipolar transistors as output. It has the characteristics of high input impedance and low output impedance. Due to the few parts, the S/N ratio is very high. When the volume is turned up to the maximum, the ear is close to the tweeter and no hissing can be heard. The sound is transparent and untainted, and the details are presented naturally. It is an extremely cheap single-gain preamplifier with excellent sound quality. Is the 　　simpler the preamplifier circuit, the more ideal it is? 　　There is a lot of nonsense talking about preamplifiers, so now is the time to clarify it. In an ideal listening environment, the fewer components the signal path design has, the more completely true and perfect this amplifier may be. This is the simple is the best theory. 　　Every additional component will increase a point of distortion, and switches and volume controls are the main offenders. But many good recordings can achieve this, and they need to do a favor in the front tone to eliminate the problems of those piercing sounds and easy listening fatigue during playback. 　　The result is a situation where the tone controls offer fine-tuned, sensitive operation (in fact, many high-end preamps use stepped resistor selectors instead of the usual potentiometers). When you audition an amplifier, try to hear the difference when you use only the bass and treble knobs to control the volume. You should get relatively small changes. This phenomenon is not just for rock or pop music, even classical music listeners will often want to find a "left-hand down" knob that tapers off the treble, taming the natural top end of the recording. The 　　volume control tries its best and still can't make the amplifier output louder - making the bass driver of the bookshelf speaker sound like a monster Cerwin Vega. Remember what we said about added distortion? For the dance party, turn the knob to increase the bass and treble, the whole sound is raised, but the distortion starts to blow the speaker. The 　　best of both worlds? A preamp with a good volume control, and a direct source output, or a "volume escape" button to bypass it when necessary. But one thing to note is that purists will even insist that the simpler the better. 　　Output and input impedance matching of preamplifier and postamplifier 　　Both preamplifier and postamplifier have output and input impedance specifications. Output impedance represents the internal resistance of the signal output of the preamplifier or postamplifier, and the unit is ohm. The lower the output impedance, the lower the internal resistance of the amplifier and the stronger the driving ability. Similarly, input impedance is the impedance encountered by the preamplifier or postamplifier when the signal is input to the device, and the unit is also ohm. The higher the input impedance, the easier it is to drive the front-end equipment, and the influence of the load effect can also be reduced. Every amplifier has input impedance and output impedance. Generally speaking, the higher the input impedance Ri, the better, and the lower the output impedance Ro, the better. Impedance matching Ideally, the lower the output impedance of the preamplifier, the better, and the higher the input impedance of the postamplifier, the 　　better, in order to avoid the influence of the load effect. Usually, the input impedance of the postamplifier is better than ten times the output impedance of the preamplifier, so that the strength of the preamplifier can be fully exerted. This is just like the principle of a locomotive pulling a carriage. The same carriage is pulled by locomotives of different horsepower, and the ease is naturally different. The locomotive with greater horsepower (lower output impedance) will naturally pull the lighter carriage (higher input impedance) with ease and pleasure. 　　Preamplifier 　　In another post about how to choose a preamplifier, L said: "This era emphasizes personality!" Indeed, the most important thing in choosing a preamplifier is the personality of the preamplifier. The 　　frequency response range of the preamplifier must be wide (5-35K Hz or more). The longer the high frequency is, the richer the harmonics, overtones, and aftertaste will be. If the high frequency is not outstanding, no matter how good the mid-low frequency is, I will not accept it, which affects the listening experience. A good preamplifier must first balance the entire sound range, the dynamic range should not be too large or too small, and the sound resolution should be very good, so that the sound will be transparent, the sound field will be natural, the instrument isolation will be exquisite, and the size will be appropriate. 　　When I asked what to consider when choosing a preamplifier, I suddenly remembered the three preamplifiers I own. I couldn't make a choice and choose one that suits my idea, so I simply bought them all (of course, I didn't buy all three preamplifiers at the same time). What a stupid method! ? If I am so stupid, am I still qualified to continue writing this article? 　　If you want a rich sound, the mid-low and bass are the most difficult to adjust. How to adjust and what materials to use depends on your personal skills. The only solution I had back then was to buy a few preamplifiers (Restek's Vector, I like its wide frequency range and strong interpretation ability, the sound it plays back is serious, clear and detailed, I call it "Yan Shou"; the other one is called "Huan Fei" is Audiolabor's Klar, the sound it plays back is rich and delicate, flesh and blood, smooth and unyielding, I like Yang Yuhuan more than Zhao Feiyan like Emperor Minghuang of Tang, especially in cold winter weather, it brings me warmth; unlike Zhao Feiyan who is as cold as ice, I only play her when I am in a hot mood, the sound it plays back can often calm me down, and has a special effect of calming the mind and reducing dryness. In addition, I also have an ARC SP 11 Mk II, which is a special measure for listening to human voices. Due to the complicated connection, unlike my "Yan Shou" and "Huan Fei", one is connected to XLR and the other is connected to RCA plugs to input my Restek It is as convenient as an Exponent power amplifier. I only need to change Bal to Unbal on the button on the back panel of Exponent to choose "slim" or "fat". 
