There are three main technical indicators of the power amplifier: frequency characteristics, rated output power, and distortion. This paper provides a measurement method for the above three technical indicators from the perspective of quantification.
First, the preparation work before the measurement
1. Equipped with the necessary instrumentation. Mainly: one XD2 audio signal generator; two DA-16 audio millivoltmeters; one SB-10 ordinary oscilloscope; one BS-1 distortion measuring instrument.
2. The output terminal of the amplifier is not connected to the speaker, and the dummy load resistor Rf is changed. The resistance of the resistor is the same as the output impedance Z of the power amplifier . The power of the resistor should be greater than or equal to 3 times of the rated output power of the amplifier (checked from the manual). For the power amplifier with the voltage indicated on the output terminal, the output impedance of the corresponding terminal can be obtained by Z=U2o/Po. Uo is the output voltage (V), Po is the rated output power (W), and Z is the impedance (Ω).
3. All instruments and equipment should be supplied according to the rated supply voltage (usually 220V/50Hz) to ensure measurement accuracy. If the grid voltage is unstable, an AC voltage regulator should be added.
4. The output impedance of the audio signal generator should be less than or equal to the input impedance of the power amplifier under test to prevent the power input impedance from being too small to affect the frequency stability of the input signal.
Second, the measurement of frequency characteristics
It refers to a frequency characteristic amplifier amplifier circuit amplification characteristic for different audio frequencies, in the range between 20 ~ 20000Hz, preferably all frequencies within the amplifier respond exactly the same range of amplification. If the power is input to the audio signal of different frequencies and the output voltage is relatively consistent, the frequency characteristics are stable. The non-uniformity of the frequency characteristics is expressed in dB, which is expressed in logarithmic form of the ratio of the output voltage to the output voltage at other frequencies at a frequency of 1000 Hz, that is, the relative level of the signal at a frequency of f Hz is: f Hz level ( dB)=20 log?f Hz output voltage / 1 kHz output voltage. There is no doubt that the reference level of the 1000 Hz signal is 0 dB. For the power amplifier , in the frequency range of 20 to 20000 Hz, the relative level of all frequencies should be between ±1dB and ±3dB. The smaller the absolute value of the relative level, the better the frequency characteristics of the power amplifier and the smaller the frequency distortion.
1. The measurement circuit is shown in Figure 1. mV is the audio millivoltmeter, RL is the dummy load resistor, and Ui and Uo are the input and output signal voltages, respectively.
2. Measurement process. First adjust the audio signal generator to 1000Hz. If the signal is input from the “microphone†port of the power amplifier , Ui=0.35mV; when the signal is sent from the “line input†port, Ui=775mV.
Adjust the amplifier volume button so that the output voltage is 70% of the rated output voltage (50% of the rated power). Keep the volume button fixed during the measurement.
In the range of 20 to 20000 Hz, change the input frequency of the signal generator from low to high (maintain Ui unchanged), record the output voltage Uo of the power amplifier point by point from tens of Hz to several hundred Hz, and fill in the corresponding table 1 Grid.
Substituting the input voltage Ui into the formula: f Hz level (dB) = 20 log f Hz output voltage / 1 kHz output voltage, find the relative level of all test frequency points, fill in the corresponding grid of Table 1.
Draw a frequency characteristic curve. On the logarithmic coordinate paper, according to the correspondence between the "relative level" data calculated in Table 1 and the input frequency, the frequency characteristic curve is made line by point. The curve reflects the frequency response characteristics of the power amplifier under test. The flatter and straighter it is, the better the frequency characteristics are.
Third, the measurement of rated output power
The rated power is also called the nominal power. It is determined by a certain degree of distortion when rated power supply voltage and rated input signal level. These are indicated in the operating instructions of the amplifier , and should be used in the use and measurement. For example, if a power amplifier has a rated output power of 100W, it is measured with a distortion of ≤ 3%. If the allowable distortion is increased, the output power can also be increased accordingly. Therefore, among the amplifier power values ​​promoted by the manufacturer, the rated power is the most accurate and most realistic representation method.
1. The measurement circuit is shown in Figure 2. The oscilloscope is used to monitor waveform distortion. The other is the same as Figure 1.
2. Measurement process. A 0.775V (0dB) 1000Hz sinusoidal signal is output from the audio signal generator and sent to the "line input" port of the power amplifier ; or a 0.35mV (-67dB) 1000Hz sinusoidal signal is output by the audio signal generator. The "microphone" port of the amplifier . Slowly turn on the corresponding volume knob of the large amplifier and observe that the output waveform of the oscilloscope is just not distorted, stop adjusting the volume button. The Uo data is known from the output voltage meter. Then, the rated output power P is obtained by the formula P=U2o/RL. If the P value is greater than or equal to the P value in the specification, it means that it meets the requirements. Of course, on this basis, the volume button of the power amplifier is turned on to the maximum, and the output power can also be increased, that is, the maximum output power.
