The power source noise referred to by LBT in this article refers to AC noise and switching noise of electrical equipment. Power noise in audio equipment systems is an old problem, as the broadcasting system coexists with a large lighting system, so the broadcasting system itself also comes from the lighting system.

1、 The specific sources of power supply noise

1. The indicators of the audio equipment are poor. The preamplifier, modulator, equalizer, etc. have the greatest impact on the system's AC sound. Some equipment (including imported equipment) have low costs and high noise levels.

2. Sound equipment leakage. If there is a leakage in a certain part of the system, the leakage current will enter the system through the signal ground wire or the chassis ground wire, forming an AC sound. This situation cannot be detected with direct discharge. The power cord of the suspected device must be unplugged to confirm.

3. Introducing AC sound through the coaxial cable of the AV link. Due to the fact that most household audio equipment systems are audio and video synchronized. All excessively long coaxial cables may introduce AC sound because the shielding layer of coaxial cables is made of non-magnetic materials, which is ineffective in shielding low-frequency electromagnetic fields. Moreover, it is difficult to avoid grounding coaxial cables with audio systems in AV equipment.

4. Introduce power supply noise from the power supply system. When the lighting switching and dimming devices with large capacity are running, the power supply will emit significant fluctuations, causing interference. The power harmonics generated by the thyristor will also cause interference.

5. Introducing power noise through lighting system wiring. When high-capacity lighting wiring approaches the audio signal line, it can also cause power noise.

Television studio sound system

2、 Resolve corresponding measures

1. The selection of equipment should not only focus on indicators, but also consider the actual situation of low improvement.

2. All metal casings of equipment in the system must be grounded and a "one point grounding" must be implemented. The grounding wire must be in a star shape and chain connection is absolutely not allowed.

3. The sound equipment system should avoid sharing the same power supply with the lighting system. When the equipment capacity is not very large, one phase of the three-phase power supply can be allocated to the audio system and two phases to the lighting. Otherwise, a dedicated line should be directly allocated to the audio equipment system from the distribution room. In addition, all audio cables are kept away from the lighting wiring, especially the wiring on the lamp rack.

4. When selecting dimming equipment, the new generation of equipment should be chosen instead of outdated thyristor dimming equipment, as outdated dimming equipment can seriously deteriorate the power waveform and fill the space with malignant clutter radiation. 5. Insert a noise suppressor after the system equalizer and before the main amplifier. This is very effective in suppressing the basic noise of audio equipment, but it is basically ineffective for switching noise, as the level of switching noise is usually quite high.

In short, as long as we correctly analyze the source of noise and take corresponding noise reduction measures, the noise problem will be solved.