Power amplifier is referred to as power amplifier, it can be said to be the largest family of various audio equipment. There are so many brands and models that it is indeed endless. Although they are all called power amplifiers, in terms of their main uses, power amplifiers can be divided into two main categories, which are dedicated power amplifiers and civilian power amplifiers.
Amplifiers used in sports venues, movie theaters, dance halls, conference halls, public places, sound reinforcement, and recording monitoring, etc., generally speaking, their technical parameters often have some unique requirements. Such amplifiers are usually called dedicated Amplifier or professional amplifier.
Hi-Fi music appreciation for home use, AV system playback, and karaoke entertainment amplifiers are usually called civilian amplifiers or household amplifiers.
Although special power amplifiers and civilian power amplifiers are different in some characteristic parameters, it is also difficult to say that there is a clear line. For example, the power amplifier used for music recording monitoring is likely to be a family Hi-Fi or even Hi-end amplifier .
Hi-Fi Amplifier and AV Amplifier Hi-Fi Amplifier and AV Amplifier are currently the two main categories of home amplifiers. These two types of power amplifiers are used for different purposes, and the design focuses differently. Hi-Fi amplifiers are used to enjoy music, and users are pursuing as much "original" as possible. The users of AV amplifiers are pursuing the "live" effect matched with the picture, and even the exaggerated "live" effect. These two types of amplifiers are not very good, which is directly better or worse. For example, Hi-Fi amplifiers and AV amplifiers with the same price of more than three thousand yuan, the cost of Hi-Fi amplifiers is only invested in two channels, and the AV amplifiers The cost investment must take into account 5-6 channels, and also has a certain effect processing function. If you only look at the input of its two main channels, it is definitely lower than the input of the two channels of the Hi-Fi amplifier. The difference in its playback effect is obvious. But whether it is a Hi-Fi amplifier or an AV amplifier, there are high-end boutique type and value popular type, such as Tianlong's AVC-A1 type AV amplifier, when it is used for music playback, its sound effect will not be better than a set Four to five thousand yuan Hi-Fi amplifier is inferior. Generally speaking, it is difficult to have an AV amplifier that is fully compatible with Hi-Fi and AV. AV amplifiers have conditions for Hi-Fi music appreciation. This condition is the requirements and standards for users to enjoy music. The user is only used to enjoy some casual music, or only needs to be able to hear the melody of the music. The AV amplifier is relatively easy to meet, but if there are higher requirements for music appreciation, the general AV amplifier is difficult to meet.
Transistor power amplifiers and tube power amplifiers The power amplifiers used for Hi-Fi appreciation can be divided into two categories: transistor power amplifiers and tube power amplifiers. In the past, there were Hi-Fi power amplifiers that used integrated circuits or module circuits.
There is no difference in merits between transistor power amplifiers and tube power amplifiers, but the applied devices are different (one is the transistor and the other is the tube). Because the two types of devices are different, their physical principles and circuit characteristics are also different. The electric current of the electron tube is formed by the attracting movement of electrons in the vacuum by the electric field force. The current of the transistor is formed by the outer electrons carried by the semiconductor burning at the position of the electric field force. This difference in physical rationale causes different circuit characteristics in practical applications. Relatively speaking, the working voltage of the tube power amplifier is high, but the working current is relatively small, while the working voltage of the transistor power amplifier is low, and the working current is relatively large.
The timbre of the tube power amplifier and the transistor power amplifier is indeed a certain difference, and the two have different responses to transient signals. This difference has been adapted to different types of music and different music viewers, so the current Hi-Fi amplifier has formed the coexistence of transistor amplifiers and tube amplifiers. However, in terms of brand, model, and quantity, the share of transistor power amplifiers is still absolutely greater than that of tube power amplifiers. The working state of the output stage transistors of the class A power amplifier and the class B power amplifier transistor can be divided into class A and class B. The so-called class A is simply to make the output stage transistors work in the linear region during the positive and negative half cycles of the sinusoidal AC signal, while the class B is to only make the output stage transistors in the positive half cycle (or negative half cycle) ) Work in the linear zone. Due to the different working states of the output stage transistors, the power utilization efficiency of the output stage (ie, the ratio of output power amplifier to power consumption) is also different. In a practical output circuit, the efficiency of category B is 2-3 times higher than that of category A. For example, Marantz PM80 transistor power amplifier, under certain power supply conditions, has an output power of 100W when working in category B, but only 20W in category A.
