IsoTek V5 Sigmas: Mains power filter for a “clearer, more open and more convincing sound

In August 2026, Belgian online magazine bestofhighend.com reviews the IsoTek V5 Sigmas mains power filter and concludes: “With the V5 Sigmas, a Hi-Fi system sounds clearer, more open and ultimately more convincing.” The English-language review also includes several detailed descriptions of the listening tests – so it is well worth visiting the website!

“For this review, I integrated the IsoTek V5 Sigmas into my reference system and compared it directly with the PS Audio PowerPlant 12.

The standout characteristic of the IsoTek V5 Sigmas is its transparency. It does not make the Hi-Fi system sound warmer, brighter or more forward. Instead, it seems to remove a layer of electrical noise that prevents the existing components from reaching their full potential.

With the V5 Sigmas, recordings seemed to have greater depth and a more spacious presentation. Instruments occupied more clearly defined positions, while quiet details that had previously been easier to overlook became more apparent. This is the kind of improvement that can be difficult to identify during a short demonstration but becomes obvious over longer listening sessions. You do not necessarily hear a dramatically different system. Instead, you begin to notice that you are hearing deeper into familiar recordings.

Bass reproduction also improved – not through more bass, but through a more controlled, structured and precise low-frequency presentation. Bass notes started and stopped with greater accuracy, while complex bass passages became easier to follow.

Above all, however, the IsoTek V5 Sigmas preserved the dynamics across every track I played. One problem with passive mains filters is that filtering can sometimes improve clarity at the expense of musical energy. If the filtering is too aggressive, a system may sound clearer but less lively. Here, large dynamic swings remained powerful. Percussion retained its impact. Crescendos maintained their sense of scale, while microdynamics became easier to perceive.

In direct comparison with the PowerPlant 12, the differences were subtle but consistent. The PowerPlant 12 gave the impression of a highly controlled electrical foundation. With the Sigmas, it felt more as though it was simply removing obstacles between the recording and the listener.