Power and grounding for high performance AV systems: A Primer
The diagram below presents the Acoustic Frontiers approach for thinking about power and grounding as it relates to the high performance audiovisual systems found in our audiophile listening rooms and home theaters.
- The utility power enters through a service panel. The utility power comes in single or three phase variants. Most residences are supplied with a single phase, three-wire service, comprised of two 120V legs and a neutral. This incoming feed can be connected to provide either 120V (one leg to neutral) or 240V (across both legs). Larger commercial and industrial facilities are given three phases of power. It is important to note that the utility company does not provide a ‘safety ground’ – this is made locally.
- The service panel contains a number of circuit breakers which are devices designed to protect connected electrical circuits from over-current conditions.
- A ground rod, sunk into the earth, is connected to the service ground to protect the building from lighting. One service panel may have many electrical circuits, each of which supplies a number of wall outlets. We plug our audiovisual systems into these wall outlets so they can get power.
- Connected systems, including cable TV, satellite and phones are external to the power system but can interact with it in important ways. All these systems are generally connected to the ground rod to protect from lightning related voltage surges being carried in from an external cable TV line or roof mounted satellite dish. Occasionally the safety grounding for these systems is made at another convenient location if, for example, the electrical service enters at one end of a property and the cable at the other.
What is clear from the diagram below and explanation above is that the electrical circuit feeding our AV systems is quite complex and that there are a lot of ways for issues to occur which can degrade and damage our systems!
Protection and performance issues related to the quality of power on by the utility powerline entering the home or studio. These issues include powerline noise, surges, sags and swells, long term under and over voltage events, outages, waveform distortion and DC offset. The causes are natural events such as storms and pollution from other power users including industrial facilities and other homes / commercial buildings. Learn More.
Protection and performance issues related to reductions in power quality caused by devices within the home or studio.
Noise, surges, waveform distortion, sags, waveform distortion and DC offset are often caused by devices within our home or studio such as kitchen appliances, lighting dimmers, compact florescent lighting, power tools and air conditioning units. Often these devices are on the same circuit as our sensitive audiovisual electronics which makes the matter worse, but even with dedicated circuits these devices may still cause noticeable issues. Learn More.
Performance issues caused by electrical circuits within the home or studio.
The most common issue is that the path from component to service panel lacks the ability to meet the instantaneous power draw requirement of electronics. All parts of the path make a difference – power cables, wall outlets, electrical circuits and circuit breakers.
Performance issues created by our audiovisual components themselves.
The rectifiers that turn AC to DC inside linear power supplies and the switch mode power supplies create noise on the powerline that can worsen the performance of connected electronics.
Performance issues created by power strips or conditioners.
These components can actually cause harm as well as doing good. For example: metal oxide varistors (MOVs) based surge protectors couple noise into the sensitive equipment ground; resistor-inductor-capacitor (RLC) filters can also limit the ability of components to draw instantaneous power.
Performance issues due to ‘hum’ and ‘buzz’ created by power supply leakage current, ground loops and electromagnetic interference. These issues, not power quality, are the major causes of 60Hz hum. Learn More.
Protection issues caused by connected systems, such as CATV, satellite and phone.
Each system that connects to our audiovisual gear is another way for power quality issues to appear. Surges for example, are sometimes coupled in through CATV lines or from the satellite dish mounted on the roof.
Performance issues created ground loops with connected systems.
Ground loops can be created anytime that the ground impedance is different between connected devices. External systems are another way for this issue to manifest itself. Learn More.