Class A amplifiers have no crossover distortion, and regardless of the actual output power, the internal resistance of the output stage crystal is constant. Class B amplifiers will always have a certain crossover distortion (although this distortion may be extremely small). In addition, the internal resistance of the output stage transistor is small when the output is large, but the internal resistance of the output stage transistor is relatively large when the output is small. . These differences make the sense of hearing different. The sound of Class A amplifiers is softer than that of Class B amplifiers. In addition, the low frequency control of the speakers is stronger than that of Class B amplifiers, especially at low volumes. The bass texture is better. These characteristics of the Class A amplifier make the Class A amplifier need not have a large output power margin in practical applications. A 20W-30W Class A amplifier can already drive most speakers very well.
As mentioned earlier, the power efficiency of the Class A power amplifier is low, which causes a large amount of heat to be emitted when the Class A power amplifier is working. In order to ensure that the operating temperature of the transistor does not exceed a certain limit, a heat sink with a larger volume and area is required, which makes the size and weight of the Class A power amplifier relatively large. For example, KRELL's KSD-50S Class A amplifier has an output of 50W + 50W and weighs nearly 30Kg. The Marantz PM-80 outputs 20W + 20W and 13Kg in weight.
Pure post-stage power amplifier and mono power amplifier Our common power amplifiers are preamplifiers (pre-stage) and power amplifiers (post-stage) that amplify small signals in a chassis. This kind of power amplifier is often called "merging" Amplifier ". The combined amplifier is easy to use and has a relatively good performance-price ratio. But this combined power amplifier has some inherent shortcomings, and the most difficult to overcome is the mutual interference between the pre-stage and the post-stage. In order to solve this problem, the front stage and the rear stage are made in two cabinets, so that there is a pure rear stage power amplifier. Most pure post-stage power amplifiers are two-channel structural forms, but this structural form makes the problem of mutual interference between the two channels not very easy to solve. In order to solve the interference between the two channels, there have been two Single channel pure power amplifier with separate channels.
The main meaning of separating power amplifiers like this is to improve the quality of the power amplifier, not to pursue this form. If the separation is only achieved in form, although the mutual interference problem can be solved, but other parameters have not been significantly improved, then this separation is still limited for the amplifier to improve the overall quality.
For most pure post-stage amplifiers and mono amplifiers, a pre-stage is required. (For an introduction to the previous level, please refer to the article "The Palette of Audio Equipment" in the fourth issue of this magazine this year). Since pure power amplifiers and mono power amplifiers appear to improve the quality of power amplifiers, the quality requirements of the front stage should also be adapted to them. The power amplifier is divided into a transistor and a tube, and the front stage is also divided into a transistor and a tube. For audio lovers and music lovers, there are a variety of combinations in the selection of pre-stage and post-stage, and different combinations have different sound characteristics, which gives users more room for choice. The front stage connected with the pure rear stage power amplifier has a greater impact on the quality of the entire audio system. First of all, it must have a certain quality, otherwise, the advantages of pure post or mono will not be exerted, and it may even highlight the "fault" of a poor pre-level, and the overall sound effect is worse. Furthermore, different pre- and post-levels have different timbre characteristics, and users can choose different combinations according to their personal preferences. For example, many audio and music lovers like to use the combination of "before the gallbladder and the back of the stone" (that is, the front stage of the tube and the rear stage of the transistor). Features, and also appreciate the sweet and mellow "smoothness" of the preamp of the tube. However, this combination is not a "golden rule", because the specific pre-level and post-level have their own characteristics, and the preference for tone varies from person to person, users can find their favorite combination according to the specific situation the way. How much output power should the Hi-Fi amplifier have? The output power of the Hi-Fi amplifier is affected by many factors. First, this output power has a greater relationship with the speaker that is connected, and secondly it is related to the quality of the amplifier. It is related to the environment used, that is, the volume of the room. The speaker has a parameter called sensitivity, and its unit is dB / m · W, which means the sound pressure (dB) generated 1m away from the speaker when the speaker gets 1W of electric power. If the sensitivity of a certain speaker is 90dB, then 1W of power is needed to get 90dB of sound pressure at 1m. To get 100dB of sound pressure, it needs 10W of power to push. But if the sensitivity of the speaker is 80dB (such as ATC's SCM-10), to achieve a sound pressure of 100dB, 100W of power is required to drive it. The sensitivity of most speakers is about 85dB-90dB. For these speakers, 10W-30W of undistorted power can already have enough sound pressure.