 


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
　　This example shows that the preamplifier has a direct relationship with the listener's preference. I listen to a wide variety of music, so I use multiple units. Other audiophiles should choose according to the type of music they listen to. For those who like classical music, of course, the frequency response range must be wide (5-35K Hz or more); the requirements for sound pressure and frequency domain for listening to human voices can be lower... 　　In short, the key is to listen more and listen in combination with the selected speakers. Only in this way can the sound played back be the sound you want to listen to in the future. 　　If the preamplifier of the audio equipment can restore the speed, transient, dynamic, sound pressure and other factors more realistically, you can sit down and listen to the music calmly, enter the beautiful realm of music, appreciate the connotation of music and be deeply moved. 　　Friends who play HiFi often focus on adjusting certain links and neglect the influence of other factors. In addition to proper matching of equipment, there must be a good listening environment, careful adjustment and use to achieve the goal, which will not be achieved overnight. I believe that most audiophiles understand these principles, but there are not many friends who can take all aspects into consideration. In terms of equipment use alone, many audiophiles do not know much about the performance of their own equipment, and often attribute the poor sound to certain equipment due to improper use. As a result, "playing" HiFi has become "changing" HiFi constantly. In the small town where I live, there is such an audiophile friend who has only been playing with audio for five or six years, and has changed no less than six systems. I said "set", and I changed the whole set! Guess how he plays the preamplifier now? He now uses the CD Wadia 861 as the signal source (half a year ago, he played an LP turntable, but could not produce good sound and transferred or returned it to the agent). This machine can be directly connected to the post-amplifier because it has been set up with a digital volume remote control. However, this audiophile, probably because of its reputation or because he thought the Wadia 861 digital sound was too heavy, connected an ARC Reference II preamplifier, and then connected it to a Pass power amplifier with an output of 600W on each side to drive a pair of Wilson WATT / Puppy 6. Money can be spent like this! ? Maybe he thought that this would make the sound like a vacuum tube! 　　The preamplifier can be said to be the control center of the entire system. Most people think that the preamplifier is just a piece of equipment used to control the volume and select the source. They often turn a blind eye to the buttons and facilities on the machine, and even don't bother to understand the purpose of each button. They are actually wasting their money and the designer's efforts, and not making good use of its performance. 　　Take the simplest preamplifier as an example. It usually only has the function of selecting the source and controlling the volume, but you should not underestimate it. In fact, the quality of the sound is closely related to whether the preamplifier is operated correctly and adjusted. Let's put aside the adjustment, and control the volume knob. It can be said to be an art. The volume is enough to affect the quality of the whole system. In the small town where I live, there is another audiophile friend who likes to appreciate the sound of drums. When entertaining guests, he always plays drums. The volume knob is usually turned to 12.00 o'clock or 13.00 o'clock. Who can stand it? No matter what kind of music he listens to, he listens to it at the same volume, thinking that the natural sound of a good recording must be good. What's more terrible is that he thinks loud is good, so whether listening to a symphony or a single instrument, he listens to it at the same volume. As a result, you hear Teresa Teng's voice like a huge bell, her petite body becomes as majestic as Yao Ming, the size of the violin expands to a double cello, the high pitch of the guitar is like a harpsichord, and the bass part is like a drum. When you frown and feel depressed, he still tells you how powerful his system is, how strong the singer is, and how many details are in the recording, which can make you angry to death! 　　Why do these friends listen to music in this way? It is simply because they have rarely listened to concerts, authentic live concerts. When they have heard the symphony orchestra playing in the same concert hall, the volume of a single instrument, and the sound of a real instrument, they will understand what is the ratio of sound, and then they can understand the loudness of the volume of a single instrument. In addition to listening to live performances, another way to understand the sound and volume of instruments is to listen to some real people playing without amplification systems. Then when you listen to those canned music on CDs, you will not adjust the volume without any rules, which will not only distort the sound, deform the instruments, and cause pain to your ears, but also damage your hearing! The 　　highest skill of volume control is to make your own audio equipment achieve the best performance, and to restore the volume of the band, solo instruments, and real people singing to the original flavor! It is the 1:1 volume of HiFi, the same proportion of volume and the same size of stereo sound field, as if the entire symphony orchestra is performing live in your home listening room! Audiophiles think: As long as you bring the most expensive equipment in the world home, you can achieve such a scene. In fact, it is not as simple as he imagined. There is a lot of knowledge involved. 　　How to choose a preamplifier correctly 　　Translator's note: This is an article that I just started translating these two days. The purpose is to meet the requirements of netizens in the forum. It will be posted in sections. I hope everyone will wait patiently. 　　