Fourth, the measurement of distortion
When the audio signal passes through the power amplifier , the waveform of the output signal and the input signal are not exactly the same, which is called distortion.
The degree of distortion is usually described by the distortion coefficient. That is, the ratio of the effective value of each harmonic synthesis voltage in the output signal to the effective value of the fundamental voltage is expressed, and the value is directly read by the distortion tester.
1. The measuring circuit is shown in Figure 3. When measuring, the outer casing of all test instruments should be grounded to prevent other interferences from affecting the measurement accuracy.
2. Measurement process. The measuring method of the rated output power of the amplifier from the input feed respectively 20Hz, 100Hz, 1000Hz, 5000Hz, 10000Hz, 15000Hz , etc. sinusoidal signals of different frequencies, will be sequentially transferred to the amplifier rated output power value, and to adjust the distortion of the instrument were measured The distortion coefficient of each frequency point is obtained. It is generally compared with the data of other frequency points based on the distortion coefficient of 1000 Hz. The difference is large, indicating that the distortion of the power in the entire audio segment is not balanced. The difference is small, indicating that the distortion of the power amplifier in the entire audio segment is relatively balanced.
There are three main technical indicators of the power amplifier: frequency characteristics, rated output power, and distortion. This paper provides a measurement method for the above three technical indicators from the perspective of quantification.
First, the preparation work before the measurement
1. Equipped with the necessary instrumentation. Mainly: one XD2 audio signal generator; two DA-16 audio millivoltmeters; one SB-10 ordinary oscilloscope; one BS-1 distortion measuring instrument.
2. The output terminal of the amplifier is not connected to the speaker, and the dummy load resistor Rf is changed. The resistance of the resistor is the same as the output impedance Z of the power amplifier . The power of the resistor should be greater than or equal to 3 times of the rated output power of the amplifier (checked from the manual). For the power amplifier with the voltage indicated on the output terminal, the output impedance of the corresponding terminal can be obtained by Z=U2o/Po. Uo is the output voltage (V), Po is the rated output power (W), and Z is the impedance (Ω).
3. All instruments and equipment should be supplied according to the rated supply voltage (usually 220V/50Hz) to ensure measurement accuracy. If the grid voltage is unstable, an AC voltage regulator should be added.
4. The output impedance of the audio signal generator should be less than or equal to the input impedance of the power amplifier under test to prevent the power input impedance from being too small to affect the frequency stability of the input signal.
Second, the measurement of frequency characteristics
It refers to a frequency characteristic amplifier amplifier circuit amplification characteristic for different audio frequencies, in the range between 20 ~ 20000Hz, preferably all frequencies within the amplifier respond exactly the same range of amplification. If the power is input to the audio signal of different frequencies and the output voltage is relatively consistent, the frequency characteristics are stable. The non-uniformity of the frequency characteristics is expressed in dB, which is expressed in logarithmic form of the ratio of the output voltage to the output voltage at other frequencies at a frequency of 1000 Hz, that is, the relative level of the signal at a frequency of f Hz is: f Hz level ( dB)=20 log?f Hz output voltage / 1 kHz output voltage. There is no doubt that the reference level of the 1000 Hz signal is 0 dB. For the power amplifier , in the frequency range of 20 to 20000 Hz, the relative level of all frequencies should be between ±1dB and ±3dB. The smaller the absolute value of the relative level, the better the frequency characteristics of the power amplifier and the smaller the frequency distortion.
1. The measurement circuit is shown in Figure 1. mV is the audio millivoltmeter, RL is the dummy load resistor, and Ui and Uo are the input and output signal voltages, respectively.
2. Measurement process. First adjust the audio signal generator to 1000Hz. If the signal is input from the “microphone†port of the power amplifier , Ui=0.35mV; when the signal is sent from the “line input†port, Ui=775mV.
Adjust the amplifier volume button so that the output voltage is 70% of the rated output voltage (50% of the rated power). Keep the volume button fixed during the measurement.
In the range of 20 to 20000 Hz, change the input frequency of the signal generator from low to high (maintain Ui unchanged), record the output voltage Uo of the power amplifier point by point from tens of Hz to several hundred Hz, and fill in the corresponding table 1 Grid.
Substituting the input voltage Ui into the formula: f Hz level (dB) = 20 log f Hz output voltage / 1 kHz output voltage, find the relative level of all test frequency points, fill in the corresponding grid of Table 1.
