How to solve the sound noise problem
(i) Good grounding treatment
In order to shield the cable from the outside of the stray electromagnetic interference, the shielding layer must be properly connected and good grounding. Equipment suspension is a kind of measure under the condition of no special ground wire, this is an unstable working state. Often produces random noises. Therefore, there must be a special ground wire. In the outdoor site can be temporarily buried ground, the simplest way is to use steel tubes or aluminum alloy tube inserted underground.
The general system is the link system with multiple devices connected by cable, it is easy to form the chain grounding mode by its shielding system. When an electromagnetic radiation or static induction noise is generated on a device. The grounding system which is composed of the shielding layer of the transmission line and the iron equipment shell makes the whole system produce the inductive voltage, which makes the system produce a certain noise level. Therefore, the system should try to avoid the use of chain grounding mode, and the use of star-shaped grounding. This requires that the shielding layer of the audio cable that connects all the devices is grounded at one end (the shielding layer), and the ground wire of each device is connected to a connecting place through a special wire.
To ensure that the system does not appear in the loop structure. It is required that only one grounding conductor interconnect between the equipment. In the case of strict requirements, you can let unbalanced equipment suspension, through the audio signal Line common ground of the next level of equipment, that is, the use of chain-shaped grounding. This chain-shaped grounding series can not be too many, generally no more than two levels, otherwise it will make a serious increase in noise.
(ii) Systematic isolation
In some large audio systems. Often made up of many child systems. These systems are mostly long-distance connections and have independent grounding systems. Once the grounding of 2 systems is connected, the ground noise must be formed. On the other hand, due to the long transmission distance, the transmission line shielding layer of the grounding resistance increased, it is easy to introduce a large number of external electromagnetic radiation interference noise.
In practice, if each system works alone, the noise can be controlled within the allowable level through reasonable wiring and grounding. However, when the 2 subsystems interconnect, the single end shielding earthing and the long line segment grounding are used, and there is no way to solve the radiated noise caused by long-distance transmission. The best way to do this is to install an audio isolation transformer. The audio isolating transformers are installed between 2 systems to isolate each other and the ground wires of the 2 systems shall not be connected to one another.
Now many systems are connected with fiber, the effect is best. Long-distance audio transmission of optical fiber is not due to the skin effect of the cable to introduce SCR dimming equipment and other stray electromagnetic waves on the audio system caused by interference, but also to the transmission of the audio system to form electrical isolation, so as to avoid the interference between the various audio systems.
(iii) Proper connection of the system
There are many devices used in the audio system. The device has different interface forms, and has a balanced and unbalanced input and output form. In order to effectively shield the external electromagnetic radiation and interference, the use of shielded cables must be unified and the correct connection method.
When the audio signal transmission is balanced. The common mode interference level generated by the external interference power to the 2 signal lines in the cable is almost equal to the ground loop. In the device internal amplifier of the receiver, 2 of the common-mode voltage on the signal line will be replaced by the differential mode voltage and mutual cancellation, the formation of interference voltage. Therefore, we should use the balanced connection method as far as possible.
When connected to an unbalanced output device. A single core shielded cable is used to connect the port of the balancing device to the port of the unbalanced device without using a balanced Shang unbalanced converter. The noise induced by the shielding layer is mixed into the audio signal, which increases the noise, which is a main way to introduce noise. Therefore, both the balance and unbalanced transmission should be shielded by a dual-core shielding cable, and the shielding layer is only grounded at one end of the balance output or input.
When both ends are unbalanced devices, if the transmission distance is far, it is best to use a balanced, unbalanced converter or audio isolation transformer to convert to balanced transmission.