The quality of the power amplifier has a great relationship with the output power that the power amplifier should have. One of the parameters of the power amplifier is called the damping coefficient, which is a parameter that represents the control ability of the speaker, but this parameter has a moderate range and is directly related to the specific speaker. In general, if the quality of a power amplifier is very good, it can still maintain its performance parameters at a certain level at 30W output. Then there is no need to ask the amplifier to have a greater power output. However, if the quality of the power amplifier is not ideal, it will cause the deterioration of its performance parameters when the output power increases, then the output power of the power amplifier should have a certain margin to ensure that there are still certain good parameters under the practical output power . Normally, when the power amplifier is a Class A output or a tube power amplifier, there is no need to have too much output power margin, and the output power of 20W-30W is enough. But if it is a Class B power amplifier or a power amplifier with poor quality, then the output power of the power amplifier should have a large margin. In addition, if the matched speaker is a large inverter type, the power amplifier should also have a larger output power margin. When considering the output power due to the power amplifier from the quality of the power amplifier, choosing a larger power margin can indeed improve the adaptation between the power amplifier and the speaker. But here we still have to make it clear that the main significance of choosing a power amplifier with a larger output power is not because we need such a large sound pressure, but to improve the adaptation state of the power amplifier to the speaker. If a power amplifier with moderate output power is already able to control the speakers, then there is no need to put forward higher output power requirements for this power amplifier. The use environment, that is, the space volume of the room has a certain relationship with the power that the amplifier should output. The output power we have discussed above is based on the room volume below 40. If the room volume is large, Then the output power of the power amplifier should be increased.
The characteristics of the output stage of the tube power amplifier There are three circuit types for the power output stage of the tube power amplifier. One type is the push-pull output circuit with an output transformer. This type of output circuit accounts for the vast majority of tube power amplifiers. The output transformer in the push-pull circuit has few DC components, and the second harmonic distortion is also very small. The output power of this type of circuit can be made larger, so the scope of application is also relatively large. Generally speaking, for audio enthusiasts who are interested in the sound of the amplifier, this type of output stage amplifier is very suitable. However, for this type of power amplifier, the design and process of the output transformer are crucial. If the design and process of the output transformer are inadequate, the frequency response and transient response of this type of power amplifier are often not ideal. In addition, due to the constraints of the output transformer, the adaptation range of the matching speaker is relatively small.
Another type of circuit for the power output stage is a single-ended Class A circuit. This type of circuit also has a transformer, but the output transformer of this type of circuit has a large DC component, and the requirements for the output transformer are higher than those for the output transformer in the push-pull output circuit. In addition, the requirements for power supply are relatively high. The characteristic of this type of output circuit is that there are many second harmonic components. Although this is a kind of harmonic distortion, for music signals, the second harmonic is a highly harmonious sound, so it sounds very ear. This feature makes the power of this output circuit very distinctive in the timbre of the sound, especially when the power amplifier stage uses a triode, the human voice sounds very sweet, and the string music in the chamber music also sounds delicate, or, The sound of this type of power amplifier is very tasteful. However, the output power of this type of power amplifier is not easy to be large, so if the sensitivity of the matched speaker is low, it will be more reluctant when broadcasting large orchestral music. This kind of tube amplifier is very popular with some audio players. In addition to a high-power transistor amplifier, there is another such amplifier. I think it is complementary to the sound, but this also shows that this type of amplifier The timbre characteristics are really touching.
There is also a class of output stage circuits for tube power amplifiers, which is an OTL circuit. The so-called OTL circuit is a non-output transformer circuit. Modern transistor power amplifier output stages are almost all OTL circuits or improved versions of OTL circuits. The characteristic parameters of the tube and the transistor are different from the working state. The transistor amplifier is easily suitable for speakers with an impedance of 4-8, and it takes a lot of trouble for the tube amplifier to adapt to the 4-8 speaker without an output transformer. Because the output transformer is removed from the OTL power amplifier of the electronic tube, the technical parameters are greatly improved compared to the two types of circuits mentioned above. The power amplifier sound of this type of output circuit is very distinctive. It has a magnificent momentum and a wide sound field. Compared with the transistor amplifier, its tone is warm and delicate. Since this type of power amplifier has no output transformer, it can adapt to a wide range of speaker impedances. However, the power efficiency of this type of output stage power amplifier is low, and the design, process, and debugging are relatively complicated. At present, the power amplifier of this type of output circuit is only found in some high-end models.
