Russ Andrews states DC on the mains is a problem for linear power supplies, especially ones with larger toroidal transformers, which are common in integrated and power amplifiers, as they have a very low resistance to DC. According to the brand, this is often caused by other equipment in the house, which, by nature of their age or design, can introduce DC to the AC mains supply. We are told that even 500mV of DC, or lower, can affect the magnetic field within the transformer by saturating the core, creating a mechanical vibration within the coils of copper wire, which is heard as a noticeable buzz.

Traditional mains filters, including the parallel (as opposed to in-line) type produced by Russ Andrews, are not designed to block this unwanted DC — a purposeful design choice as parallel filters do not harm sound quality. Blocking DC requires an in-line device, but these can have inherent problems.

Russ Andrews, technical director, explains:

There are many DC blockers available, and they all reduce the buzz, which is exactly what they are supposed to do. However, every model we have tested has also sapped the music of its dynamics and musicality. This is explained as the result of the impedance being increased by the components that sit in line with the power supply.

According to the manufacturer, the design of the Russ Andrews DC Blocker is based on sound engineering principles, such as the use of extra-wide, double-layer tracks on the circuit board made from 4oz pure copper for a solid low resistance and current handling capability.

The internal components include Kimber Kaps for additional smoothing of the mains supply; two large-capacity 10,000uF capacitors for superior current handling; Kimber Kable TCX internal wiring; high-current Vishay diodes for DC blocking up to 1.5V; and a non-resonant/non-ferrous ABS case. It is rated for equipment whose power requirement is a maximum of 1,500 watts.

Despite the introduction of the DC Blocker, Russ Andrews advocates the use of such devices as a tool of last resort, as Russ further explains:

DC can be transient in that it comes and goes, perhaps caused by someone using a hairdryer in the house, for example. The buzzing can also be barely evident and is masked by the music, so therefore don't try to treat it. And transformer buzz isn't always caused by DC; it can be the result of over-voltage on the AC mains, so it's always worth testing for this before resorting to fixing an issue that may not exist. But if there is still a consistent problem, then use one of our new DC Blockers, as it is a very carefully considered design that won't interfere with your enjoyment of the music.

The Russ Andrews DC Blocker is available now for £549 and comes with the company's risk-free, 60-day money-back guarantee. You can try it at home and return it for a full refund if you are not entirely satisfied. It is also covered by the company's 25-year warranty.

Visit Russ Andrews for more information