Articles and whitepapers

Mains Cleaning for High-Quality Audio and AV (2/1/2004)

By David Allcock

Mains treatment has been a subject of much debate for many years as to its effectiveness and relevance in high-quality stereo. This has now been extended in the UK to its application in multiroom systems and AV systems. In the USA, where they are currently about two years ahead of the UK and Europe in the design and evolution of these systems, it is almost unheard of to find a system without mains treatment. So, in answer to the most obvious question, 'Do I need mains filtration?' the answer is undoubtedly 'Yes.'

Mains Problems

Starting with EMI/RFI (Electro-Magnetic Interference/Radio Frequency Interference), this duo is responsible for many problems within an audio and AV system. Any long piece of unshielded wire acts as an aerial. Long pieces of copper wire, such as the ring mains, make a great aerial for picking up this kind of interference, and the mains cables running from the wall socket to your equipment are even better. This noise frequently makes it through the relatively minimal filtering in most audio components, and then proceeds to wreak havoc inside your equipment, smearing fine details, damaging the imaging, introducing grain and harshness in the high frequencies and generally resulting in lower performance than you paid for.

Noise from other equipment in the system is the next problem. Most equipment sinks any noise generated internally straight into the earth plane, which goes out uncontrolled into your mains supply and proceeds to pollute the power feeding other equipment. Digital components and power amps are especially bad at polluting the mains, with pre-amp stages and anything analogue suffering badly from this noise. To add further to the problem, satellite boxes, DVD players, video recorders, AV amps, video projectors and televisions are all responsible from generating a great deal of noise from their cheap, unfiltered, switch-mode power supplies, causing further problems for the precision power supplies in AV and audio equipment.

The next problem is caused by mains sagging. Quite simply, your mains does not deliver the 230V it is meant to. Today's power supply regulations mean your electricity company must only provide power between 217V and 253V. Given that some power amps will see a doubling of distortion if the power supply drops by 10V, this is a very real problem.

Finally there is the problem of waveform clipping, where the top and bottom of the 50Hz sine wave becomes clipped or flattened. This is caused by power supplies only taking their power at the top and bottom of the sine wave, and this will result in your equipment failing to get the power required to allow it to perform to its fullest capability.

Unswitched sockets

Fortunately, there is a great deal you can do to deal with these problems and ensure you get the performance you paid for. The basics are to ensure that the sockets feeding your equipment are of high quality and unswitched. Unswitched sockets do not have the contacts required for the switch in the line of the mains supply. Over time, switches in a switched socket get a layer of carbon across their face caused by arcing when the switch is thrown. Instead of a solid conductor you get a semi conductor, introducing unwanted resistance and capacitance into your mains supply and degrading the current delivery capability of the socket. Furthermore, high-quality MK unswitched sockets have high-quality contacts within the socket with a larger surface area than cheaper sockets, ensuring excellent conductivity and current delivery.

MK unswitched sockets

Direct Spurs

If you have a dedicated listening room, home theatre or equipment cabinet, a spur direct from the breaker box is an excellent investment. By removing other sources of noise from the mains ring supplying your system, you remove much of the noise which can degrade the performance of your system from within your home. A further benefit is that the direct run of cable gives a shorter length of copper to act as an aerial directing EMI/RFI into your system.

High-quality mains cable

High-quality, fully-shielded mains cables will also prevent the ingress of further EMI/RFI into the system. Isotek mains cables are designed with this in mind, and the Elite and Super Elite cables use very high-quality Furutech cryogenically-treated connectors to give a greater contact area to the pins in the IEC connector, allowing greater current delivery and a cleaner path for the mains supply into the equipment.

Whilst this has been found to have a remarkable effect on the sound quality of amplification components, we have also seen this make a noticeable improvement in the quality of video displays such as plasma, DLP and LCD projectors - undoubtedly giving the analogue-to-digital converters in the driver stages, cleaner power and less interference to allow them to carry out A to D conversion more accurately.

