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The hand-held microphone sometimes swings the microphone line, causing a "bang" sound, most of which is that at least 1 of the 3 pins of the cannon plug is loose before and after or the welding point indicates that the welding is good and touches other welding points. If there is a switch on the microphone, the contact point of the switch is loose, and sometimes it is contacted and sometimes it is removed, which is also a reason for the "bang" sound. The remedy is to replace the cannon plug. Plastic cannon plugs often appear in the market with poor temperature resistance. After soldering the pin, the pin becomes loose, which makes the microphone have poor contact. The welding process is to twist the metal wire of each wire into one strand and weld it into one strand, and then weld it with the tip of the needle. When the microphone switch is in poor contact, it should be replaced or tinned directly after removal to delete the switch function.
When holding a microphone, the "buzzing" hum is caused by the fact that the shielded wire between the metal shell of the microphone and the microphone wire is not welded properly, and the human-induced AC signal enters the signal line of the microphone, causing the hum. The solution is to weld the shielding wire of the microphone wire to the metal shell of the microphone or to add a weld piece to the end of the shell screw, and weld the shielding wire to the weld piece.
The reason may be that the switch on the microphone is not opened, it may be that the microphone signal line is open, and it may be that the microphone is damaged. The solution is to turn on the microphone switch, check the microphone connection line, and test the sound with another microphone with the same structure.
Generally speaking, the two microphone signals are reversed, and after entering the mixing table, they are reversed superimposed to cancel each other, because the amplitude of the two signals is not exactly the same, so there will be some sound after the cancellation, but the volume is smaller than that of a single channel. The solution is that if each input channel card of the mixer is equipped with a phase reversal key (φ), press the phase reversal key along the way, so that the two sound transmitter signals are in phase into the mixer, and the sound is increased. If there is no phase reversal key on each input channel of the mixer, the two microphone signal lines on one of them can be switched and welded.
When the number of microphones inserted into the sound console, the pickup gain increases, and the area of receiving the reflected sound in all directions also increases, thus the possibility of acoustic feedback increases, and it is easy to whistle. In this case, it is best to use an intelligent microphone controller, which can accept 40 to 80 microphones, control the number of speaking microphones (for example, 1 to 6), and ensure the volume of sound amplification of each microphone. The number of pickup microphones can also be increased by combining wired microphones with wireless microphones.
The difference in pickup volume between the two microphones under the same conditions is mainly due to the large difference in sensitivity, while the frequency response curve of the two microphones is different, the various frequency gains are different, the sound signal generated is not consistent, and the sound emitted by the speaker is different. In order to maintain the consistency of the volume when the two microphones pick up at the same time, so that the sound box is basically the same, it can be compensated by operating the relevant function keys on the input channel of the mixer. For example, the gain knob and the parametric equalizer are used for some compensation.
（1）The battery on the wireless microphone is insufficient, and the battery should be replaced at this time.
（2）The volume knob of the tuner is not open, and the knob should be adjusted to more than 3/5 at this time.
（3）The receiving antenna Angle of the tuner is not adjusted well, and the antenna Angle should be rotated at this time to avoid receiving signal dead Angle in the user's active area.
（4）The carrier frequency of the microphone deviates from the receiving frequency range of the tuner, which must be re-adjusted and fixed with the relevant test equipment.
Usually, the output of the tuner should be connected to the Line input terminal (Line) of the input channel of the mixer, and this port is the high resistance terminal (Hi-Z), that is, the preamplifier from which the signal enters the input channel of the mixer needs to pass two high resistance resistors, which plays a certain isolation role, if the signal directly enters the microphone interface of the Low resistance (low-Z), There will be a decrease in isolation and impedance mismatch. In some cases, the crosstalk problem can be solved by simply reconnecting the Line input jack (Line). Of course, some tuners are equipped with their own dedicated cannon jack, so crosstalk interference will not occur.
When the carrier frequencies of two wireless microphones are similar, the beat phenomenon can be caused, and the beat signal is superimposed on the frequency modulation wave of the less powerful microphone, causing frequency deviation, so that the tuner corresponding to the microphone can not receive the information of that microphone. The method is to use a measuring device to signal the carrier frequency of one of the wireless microphones. Because the current production of wireless microphone companies to raise the carrier frequency outside the FM radio broadcast frequency range (88~108MHz), to avoid crosstalk by the local FM radio station. Obviously, in this case, it is very difficult to do it manually.