Draw a frequency characteristic curve. On the logarithmic coordinate paper, according to the correspondence between the "relative level" data calculated in Table 1 and the input frequency, the frequency characteristic curve is made line by point. The curve reflects the frequency response characteristics of the power amplifier under test. The flatter and straighter it is, the better the frequency characteristics are.
Third, the measurement of rated output power
The rated power is also called the nominal power. It is determined by a certain degree of distortion when rated power supply voltage and rated input signal level. These are indicated in the operating instructions of the amplifier , and should be used in the use and measurement. For example, if a power amplifier has a rated output power of 100W, it is measured with a distortion of ≤ 3%. If the allowable distortion is increased, the output power can also be increased accordingly. Therefore, among the amplifier power values ​​promoted by the manufacturer, the rated power is the most accurate and most realistic representation method.
1. The measurement circuit is shown in Figure 2. The oscilloscope is used to monitor waveform distortion. The other is the same as Figure 1.
2. Measurement process. A 0.775V (0dB) 1000Hz sinusoidal signal is output from the audio signal generator and sent to the "line input" port of the power amplifier ; or a 0.35mV (-67dB) 1000Hz sinusoidal signal is output by the audio signal generator. The "microphone" port of the amplifier . Slowly turn on the corresponding volume knob of the large amplifier and observe that the output waveform of the oscilloscope is just not distorted, stop adjusting the volume button. The Uo data is known from the output voltage meter. Then, the rated output power P is obtained by the formula P=U2o/RL. If the P value is greater than or equal to the P value in the specification, it means that it meets the requirements. Of course, on this basis, the volume button of the power amplifier is turned on to the maximum, and the output power can also be increased, that is, the maximum output power.
Fourth, the measurement of distortion
When the audio signal passes through the power amplifier , the waveform of the output signal and the input signal are not exactly the same, which is called distortion.
The degree of distortion is usually described by the distortion coefficient. That is, the ratio of the effective value of each harmonic synthesis voltage in the output signal to the effective value of the fundamental voltage is expressed, and the value is directly read by the distortion tester.
1. The measuring circuit is shown in Figure 3. When measuring, the outer casing of all test instruments should be grounded to prevent other interferences from affecting the measurement accuracy.
2. Measurement process. The measuring method of the rated output power of the amplifier from the input feed respectively 20Hz, 100Hz, 1000Hz, 5000Hz, 10000Hz, 15000Hz , etc. sinusoidal signals of different frequencies, will be sequentially transferred to the amplifier rated output power value, and to adjust the distortion of the instrument were measured The distortion coefficient of each frequency point is obtained. It is generally compared with the data of other frequency points based on the distortion coefficient of 1000 Hz. The difference is large, indicating that the distortion of the power in the entire audio segment is not balanced. The difference is small, indicating that the distortion of the power amplifier in the entire audio segment is relatively balanced.
There are three main technical indicators of the power amplifier: frequency characteristics, rated output power, and distortion. This paper provides a measurement method for the above three technical indicators from the perspective of quantification.
First, the preparation work before the measurement
1. Equipped with the necessary instrumentation. Mainly: one XD2 audio signal generator; two DA-16 audio millivoltmeters; one SB-10 ordinary oscilloscope; one BS-1 distortion measuring instrument.
2. The output terminal of the amplifier is not connected to the speaker, and the dummy load resistor Rf is changed. The resistance of the resistor is the same as the output impedance Z of the power amplifier . The power of the resistor should be greater than or equal to 3 times of the rated output power of the amplifier (checked from the manual). For the power amplifier with the voltage indicated on the output terminal, the output impedance of the corresponding terminal can be obtained by Z=U2o/Po. Uo is the output voltage (V), Po is the rated output power (W), and Z is the impedance (Ω).
3. All instruments and equipment should be supplied according to the rated supply voltage (usually 220V/50Hz) to ensure measurement accuracy. If the grid voltage is unstable, an AC voltage regulator should be added.
4. The output impedance of the audio signal generator should be less than or equal to the input impedance of the power amplifier under test to prevent the power input impedance from being too small to affect the frequency stability of the input signal.
Second, the measurement of frequency characteristics
It refers to a frequency characteristic amplifier amplifier circuit amplification characteristic for different audio frequencies, in the range between 20 ~ 20000Hz, preferably all frequencies within the amplifier respond exactly the same range of amplification. If the power is input to the audio signal of different frequencies and the output voltage is relatively consistent, the frequency characteristics are stable. The non-uniformity of the frequency characteristics is expressed in dB, which is expressed in logarithmic form of the ratio of the output voltage to the output voltage at other frequencies at a frequency of 1000 Hz, that is, the relative level of the signal at a frequency of f Hz is: f Hz level ( dB)=20 log?f Hz output voltage / 1 kHz output voltage. There is no doubt that the reference level of the 1000 Hz signal is 0 dB. For the power amplifier , in the frequency range of 20 to 20000 Hz, the relative level of all frequencies should be between ±1dB and ±3dB. The smaller the absolute value of the relative level, the better the frequency characteristics of the power amplifier and the smaller the frequency distortion.
