Common troubleshooting methods for professional audio equipment

1. Common faults of mixers:
1. The volume fader has poor contact, and the sound is intermittent when working.
2. Channel input port failure, such as the XLR input port of the old Budweiser mixer is easy to "uproot". When I first encountered this kind of failure, I really couldn't believe my eyes.
3. The control system is disordered. Once I used a Soundcraft 16-channel mixer, and found that there was no signal coming out of the total output. Later, I changed to the group output. Later, there was no signal output from the group, and when I pushed the 10th channel fader, the sound of the 11th channel was indeed output. Later, I used AUX output signals and other methods, and finally this mixer went on strike completely. At this time, the performance could not be cold, so I simply gave the CD player signal directly to the power amplifier to play some music. This is the first time I have encountered such a mixer failure in so many years, and I have never heard of it before. In short, the failure of the mixer is nothing more than the input part, output part, control part, power supply part, etc., which is generally caused by aging equipment.

2. Common faults of equalizers:
1. Failure of push-pull key contact of equalizers. This is the most common one, mainly due to aging of equipment and bad environment.
2. Internal circuit failure of equalizers. I have seen some equalizers with only one signal output. Later, I found that the circuit was broken. There are many such equalizers. I have encountered them several times.

3. Common faults of compressors, electronic crossovers, professional feedback suppressors, professional delayers, etc.:
These devices generally do not have major problems except that they are seriously aging. At most, there are some minor problems with the adjustment knobs and the rear panel signal jacks.

4. Common faults of digital effects:
1. Noise problem. Digital effects have a certain amount of digital noise when processing audio signals. If the signal line is not well shielded, the noise will be like rain in serious cases.
2. The core part of the digital effects is the digital processing chip. These digital chips also have failures. I have seen a YAMAHA500 effects that can be turned on but cannot work. All the programs inside cannot be adjusted and used, and such a complex digital chip cannot be repaired at all.

5. Common faults of power amplifiers and speakers:
1. The most common fault of power amplifiers is bad capacitors or burnt power amplifier tubes. This is a problem we use, but most of the time it is the instability of the equipment itself.
2. Another thing I found is that some power amplifiers have a channel without sound, and the problem is still the circuit problem inside.
3. As for other faults, there are problems such as poor contact of the power amplifier volume potentiometer, imbalance of left and right channels, too frequent protection functions, poor contact of the rear panel work conversion switch and signal jack. In short, power amplifiers are an electrical device that is more prone to failure in current audio systems.
4. The most common fault of the speaker part is of course the speaker problem. It can be said that the most likely fault in a set of audio systems is the burning of the speaker. Of course, there are human factors, but most of them are quality problems of the speaker itself.
5. Another common fault of the speaker is the aging of the wiring port and poor contact, especially for speakers that are often moved. This kind of fault is prone to occur. Generally, sound engineers cannot repair the faults of the above equipment. I have said in the previous article that sound engineers must be "professional". If the power amplifier or speaker is broken, it is the job of the maintenance engineer. The scope of our work is to match the sound system and adjust various sounds.

6. Multimedia speakers: crackling sounds occur when adjusting the volume, and the volume is sometimes loud and sometimes small.

This is the most common fault in multimedia speakers. I believe many users have such experience. After using it for a period of time, this situation often occurs when adjusting the volume of the speaker. Many users choose to use the volume adjustment of the computer system to adjust it, which is undoubtedly a stopgap measure.

In fact, as long as this situation occurs, it can be judged that there is a problem with the phaser that adjusts the volume. Most speakers use potentiometers to change the strength of the signal (except digital tuning potentiometers) to adjust the volume and subwoofer. The potentiometer changes the position on the carbon baffle through an active contact, thereby changing the size of the resistance value. As the use time increases, dust or impurities will fall into the potentiometer, and the contacts of the potentiometer may also oxidize and rust, causing loose contact. At this time, there will be a "crackling" noise when adjusting the volume.
The solution is relatively simple. Just replace a new potentiometer, which will cost no more than 2 yuan. However, the simplest way to deal with it is to open the speaker, open the four crimping pieces behind the potentiometer, and expose the active contacts of the potentiometer. Then, clean the carbon resistor with anhydrous alcohol, drop a drop of oil on the carbon resistor, and finally install the potentiometer in its original position to solve the noise problem.
Of course, the above is the situation that most people will encounter. But there is another reason that can cause the above fault: the quality of the potentiometer is unstable. When in use, the reeds of the left and right channels were originally separated, but now they are misaligned, causing them to be on and off when in use, which produces the "crackling" noise. It is also very simple to deal with this. We just need to use pointed tweezers to gently pull it straight and then install it back in place.

