Analysis of noise problems in professional audio systems

　　Analysis of noise problems in professional audio systems

　　In a professional audio system, there are generally many equipment used, from professional to civilian. Different equipment has different interface methods, and the connectors used are different, from balanced. There are also balanced inputs. Output method. In order to effectively shield the interference of external electromagnetic radiation, it is necessary to use shielded cables and choose the correct connection method. We know that when the balanced transmission method is used for audio signal transmission, the external interference source affects the two cables in the balanced cable. The common mode interference level of each signal line is almost equal to the ground loop. At the input end of the internal amplifier of the device, the common mode voltage drop on the two signal lines is replaced by a differential mode voltage to cancel each other, which constitutes interference. Voltage, so balanced connection methods should be used as much as possible.

　　When connecting with some unbalanced output devices, most of them are now mostly in order to save costs, convenience and labor, directly use single-core shielded cables to connect the balanced ports and sub-balanced ports, instead of using a balanced or unbalanced variator. This kind of connection shielding layer is also in the audio loop. The noise induced by the shielding layer is also mixed into the audio signal, and then the noise is added. This will be the main way to introduce noise. The correct way is to do both balanced and unbalanced transmission. Two-core shielded cables are used, and the shielding layer is only grounded at one end of the balanced output or input.

　　When both ends are unbalanced devices, if the transmission distance is large, it is best to use a balanced-unbalanced converter or audio blocking transformer to convert to balanced transmission.

　　The connection of current professional audio equipment covers the selection of voltage jumper methods. They all comply with the IEC268-15 specification when they leave the factory, that is, the line output of professional audio equipment is ground resistance output, and the line input terminal as the load is selected For high-impedance input, in addition to the connection between the power amplifier and the speaker, there is generally no need to specifically consider the impedance problem.

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