1. The measurement circuit is shown in Figure 1. mV is the audio millivoltmeter, RL is the dummy load resistor, and Ui and Uo are the input and output signal voltages, respectively.
2. Measurement process. First adjust the audio signal generator to 1000Hz. If the signal is input from the “microphone†port of the power amplifier , Ui=0.35mV; when the signal is sent from the “line input†port, Ui=775mV.
Adjust the amplifier volume button so that the output voltage is 70% of the rated output voltage (50% of the rated power). Keep the volume button fixed during the measurement.
In the range of 20 to 20000 Hz, change the input frequency of the signal generator from low to high (maintain Ui unchanged), record the output voltage Uo of the power amplifier point by point from tens of Hz to several hundred Hz, and fill in the corresponding table 1 Grid.
Substituting the input voltage Ui into the formula: f Hz level (dB) = 20 log f Hz output voltage / 1 kHz output voltage, find the relative level of all test frequency points, fill in the corresponding grid of Table 1.
Draw a frequency characteristic curve. On the logarithmic coordinate paper, according to the correspondence between the "relative level" data calculated in Table 1 and the input frequency, the frequency characteristic curve is made line by point. The curve reflects the frequency response characteristics of the power amplifier under test. The flatter and straighter it is, the better the frequency characteristics are.
Third, the measurement of rated output power
The rated power is also called the nominal power. It is determined by a certain degree of distortion when rated power supply voltage and rated input signal level. These are indicated in the operating instructions of the amplifier , and should be used in the use and measurement. For example, if a power amplifier has a rated output power of 100W, it is measured with a distortion of ≤ 3%. If the allowable distortion is increased, the output power can also be increased accordingly. Therefore, among the amplifier power values ​​promoted by the manufacturer, the rated power is the most accurate and most realistic representation method.
1. The measurement circuit is shown in Figure 2. The oscilloscope is used to monitor waveform distortion. The other is the same as Figure 1.
2. Measurement process. A 0.775V (0dB) 1000Hz sinusoidal signal is output from the audio signal generator and sent to the "line input" port of the power amplifier ; or a 0.35mV (-67dB) 1000Hz sinusoidal signal is output by the audio signal generator. The "microphone" port of the amplifier . Slowly turn on the corresponding volume knob of the large amplifier and observe that the output waveform of the oscilloscope is just not distorted, stop adjusting the volume button. The Uo data is known from the output voltage meter. Then, the rated output power P is obtained by the formula P=U2o/RL. If the P value is greater than or equal to the P value in the specification, it means that it meets the requirements. Of course, on this basis, the volume button of the power amplifier is turned on to the maximum, and the output power can also be increased, that is, the maximum output power.
Fourth, the measurement of distortion
When the audio signal passes through the power amplifier , the waveform of the output signal and the input signal are not exactly the same, which is called distortion.
The degree of distortion is usually described by the distortion coefficient. That is, the ratio of the effective value of each harmonic synthesis voltage in the output signal to the effective value of the fundamental voltage is expressed, and the value is directly read by the distortion tester.
1. The measuring circuit is shown in Figure 3. When measuring, the outer casing of all test instruments should be grounded to prevent other interferences from affecting the measurement accuracy.
2. Measurement process. The measuring method of the rated output power of the amplifier from the input feed respectively 20Hz, 100Hz, 1000Hz, 5000Hz, 10000Hz, 15000Hz , etc. sinusoidal signals of different frequencies, will be sequentially transferred to the amplifier rated output power value, and to adjust the distortion of the instrument were measured The distortion coefficient of each frequency point is obtained. It is generally compared with the data of other frequency points based on the distortion coefficient of 1000 Hz. The difference is large, indicating that the distortion of the power in the entire audio segment is not balanced. The difference is small, indicating that the distortion of the power amplifier in the entire audio segment is relatively balanced.
First, the preparation work before the measurement
1. Equipped with the necessary instrumentation. Mainly: one XD2 audio signal generator; two DA-16 audio millivoltmeters; one SB-10 ordinary oscilloscope; one BS-1 distortion measuring instrument.