7. Multimedia speakers: The sound can be played normally, but there will be "crackling" noise from time to time.
Some users may encounter such a situation that the sound box will make "crackling" noise from time to time when using the speaker, but it is very normal when using headphones. Moreover, the noise of the speaker sometimes lasts longer and sometimes shorter, but it will be normal afterwards. At first, I also suspected that the audio signal plug was not in good contact, but I also unplugged and plugged it again, and changed the line but it still did not solve the problem.
In fact, the root of this problem lies in the power socket. A low-quality power socket uses phosphor copper sheets of poor quality and poor elasticity. After long-term use, it will cause poor contact, sometimes contact, and sometimes disconnected. At this time, the power supply of the box is connected and disconnected.
And there is a large-capacity filter capacitor inside the power supply, which causes the power supply voltage of the power amplifier circuit to be high and low. Therefore, the strength of the sound it emits has obvious changes. At the same time, because at the moment of on-off, there will be interference signals from the current on-off that will enter the amplifier circuit, which will cause other noises, which is the "crackling" sound you hear.
The solution is very simple: replace a new high-quality power socket. Some unscrupulous merchants may take advantage of the reasons that customers do not understand and use this to demonstrate to customers: the speaker has been repaired, and use this to collect money. Everyone understands this point, so don't be fooled easily in the future.

8. Multimedia speakers: The sound plays normally, but one speaker is loud and the other speaker is soft. If you use your hand to bend the volume potentiometer to one side, the volume of the two channels will be the same.
This fault is very similar to the previous page, and it is also a problem with the volume potentiometer. Because the left and right channels of the volume potentiometer are independent. Because the reed has been used for too long, the elasticity of the inner reed is too weak and cannot be in close contact with the carbon resistance. This is also relatively simple, just adjust the reed by hand.

9. Multimedia speakers:There is sound, but only high pitch, but no bass.
This kind of fault is usually caused by the speaker volume being too high, so after long-term use, the subwoofer is burned. This is very normal. Friends who like bass think that the higher the volume, the better. Some friends can even adjust it very high, and the volume is also adjusted to more than 70%, which is the easiest way to burn the bass. Under normal circumstances, it is recommended to choose 30%-50% volume and 30%-40% bass. In addition, this situation may also be that the wire head is broken. In this case, just spend money to replace a new wire head.

10. Multimedia speakers:There is sound, but the sound is not clear, and the specific content cannot be heard clearly.
In addition to the damage of the tweeter, this kind of fault may also be caused by the signal line being broken, or the integrated block of the tweeter amplification being damaged. In addition, it should be noted that if you are using a sound card, sometimes because of inadvertent changes in the settings, the speaker can only hear the female voice clearly, but the male voice cannot be heard clearly.

11. Multimedia speakers:As soon as it is turned on, it will "buzz" and the noise cannot be eliminated no matter how the volume is adjusted.
This situation is usually caused by long-term use, and the speaker is closed, so the heat cannot be dissipated. Therefore, the internal temperature is too high, causing the amplifier integrated circuit to overheat and be damaged. In fact, genuine power amplifier integrated circuits are equipped with temperature protection functions. When overheated, the power amplifier integrated circuit will automatically stop output; and when the temperature drops, it can automatically resume work.

However, in order to reduce production costs, some speaker manufacturers do not use integrated circuits of big manufacturers' famous brands, but use some small factories' imitation integrated circuits with poor quality. The solution is to buy an integrated circuit of the same model and replace it, and the cost is only 5 yuan. However, the replacement process requires a little professional technology, and not all users can complete it.