Active mains filtration

These measures are mostly passive in nature, and form a solid foundation for your system, but far more aggressive action can be taken with active mains filtration. Starting with basic plug-in noise suppressors, such as Isoplugs and Audioprism Quiet lines, these are the size of a wall-wart-type power supply, but actually suppress noise from other components. Whilst there are no definitive rules to using these, plugging them into a socket adjacent to that of a noisy device at source tends to bring about the greatest benefit. It is relatively easy to find such trouble makers. Start by turning off all electrical equipment in the house then turning on one piece at a time and listening to your system for harshness in the high frequencies, loss of resolution in the bass frequencies and an increase in the noise floor of the system when it is not playing. This will indicate an electrically noisy component that needs a suppressor. The idea is to suppress the noisiest components in the home in order to give your system the cleanest possible mains to work with. The effect of these may be diminished if a spur has been put in.

In-line mains filtration

Using in-line mains filtration, where the mains runs through a filter network to remove unwanted frequencies on the mains supply, is highly effective. Products such as the Isotek Mini Sub and the Kemp Power Source are high-current filters that allow the entire system to be filtered, including high-power items such as AV amps and power amps. What is critical here, is that each socket is filtered individually, not only preventing noise from entering equipment, but ensuring that the component does not further pollute the power supply for other components - known as mutual isolation.

Kemp Power Source mains conditioner

Today's AV amps, video scalers and AV processors look more like computers with power DSPs, all using switch-mode power supplies, and with the DSPs being inherently designed to dump noise to the earth plane. These devices are amongst the worst mains polluters of them all, and all of this noise is allowed into other components in your equipment rack, thus significantly degrading its performance.

The Mini Sub uses individual filters that are targeted at preventing the intrusion of mains noise into components, and then isolating at specific frequencies the noise from analogue components, digital components and power amps, thus preventing it from returning to the mains. A hybrid product is the Isotek Main Line, a mains cable which is fully-shielded and has a none-current-limiting two-way filter built into it. This protects both the component it is connected to and other components, simultaneously.

Isolation transformers

From filtering we move to isolation transformers. These use the principle of a transformer which allows 50Hz mains sine waves to pass through, but blocks everything else from entering or leaving the transformer. These are the best possible barrier to EMI/RFI and mutual interference problems. Whilst their advantages have been know for some time, they have always had problems of lack of capacity, unpredictable interactions with components and current-limiting power amps and AV receivers, doing more harm than good by compressing dynamics and increasing the distortion of power amps. The Isotek Substation and Qube have removed these problems. By isolating each component separately in a flexible, custom-designed chassis, each component can realise its full potential while being completely isolated from the mains supply driving it. Power amps and digital components show great improvements when powered by isolation transformers, and with the Substation and Qube available in standard rackmount sizes, these components can be easily integrated into an audio or AV system.

Isotek Substation isolation transformer

Mains regeneration Finally, to deal with the problem of clipped sine waves or voltage sags, mains regenerators represent the ultimate solution. Acting as dedicated amplifiers, these units take in mains power, generate a sine wave at 50Hz (although some of the more sophisticated units can generate different sine wave frequencies which some components respond favourably to), and amplify this to deliver 230V at their outputs to power the components. Two current problems with this solution centre around price, which is invariably high, and power delivery, which is currently inadequate for all but the smallest systems and totally unsuitable for AV amps. This solution is therefore restricted to source components, but if you want the very best, this is it.

Another solution which has recently emerged, is the voltage stabilizer. This device actively adjusts the output voltage to ensure 230V is always delivered to the outputs, even if the voltage sags significantly. This is ideal for power-hungry components which show serious degradation when the mains sags. Currently, Monster Cable, Isotek and Equitech manufacture these products, although units dedicated to the UK and Europe are only starting to emerge.

Conclusion

To answer our initial question, 'Do I need mains treatment?' as I am sure you can see, the answer is an unequivocal 'YES!' With today's world becoming littered with increasing numbers of switch-mode power supplies, digital mobile phones, 3G communications networks, wireless Internet and an increasing number of terrestrial digital TV and radio broadcasts, greater levels of noise and interference are being introduced into our systems. So to ensure we get all the performance we have paid for, mains filtration is our best line of defence.

Written by David Allcock for hififorsale.com, a mail order and online retailer of audio and AV accessories, cables, racks, and mains products from around the world.

www.hififorsale.com