2. The output terminal of the amplifier is not connected to the speaker, and the dummy load resistor Rf is changed. The resistance of the resistor is the same as the output impedance Z of the power amplifier . The power of the resistor should be greater than or equal to 3 times of the rated output power of the amplifier (checked from the manual). For the power amplifier with the voltage indicated on the output terminal, the output impedance of the corresponding terminal can be obtained by Z=U2o/Po. Uo is the output voltage (V), Po is the rated output power (W), and Z is the impedance (Ω).
3. All instruments and equipment should be supplied according to the rated supply voltage (usually 220V/50Hz) to ensure measurement accuracy. If the grid voltage is unstable, an AC voltage regulator should be added.
4. The output impedance of the audio signal generator should be less than or equal to the input impedance of the power amplifier under test to prevent the power input impedance from being too small to affect the frequency stability of the input signal.
Second, the measurement of frequency characteristics
It refers to a frequency characteristic amplifier amplifier circuit amplification characteristic for different audio frequencies, in the range between 20 ~ 20000Hz, preferably all frequencies within the amplifier respond exactly the same range of amplification. If the power is input to the audio signal of different frequencies and the output voltage is relatively consistent, the frequency characteristics are stable. The non-uniformity of the frequency characteristics is expressed in dB, which is expressed in logarithmic form of the ratio of the output voltage to the output voltage at other frequencies at a frequency of 1000 Hz, that is, the relative level of the signal at a frequency of f Hz is: f Hz level ( dB)=20 log?f Hz output voltage / 1 kHz output voltage. There is no doubt that the reference level of the 1000 Hz signal is 0 dB. For the power amplifier , in the frequency range of 20 to 20000 Hz, the relative level of all frequencies should be between ±1dB and ±3dB. The smaller the absolute value of the relative level, the better the frequency characteristics of the power amplifier and the smaller the frequency distortion.
1. The measurement circuit is shown in Figure 1. mV is the audio millivoltmeter, RL is the dummy load resistor, and Ui and Uo are the input and output signal voltages, respectively.
2. Measurement process. First adjust the audio signal generator to 1000Hz. If the signal is input from the “microphone†port of the power amplifier , Ui=0.35mV; when the signal is sent from the “line input†port, Ui=775mV.
Adjust the amplifier volume button so that the output voltage is 70% of the rated output voltage (50% of the rated power). Keep the volume button fixed during the measurement.
In the range of 20 to 20000 Hz, change the input frequency of the signal generator from low to high (maintain Ui unchanged), record the output voltage Uo of the power amplifier point by point from tens of Hz to several hundred Hz, and fill in the corresponding table 1 Grid.
Substituting the input voltage Ui into the formula: f Hz level (dB) = 20 log f Hz output voltage / 1 kHz output voltage, find the relative level of all test frequency points, fill in the corresponding grid of Table 1.
Draw a frequency characteristic curve. On the logarithmic coordinate paper, according to the correspondence between the "relative level" data calculated in Table 1 and the input frequency, the frequency characteristic curve is made line by point. The curve reflects the frequency response characteristics of the power amplifier under test. The flatter and straighter it is, the better the frequency characteristics are.
Third, the measurement of rated output power
The rated power is also called the nominal power. It is determined by a certain degree of distortion when rated power supply voltage and rated input signal level. These are indicated in the operating instructions of the amplifier , and should be used in the use and measurement. For example, if a power amplifier has a rated output power of 100W, it is measured with a distortion of ≤ 3%. If the allowable distortion is increased, the output power can also be increased accordingly. Therefore, among the amplifier power values ​​promoted by the manufacturer, the rated power is the most accurate and most realistic representation method.
1. The measurement circuit is shown in Figure 2. The oscilloscope is used to monitor waveform distortion. The other is the same as Figure 1.
2. Measurement process. A 0.775V (0dB) 1000Hz sinusoidal signal is output from the audio signal generator and sent to the "line input" port of the power amplifier ; or a 0.35mV (-67dB) 1000Hz sinusoidal signal is output by the audio signal generator. The "microphone" port of the amplifier . Slowly turn on the corresponding volume knob of the large amplifier and observe that the output waveform of the oscilloscope is just not distorted, stop adjusting the volume button. The Uo data is known from the output voltage meter. Then, the rated output power P is obtained by the formula P=U2o/RL. If the P value is greater than or equal to the P value in the specification, it means that it meets the requirements. Of course, on this basis, the volume button of the power amplifier is turned on to the maximum, and the output power can also be increased, that is, the maximum output power.
Fourth, the measurement of distortion
When the audio signal passes through the power amplifier , the waveform of the output signal and the input signal are not exactly the same, which is called distortion.
