Common faults and repair methods of audio systems
Introduction: Common faults and repair methods of audio systems. There are various problems with the audio system. Don't rush to send it for repair. First, see if some of the audio system maintenance tips introduced here are useful. After passing my introduction, do you feel that you have mastered the relevant knowledge and skills?
Common faults and repair methods of audio systems
1. The sound of the speakers is abnormal
1. It is generally impossible for a speaker to burn out all the high, mid, and bass units at once. Therefore, if the speaker is silent, please first check whether there is a problem with the VOD, preamplifier, and power amplifier, and then check the speaker after confirmation.
2. The speaker makes an abnormal sound.
① Disassemble the box net, check whether there is air leakage in the box, and whether the unit is firmly installed on the box (sometimes the unit is not installed firmly, and the iron edge of the unit is in contact with the box during high-power and dynamic use. A strange sound of air leakage will occur when the body collides.) If each unit is installed firmly, listen carefully to determine which unit the abnormal sound is coming from.
② Remove the unit with abnormal sound, place the unit flat on the ground, and check whether the bubble edge is leaking and unglued, and whether the dust cap is unglued (usually the "bubble" sound is related to the above reasons). If there is no degumming or leakage, use your right fingers to make a triangular balance and naturally push the paper plate of the unit downwards (normal units should not make any noise when pushed downwards, while there should be no noise when the unit is pushed downwards, while scraping the edges, deforming the voice coil, etc. The unit will make abnormal noises. )
③If the unit is not installed firmly and makes noise, just reinstall it firmly. If the unit is soaked or the dust cap is deglued and leaking, use agricultural machinery glue (roadside glue). The glue used to repair leather shoes) can be sealed and repaired and allowed to dry naturally.
④ Check whether there is a foam rubber buffer strip at the contact point between the speaker mesh and the cabinet. If not, add a rubber strip to eliminate the noise.
⑤ If the speaker unit is burned out, it should be returned to the manufacturer for repair, because the voice coil and paper cone will affect the timbre. If the original voice coil and paper cone are not used, the timbre of the speaker will change.
2. Speaker inversion
In actual use, the sound feels good when one speaker is turned on, but after two speakers are turned on at the same time, the sound becomes dry and low volume. The energy is not multiplied, but the amount of energy becomes smaller or has no obvious enhancement. This phenomenon is due to the inversion of the speakers. It can be solved by the following methods.
1. Check whether the speaker cable at the output end of the power amplifier is connected correctly (the positive pole should be connected to the positive pole, the negative pole should be connected to the negative pole, generally the positive pole is red.), and then check whether the port where the speaker cable is connected to the speaker is connected correctly. , if the system connection error causes phase inversion, just restore the correct connection.
2. If the speaker unit is installed in reverse phase, disassemble the speaker and check whether the connecting wire of the bass unit is connected incorrectly. If so, just reconnect the two wires correctly. In addition, you can use a battery for polarity testing and touch the battery lightly with the speaker cable to see the direction of the speaker unit. After the positive and negative terminals of the speaker cable collide with the positive and negative terminals of the battery, if the woofer moves outward, the phase is normal. If the speaker shrinks inward, the phase is reversed.
3. In addition, if the speaker is installed in reverse phase, the simplest method is to reverse the positive and negative poles of the speaker cable of one speaker at the output end of the power amplifier.
3. The microphone makes "tiny" noise
1. Check whether the connecting wire (especially the ground wire) is desoldered or has poor contact. If so, just re-solder it.
2. Check whether the microphone cable is internally broken or has poor contact. If there is an internal break, the line should be replaced.
4. Audio and music are silent
1. Take a wired microphone and connect it to the M1C (microphone) input port of the integrated power amplifier, turn on the power of the power amplifier, and turn on the microphone pre-input control Turn the knob to the twelve o'clock position, and turn the microphone output volume knob to the twelve o'clock position.
Turn on the microphone switch and speak. If there is no sound from the microphone, put the microphone's ** to the other two microphone input ports in order to test. If there is still no sound after trying all the input ports, the power amplifier may be faulty. You can contact the factory's technical support by phone. The engineer consulted the solution. If there is no electronic technical support, the fault condition of the power amplifier should be written on a small piece of paper and attached to the power amplifier. After packaging, it should be returned to the factory for repair.