12. Multimedia speakers:The computer plays sound normally, but after using it for a period of time, it will "buzz" and the ears can't stand it.

This fault is similar to the sixth case, but the power amplifier integrated circuit has not been completely damaged, and it only fails when it is overheated. We can open the chassis and solve it by increasing the area of ​​the scattered pieces of the power amplifier integrated circuit. Of course, you can also replace the heat sink with good quality.

13. Multimedia speakers:Turn on the power switch of the speaker, and the speaker does not make a "bang" sound when it is turned on normally. Open the music player software to adjust the volume, and the speaker does not make any sound.
This kind of fault is also common: the speaker has no sound after turning on. Does this mean that the speaker is broken, and how to judge? First, before powering on the speaker, turn the volume potentiometer to the maximum position. Then, when turning on the power switch, pay attention to whether the speaker has a "bang" sound. If so, it means that there is nothing wrong with the speaker and the power supply is good. Then, the lack of sound may be due to a driver error or sound failure of the sound card, or it may be muted or the volume is too low. Another possibility is that the signal cable plug is not plugged in properly, or the signal cable is broken.
In addition, the speaker has been used for too long, and the internal temperature is too high, causing the temperature fuse in the power transformer in the speaker to fuse, which will also cause the above fault manifestations. Don't worry, we don't have to replace the power transformer. You just need to carefully remove the transformer and observe the primary coil of the power transformer (that is, the end connected to the 220V power) from the outside to see which side is more convex. For the convex side, carefully remove the plastic film on the surface with sharp tweezers, and you will find a small white square with the words "250V2A" written on it. This is the temperature fuse resistor.
If the transformer is used for too long and the temperature is too high, then in order to avoid fire, the fuse resistor will be activated to cut off the current supply. We just need to short-circuit the two ends of this fuse resistor, but in future use, we need to pay attention to heat dissipation and do not use it for too long.

14. What are the factors that cause speakers to burn out?
1. Improper configuration of speakers and power amplifiers
Inexperienced tuners will think that the output power of the power amplifier is too large, causing damage to the tweeter, but this is not the case. In professional situations, speakers can generally withstand large signal impacts that are 3 times the rated power, and can instantly withstand peak impacts that are 5 times the rated power without any problems. Therefore, it is rare that the tweeter is burned out due to the high power of the power amplifier, not due to unexpected strong impacts or long-term howling of the microphone.
As we all know, there are multiple speakers in the speaker, and the power borne by the speaker is distributed differently according to the different crossover points.
The rated power of the speaker, generally professional speakers indicate the maximum pink noise power, that is, the rated power of the speaker refers to the analog signal power that pink noise or broadband can withstand. A two-way speaker with a crossover point of 1.6kHz and a rated power of 100W, at rated power, the woofer can be allocated 78W of output power, while the tweeter is only allocated 22W. Therefore, the speaker can withstand 100W pink noise power or ordinary program signal power; when tested with 100W single-frequency signal, both the tweeter and the woofer may be damaged.
Before equipping the speaker amplifier with Bellary, you can consult the customer service of Bellary professional audio manufacturer. Bellary manufacturer's engineers will design a plan based on the size, purpose, construction conditions, users and other comprehensive considerations of the use site.
2. Improper use of crossover
Improper use of the input crossover point or unreasonable working frequency range of the speaker is also a reason for the damage of the tweeter. When using the crossover, the crossover point should be reasonably selected according to the working frequency range of the speaker provided by the Bellary manufacturer. If the crossover point of the tweeter is selected too low and the power burden is too heavy, it is easy to burn the tweeter, and the same is true for the midrange horn.
3. Improper equalizer debugging
The adjustment of the equalizer is also crucial. The frequency equalizer is set to compensate for various defects in the indoor sound field and the uneven frequencies of the speakers. It should be debugged with an actual spectrum analyzer or other instruments. The transmission frequency characteristics after debugging should be relatively flat within a certain range. Many tuners who do not have audio knowledge debug arbitrarily, and even quite a few people raise the high and low frequency parts of the equalizer too high, forming a "V" shape. If these frequencies are raised by more than 10dB compared with the mid-range frequency (the adjustment amount of the equalizer is generally 12dB), not only will the phase distortion caused by the equalizer seriously color the music sound, but it will also easily cause the audio tweeter to burn out. This type of situation is also the main reason for burning out the speakers. Of course, the design of the audio system should be based on the actual situation, such as the size of the venue, purpose, building acoustic conditions, etc., and the maximum continuous sound pressure level should be determined according to the actual conditions of use, and then the maximum SPL value of the speaker should be determined.
4. Volume adjustment
Many users set the attenuator of the power amplifier to -6dB, -10dB, that is, 70%-80% of the volume knob, or even at a normal position, and rely on increasing the input of the mixer to achieve the appropriate volume, thinking that the power amplifier has a margin and the speaker is safe. In fact, this is also wrong. The attenuation knob of the power amplifier attenuates the input signal. If the input of the power amplifier is attenuated by 6dB, it means that to maintain the same volume, the mixer or pre-stage must output 6dB more, the voltage must be 1 times higher, and the upper dynamic margin of the input, commonly known as the "head space", will be cut in half. At this time, if there is a sudden large signal, it will overload the mixer output by 6dB earlier, resulting in a clipping waveform. Although the power amplifier is not overloaded, the input is a clipping waveform, and the treble component is too heavy, not only the treble is distorted, but the tweeter may also burn out.
Based on the above analysis, we can clearly understand that an important reason for the speaker to burn out the tweeter is that the power of the power amplifier is too small, not too large. The signal sent by the power amplifier is a clipping signal, which causes damage to the speaker. Therefore, when configuring the audio system, you must establish a correct understanding and use the "big horse pulling a small cart" solution to prevent the power amplifier from sending clipping signals and damaging the high and mid-range speaker units. When designing the audio system, the design power of the power amplifier and the audio system must be matched according to the above principles. In actual operation, the equipment in each link must be used reasonably to protect the equipment and achieve the best effect of the audio system.