In the process of sound amplification, a pair of speakers are suddenly silent, mostly because the power amplifier on the output channel is overloaded, and the fast fuse is blown, in this case, replace the same capacity of the fast fuse, reduce the input signal level of the power amplifier, you can resume normal operation. If there is still no sound after replacing the fuse, you must check whether the front device has sent a signal. Using the jumper method, that is, skip the previous device, the input signal of the previous device is inserted into the input end of the power amplifier, if it is still silent, it may be the power part of the power amplifier is damaged or the final power tube of the two channels is burned out, using the jumper method, it is easy to check the faulty equipment. In order to ensure that the power amplifier and the speaker are not burned out by overload, a limiter should be added to the head of the power amplifier or in front of the electronic frequency divider.
If this happens, the problem is more in the power amplifier or speaker. In order to quickly check the fault, the crossover method can be used, that is, the two pairs of speaker lines on the output terminal of the power amplifier are switched to each other and the sound signal is connected to listen to, if the sound box is reversed, it is not the problem of the speaker, but the problem of the power amplifier, the power tube of the channel that is silent or small is burned or the power supply is damaged, and the failure of other parts is rare. If the sound box has no change, it means that the silent or small sound box is likely to burn or local short circuit, and the voice coil must be replaced at this time.
（1）The sensitivity of the left and right channel speaker is inconsistent, and the sound box can be nearly consistent by adjusting the output level of the left and right channel.
（2）The left and right channel output power signal is unbalanced, and the input and output gains of each device on the left and right channel can be adjusted at approximately the same indicating value.
（3）The average volume level of the left and right channels of the sound source is often different, and the sound imbalance between the two channels can be solved by adjusting the gain knob of the input channel of the mixer or the channel fader, so that the average volume of the double sound box is roughly the same.
The crossover point of the electronic divider on the two channels is not adjusted well, forming the uneven sound of each speaker, and must be strictly adjusted by the use of the electronic divider, the increase of the output frequency band should be placed in the same position to maintain the balance of the high, middle and low of the original music, and the adjustment of the crossover frequency point should make the split frequency band consistent with the sound frequency band of the speaker.
In order to accurately determine whether the treble speaker without a treble is burned, you can use the cross exchange method to replace the two pairs of lines of the speaker. If the high-frequency head of the speaker has a high-frequency sound after the exchange, it indicates that the fault comes from the front equipment. If the high-frequency head of the speaker is still no treble after the replacement, it indicates that the high-frequency head of the speaker has been damaged, or the high-pass capacitor of the power division is open, or the high-frequency voice coil is burned out, and the high-frequency voice coil can be judged and repaired by short-circuit high-pass capacitor method or using a multimeter ohm file to measure whether the high-frequency voice coil is on and off. The high-pitched whistle caused by the microphone or the power amplifier arbitrarily switches the power supply of other sound amplification equipment or the plug and switch equipment connection line when the power amplifier is working, will cause a pulse signal, and form a power pulse after the power amplifier, burning the high-frequency head.
The muffling and turbidity of the sound reinforcement system may be caused by the adjustment of the low frequency band lift of the electronic frequency divider too high, or the compensation of the bass thickness of the driver or the high level of the input channel parameter equalization of the mixer, which can be solved by lowering the corresponding knob. Some speakers themselves sound bass dull turbidity, you can also lower the above knob to solve. Some sound reinforcement equipment in the connection of unreasonable places, may also lead to the appearance of bass turbidity, such as the use of electronic frequency division only low-band signal, after the power amplifier to drive the bass speaker or sub-heavy bass speaker sound, and the middle band, high band or high band signal is idle, high, medium and low frequency combination speaker alone use the full band power signal sound. Obviously, there are bass overlapping sound segments between the two, resulting in bass imbalance, heavy, turbidity phenomenon. To this end, the medium and high frequency frequency division signal should be sent to the full band combination speaker after the power amplifier, and the low frequency sound is sent to the independent bass (sub-bass) speaker.
There is no end sound when the sound reinforcement system revocates, which is generally caused by the noise gate on the pressure limiter being adjusted too high. Professional sound reinforcement equipment above the mid-range, as long as the wiring is strict and standardized, the system noise is very small, 1.5~2m from the speaker can hear a small amount of "rustling" is a normal phenomenon, the noise door should be closed. If you leave the speaker 10m, you can still hear the noise, you should lift the noise gate threshold slightly, remove part of the noise, and retain a small amount of noise in front of the speaker, in this case, the music played (including singing) appears natural and true. If the noise threshold is raised too high, the low-level signal is also cut off, and there is no ending in the music, the sound is unnatural and ugly.
When the compression threshold and compression ratio adjustment on the pressure limiter panel do not work, there are definitely two reasons:
（1）the two channels of the pressure limiter are in the side state, and the sound signal is directly output without the pressure limiter.
（2）The rear cover plate of the pressure limiter is connected incorrectly, and its input or output plug is inserted into the "in" or "out" end of the side chain circuit, resulting in the level detector of the pressure limiter being in an externally controlled or non-working state, making the adjustment of its compression threshold, compression ratio, starting time and recovery time ineffective.
