Russ Andrews DC Blocker

• Eliminates degrading DC


• Audiograde components throughout


• 1500 watt capacity


• Inline device designed to use with a single component


• Multi-layer composition PCB

We believe this is by far the highest-specified DC blocker on the market.

One of the key issues with the application of a DC blocker it that it has to sit ‘in-line’ with the power - unlike all our other filters and mains conditioners, which are parallel designs. This inevitably raises impedance, which goes a long way to explaining some of the potential negative effects we mention below (see 'The Solution').

So, to ensure minimum impact on mains impedance and maximum filtering capability, the design of every element of the Russ Andrews DC Blocker has been carefully considered, and the circuit design features components specifically chosen for use in audio applications.

Our DC Blocker is designed to solve a specific problem of DC (Direct Current) on your domestic mains supply. DC can be in the form of an audible transformer buzz, or sit in the background, potentially degrading sound quality. But what is 'DC on the mains'?


In a perfect world, the domestic power supply to your system should be a pure AC feed. However, along with common mode and differential mode mains noise - addressed by our range of mains conditioners - small amounts of DC current can often find their way into components. This is due to the presence of other domestic electrical devices in the home which, due to their design and/or age, can add DC onto your AC line.


Let’s assume that the waveform of the AC voltage supplying your system is a perfect sine wave. It isn't actually - contrary to most explanations of DC blockers out there, if you look at the waveform on an oscilloscope (via a transformer) it looks awful. But, for the moment, let’s assume it is a perfectly clean and symmetrical sine wave.

Now, if you were to feed that into a component containing a toroidal transformer, assuming it is a perfect sine wave, there would be no issues. However, as we’ve just stated, it’s not at all uncommon to have small amounts of DC present. The problem is that many components with a linear power supply (which use a toroidal transformer to ‘step down’ AC voltage) do not react well to this, as the DC interferes with the magnetic field and causes mechanical vibration as a result.

This is most acute in integrated or power amplifiers which use a large toroidal transformer and can have a very low resistance to DC. Even a very small amount - 500mV or lower, which is not uncommon in an average UK supply - can saturate the core and create quite noticeable mechanical vibration (buzz) in the windings as a result.


Sadly, the solution is also the problem. All the DC blockers we have tested - and there are many of them - have lowered the buzzing but at the expense of sapping musicality and dynamics from the music. So, before you do anything, our advice is to consider the following:

DC tends to be transient - it comes and goes - so, in many cases, the noise doesn’t last and it’s just a case of waiting a short time until it subsides. A common example would be where the DC is caused by someone using a hairdryer in another room.

Likewise, if the buzzing is barely evident, leave it.

Transformer hum can also be caused by over-voltage, so it’s worth checking this first, rather than immediately trying to solve a DC issue you don’t have.

However, if you have a more constant buzzing which is interfering with your enjoyment of the music, we now have a high-quality, low-impact solution: The Russ Andrews DC Blocker.






Don't forget! We are so confident in the performance of this product that it is covered by our 60 Day Home Trial with Money Back Guarantee. Buy the product and if you're not completely satisfied, you can return it within 2 months for a refund. For full details click here.

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