2. If the microphone has sound but the music is silent after following the above method, you should first check whether the input of the audio source (VOD) is correct, whether the input cable is intact and has been properly connected to the amplifier, such as In good condition, the connection is correct, but the music is still silent. You can check whether the music input port selection on the front panel of the power amplifier is consistent with the audio input port, and reselect the input port to have music sound (if the cable is output from the VOD and then connected to the power amplifier "CD" input port, but the "VOD" port is selected on the front panel of the amplifier, then the music will definitely be silent).
3. If the music is still silent but the microphone has sound after the above inspection operations, you should check whether the VOD is faulty. You can move the amplifier to a room where both the music and the microphone are sound for comparison and inspection. If the music is sound in another room, you can check whether there is a problem with the VOD (Video On Demand computer). If there is a problem with the VOD settings or output, just reset it and solve it.
4. If the speaker uses a combination of professional preamplifier and professional power amplifier, the inspection method is roughly the same as above.
5. Warm Tips:
When returning the preamplifier and power amplifier to the manufacturer for repair, the fault condition should be written on a small piece of paper, and the paper should be firmly attached to the machine, so that Your machine will receive the fastest and most timely repairs.
If you feel a little messy after reading this, then let’s review the components of the sound system. I believe that after reading this, you will have a clear idea of ??the sound system, which will make it easier to maintain the sound system.
Content expansion:
Sound system composition
1. Sound source
Microphone
Cannon head or ** head. Directivity, sensitivity and sound quality. Noise introduction.
CD, deck, hard disk player
Lotus head, cannon head.
Audio synthesizer
Cannon head or ** head.
Musical instruments
USB cable or USB cable.
Computer
USB cable or USB cable or lotus cable.
2. Control center
Mixing console
Fixed number of input signal processing (input level, phase, 3-band equalization adjustment, monitoring button and other functions )
Fixed number of output signal processing (main output, group output, auxiliary output, matrix output)
Audio matrix
Integrated signal input and output processing equipment. (Processing signal input and output channels, level, frequency division, compression, phase, delay and other functions)
3. Peripheral adjustment equipment
Noise gate
Eliminates electrical noise brought in from outside or inside the audio system. Threshold, attack time, compression ratio.
Compressor
Adds the input signal to the output signal within a controllable range. Starting threshold, compression ratio, attack time, release time, level value.
Balance
Divide the sound range according to frequency points, and you can enhance or suppress the audio response according to frequency points. Graphic equalization (15-segment, 31-segment). Parametric equalization (frequency, Q value, level value, 5-band, 10-band).
Delay device
Processes the signal by channel, corrects the time difference of the final speaker sound signal, and unifies the sound field. (Sound 340 meters/second)
The controller
performs functions such as frequency division, phase, input and output adjustment, parametric equalization adjustment, and output compression of the audio signal.
The effect device
collects the human voice, simulates reverb, echo and other effects through the DSP effect computing chip, and then integrates it into the original sound for output.
4. Power amplifier
Impedance
The resistance characteristic of the power amplifier with a certain degree of stability when outputting with load.
Power
The actual output energy of the amplifier under a certain impedance.
Connections
Three connections, ST (stereo), PA (mono), BR (bridge)
Ground switch
Whether the signal is grounded and adjust the signal background noise.
Input response level selection (0.7V, 1.4V) selection.
5. Speaker
Impedance
The constant resistance characteristic determined by the speaker coil.
Power
The energy that the speaker can accept and the energy it can convert under its own impedance characteristics.
Paper cones, coils, magnets
The copper wires are wound into a circle to form an electrified electric field, which is suspended in the slit of the magnetic base. When the current flows through the coil, an electromagnetic field is formed. Switch, push the paper cone to vibrate.
The ratio of amplifier power reserve to speaker power is 1.5:1. Using a small amplifier to push a large speaker can easily damage the unit.
Audio evaluation index
Sound pressure level SPL
Calculated in db units. Generally, the maximum sound pressure level requirement for KTV is around 100db. The sound pressure level requirement of disco halls is about 110db.
