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Mains interference


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has anyone had much luck with mains noise isolators, suppressors, filter blocks, mains cleaners, power conditioners etc?


reason for asking is a pal is touring a dance act with the usual spaghetti of laptops, VJ's, DJ's, electronica etc.. playing a very varied mix of international venues and festivals. he's looking for a 'magic box' that sorts out problems on those occasions when mains noise occurs and you've tried all the usual options and you're supposed to be on in 5 mins. there is a bit of rationalisation to be done with the backline, so he could introduce a light-weight mains filter into the touring backline if needs be.


he's been looking at the usual offerings from canford, bryant etc and the ISOplug from - www.isoteksystems.com.


thoughts, suggestions?


ta mucho



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Most of the problems I come across seem to be more to do with current flowing in the shield of a mic cable and equipment with Pin 1 issues.


Furthermore, most UK power is actually quite clean (can't vouch for Euro power!) and although not perfect, seems to offer better better tolerance than (say) US power.


I would be inclined to first spend money on some good quality DI boxes (to provide level + impedance matching and galvanic isolation), and spend time checking for correct wiring of audio and related equipment. This then provides a solid basis for tackling any genuine mains related issues (superimposed harmonics, surge, over/undervolatge conditions etc.).


I understand that many of the surge suppressors available today sacrifice themselves in an overvoltage or surge condition, and may not indicate this fact to the user. Shunt mode suppressors are therefore not recommended by a number of experts, since they can bring more problems than they solve. There can be a place for mains filtering, and in some sensitive applications it may be prudent to use a UPS. However, I have not found a need for a filter for many years, and wouldn't consider it to be the first place to solve problems.


Oh, at the risk of canonising its author, have a look at this technical paper taht addresses many of the issues with grounding and noise. Be sure to read the very ueful appendix (written by the ISCE's John Woodgate) that addresses differences between the US and UK.


Just my 2p...



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hi, thanks for the replies.


there isn't a problem at the moment, but this act has about 12 channels of laptop / choas pad / mackie mixer etc and given the large amount of signal loops and interconnects has the potential to be a problem.


fortunately the laptop power supplies have been fine on european mains. but I'm aware that sometimes they can cause problems. I had with an old Dell that used to buzz badly if the mains wasn't perfect. (had to run one gig on battery).


they also spec 'quality' active di's on their rider. last time I saw them they were using BSS AR-133's.


simon - thanks for your helpful comments.


anyone else here with good/bad experience of these sorts of devices?

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