The degree of distortion is usually described by the distortion coefficient. That is, the ratio of the effective value of each harmonic synthesis voltage in the output signal to the effective value of the fundamental voltage is expressed, and the value is directly read by the distortion tester.
1. The measuring circuit is shown in Figure 3. When measuring, the outer casing of all test instruments should be grounded to prevent other interferences from affecting the measurement accuracy.
2. Measurement process. The measuring method of the rated output power of the amplifier from the input feed respectively 20Hz, 100Hz, 1000Hz, 5000Hz, 10000Hz, 15000Hz , etc. sinusoidal signals of different frequencies, will be sequentially transferred to the amplifier rated output power value, and to adjust the distortion of the instrument were measured The distortion coefficient of each frequency point is obtained. It is generally compared with the data of other frequency points based on the distortion coefficient of 1000 Hz. The difference is large, indicating that the distortion of the power in the entire audio segment is not balanced. The difference is small, indicating that the distortion of the power amplifier in the entire audio segment is relatively balanced.
There are three main technical indicators of the power amplifier: frequency characteristics, rated output power, and distortion. This paper provides a measurement method for the above three technical indicators from the perspective of quantification.
First, the preparation work before the measurement
1. Equipped with the necessary instrumentation. Mainly: one XD2 audio signal generator; two DA-16 audio millivoltmeters; one SB-10 ordinary oscilloscope; one BS-1 distortion measuring instrument.
2. The output terminal of the amplifier is not connected to the speaker, and the dummy load resistor Rf is changed. The resistance of the resistor is the same as the output impedance Z of the power amplifier . The power of the resistor should be greater than or equal to 3 times of the rated output power of the amplifier (checked from the manual). For the power amplifier with the voltage indicated on the output terminal, the output impedance of the corresponding terminal can be obtained by Z=U2o/Po. Uo is the output voltage (V), Po is the rated output power (W), and Z is the impedance (Ω).
3. All instruments and equipment should be supplied according to the rated supply voltage (usually 220V/50Hz) to ensure measurement accuracy. If the grid voltage is unstable, an AC voltage regulator should be added.
4. The output impedance of the audio signal generator should be less than or equal to the input impedance of the power amplifier under test to prevent the power input impedance from being too small to affect the frequency stability of the input signal.
Second, the measurement of frequency characteristics
It refers to a frequency characteristic amplifier amplifier circuit amplification characteristic for different audio frequencies, in the range between 20 ~ 20000Hz, preferably all frequencies within the amplifier respond exactly the same range of amplification. If the power is input to the audio signal of different frequencies and the output voltage is relatively consistent, the frequency characteristics are stable. The non-uniformity of the frequency characteristics is expressed in dB, which is expressed in logarithmic form of the ratio of the output voltage to the output voltage at other frequencies at a frequency of 1000 Hz, that is, the relative level of the signal at a frequency of f Hz is: f Hz level ( dB)=20 log?f Hz output voltage / 1 kHz output voltage. There is no doubt that the reference level of the 1000 Hz signal is 0 dB. For the power amplifier , in the frequency range of 20 to 20000 Hz, the relative level of all frequencies should be between ±1dB and ±3dB. The smaller the absolute value of the relative level, the better the frequency characteristics of the power amplifier and the smaller the frequency distortion.
1. The measurement circuit is shown in Figure 1. mV is the audio millivoltmeter, RL is the dummy load resistor, and Ui and Uo are the input and output signal voltages, respectively.
2. Measurement process. First adjust the audio signal generator to 1000Hz. If the signal is input from the “microphone†port of the power amplifier , Ui=0.35mV; when the signal is sent from the “line input†port, Ui=775mV.
Adjust the amplifier volume button so that the output voltage is 70% of the rated output voltage (50% of the rated power). Keep the volume button fixed during the measurement.
In the range of 20 to 20000 Hz, change the input frequency of the signal generator from low to high (maintain Ui unchanged), record the output voltage Uo of the power amplifier point by point from tens of Hz to several hundred Hz, and fill in the corresponding table 1 Grid.
Substituting the input voltage Ui into the formula: f Hz level (dB) = 20 log f Hz output voltage / 1 kHz output voltage, find the relative level of all test frequency points, fill in the corresponding grid of Table 1.
Draw a frequency characteristic curve. On the logarithmic coordinate paper, according to the correspondence between the "relative level" data calculated in Table 1 and the input frequency, the frequency characteristic curve is made line by point. The curve reflects the frequency response characteristics of the power amplifier under test. The flatter and straighter it is, the better the frequency characteristics are.