PHASE
If the two speakers are in the same phase, the sound energy will be superimposed. If the phases are opposite, the sound energy will cancel out.
Dynamic dynamic
The sound pressure level span from the lowest sound pressure to the highest sound pressure. Relatively speaking, the higher the better.
Frequency curve
The continuity of sound response at different frequency points can be expressed by a curve. The smoother the curve, the better the sound response.
Frequency point response
The response of a single frequency point to sound is related to the site construction conditions, audio equipment, and speakers.
Concave, upturned, howling.
Distortion
The difference in frequency response between the input signal, the output signal and the original signal.
Audio debugging experience
Signal range
Add the input signal to the mixer and adjust the level until the peak value is around 0db. The output signal is adjusted to near 0db.
Phase unity
Pay attention to the signal line welding 1 shield, 2 signal hot end, 3 signal cold end. The positive and negative ends of the speaker cable cannot be connected reversely. If there is reverse-phase equipment, connect the reverse-phase wires (2 hot-3 cold).
Dynamic protection
The compressor start-up threshold is about -2-0db for treble, -1-0db for midrange, about 0db for bass, and about 0-4db for ultra-low frequency.
Sound quality compensation
The conditions of each room are different. Equalization boosts or suppresses the frequencies that need to be adjusted.
Unify the sound field
The best solution for sound field construction (2-point sound creation)
When creating sound at multiple points, the sound field needs to be unified. (panning, delay)
KTV system composition
Sound source
Microphone, set-top box
Effect device
Adjustment of reverb and echo proportion effects.
Microphone and sound adjustment
Power amplifier
Stereo output
Speaker
Built-in 2-way speaker .
KTV audio debugging
Accompanying sound and vocal balance
Volume ratio adjustment, overall volume adjustment.
Audio volume and sound quality adjustment
7-segment parametric equalization adjustment, the main frequency points are selected from 100, 250, 400, 630, 1K, 3.15K, 5K, 8K and 10K. point.
Vocal volume and sound quality adjustment
7-segment parametric equalization adjustment, the main frequency points are selected from 400, 630, 800, 1K, 2K, 3.15K, 4K and 5K. .
Vocal effect integration adjustment
Effect type, ratio of reverb and echo, and total effect volume.
How to listen to audio noise, air leakage, vibration, distortion, thank you experts
Do not turn on the sound source, turn the audio sound to the maximum, listen to the current sound level, generally good speakers If there is no noise, then perform a sound test with songs that express high, medium and low respectively. The volume should be higher. If the high notes pop and the bass buzzes, it means that the speaker has distortion and other problems. Generally, songs of different styles are used to test the speakers. sound. It is recommended to use 2.0 for listening to music and equip it with a sound card.
Why does one of the speakers in the KTV box have sound and the other has no sound? How to find out the reason? Where to check?
1. Karaoke private room audio and music are silent
1. Take a wired microphone and insert it into the M1C (microphone) input port of the integrated power amplifier, turn on the power of the power amplifier, and turn on the front of the microphone Set the input control knob to the twelve o'clock position, and turn the microphone output volume knob to the twelve o'clock position. Turn on the microphone switch and speak. If there is no sound from the microphone, insert the direct plug of the microphone into the other two microphone input ports in order to test. If there is still no sound after trying all the input ports, the power amplifier may be faulty. You can contact the factory's technical engineer by phone. To inquire about the solution, if there is no electronic technical support, the fault condition of the power amplifier should be written on a small piece of paper and attached to the power amplifier, then packaged and returned to the factory for repair.
2. If the microphone has sound but the music is silent after following the above method, you should first check whether the input of the audio source (VOD) is correct and whether the input cable is intact and properly connected to the amplifier. If the cable is intact, , the connection is correct, but the music is still silent, you can check whether the music input port selection on the front panel of the power amplifier is consistent with the audio input port, and reselect the input port to have music sound (if the cable is connected from the VOD output to the power amplifier "CD" input port, but the "VOD" port is selected on the front panel of the amplifier, then the music will definitely be silent).