When the questions about how to choose a preamplifier need to be considered, I suddenly remembered that the three preamplifiers I own are the ones that I bought all of them when I couldn't make a choice and choose one that suits my idea (of course, I didn't buy all three preamplifiers at the same time). What a stupid method! ? Since I am so stupid, am I still 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 in your system, you can't tell which one sounds better than the other. The reason is that the better sounding one is usually more or less expensive, or the preamplifier has done a lot more work in circuit design. 　　When choosing the ideal preamplifier, you must know two things 　　: A. The output voltage of your source (most CD-ROMs are 2 volts) and 　　B. The input sensitivity of your amplifier (most amplifiers are around 1 volt) 　　. You must know whether the output level of your CD-ROM or other source is less than or greater than 2 volts. You must also know if the input sensitivity of your power amplifier is less than or greater than 1 volt on the same note. Once you know these voltages, you can make a good choice of the right preamplifier. 　　First understand what two terms mean. 　　Output voltage of your source The output voltage of your source is a fixed level that does not change, unless your source has a "variable output". This 2 volt signal (music) drives the input stage of the power amplifier, or drives the preamplifier, which in turn drives the input of the amplifier's preamplifier or the input stage of the power amplifier. 　　Input sensitivity of an amplifier 　　Simply put, the input sensitivity of an amplifier means how many volts the signal is sent to the power amplifier. Any voltage above this amount will cause your power amplifier to try to use more power than it actually has, which will overload it and cause what is called "clipping". 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
　　So in all cases, a preamplifier is used to control the voltage from the sound source. When the preamp volume is turned all the way to the left, you can measure that there is only zero volts output, and the power amplifier is therefore silent. When you turn the volume knob to the right to increase the output voltage, your power amplifier can drive the speakers to produce sound. The ideal operating range on the volume control should be between 1/4 to 3/4 to the right, which is the normal position for listening levels (in fact, when it exceeds the 1/2 position to the right, distortion already exists). This means that the preamplifier will never add any voltage to the input signal, which is also known as "gain". 　　When does the preamplifier need to set "gain"? There are two reasons why you may want to increase the gain of the preamplifier: 　　A. When the power amplifier needs more than 1 volt to reach full power output. 　　B. When your sound source has less than 2 volts output. 　　Some power amplifiers require 5 volts input to reach full power output, and amplifiers are usually designed to reach full power output with all settings set at 2 volts input. Occasionally we see an amplifier that requires only 1/2 volt input to reach full power. 　　Some modified CD players have output levels of less than 2 volts, and some DACs have output levels of less than 2 volts. (Although most DACs have at least 2 volts or slightly more, sometimes up to 5 volts.) For 　　those who love vinyl, it can sometimes be difficult to find an output stage with a 2 volt cartridge and turntable terminal block. Most I have seen are 1 volt. 　　If the source has only 1 volt output level, and the amplifier has an input sensitivity of only 2 volts, you must add a preamplifier with gain, otherwise the power amplifier will not be able to play back the sound pressure properly. Even with a pair of super efficient speakers, the listening requirements are only very soft, but the music will lack dynamics and weight. 　　Once you have decided whether you need gain or no gain, you have narrowed the range of choices greatly. But whether you choose gain or no gain, you must consider the matching "impedance". 　　All sound sources and amplifiers have something called "output impedance". Think of it as the unit's ability to drive a difficult load, such as a long signal line to the amplifier. 　　Conversely, all amplifiers have something called "input impedance". Think of it as the level the unit sees from the preamp or CD player. The 　　general rule is that the lower the output impedance, the easier it is to drive a difficult load. Likewise, the higher the input impedance, the easier it is to drive. A preamp with an output impedance of less than 1000Ω is best used to drive an amplifier with an input impedance of 100,000Ω. The 　　output impedance of commercial CD players is usually quite low, but unfortunately the output impedance of power amplifiers is usually between 10,000Ω and 500,000Ω, most of which are in the 50KΩ range. 　　50KΩ is a reasonable load that most audio sources and preamps will drive without problems. The only problem is trying to drive a 50KΩ amplifier with an extra long signal line from a high output impedance preamp. The result is often either a roll-off in the bass response or a lack of dynamics, or both. Listeners don't want the sound to sound thin, so try to use short signal cables. If the output impedance of the preamp is low, it doesn't matter, even if the power amplifier is on the other side of the house, the low frequency response is still strong and heavy, and there will be no decline. 　　There are three preamp models: 　　the top-level A model has a lot of gain or no gain, or a normal output impedance or a low output impedance, depending on how the selector switch on the back panel is set. This ensures that it really produces a unique or regular good sound. 　　Model B has no gain and a low output impedance, which is the best match for most systems. 　　Model C has more gain and higher input sensitivity, which caters to lower output sound sources or higher output sensitivity amplifiers, or both. 　　If the player's signal is only a CD player, and the power amplifier used in the sound system has a volume control, it is possible to use or not use a preamp. In fact, in most cases, it is recommended not to use a preamp.