When a signal must have a particular impedance in order to function properly, controlled impedance should be used. In high frequency applications matching the impedance of PCB traces is important in maintaining data integrity and signal clarity. If the impedance of the PCB trace connecting two components does not match the components` characteristic impedance, there may be increased switching times within the device or the circuit. There may also be random errors.
Please note that we also need special instructions here:In DC circuits there is no reactance and the resistance of copper conductors is typically insignificant. However in high speed AC circuits (those with sharp changes in voltage and/or current) the reactance and thus the impedance can become very significant. This can become critical to a design's functionality because of the effects that changes in the impedance along the signals path from transmitter to receiver will have on the efficiency of power transfer as well as signal integrity. While a circuit`s speed is often expressed as the frequency of the wave form: the critical concern is the speed at which the voltage and/or current is required to change.
The characteristic impedance of a PCB trace is typically determined by its inductive and capacitive reactance, resistance, and conductance. These factors are a function of the physical dimensions of the trace, the dielectric constant of the PCB substrate material, and dielectric thickness. Typically PCB trace impedance can range from 25 to 125 ohms. The impedance value generated from the PCB structure will be determined by the following factors:
– Width and thickness of the copper signal trace (top and bottom)
– Thickness of the core or prepreg material on either side of the copper trace
– Dielectric constant of the core and prepreg material
– Distance from other copper features
Controlled Impedance should be considered for PCBs used in fast digital applications such as:
– Telecommunications
– Computing 100MHz and above
– High Quality Analog Video
– Signal Processing
– RF Communication
In order to meet the growing demand of impedance control PCB, PCB manufacturers have invested a lot of money and manpower and material resources in production technology, in order to meet the production requirements of customers.
Due to the difficulty of impedance control PCB production, PCB manufacturers generally require PCB designers or purchasers to provide more detailed information and requirements, such as the type of material required, copper weight and thickness of the board, the number of layers, gerber file, so that the manufacturer can prepare the bill of materials (BOM). Impedance information should be clearly marked in Gerber file. If the necessary information is lacking, even a little key information will make it difficult or impossible for the manufacturer's engineers to know exactly what the customer needs.
No Impedance Control: This is a situation where you do not need any extra design elements to ensure correct impedance because you have very loose impedance tolerance. Naturally, this will result in a faster-completed, less expensive board because the manufacturer does not have to include any special measures.
Impedance Watching: What is impedance watching? This is a situation where the designer will outline the impedance control trace and the PCB provider adjusts the trace width and dielectric height accordingly. Once the manufacturer approves these specifications, they can begin to manufacture the board. You can request a Time Domain Reflectometry (TDR) test to confirm the impedance for a fee.
Impedance Control: Actual impedance control is something you will typically only request when your design has tight impedance tolerances that could be tough to hit the first time around. When the capability limits of the manufacturer get close to the dimension requirements, it can be tough to ensure target impedance on the initial attempt.
In the case of impedance control, the manufacturer makes the circuit board achieve the target impedance as far as possible. Then they tested TDR to see if they succeeded. If not, they adjust accordingly and try again until they reach the required impedance.
Amplifiers used in sports venues, movie theaters, dance halls, conference halls, public places, sound reinforcement, and recording monitoring, etc., generally speaking, their technical parameters often have some unique requirements. Such amplifiers are usually called dedicated Amplifier or professional amplifier.
Hi-Fi music appreciation for home use, AV system playback, and karaoke entertainment amplifiers are usually called civilian amplifiers or household amplifiers.
Although special power amplifiers and civilian power amplifiers are different in some characteristic parameters, it is also difficult to say that there is a clear line. For example, the power amplifier used for music recording monitoring is likely to be a family Hi-Fi or even Hi-end amplifier .