Third, the measurement of rated output power
The rated power is also called the nominal power. It is determined by a certain degree of distortion when rated power supply voltage and rated input signal level. These are indicated in the operating instructions of the amplifier , and should be used in the use and measurement. For example, if a power amplifier has a rated output power of 100W, it is measured with a distortion of ≤ 3%. If the allowable distortion is increased, the output power can also be increased accordingly. Therefore, among the amplifier power values ​​promoted by the manufacturer, the rated power is the most accurate and most realistic representation method.
1. The measurement circuit is shown in Figure 2. The oscilloscope is used to monitor waveform distortion. The other is the same as Figure 1.
2. Measurement process. A 0.775V (0dB) 1000Hz sinusoidal signal is output from the audio signal generator and sent to the "line input" port of the power amplifier ; or a 0.35mV (-67dB) 1000Hz sinusoidal signal is output by the audio signal generator. The "microphone" port of the amplifier . Slowly turn on the corresponding volume knob of the large amplifier and observe that the output waveform of the oscilloscope is just not distorted, stop adjusting the volume button. The Uo data is known from the output voltage meter. Then, the rated output power P is obtained by the formula P=U2o/RL. If the P value is greater than or equal to the P value in the specification, it means that it meets the requirements. Of course, on this basis, the volume button of the power amplifier is turned on to the maximum, and the output power can also be increased, that is, the maximum output power.
Fourth, the measurement of distortion
When the audio signal passes through the power amplifier , the waveform of the output signal and the input signal are not exactly the same, which is called distortion.
The degree of distortion is usually described by the distortion coefficient. That is, the ratio of the effective value of each harmonic synthesis voltage in the output signal to the effective value of the fundamental voltage is expressed, and the value is directly read by the distortion tester.
1. The measuring circuit is shown in Figure 3. When measuring, the outer casing of all test instruments should be grounded to prevent other interferences from affecting the measurement accuracy.
2. Measurement process. The measuring method of the rated output power of the amplifier from the input feed respectively 20Hz, 100Hz, 1000Hz, 5000Hz, 10000Hz, 15000Hz , etc. sinusoidal signals of different frequencies, will be sequentially transferred to the amplifier rated output power value, and to adjust the distortion of the instrument were measured The distortion coefficient of each frequency point is obtained. It is generally compared with the data of other frequency points based on the distortion coefficient of 1000 Hz. The difference is large, indicating that the distortion of the power in the entire audio segment is not balanced. The difference is small, indicating that the distortion of the power amplifier in the entire audio segment is relatively balanced.
There are three main technical indicators of the power amplifier: frequency characteristics, rated output power, and distortion. This paper provides a measurement method for the above three technical indicators from the perspective of quantification.
First, the preparation work before the measurement
1. Equipped with the necessary instrumentation. Mainly: one XD2 audio signal generator; two DA-16 audio millivoltmeters; one SB-10 ordinary oscilloscope; one BS-1 distortion measuring instrument.
2. The output terminal of the amplifier is not connected to the speaker, and the dummy load resistor Rf is changed. The resistance of the resistor is the same as the output impedance Z of the power amplifier . The power of the resistor should be greater than or equal to 3 times of the rated output power of the amplifier (checked from the manual). For the power amplifier with the voltage indicated on the output terminal, the output impedance of the corresponding terminal can be obtained by Z=U2o/Po. Uo is the output voltage (V), Po is the rated output power (W), and Z is the impedance (Ω).
3. All instruments and equipment should be supplied according to the rated supply voltage (usually 220V/50Hz) to ensure measurement accuracy. If the grid voltage is unstable, an AC voltage regulator should be added.
4. The output impedance of the audio signal generator should be less than or equal to the input impedance of the power amplifier under test to prevent the power input impedance from being too small to affect the frequency stability of the input signal.
Second, the measurement of frequency characteristics
It refers to a frequency characteristic amplifier amplifier circuit amplification characteristic for different audio frequencies, in the range between 20 ~ 20000Hz, preferably all frequencies within the amplifier respond exactly the same range of amplification. If the power is input to the audio signal of different frequencies and the output voltage is relatively consistent, the frequency characteristics are stable. The non-uniformity of the frequency characteristics is expressed in dB, which is expressed in logarithmic form of the ratio of the output voltage to the output voltage at other frequencies at a frequency of 1000 Hz, that is, the relative level of the signal at a frequency of f Hz is: f Hz level ( dB)=20 log?f Hz output voltage / 1 kHz output voltage. There is no doubt that the reference level of the 1000 Hz signal is 0 dB. For the power amplifier , in the frequency range of 20 to 20000 Hz, the relative level of all frequencies should be between ±1dB and ±3dB. The smaller the absolute value of the relative level, the better the frequency characteristics of the power amplifier and the smaller the frequency distortion.