3. If the music is still silent but the microphone has sound after the above inspection operations, you should check whether the VOD is faulty. You can move the amplifier to a room where both the music and the microphone are sound for comparison and inspection. If the music is sound in another room, you can check whether there is a problem with the VOD (Video On Demand computer). If there is a problem with the VOD settings or output, just reset it and solve it.
4. If the private room audio uses a combination of professional preamplifier and professional power amplifier, the inspection method is roughly the same as above.
2. The speaker sound is abnormal
1. It is generally impossible for private room speakers to burn out all high, mid and bass units at once, so if the private room speakers are silent, please check first If there is any problem with the VOD, preamp, or power amplifier, check the speakers after confirming.
2. The speaker in the private room makes an abnormal sound.
① Disassemble the box net, check whether there is air leakage in the box, and whether the unit is firmly installed on the box (sometimes the unit is not installed firmly, and the iron edge of the unit is in contact with the box during high-power and dynamic use. A strange sound of air leakage will occur when the body collides.) If each unit is installed firmly, listen carefully to determine which unit the abnormal sound is coming from.
② Remove the unit with abnormal sound, place the unit flat on the ground, and check whether the bubble edge is leaking and deglued, and whether the dust cap is deglued (usually the "bubble" sound is related to the above reasons). If there is no degumming or leakage, use your right fingers to make a triangular balance and naturally push the paper plate of the unit downwards (normal units should not make any noise when pushed downwards, while there should be no noise when the unit is pushed downwards, while scraping the edges, deforming the voice coil, etc. The unit will make abnormal noises. )
③If the unit is not installed firmly and makes noise, just reinstall it firmly. If the unit is soaked or the dust cap is deglued and leaking, use agricultural machinery glue (roadside glue). The glue used to repair leather shoes) can be sealed and repaired and allowed to dry naturally.
④ Check whether there is a foam rubber buffer strip at the contact point between the speaker mesh and the cabinet. If not, add a rubber strip to eliminate the noise.
⑤ If the speaker unit is burned out, it should be returned to the manufacturer for repair, because the voice coil and paper cone will affect the timbre. If the original voice coil and paper cone are not used, the timbre of the speaker will change.
3. Speaker inversion
In actual use, the private room sound feels good after one speaker is turned on, but after two speakers are turned on at the same time, the sound becomes dry and dry. The low volume energy is not doubled, but the volume energy becomes smaller or has no obvious enhancement. This phenomenon is due to the inversion of the speakers. It can be solved by the following methods.
1. Check whether the speaker cable at the output end of the power amplifier is connected correctly (the positive pole should be connected to the positive pole, the negative pole should be connected to the negative pole, generally the positive pole is red.), and then check whether the port where the speaker cable is connected to the speaker is connected correctly. , if the system connection error causes phase inversion, just restore the correct connection.
2. If the speaker unit is installed in reverse phase, disassemble the speaker and check whether the connecting wire of the bass unit is connected incorrectly. If so, just reconnect the two wires correctly. In addition, you can use a battery for polarity testing and touch the battery lightly with the speaker cable to see the direction of movement of the speaker unit. After the positive and negative terminals of the speaker cable collide with the positive and negative terminals of the battery, if the woofer moves outward, the phase is normal. If the speaker shrinks inward, the phase is reversed.
3. In addition, if the speaker is installed in reverse phase, the simplest method is to reverse the positive and negative poles of the speaker cable of one speaker at the output end of the power amplifier.
How to test multimedia active speakers
How to test multimedia active speakers? Do you know it? The following is the multimedia active speaker test standard I shared, everyone is welcome to refer to it!