Hi-Fi Amplifier and AV Amplifier Hi-Fi Amplifier and AV Amplifier are currently the two main categories of home amplifiers. These two types of power amplifiers are used for different purposes, and the design focuses differently. Hi-Fi amplifiers are used to enjoy music, and users are pursuing as much "original" as possible. The users of AV amplifiers are pursuing the "live" effect matched with the picture, and even the exaggerated "live" effect. These two types of amplifiers are not very good, which is directly better or worse. For example, Hi-Fi amplifiers and AV amplifiers with the same price of more than three thousand yuan, the cost of Hi-Fi amplifiers is only invested in two channels, and the AV amplifiers The cost investment must take into account 5-6 channels, and also has a certain effect processing function. If you only look at the input of its two main channels, it is definitely lower than the input of the two channels of the Hi-Fi amplifier. The difference in its playback effect is obvious. But whether it is a Hi-Fi amplifier or an AV amplifier, there are high-end boutique type and value popular type, such as Tianlong's AVC-A1 type AV amplifier, when it is used for music playback, its sound effect will not be better than a set Four to five thousand yuan Hi-Fi amplifier is inferior. Generally speaking, it is difficult to have an AV amplifier that is fully compatible with Hi-Fi and AV. AV amplifiers have conditions for Hi-Fi music appreciation. This condition is the requirements and standards for users to enjoy music. The user is only used to enjoy some casual music, or only needs to be able to hear the melody of the music. The AV amplifier is relatively easy to meet, but if there are higher requirements for music appreciation, the general AV amplifier is difficult to meet.
Transistor power amplifiers and tube power amplifiers The power amplifiers used for Hi-Fi appreciation can be divided into two categories: transistor power amplifiers and tube power amplifiers. In the past, there were Hi-Fi power amplifiers that used integrated circuits or module circuits.
There is no difference in merits between transistor power amplifiers and tube power amplifiers, but the applied devices are different (one is the transistor and the other is the tube). Because the two types of devices are different, their physical principles and circuit characteristics are also different. The electric current of the electron tube is formed by the attracting movement of electrons in the vacuum by the electric field force. The current of the transistor is formed by the outer electrons carried by the semiconductor burning at the position of the electric field force. This difference in physical rationale causes different circuit characteristics in practical applications. Relatively speaking, the working voltage of the tube power amplifier is high, but the working current is relatively small, while the working voltage of the transistor power amplifier is low, and the working current is relatively large.
The timbre of the tube power amplifier and the transistor power amplifier is indeed a certain difference, and the two have different responses to transient signals. This difference has been adapted to different types of music and different music viewers, so the current Hi-Fi amplifier has formed the coexistence of transistor amplifiers and tube amplifiers. However, in terms of brand, model, and quantity, the share of transistor power amplifiers is still absolutely greater than that of tube power amplifiers. The working state of the output stage transistors of the class A power amplifier and the class B power amplifier transistor can be divided into class A and class B. The so-called class A is simply to make the output stage transistors work in the linear region during the positive and negative half cycles of the sinusoidal AC signal, while the class B is to only make the output stage transistors in the positive half cycle (or negative half cycle) ) Work in the linear zone. Due to the different working states of the output stage transistors, the power utilization efficiency of the output stage (ie, the ratio of output power amplifier to power consumption) is also different. In a practical output circuit, the efficiency of category B is 2-3 times higher than that of category A. For example, Marantz PM80 transistor power amplifier, under certain power supply conditions, has an output power of 100W when working in category B, but only 20W in category A.
Class A amplifiers have no crossover distortion, and regardless of the actual output power, the internal resistance of the output stage crystal is constant. Class B amplifiers will always have a certain crossover distortion (although this distortion may be extremely small). In addition, the internal resistance of the output stage transistor is small when the output is large, but the internal resistance of the output stage transistor is relatively large when the output is small. . These differences make the sense of hearing different. The sound of Class A amplifiers is softer than that of Class B amplifiers. In addition, the low frequency control of the speakers is stronger than that of Class B amplifiers, especially at low volumes. The bass texture is better. These characteristics of the Class A amplifier make the Class A amplifier need not have a large output power margin in practical applications. A 20W-30W Class A amplifier can already drive most speakers very well.
As mentioned earlier, the power efficiency of the Class A power amplifier is low, which causes a large amount of heat to be emitted when the Class A power amplifier is working. In order to ensure that the operating temperature of the transistor does not exceed a certain limit, a heat sink with a larger volume and area is required, which makes the size and weight of the Class A power amplifier relatively large. For example, KRELL's KSD-50S Class A amplifier has an output of 50W + 50W and weighs nearly 30Kg. The Marantz PM-80 outputs 20W + 20W and 13Kg in weight.
Pure post-stage power amplifier and mono power amplifier Our common power amplifiers are preamplifiers (pre-stage) and power amplifiers (post-stage) that amplify small signals in a chassis. This kind of power amplifier is often called "merging" Amplifier ". The combined amplifier is easy to use and has a relatively good performance-price ratio. But this combined power amplifier has some inherent shortcomings, and the most difficult to overcome is the mutual interference between the pre-stage and the post-stage. In order to solve this problem, the front stage and the rear stage are made in two cabinets, so that there is a pure rear stage power amplifier. Most pure post-stage power amplifiers are two-channel structural forms, but this structural form makes the problem of mutual interference between the two channels not very easy to solve. In order to solve the interference between the two channels, there have been two Single channel pure power amplifier with separate channels.