15. Judgment and elimination of common faults of professional power amplifiers:
The fault of the whole machine not working is manifested as no display on the amplifier after power on, all function keys are invalid, and there is no sound, just like when there is no power on.
When repairing, the power circuit should be checked first. The DC resistance value at both ends of the power plug can be measured with a multimeter (the power switch should be turned on). Under normal circumstances, there should be a resistance value of hundreds of ohms. If the measured resistance is much smaller and the power transformer is seriously heated, it means that there is a local short circuit in the primary circuit of the power transformer;
If the measured resistance in the stage sound equipment is infinite, check whether the fuse is blown, whether the primary winding of the transformer is open, and whether there is a break between the power cord and the plug. Some machines have added temperature protection devices, and a current fuse is connected to the primary circuit of the power transformer (usually installed inside the power transformer, and you can see it by removing the insulating paper on the outside of the transformer). If it is damaged, it will also open the primary circuit of the power transformer.
If the resistance at both ends of the power plug is normal, you can turn on the power to measure whether the output voltages of the power circuit are normal. For amplifiers that use system control microprocessors or logic control circuits, you should focus on checking whether the power supply voltage (usually +5V) of the control circuit is normal. If there is no +5V voltage, you should measure whether the input voltage of the three-terminal voltage regulator integrated circuit 7805 is normal. If the input voltage is abnormal, check the internal rectification and filtering circuits.
If the voltage at the input of 7805 is normal, but there is no +5V voltage or the voltage is low at the output, disconnect the load to see if the +5V voltage can return to normal. If the +5V voltage is normal, the fault is in the load circuit; if the +5V voltage is still abnormal, the fault is in the 7805 itself. If the +5V power supply voltage of the system control circuit is normal, check whether the clock and reset signals of the microprocessor are normal, and whether the keying and display drive circuits are damaged.