Test equipment:
Distortion tester/dual-channel oscilloscope/signal generator/dual-channel AC millivolt meter/load resistance 4 ohms/load resistance 6 ohms/load resistance 8 ohms/ (BTL default is 8 ohms)
Instrument connection:
a. Connect the load resistor to the amplifier output
b. Distortion tester, dual-channel oscilloscope, dual Correct wiring diagram of channel AC millivolt meter and load resistor parallel instrument
Test methods and steps:
1. Undistorted power test
1. Satellite box channel Rated output power
Input a 1khz, 500mv sine wave signal source (the load resistor value is 4 ohms; if there is no special indication, the BTL circuit is 8 ohms). Adjust the master volume potentiometer to the maximum volume (THD10), read the AC millivolt meter value, and calculate the rated output power according to P=U2/R (each channel is required to be tested separately when testing power)
2. Rated output power of the bass channel
Input a 70hz, 200mv sine wave signal source (load resistance 4 ohms, BTL resistance 8 ohms). Set the bass volume potentiometer to the maximum output state (THD state 10, displayed by the distortion meter), read the AC millivolt meter value, and calculate the rated output power according to P=U2/R (when testing the bass channel power, the satellite box channels are required to be equal Add load)
2. Channel separation
Input a 1khz, 500mv sine wave signal source, adjust the master volume potentiometer to make the output power 1W (4 ohm load is 2V, When the 8-ohm load is 2.828V and the 6-ohm load is 2.45V), remove the other channel signal source and read the left and right channel data from the two-pin millivolt meter. The R/L channel difference is =37db.
3. Channel balance (satellite box channel balance)
Input a 1khz, 500mv sine wave signal source, adjust the master volume, and observe the two-channel AC millivolt meter at the same time. db value, the difference between L/R channels at any output point should be = 1db
Fourth harmonic distortion
1. Total harmonic distortion of satellite box channel
a. Input 1khz, 500mv sine wave signal source, adjust the master volume potentiometer to make the output power 1W (4 ohm load is 2.0V, 8 ohm load is 2.828V, 6 ohm load is 2.45V) In this case, select the appropriate range of the distortion test instrument.
b. Observe the distortion degree from the distortion meter. If there is no special instructions, the test result distortion degree is required to be 1.
2. Total harmonic distortion of the subwoofer channel
a. Input a 70, 200mv sine wave signal source, adjust the master volume potentiometer to make the output power 1/5 of the rated power, and select the appropriate range of the distortion meter.
b. Observe the distortion degree from the distortion meter. If there is no special instructions, the test result distortion degree is required to be 1.
5. Signal-to-noise ratio
1. Satellite box channel signal-to-noise ratio
a. Input 1khz, 500mv sine wave signal source, adjust the master volume potentiometer to make the output power 1W (4 ohm load is 2.0V, 8 ohm load is 2.828V , 2.45V at 6 ohm load), write down the level pair data at this time A
b. Remove the signal source
c. Select the two-pin millivolt meter The appropriate range, read the level logarithmic value B, and then calculate the level difference between A and B, which is the satellite box signal-to-noise ratio
d. (line input) broadband = 65db
2. Subwoofer channel signal-to-noise ratio
a. Input a 1khz, 500mv sine wave signal source, adjust the master volume potentiometer to make the output power 1/5 of the rated output power, record this time The level value A
B. Remove the signal source
C. Select the appropriate range of the two-pin millivolt meter, read the level value B, and then calculate the A/B voltage The adjustment value is the low channel communication signal-to-noise ratio
d. (line input) broadband = 65db
6. Maximum hum sound
1. Satellite box Maximum hum of the channel
a. Set the master volume potentiometer to the maximum position
b. Remove the signal source
c. Select a two-pin millivolt meter Appropriate range, read the level value as the maximum hum
d. The required maximum hum = 3mv
2. The maximum hum of the subwoofer channel
a .Set the master volume potentiometer to the maximum position
b. Remove the signal source
c. Select the appropriate range of the double-pin millivolt meter, and read the level value as the maximum hum
d. Required maximum hum = 5mv
7. Minimum hum
1. Minimum hum of satellite box amplifier
a .Turn down the master volume potentiometer to the minimum value
bSelect the appropriate range of the two-pin millivolt meter, and read the level value as the minimum hum
cThe minimum hum = 1mv
2. Minimum hum of the bass box amplifier
a. Turn off the master volume potentiometer and bass potentiometer to the minimum value
b Select double-pin millivolts The appropriate range of the meter, the reading level value is the minimum value
d. Minimum hum required = 1mv
8. Frequency response
1. Satellite box channel Frequency response
a. Input 1khz, 500mv sine wave signal source, let the amplifier work at an output power of 1W (4 ohm load is 2.0V, 8 ohm load is 2.828V, 6 ohm load is 2.45 V) state.