The main meaning of separating power amplifiers like this is to improve the quality of the power amplifier, not to pursue this form. If the separation is only achieved in form, although the mutual interference problem can be solved, but other parameters have not been significantly improved, then this separation is still limited for the amplifier to improve the overall quality.
For most pure post-stage amplifiers and mono amplifiers, a pre-stage is required. (For an introduction to the previous level, please refer to the article "The Palette of Audio Equipment" in the fourth issue of this magazine this year). Since pure power amplifiers and mono power amplifiers appear to improve the quality of power amplifiers, the quality requirements of the front stage should also be adapted to them. The power amplifier is divided into a transistor and a tube, and the front stage is also divided into a transistor and a tube. For audio lovers and music lovers, there are a variety of combinations in the selection of pre-stage and post-stage, and different combinations have different sound characteristics, which gives users more room for choice. The front stage connected with the pure rear stage power amplifier has a greater impact on the quality of the entire audio system. First of all, it must have a certain quality, otherwise, the advantages of pure post or mono will not be exerted, and it may even highlight the "fault" of a poor pre-level, and the overall sound effect is worse. Furthermore, different pre- and post-levels have different timbre characteristics, and users can choose different combinations according to their personal preferences. For example, many audio and music lovers like to use the combination of "before the gallbladder and the back of the stone" (that is, the front stage of the tube and the rear stage of the transistor). Features, and also appreciate the sweet and mellow "smoothness" of the preamp of the tube. However, this combination is not a "golden rule", because the specific pre-level and post-level have their own characteristics, and the preference for tone varies from person to person, users can find their favorite combination according to the specific situation the way. How much output power should the Hi-Fi amplifier have? The output power of the Hi-Fi amplifier is affected by many factors. First, this output power has a greater relationship with the speaker that is connected, and secondly it is related to the quality of the amplifier. It is related to the environment used, that is, the volume of the room. The speaker has a parameter called sensitivity, and its unit is dB / m · W, which means the sound pressure (dB) generated 1m away from the speaker when the speaker gets 1W of electric power. If the sensitivity of a certain speaker is 90dB, then 1W of power is needed to get 90dB of sound pressure at 1m. To get 100dB of sound pressure, it needs 10W of power to push. But if the sensitivity of the speaker is 80dB (such as ATC's SCM-10), to achieve a sound pressure of 100dB, 100W of power is required to drive it. The sensitivity of most speakers is about 85dB-90dB. For these speakers, 10W-30W of undistorted power can already have enough sound pressure.
The quality of the power amplifier has a great relationship with the output power that the power amplifier should have. One of the parameters of the power amplifier is called the damping coefficient, which is a parameter that represents the control ability of the speaker, but this parameter has a moderate range and is directly related to the specific speaker. In general, if the quality of a power amplifier is very good, it can still maintain its performance parameters at a certain level at 30W output. Then there is no need to ask the amplifier to have a greater power output. However, if the quality of the power amplifier is not ideal, it will cause the deterioration of its performance parameters when the output power increases, then the output power of the power amplifier should have a certain margin to ensure that there are still certain good parameters under the practical output power . Normally, when the power amplifier is a Class A output or a tube power amplifier, there is no need to have too much output power margin, and the output power of 20W-30W is enough. But if it is a Class B power amplifier or a power amplifier with poor quality, then the output power of the power amplifier should have a large margin. In addition, if the matched speaker is a large inverter type, the power amplifier should also have a larger output power margin. When considering the output power due to the power amplifier from the quality of the power amplifier, choosing a larger power margin can indeed improve the adaptation between the power amplifier and the speaker. But here we still have to make it clear that the main significance of choosing a power amplifier with a larger output power is not because we need such a large sound pressure, but to improve the adaptation state of the power amplifier to the speaker. If a power amplifier with moderate output power is already able to control the speakers, then there is no need to put forward higher output power requirements for this power amplifier. The use environment, that is, the space volume of the room has a certain relationship with the power that the amplifier should output. The output power we have discussed above is based on the room volume below 40. If the room volume is large, Then the output power of the power amplifier should be increased.