16. Suppression measures for acoustic feedback (howling)
The self-excited howling sound caused by microphone acoustic feedback is a common phenomenon in e-sports performance halls. Due to the existence of acoustic feedback, the gain of the sound reinforcement system in general e-sports performance halls cannot be very large. The reasons for acoustic feedback howling are:
(1) The microphone is too close to the speaker or is placed in the wrong direction;
(2) The reverberation adjustment on the mixer is too high;
(3) The microphone volume is adjusted too high;
(4) The mid-high frequency of the microphone is too high;
(5) The speaker crossover is faulty;
The following measures can be taken to address the above reasons:
(1) Define a rough range for the activity stage of the e-sports performance hall singer, and howling should not occur within this range. In other words, the singer should not be too close to the main speaker, and the main speaker should be symmetrical on both sides of the e-sports performance hall stage; the singer's position should not make the microphone point directly at the speaker.
(2) Do not turn up the reverberation adjustment and volume on the mixer too high.
(3) Lower the microphone volume.
(4) Adjust the microphone sound frequency.

17. The whole power amplifier (power amplifier) ​​does not work
The whole machine does not work. The fault manifestation is that the amplifier has no display after power is turned on, all function keys are invalid, and there is no sound, just like when the power is not turned on.
When repairing, the power circuit should be checked first. The DC resistance value at both ends of the power plug can be measured with a multimeter (the power switch should be turned on). Under normal circumstances, the resistance value should be hundreds of ohms. If the measured resistance value is much smaller and the power transformer is seriously heated, it means that there is a local short circuit in the primary circuit of the power transformer; if the measured resistance value is infinite, check whether the fuse is blown, whether the primary winding of the transformer is open, and whether there is a break between the power cord and the plug. Some machines have added temperature protection devices, and current fuses are connected to the primary circuit of the power transformer (usually installed inside the power transformer, and can be seen by removing the insulating paper outside the transformer). If it is damaged, it will also cause the primary circuit of the power transformer to open.
If the resistance value at both ends of the power plug is normal, you can turn on the power to measure whether the output voltages of the power circuit are normal. For amplifiers that use system control microprocessors or logic control circuits, the power supply voltage (usually +5V) of the control circuit should be checked to see if it is normal. If there is no +5V voltage, the input voltage of the three-terminal voltage regulator integrated circuit 7805 should be measured to see if it is normal. If the input voltage is abnormal, the rectification and filtering circuits should be checked. If the input voltage of 7805 is normal, but there is no +5V voltage or the voltage is low at the output, the load can be disconnected to see if the +5V voltage can return to normal. If the +5V voltage is normal, the fault is in the load circuit; if the +5V voltage is still abnormal, the fault is in 7805 itself. If the +5V power supply voltage of the system control circuit is normal, the clock and reset signals of the microprocessor should be checked to see if they are normal, and whether the keying and display drive circuits are damaged.

18. The power amplifier (power amplifier) ​​has high noise
The noise of the amplifier includes AC noise, crackling noise, induction noise and white noise.
During maintenance, it should be determined whether the noise comes from the front stage or the back stage circuit. The signal connection plugs of the front and rear stages can be removed. If the noise is significantly reduced, it means that the fault is in the front stage circuit; otherwise, the fault is in the rear stage circuit. AC noise refers to a low, monotonous and stable 100Hz AC hum, which is mainly caused by poor filtering of the power supply part. The power supply rectification, filtering and voltage stabilization components should be checked for damage. If the decoupling capacitors at the power supply end of the front and rear stage amplifier circuits are poorly soldered or fail, a low-frequency oscillation noise similar to AC noise will also be generated.
Inductive noise is a complex and harsh AC noise, which is mainly caused by poor grounding of the conversion switch and potentiometer in the front stage circuit or poor shielding of the signal connection. Explosive sound refers to intermittent "crackling" and "clicking" sounds. In the front stage circuit, check whether the signal input plug and socket, conversion switch, potentiometer, etc. are in poor contact, and whether the coupling capacitor has poor soldering or leakage. The rear stage amplifier circuit should check whether the relay contacts are oxidized and whether the input coupling capacitor has leakage or poor contact. In addition, the soft breakdown of the differential input tube or constant current tube in the rear stage circuit will also produce a "clicking" noise similar to electric sparks. White noise refers to irregular and continuous "rustling" sound, which is usually the background noise generated by the poor performance of the input stage transistors, field effect tubes or op amp integrated circuits in the front and rear stage amplifier circuits. When repairing, you can replace it with components of the same specification.

