Obsessing over mains filtration and conditioning systems is not part of my life. One of the primary reasons I sunk my life savings into building a dream listening room was to avoid the problems created by noisy, grungy mains. Thus, I did what can only be done when you start from scratch: I specified audiophile-grade mains wiring, the finest consumer units (separated from the house) and AC outlets, PVC trunking - everything which is today accepted as beneficial for mains purity, but which can only be incorporated into a system when you're either re-wiring your home or building a new dwelling. I had assumed the room would then be immune to AC tweaking.

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As each and everyone one of you knows, I have been proven wrong abut this on more than one occasion, not the least being shown what can still be achieved by the incorporation of myriad AudioPrism accessories and the use of a Nightingale mains distribution unit with filtering and conditioning. Yes, these do make audible improvements pretty much across the board. But it wasn't until Nic Poulsen, late of Trilogy, turned up with his IsoTek SubStation - configured as he thought I would need it - that I felt such add-ons could fall under the 'utterly indispensable' heading.

'Configured' is the key word because the IsoTek SubStation is not a fixed, off-the-shelf purchase. I'm loathe to say that none of its competitors are prepared to custom-build units to an individual's requirements, but if they are, then they're keeping pretty quite about it. The one Nic provided for this review consisted of the 'full monty' Hybrid version, but with two of the six unswitched AC outlets which fill the back of the 440x140x345mm unit wired for America's 120V; you'd be surprised how much stuff arrives from abroad NOT wired for UK voltages.

In the Hybrid SubStation, Poulsen installs both overkill filter modules and isolation transformers. The standard filter module is a multi-stage compound filter design with transient two-stage suppression between live/neutral, live/earth and neutral/earth, while the isolation modules feature hand-wound EI transformers with Faraday screens. Nic specifies top-quality parts throughout, including internal wiring made with sliver plated PTFE cable and double-sided PCBs mounted on a stainless steel base. All modules are individually fused, with the fuse in the neutral line so that it also protects the transient suppression devices between neutral and earth. The live-to-earth devices are protected by the external fuse located in the IEC socket. An LED mounted on the PCB shows that the module is on and the fuse intact.

Read more about the Isotek Substation on Page 2.