The characteristics of the output stage of the tube power amplifier There are three circuit types for the power output stage of the tube power amplifier. One type is the push-pull output circuit with an output transformer. This type of output circuit accounts for the vast majority of tube power amplifiers. The output transformer in the push-pull circuit has few DC components, and the second harmonic distortion is also very small. The output power of this type of circuit can be made larger, so the scope of application is also relatively large. Generally speaking, for audio enthusiasts who are interested in the sound of the amplifier, this type of output stage amplifier is very suitable. However, for this type of power amplifier, the design and process of the output transformer are crucial. If the design and process of the output transformer are inadequate, the frequency response and transient response of this type of power amplifier are often not ideal. In addition, due to the constraints of the output transformer, the adaptation range of the matching speaker is relatively small.
Another type of circuit for the power output stage is a single-ended Class A circuit. This type of circuit also has a transformer, but the output transformer of this type of circuit has a large DC component, and the requirements for the output transformer are higher than those for the output transformer in the push-pull output circuit. In addition, the requirements for power supply are relatively high. The characteristic of this type of output circuit is that there are many second harmonic components. Although this is a kind of harmonic distortion, for music signals, the second harmonic is a highly harmonious sound, so it sounds very ear. This feature makes the power of this output circuit very distinctive in the timbre of the sound, especially when the power amplifier stage uses a triode, the human voice sounds very sweet, and the string music in the chamber music also sounds delicate, or, The sound of this type of power amplifier is very tasteful. However, the output power of this type of power amplifier is not easy to be large, so if the sensitivity of the matched speaker is low, it will be more reluctant when broadcasting large orchestral music. This kind of tube amplifier is very popular with some audio players. In addition to a high-power transistor amplifier, there is another such amplifier. I think it is complementary to the sound, but this also shows that this type of amplifier The timbre characteristics are really touching.
There is also a class of output stage circuits for tube power amplifiers, which is an OTL circuit. The so-called OTL circuit is a non-output transformer circuit. Modern transistor power amplifier output stages are almost all OTL circuits or improved versions of OTL circuits. The characteristic parameters of the tube and the transistor are different from the working state. The transistor amplifier is easily suitable for speakers with an impedance of 4-8, and it takes a lot of trouble for the tube amplifier to adapt to the 4-8 speaker without an output transformer. Because the output transformer is removed from the OTL power amplifier of the electronic tube, the technical parameters are greatly improved compared to the two types of circuits mentioned above. The power amplifier sound of this type of output circuit is very distinctive. It has a magnificent momentum and a wide sound field. Compared with the transistor amplifier, its tone is warm and delicate. Since this type of power amplifier has no output transformer, it can adapt to a wide range of speaker impedances. However, the power efficiency of this type of output stage power amplifier is low, and the design, process, and debugging are relatively complicated. At present, the power amplifier of this type of output circuit is only found in some high-end models.
What PCB designer Must Know About Impedance Control PCB
Controlled Impedance PCB Meaning
Impedance control has been one of the essential concerns and tough problems in high-speed PCB design. Impedance is the sum of the resistance and reactance of an electrical circuit. The resistance being the opposition to current flow present in all materials. In high frequency applications, controlled impedance helps us ensure that signals are not degraded as they route around a PCB. Resistance and reactance of an electrical circuit have a major impact on functionality, as certain processes must be completed before others to ensure proper operation.
Because of complex processors, USB devices and antennas are printed directly on the circuit board surface. The speed of signal switching on the circuit board increases, and the electrical characteristics of the tracks that transmit signals between devices become more and more important. Therefore, more and more PCB designs need impedance control and testing.
Impedance control technologies are quite important in high-speed digital circuit design in which effective methods must be adopted to ensure the excellent performance of high-speed PCB. The impedance of a PCB is largely determined by some factors, such as trace width, copper thickness, dielectric thickness, dielectric constant. Impedance, generally measured in Ohms. We must control the resistance and reactance of an electrical circuit to ensure the quality of signal in the complex design. For example single-ended impedance 50 ohm ±10%, differential impedance 100ohm ±10%.
When to Use Controlled Impedance
When a signal must have a particular impedance in order to function properly, controlled impedance should be used. In high frequency applications matching the impedance of PCB traces is important in maintaining data integrity and signal clarity. If the impedance of the PCB trace connecting two components does not match the components` characteristic impedance, there may be increased switching times within the device or the circuit. There may also be random errors.