b. Adjust the signal generator so that the frequency attenuates toward the low end based on 1khz. At the same time, check the millivolt meter. When the level value attenuates to -3Db, record the low end frequency value
c. Adjust the signal generator to increase the frequency to the high end based on 1khz. At the same time, check the millivolt meter. When the level value attenuates to -3Db, record the high end frequency value
d.B/C The frequency value of the item is the frequency response of the satellite box channel
2. Frequency response of the bass box channel
a. Input a 70hz, 200mv sine wave signal source, and let the amplifier work at 1 Test under /5 rated power condition
b. Adjust the signal generator so that the frequency attenuates toward the low end based on 70hz. At the same time, check the millivolt meter. When the level value attenuates to -3Db, record the low End frequency value
c. Adjust the signal generator so that the frequency increases to the high end based on 70hz. At the same time, check the millivolt meter. When the level value attenuates to -3Db, record the high end frequency value.
The frequency value of d.B/C item is the bass channel frequency response
9. Input sensitivity
1. Satellite box channel input sensitivity
Input a 1khz, 500mv sine wave signal source, turn the amplifier master volume potentiometer to the maximum position, adjust the signal source amplitude to make the output reach the rated distortion limit output power (THD=10), the signal source output amplitude is the satellite box Channel input sensitivity. (When testing the input sensitivity of the satellite box channel, it is required to load all satellite box channels)
2. Subwoofer channel input sensitivity
Input a 70hz, 200mv sine wave signal source, and turn the amplifier Turn the master volume potentiometer to the maximum position and adjust the signal source amplitude to limit the output power by rated distortion (THD=10). The signal source output amplitude is the bass channel input sensitivity. (When testing the input sensitivity of the subwoofer channel, each channel is required to be loaded)
10. Input impedance
1. Satellite box amplifier input impedance
a. A variable resistor is connected in series to the signal source input circuit. As shown below.
b. Turn the amplifier master volume potentiometer to the maximum, adjust the signal source amplitude so that the output reaches the rated power state (THD=10)
c. Change the resistance of the variable resistor , causing the amplifier output to attenuate 6db
d. Measuring the resistance of the variable resistor is the input impedance
11. Power consumption of the whole machine
a. Use a 4.7K resistor to isolate and mix the output ends of the two signal generators. The output frequency of one is 1KHZ, and the output frequency of the other is set to: 70HZ. See the schematic diagram below for instrument connection. .
b. Connect an AC ammeter in series to the AC 220v input circuit of the active speaker to monitor the current.
c. Combine the mixed signal source (signal amplitude depends on different models) ) is connected to the amplifier input terminal
d. Adjust signal generator A so that the satellite box channel output reaches the voltage value at 1/8 rated distortion limit output power, adjust signal generator B so that the subwoofer channel The voltage value when the output reaches the rated distortion limit output power (main volume potentiometer and low volume potentiometer are placed at the maximum position)
e. Read the ammeter reading and calculate the consumption of the whole machine according to the formula P=IU Power
12. Treble control (satellite box channel)
a. Input a 10khz sine wave signal, make the amplifier work at 1W output state, and display it with a dual-channel millivolt meter The db value is the benchmark (the balance potentiometer of the satellite box channel, the treble potentiometer/bass potentiometer are all placed at the midpoint)
b. Attenuate the treble potentiometer and monitor the db drop of the dual-channel millivolt meter. value, this data is the treble attenuation parameter
c. Increase the treble potentiometer, monitor the rising db value of the dual-channel millivolt meter, this data is the treble improvement parameter
13. Bass Control (satellite box channel)
A. Input a 100khz sine wave signal, make the amplifier work in the 1W output state, and use the db value displayed by the dual-channel millivolt meter as the benchmark; (the balance potential of the satellite box channel , the treble potentiometer and bass potentiometer are placed at the midpoint)
B. Attenuate the bass potentiometer, monitor the db value dropped by the dual-channel millivolt meter, this data is the bass attenuation parameter