The indicator light on the voltage limiter is a gain attenuation indicator, indicating how much dB the gain drops after the signal is compressed. When the compression threshold is increased, the compressed signal in the music signal is less, the gain reduction of the compressed signal is also reduced, and the number of lights is reduced. Similarly, if the compression threshold is fixed and the compression ratio is reduced, the number of lights is reduced. On the contrary, increasing the compression ratio will increase the number of lamps. This indication can visually see how much the gain of the highest level of the signal is reduced after compression, which is a functional indication, not a fault.
The left and right channels of the sound source do have output, and there is no sound signal output after entering the mixer. The reasons are as follows:
（1）The Connect key of the input channel is not pressed or the input signal selection key of the input channel is misplaced. In this case, the connect key should be pressed or the selection key should be placed correctly.
（2）The connection cable of the input mixer is disconnected or in poor contact. At this time, use a multimeter to check the connection cable and make the connection reliable.
（3）If the input channel signal is not programmed into the corresponding bus output, the corresponding allocation key on the channel should be pressed.
（4）The adjustment of the input channel sound image adjustment knob is opposite to the sound image of the input signal, and the opposite adjustment must be corrected at this time.
（5）If the fader of the input channel is not pushed or the mixer output master is not pushed, the fader should be checked and pushed.
The reason why the hum is very large when the sound reinforcement system is silent is: (
（1）The shielded line of the connection line between the devices in each channel is in poor contact or virtual welding, and it must be carefully checked at this time to make the welding firm.
（2）When the power connection socket is converted from a 3-wire (single-phase) socket to a 2-wire socket, the neutral line is switched with the live line, and it can be switched again at this time.
（3）The power cord of some audio equipment is 3 feet, the middle is the ground wire, the left is the fire wire, and the right is the neutral line. Connect it to the socket, the socket should be standardized, otherwise it is easy to cause noise, the power cord of some audio equipment is 2-pin, although it can be inserted in the single-phase fire line and neutral line, the work is not affected, but the exchange may cause hum. At this time, you can try to adjust the plug to see if you can reduce the hum.
（4）Some mixers output in the form of balance to balance, will produce a hum, then its output must be converted from a balanced connection to a non-balanced connection, this method is especially suitable for not using the noise gate on the pressure limiter to cut the hum.
（5）When the microphone wire is bundled with the AC power cord, it will cause an AC induction, resulting in a hum. At this time, it is advisable to separate the microphone wire from the power cord, preferably away from some
（6）signal shielding ground wire and output ground wire short connected or each other through the frame to form a ground loop will cause hum and interference noise. The elimination method is to avoid multi-point grounding, make the ground wire open ring, and connect the frame to the ground wire with a thick wire
The sound system and the lighting use the same single-phase electricity, and the sound box often emits a large hum when the lighting system is running, the reason is that the thyristor of the lighting system has a large working current, and it is an AC pulse type, which is directly coupled to the input end of the sound amplification equipment through the power lead, causing a large hum. The elimination methods are as follows:
（1） a single phase power supply is used for the sound system, and another single phase power supply is used for the lighting system.
（2）The sound system is powered by an isolation transformer, and the power of the isolation transformer must be greater than the power required by the sound system.
The main reason is that there is a virtual welding phenomenon in the connection of sound amplification equipment, when there is a music signal, the virtual solder joint appears intermittently connected, or the connection line is in poor contact, or the middle of the connection line is broken, the exclusion method is as follows:
（1）carefully check each connection line, it is best to re-weld the connection point.
（2）Check whether the plug of each wire is loose or unplugged in contact with the socket, tightly hire the socket, and plug the plug.
（3）Use a multimeter to check each connection line, if there is a broken line, should be replaced immediately.
The sound reinforcement system occasionally appears in the operation process of blasting like sound, most of the reasons are that the power plug of the individual equipment has bad contact phenomenon, accidentally disconnected and contact, the elimination method is to replace the power strip. Sometimes, the plug welding head of the equipment connection line is off welding, virtual welding or wire touch, will also cause a gun-like sound, at this time should carefully check each connection line, firmly welded leads, welding points should be separated well, the metal wire into a strand after soldering, so as not to touch the line.
There are the following reasons for no effect sound in the singing sound:
（1）The singing sound does not enter the effect machine, at this time, the output knob of the auxiliary bus sent to the effect machine should be turned on, the corresponding auxiliary knob on the singing sound input channel can be turned on from the effect machine input light to confirm whether the singing sound has entered.
（2）If the effect output of the effect machine is not programmed into the left and right channel bus or the grouping bus, the effect button should be pressed to return to the relevant compilation button on the channel.
（3）The effect of the effect machine fails, at this time should be replaced with other effects to try or replace the effect machine to try again.