Please note that we also need special instructions here:In DC circuits there is no reactance and the resistance of copper conductors is typically insignificant. However in high speed AC circuits (those with sharp changes in voltage and/or current) the reactance and thus the impedance can become very significant. This can become critical to a design's functionality because of the effects that changes in the impedance along the signals path from transmitter to receiver will have on the efficiency of power transfer as well as signal integrity. While a circuit`s speed is often expressed as the frequency of the wave form: the critical concern is the speed at which the voltage and/or current is required to change.
What Determines Controlled Impedance?
The characteristic impedance of a PCB trace is typically determined by its inductive and capacitive reactance, resistance, and conductance. These factors are a function of the physical dimensions of the trace, the dielectric constant of the PCB substrate material, and dielectric thickness. Typically PCB trace impedance can range from 25 to 125 ohms. The impedance value generated from the PCB structure will be determined by the following factors:
– Width and thickness of the copper signal trace (top and bottom)
– Thickness of the core or prepreg material on either side of the copper trace
– Dielectric constant of the core and prepreg material
– Distance from other copper features
Impedance Control In PCB Design
Electrical Impedance: A measure of opposition to time-varying electric current in an electric circuit.
The Problem: "A", "B" and "C" signals all reach the component at the same time.
The Solution: Apply Impedance to Circuit "C" to slow the signal enough for the component to first calculate ("A"+B").
Similar with a cable, the signal encounters a change of impedance arising from a change in material or geometry. Part of the signal will be reflected and part transmitted. These reflections are likely to cause aberrations on the signal which may degrade circuit performance (e.g. low gain, noise and random errors). In practice, board designers will specify impedance values and tolerances for board traces and rely on the PCB manufacturer to conform to the specification.
When rise times continue to reduce, inevitability the number of traces requiring impedance control will continue to increase. Where impedance control is needed it is important to control it accurately, calculating it with the most representative cross-section we can create.
Applications of Controlled Impedance
Controlled Impedance should be considered for PCBs used in fast digital applications such as:
– Telecommunications
– Computing 100MHz and above
– High Quality Analog Video
– Signal Processing
– RF Communication
Impedance Control PCB Manufacturing
In order to meet the growing demand of impedance control PCB, PCB manufacturers have invested a lot of money and manpower and material resources in production technology, in order to meet the production requirements of customers.
Due to the difficulty of impedance control PCB production, PCB manufacturers generally require PCB designers or purchasers to provide more detailed information and requirements, such as the type of material required, copper weight and thickness of the board, the number of layers, gerber file, so that the manufacturer can prepare the bill of materials (BOM). Impedance information should be clearly marked in Gerber file. If the necessary information is lacking, even a little key information will make it difficult or impossible for the manufacturer's engineers to know exactly what the customer needs.
Impedance-controlled PCBs are also divided into three different situations:
No Impedance Control: This is a situation where you do not need any extra design elements to ensure correct impedance because you have very loose impedance tolerance. Naturally, this will result in a faster-completed, less expensive board because the manufacturer does not have to include any special measures.
Impedance Watching: What is impedance watching? This is a situation where the designer will outline the impedance control trace and the PCB provider adjusts the trace width and dielectric height accordingly. Once the manufacturer approves these specifications, they can begin to manufacture the board. You can request a Time Domain Reflectometry (TDR) test to confirm the impedance for a fee.
Impedance Control: Actual impedance control is something you will typically only request when your design has tight impedance tolerances that could be tough to hit the first time around. When the capability limits of the manufacturer get close to the dimension requirements, it can be tough to ensure target impedance on the initial attempt.
In the case of impedance control, the manufacturer makes the circuit board achieve the target impedance as far as possible. Then they tested TDR to see if they succeeded. If not, they adjust accordingly and try again until they reach the required impedance.
Impedance Control PCB Fabricator
Impedance Control PCB is too complicated? No worry! JHY PCB engineers can help you at any time as we have three shifts. Free stack-up and impedance calculations can be offered upon request. We will work with your engineering team at the conceptual level of the PCB design to assist you to get better results in controlling impedance by choosing the suitable laminate and layer stack up.
Why Impedance Control PCB can be shipped timely all the time? As common materials are stored well in JHY PCB warehouse regularly. We have heavy copper thickness, 2oz, 3oz or more. Odd copper thickness H/1 oz, H/2 oz, 1/2 oz. Foil: 1/4 oz, H oz, 1 oz, 2 oz, 3 oz.
If you need order Impedance Control PCB, just make notes in Readme file, and send it together with Gerber, our engineer will take care of it. Have a try!
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