C. Increase the bass potentiometer and monitor the rising db value of the dual-channel millivolt meter. This data is the bass improvement parameter
Note: If the Yuanyuan speaker to be tested is not designed with a bass control function, no testing is required. This parameter
Fourteen. Tone tone control; (satellite box channel)
A. Input 10khz sine wave signal, make the amplifier work in 1W output state, and use dual-channel millivolt The db value displayed on the meter is the reference (the tone potentiometer of the satellite box channel is placed at the midpoint position)
B. Attenuate the tone potentiometer to monitor the `db value dropped by the dual-channel millivolt meter. This data is Tone attenuation parameter
C. Increase the tone potentiometer and monitor the rising db value of the dual-channel millivolt meter. This data is the tone improvement parameter
Note: If the active speaker to be tested has no Tone control function design, no need to test this parameter
Fifteen balance control:
A. Input 1khz.500mv sine wave signal to make the amplifier work in 1W output state (satellite box channel Balance potentiometer, treble potentiometer. The bass potentiometer is placed at the midpoint)
B. Turn the balance potentiometer counterclockwise to the minimum position and observe the level of the two pointers on the dual-channel AC millivolt meter. value, the difference between the two pointer readings is the balance control parameter (when the balance potentiometer is rotated clockwise to the maximum position, the parameter should be the same as the minimum position parameter) Balance control = 40db
Sixteen: Complete machine Temperature rise test
Input signal source: mixed dual-frequency sine wave signal of 1khz and 70hz (the 2.0-channel active speaker only inputs 1khz sine wave signal). The input amplitude is determined by the input sensitivity of different models.
Load setting: The satellite box channel is connected to a load resistor of 4 ohms (if not specified, the BTL circuit uses an 8 ohm load)
The bass channel is connected to the speaker used in this model (different models (different speaker impedance)
Temperature test point settings:
1. Power integrated circuit
A. Only use 1 single-in-line package (SIP) power amplifier integrated circuit , the test point is on the integrated circuit
B. For the use of two single-in-line package (SIP) power integrated circuits, if the distance is close, the test point is taken in the middle of the two integrated circuits. If the distance is far, The test points are taken on two integrated circuits respectively
C. For dual-row DIP packaged integrated circuits, the test points are on the ground pin (GND)
2. The rectifier diode and Rectifier bridge stack
A. The rectifier circuit uses diodes, and the test point is taken at the positive pole of the first diode
B. The rectifier circuit uses a bridge stack, and the test point is taken at the positive power output of the bridge stack On the feet
Test steps:
A. Make both the satellite channel and the bass channel work at 1/8 rated output power status
B. Test every half hour Once the temperature rise data is recorded, it must be monitored continuously for 4 hours
C. Observe the temperature rise within 4 hours to ensure that the temperature is constant. If temperature rise occurs, continue the temperature rise test until the temperature is constant.
d. The maximum temperature requirement of the power amplifier integrated circuit is 75 degrees, and the temperature of the rectifier diode and rectifier bridge stack cannot exceed the maximum temperature requirement specified by the model. (The maximum temperature requirement does not include ambient temperature)
Seventeen: Innovative model speaker unit and speaker tremolo, air leakage inspection standards
Inspection equipment: audio frequency scanner computer sound card Audio output device
The voltage and sweep setting calculation method is as follows:
1. Satellite machine
A voltage setting is based on 1/1 of the power of the satellite speaker unit. 5The calculated voltage is the setting voltage
B. Sweep frequency range, Fmin~20KHZ (Fmin is 80 of the single resonant frequency)
2. Subwoofer
a. Voltage setting, calculated according to the formula Gmain=20lg(V0/VI), where Vo is calculated from 3/4 rated output power.
B. Frequency sweep range, Fmin~20khz (Fmin is 80 of the single resonant frequency)
See details of inspection items and requirements below
FTCMeans: FederalTradeCommissionFTC Test (Federal Commercial Test)
1. Each channel is loaded with a load (the load size is determined according to the circuit of different models), input (1k 70hz) mixed signal, so that the output works at 1/8 rated output power state , work under this condition for 1 hour
After 2.1 hours, the satellite channel output reaches THD=10 (the bass channel remains unchanged)