The general effect machine has 2 in 2 out (that is, the left and right channel signal enters the effect machine, and the left and right stereo effect is output from the effect machine) or 1 in 2 out (that is, the monophonic signal enters the effect machine, and the left and right stereo effect is output from the effect machine), no matter which way is taken to connect with the mixer, For some types of effect machines, the effect may appear quiet and not full enough. To this end, it is recommended that when tuning in the karaoke hall, it is best to choose the connection mode of 2 in 2 out or 1 in 2 out, and return the left and right stereo effects output from the effect machine to the Line input terminal of the two input channels of the mixer.
The reason why the singing sound and the accompaniment music can not be integrated is:
（1）The sound source (accompaniment music) divides the left and right channels into the mono input channel, and the sound image adjustment knob on the channel is arbitrarily placed, resulting in the confusion of the sound image. To this end, the image adjustment knob must be placed correctly, the left channel input, the image adjustment knob (Pan) on the road to the left (L), the right channel input, the image adjustment knob (Pan) on the road to the right R).
（2） The adjustment of the room balance compensation curve of the room equalizer is unreasonable or the room equalizer only compensates the room balance for the accompanying music. To this end, the room balance compensation curve must be readjusted, so that vocal music and various instrumental sounds are balanced compensation, so that the treble, midrange and bass appear more balanced.
The stereo effect of the sound source is very good, and the stereo effect becomes worse or lost after the Sound console, the reason is that the sound source and the left and right sound enter the single sound channel of the Sound console, the sound adjustment knob (Pan) on the two channels is placed in the same position or placed arbitrarily, and the adjustment of the two inputs is not the same or the two Fader is not the same. The solution is to adjust the sound adjustment knob (Pan) on the road to the left (L) if the sound source comes in from the left channel. If the sound source is coming from the right channel, adjust the sound adjustment knob (Pan) on that road to the right (R). At the same time, the Gain adjustment knobs (Gain) on both paths are placed in the same position, pushing the Fader on both paths to the same height.
The "sizzle" sound when the sound amplification system is muted is mostly caused by some parasitic oscillations, its natural frequency is within the range of 2.5~10kHz, the method of suppressing this noise is as follows:
（1）The use of the room equalizer on the corresponding noise frequency of the push-pull key 12dB, you can start from 2.5khz until 10kHz. If the push-pull key does not inhibit when it is pulled down, it indicates that the noise frequency is not the frequency, and the push-pull key should be put back to the original position. As long as the aligned noise frequency is pulled down, the fixed frequency noise will be suppressed.
（2）Use the side chain circuit inlet (In) and outlet (Out) holes on the back cover of the pressure limiter to connect with the Output and Input rings of the dedicated chart equalizer, and at first all push and pull keys are placed in the 0dB position. As long as the target noise frequency is pushed up, the fixed frequency noise will be suppressed.
The method of overhauling professional audio equipment is the same as that of overhauling general household appliances. First of all, we should accurately determine the fault location, and then repair or replace the corresponding components, and then make corresponding adjustments. The former is the key link of maintenance, in order to accurately determine the fault, usually the following four methods are used:
（1）visual inspection method: Visual inspection method is immediately after disconnecting the power supply. No need to discuss the instrument, only by intuitive feeling, mobilize the visual, auditory, smell, touch and other characteristics of judgment. Although the accuracy of this method is poor, the inspection speed is faster. The visual inspection method is especially useful for the inspection of the power supply part.
（2）heuristic method: For the suspected part of the circuit, comparison, segmentation, substitution, simulation and other heuristic means are used to find the fault and then eliminate it.
（3）Static parameter measurement method: When using this method, the maintenance operator must hold the maintenance manual of the manufacturer, and measure the relevant parameters such as the endpoint voltage, current and resistance value of each component according to the circuit provided in the manual to see if it meets the nominal value, so as to make a judgment.
（4）Dynamic inspection method: The signal source is injected into the signal, the oscilloscope is used to observe the signal waveform of each end point of each part of the circuit, and the waveform provided by the manual is checked and judged. This method is direct, fast, accurate, not easy to damage the components, but also can adjust and proofread the circuit and mechanical structure, but the use of this method requires the maintenance of the maintenance technology should be more skilled.
There are many manufacturers producing professional audio equipment in the world, and the circuit design, application of components, machining, and overall structure are carefully considered, especially the components are assembled after testing, aging, and screening. The components produced by each manufacturer have their own characteristics, and the interchangeability is poor or cannot be replaced. In order to restore the original performance and technical indicators of the equipment after maintenance, the components replaced during maintenance should be manufactured by the original manufacturer as far as possible. At present, in order to expand the market share of products and improve the visibility and reliability of equipment, many manufacturers are willing to provide some components required for maintenance.