19. The volume of the power amplifier (power amplifier) ​​is low
The so-called low sound fault refers to the fact that the gain of the amplifier decreases or the output power decreases due to the change of the amplification amount of a certain amplifier stage or attenuation in a certain link during the amplification and transmission of the audio signal. When repairing, first check whether the signal source and the speaker are normal, and you can check them by replacing them. Then check various conversion switches and control potentiometers to see if the volume can be increased.
If all the above parts are normal, it should be determined whether the fault is in the front stage or the rear stage circuit. For a certain channel with low sound, the signal output by its front stage circuit can be exchanged and input to the rear stage circuit of another channel. If the sound volume of the speaker remains unchanged, the fault is in the rear stage circuit; otherwise, the fault is in the front stage circuit. The weak sound caused by the post-amplifier circuit is mainly caused by insufficient output power and insufficient gain. You can use the method of appropriately increasing the input signal (for example, directly adding the signal output by the recorder to the speaker to the input end of the post-amplifier circuit, changing the volume of the recorder, and observing the changes in the output of the amplifier) ​​to determine which reason is the cause.
If the output sound is loud enough after increasing the input signal, it means that the output power of the amplifier is sufficient, but the gain is reduced. You should focus on checking whether the contact resistance of the relay contacts increases, the input coupling capacitor capacity decreases, the isolation resistor resistance increases, the negative feedback capacitor capacity decreases or opens, and the negative feedback resistor resistance increases or opens. If the output sound is distorted after increasing the input signal, and the volume does not increase significantly, it means that the output power of the post-amplifier is insufficient. You should first check whether the positive and negative power supply voltages of the amplifier are low (if only one channel has weak sound, you don’t need to check the power supply), whether the performance of the power tube or integrated circuit has deteriorated, and whether the emitter resistance has increased. The weak sound caused by the conversion switch and potentiometer in the pre-stage circuit is easier to find by visual inspection, and can be cleaned or replaced. If you suspect that a signal coupling capacitor is ineffective, you can test it in parallel with a capacitor of the same value; if the performance of the amplifier or op amp integrated circuit is poor, you can also use the substitution method to check. In addition, if there is a problem with the negative feedback element, it will also cause the circuit gain to decrease.

20. Reasons for no signal in the wireless microphone:

1. The signal reception conditions in some KTV boxes are not good

For example, there are pillars blocking the venue, and the sound control room is far away from the venue, blocked by walls or turning a corner, etc., which will affect the normal reception of the signal.

2. There are interference sources in some KTV venues that affect signal reception
Today's communication tools are developed and diverse, such as mobile phones, walkie-talkies, wireless phones, etc., all have mutual interference, and the reflection of metal equipment and glass in the venue will also cause this situation.

Solution to no signal in KTV wireless microphone:

1. Sometimes you can change the direction and angle of the antenna, which can improve your reception conditions.
2. If the receiving conditions are more demanding, such as the sound control room is not in the venue, or there are columns or walls blocking it, generally, you can solve the problem by extending the antenna. The emergency method is as follows: take a video cable of about 10-15 meters, remove the antenna of the original receiver (or buy an antenna yourself) and connect it to the video cable, and then install the antenna in the place where you have tested and can receive the signal.
3. Some can try to change a set of frequencies, because some interference sources may conflict with the frequency of this set of microphones, and changing a set of frequencies can often solve the problem. If there are pillars in the venue and the receiving environment is not very good, try to buy a single-transmit dual-receive (that is, one microphone, two antennas) type, because the receiving range of the two antennas is larger, such as people walking and talking, at this time the two yellow lights of the receiver are on, indicating that it is in full range; if the yellow light on the left is on, it means that the receiving antenna on the left is within your left speaking range. Once you walk out of the receiving range on the left and enter the range on the right, the yellow light on the right will light up immediately, and the antenna on the right will work immediately. This ensures that your speech sound is received in all directions.
4. If the reception environment is really bad, you can choose a multi-frequency adjustable wireless microphone.