Mains filters – Howard Popeck keeps it simple


This series, written by features editor Howard Popeck  is designed to, in jargon-free terms, explain, introduce, educate and otherwise assist anyone who is interested in learning more about how music in the home is produced. It’s a growing archive.

Thank you. Neil McCauley / editor in chief



There are two types

Series and parallel

What they do

They either place a resistance between the wall socket and the connected equipment or redirect the mains noise from positive (+ve) to neutral – depending on which type they are. Series filters add resistance between the wall socket and the equipment, thus building a partial barrier between the noise and the equipment.


They work well to block some portion of noise, but they don't lower noise on the mains itself.

Compression effects

To some extent they are always current limiting. This is how and why some of them get their 'it compresses the sound' reputation.

Parallel filters

These don’t add resistance but rather redirect, or shift the noise from the positive (+ve) to the neutral. They are non-current limiting. Moreover they are much less effective at noise reduction than a series filter.

Mains noise

In either case, power line noise is not actually eliminated, it’s simply redirected. This is far less effective than actually eliminating it! Some proprietary devices (PS Audio springs to mind) collects the noise, removes it from the mains and then converts it to light.

So, does it replace a power conditioner?

No, it supplements it. Power conditioners, mains regenerators or any type of mains noise filters reduce line noise by a certain amount depending on their design. Mains regenerators are the most effective, but they aren’t perfect.


The less noise you have going into a power conditioner, the better it will work. So, a mains filter is your first line of defense against noise. Use as many as you can to lower the overall mains noise in your home.

They can be placed anywhere in the home to do their job and the more the better. They can even be placed at the output of your power conditioner and make an improvement.

That’s it – for now


More appropriate reading HERE