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MAINS DISTORTION?

The voltage that (for example) European power companies ought to deliver at your wall socket is a 230 V (+10%, -6%) sine-wave with a frequency of 50 Hz (+/- 1%). This is generally not what you get delivered! Every consumer connected to the electricity grid has a negative effect on the mains supply you actually receive. Each consumer, including you, creates a spectrum of interference that pollutes the overall supply.

Click the picture or here for more measuring plots showing mains distortion

The type of equipment creating this pollution influences the amplitude and frequency range of the interference spectrum produced. Importantly, there is a difference between narrow banded and broad banded interference spectra:

Narrow band interference is mainly created by switch mode power-supplies (e.g. those used in computers and industrial applications), digital equipment (e.g. CD players, minidisc and DAT recorders), video equipment (e.g. television sets, videos and DVDs) and broadcasting units (radio, GSM and ‘baby phones’). This distortion manifests as discrete high frequency interference at varying amplitudes. The electronic circuits of your audio/video system demodulate this interference. The residue of the distortions is an unwanted signal, in the form of electrical ‘noise’, which degrades audio and video performance, causing effects such as a muddy sound or picture.

The coarse, sharp sound of many digital devices can often be explained by noise these devices themselves create in the mains, which has a negative influence on the musical performance of the whole system.

Broad band interference with the mains supply is caused by inductive devices (e.g. electric motors) and mechanical switches (e.g. light switches, and fridge thermostats). These create noise that is mostly transferred to audio/video equipment by electromagnetic radiation. This will often cause clicking, humming, and similar kinds of distortions experienced during audio and video playback. In practice, these types of distortions are not really able to be solved by use of a line conditioner. The only way to solve this problem is to reduce the distortions at their point of origin.

Another kind of distortion is over-voltage, which is caused by electricity generators (i.e. power plants), changes due to induction, and lightning. Those distortions can be disastrous for your system. It will express itself by means of instability or even complete failure of your equipment. Fortunately, the latter rarely occurs. The Kemp Elektroniks Power Source has over-voltage protection.

From the above you can see that having a polluted mains supply that negatively affects the performance of your audio/video equipment is the rule rather than the exception. The problem is increasing as more and more electronic equipment such as computers and wireless communication is used around the world, with new developments with as yet unknown consequences in the pipeline - even as you read this, power companies are busy planning the distribution of telephone and Internet connections through the mains!