Russ Andrews' 'Purifier' accessories are all shunt-connected mains filters: that is, they sit connected to the mains supply and effectively 'suck' the interference out of it without coming between mains and audio equipment.

Many experimenters have found this approach preferable, though there are so many variables in specific designs that it may be dangerous to generalise. We looked at the Ultra Purifier some years ago and have also investigated the much cheaper 'Silencer' which implements some of the same ideas.

The crucial part of all Purifier designs, however, is a component which RA dubs a 'clamp' – in this case the Super Clamp, though the most sophisticated Mega Clamp is available for an extra £110.

This part provides very rapid reaction to over-voltage spikes on the mains, adding to the general high-frequency filtering provided by the capacitors also included.

If our comparisons between this and other items of this type are anything to go by, differences are qualitatively different from cable changes. Above all, the sound seems to acquire an extra delicacy and refinement, as if some rather rough-sounding distortion has been removed.

As a result, sounds are generally clearer and better defined and rhythm, always a concern of Russ Andrews', is fractionally more precise and convincing.

As always, we tried various combinations of kit (simply plugged into the same distribution board with the Mini Purifier) and these findings were remarkably consistent across the lot, perhaps just slightly more apparent with digital source components and analogue. Classic tweakery, really – slight, yet somehow obvious.

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