1. The measurement circuit is shown in Figure 1. mV is the audio millivoltmeter, RL is the dummy load resistor, and Ui and Uo are the input and output signal voltages, respectively.
2. Measurement process. First adjust the audio signal generator to 1000Hz. If the signal is input from the “microphone†port of the power amplifier , Ui=0.35mV; when the signal is sent from the “line input†port, Ui=775mV.
Adjust the amplifier volume button so that the output voltage is 70% of the rated output voltage (50% of the rated power). Keep the volume button fixed during the measurement.
In the range of 20 to 20000 Hz, change the input frequency of the signal generator from low to high (maintain Ui unchanged), record the output voltage Uo of the power amplifier point by point from tens of Hz to several hundred Hz, and fill in the corresponding table 1 Grid.
Substituting the input voltage Ui into the formula: f Hz level (dB) = 20 log f Hz output voltage / 1 kHz output voltage, find the relative level of all test frequency points, fill in the corresponding grid of Table 1.
Draw a frequency characteristic curve. On the logarithmic coordinate paper, according to the correspondence between the "relative level" data calculated in Table 1 and the input frequency, the frequency characteristic curve is made line by point. The curve reflects the frequency response characteristics of the power amplifier under test. The flatter and straighter it is, the better the frequency characteristics are.
Third, the measurement of rated output power
The rated power is also called the nominal power. It is determined by a certain degree of distortion when rated power supply voltage and rated input signal level. These are indicated in the operating instructions of the amplifier , and should be used in the use and measurement. For example, if a power amplifier has a rated output power of 100W, it is measured with a distortion of ≤ 3%. If the allowable distortion is increased, the output power can also be increased accordingly. Therefore, among the amplifier power values ​​promoted by the manufacturer, the rated power is the most accurate and most realistic representation method.
1. The measurement circuit is shown in Figure 2. The oscilloscope is used to monitor waveform distortion. The other is the same as Figure 1.
2. Measurement process. A 0.775V (0dB) 1000Hz sinusoidal signal is output from the audio signal generator and sent to the "line input" port of the power amplifier ; or a 0.35mV (-67dB) 1000Hz sinusoidal signal is output by the audio signal generator. The "microphone" port of the amplifier . Slowly turn on the corresponding volume knob of the large amplifier and observe that the output waveform of the oscilloscope is just not distorted, stop adjusting the volume button. The Uo data is known from the output voltage meter. Then, the rated output power P is obtained by the formula P=U2o/RL. If the P value is greater than or equal to the P value in the specification, it means that it meets the requirements. Of course, on this basis, the volume button of the power amplifier is turned on to the maximum, and the output power can also be increased, that is, the maximum output power.
Fourth, the measurement of distortion
When the audio signal passes through the power amplifier , the waveform of the output signal and the input signal are not exactly the same, which is called distortion.
The degree of distortion is usually described by the distortion coefficient. That is, the ratio of the effective value of each harmonic synthesis voltage in the output signal to the effective value of the fundamental voltage is expressed, and the value is directly read by the distortion tester.
1. The measuring circuit is shown in Figure 3. When measuring, the outer casing of all test instruments should be grounded to prevent other interferences from affecting the measurement accuracy.
2. Measurement process. The measuring method of the rated output power of the amplifier from the input feed respectively 20Hz, 100Hz, 1000Hz, 5000Hz, 10000Hz, 15000Hz , etc. sinusoidal signals of different frequencies, will be sequentially transferred to the amplifier rated output power value, and to adjust the distortion of the instrument were measured The distortion coefficient of each frequency point is obtained. It is generally compared with the data of other frequency points based on the distortion coefficient of 1000 Hz. The difference is large, indicating that the distortion of the power in the entire audio segment is not balanced. The difference is small, indicating that the distortion of the power amplifier in the entire audio segment is relatively balanced.
Led display screen Control System
LED display screens can't work without controller. The controller works together with led display panel to get beautiful vision world.
LED Display Control system is made up of hardware and software components and it mainly contains the following parts:
LED Video Processor (Optional)
Sender card which is installed in the controlling PC
Receiver cards which are installed in each cabinet of LED display
Hub cards which are also installed in each cabinet of the LED display
Accessories like fiber optic converter, multi-function card, etc
The DVI signal comes from the sender card in the controlling computer and is then given to the receiver cards in the LED display cabinets. If the input signal is from any other device such as a camera, DVD player, etc, then it is captured by the sender card installed in a small device called a LED video processor which is then given to the receiver cards in the LED displays.
LED Display Controller,VD Wall LED Display Video Processor,Novastar Controller,Linsn Controller
Shenzhen Priva Tech Co., Ltd. , http://www.privaled.com