DC on the mains supply has been a hot topic in the last few years as audiophiles understand the importance of a “clean” supply. Ian Ringstead fits the MCRU Excelsior DC Blocker to his system to see what effect it has. 

Mains power is something most people take for granted and never give it a second thought unless there is a power cut. Now as a hifi enthusiast I’ve known for a long time how important a good power supply is to the quality of the sound an amplifier or source component produces, but it wasn’t until more recently that I read articles on the quality of one’s mains power and how it is affected by many outside influences. Dirty mains can cause transformers to hum because the laminates rattle due to interference on the power supply with mains voltage variations or from industrial plants etc. Also our home is full of mains borne pollution from switch mode power supplies in our computers, routers etc. the-excelsior-dc-blocker- (1)

Life is therefore quite hard for a decent hifi system to perform at its best if mains pollution is bad in your home. The wiring in your home is usually on a ring main (or radial) and this means many sockets can be joined together on a common circuit. Anything plugged into that circuit will therefore be affected by a component when it is plugged into that circuit and will interfere with the circuit as a whole. I decided to get around this problem by installing a dedicated circuit isolated from my house’s mains by having a separate consumer unit, using 30 amp wiring and a dedicated earth spike buried outside my house in the garden to provide a separate earth point. This may sound extreme to some readers and I have been scoffed at by some friends, but the effort in my view was well worth it. I got a lot less interference from things like my fridge freezer or central heating thermostat switching on and off and the bass was a lot better.

I have also invested time and money in buying or making up good quality mains leads and have a good quality mains block. The socket my hifi plugs into on the wall is silver plated, again for better contact and it enhances the performance. I think anyone who spends a reasonable amount of money on hifi and listens to music a lot should try to do what I have. It is up to individuals how much they spend on doing this and thousands can be spent on exotic mains conditioners, leads and cables, but this does not guarantee good results.

The reason for this lengthy introduction is because I was recently asked to try out a new mains product by Huddersfield based company Mains Cables Are Us (MCRU). David Brook the proprietor and down to earth Yorkshire man contacted me to see how I wanted my DC mains blocker configuring. Basically this is a very high quality mains lead that has a filter placed between the mains plug and the other end of the lead that plugs into your mains block to supply current to your equipment. Mine came fitted with a Furutech mains plug (others countries are available) and 16 amp IEC socket to plug into my mains block.

Sophisticated technology has been used to produce a mains power lead unlike any other manufactured and designed to block the DC that occurs in the mains supply. Manufactured using the best available materials the Excelsior Mains Lead utilises substantial OFC mains cable with 4mm sq individual conductors which are terminated with a gold plated audiophile mains plug and gold plated IEC connector (either the standard C15 IEC or C19 high current) and used solely on their own this would be a formidable mains power lead in its own right.

MCRU have taken the design further and housed a powerful mains filter in the centre of the cable, the aluminium enclosure houses a specially designed DC blocker. As mentioned earlier DC (direct current) occurs in the mains supply from house-hold appliances and has been present in the supply but not correctly addressed or acknowledged until recently.

Transformer hum is as a result of DC in the mains. MCRU state their power cord will remove it and also improve the overall sound quality from your system. The power lead has been tested to prove its effectiveness on a live mains supply and also in a computer simulation programme specifically for this task. Standard length is 3 metres overall, but longer lengths can be made to order.

Now I know for a fact what mains hum can do to power amps in particular. Back in the 80’s when I sold Naim amplifiers we would every so often get a customer who would ring up or call in to say their amp was buzzing badly. We would try it in the shop and have no problem, but as soon as they took it back home it would buzz again. We contacted the manufacturer who said it could only be bad /dirty mains causing the trouble. If it persisted we would change the amp as part of our good customer service, just in case that particular transformer was sensitive to dirty mains. At the time mains filters weren’t really talked about and better quality mains leads were not considered necessary. Then in the 90’s this problem of dirty mains was talked about far more and companies started to sell mains filters, power blocks and leads that they claimed would dramatically improve the sound of your hifi system.the-excelsior-dc-blocker-

The sceptics amongst you might still think this is all snake oil and how or why should good mains cabling and isolation products make any difference. Well I for one have definitely reaped the benefits of taking care with my system and using good components to address the issues. I haven’t gone crazy and spent thousands, but just been sensible; I like anyone else have become sceptical of wild claims for cables and other products transforming your system, especially when these items cost a lot of money. David just said to me try it in your system and if it sounds better then great.


Having used the Excelsior DC Blocker now for a few weeks I can say it has just sat there and done what it is supposed to do, improve your systems sound. It isn’t a “wow what an amazing change has been made” type of experience, simply my system sounds great and I can really appreciate what the units are doing and all my music is highly enjoyable. Sound staging is solid and clear and there are no nasty harsh higher frequencies. I have had several different components I have been evaluating over the last few weeks and they have all worked flawlessly with no mains pops or the sound being grungy. Often when I listen to the system during the day it can sound variable and they say your system will always sound at its best late at night when most people are in bed and industrial plants are running down.

All I can say is that MCRU Excelsior DC Blocker works. It is very well made and unobtrusive. The fact David will make it to whatever specification you want is a bonus and at £599, although not cheap due to the quality of components used, I feel offers good value compared to the other items I have either had or tried over the years.

Sound Quality – 8.6/10RECOMMENDED LOGO NEW

Build Quality – 8.7/10

Value for money – 8.5/10

Overall – 8.6


Great build quality, easy to install and unobtrusive. Your system will sound better.


Not cheap but if you want to try it David will happily let you buy on a trial basis so nothing is lost.

Ian Ringsted

Designer’s Comments

The Excelsior started life as an idea aimed at owners of amplifiers that hum loudly. Customers were contacting us asking if the hum could be eradicated, we explained it’s not really the amp humming its the transformer inside the amplifier. Usually caused by DC present on the mains. Eradicating DC kills the hum and improves system performance.

​DC offset can be introduced into your mains supply by both other devices in your house and from other houses in the street, or light industry that you are unlucky in sharing a phase with.
Another way of considering DC offset is asymmetric mains waveform, the peaks one way are smaller than the other.

DC offset on the mains will cause the transformers in your equipment to saturate.  Saturating transformers work far less efficiently and generate a lot of noise both physical and electrical.

The DC blocker removes the offset from your mains, while maintaining the low impedance supply to your equipment.​

As well as blocking DC we wanted the Excelsior to function as a high end power lead so even if the dc blocker was not present it would still improve sound quality when compared to kettle leads, we think we have achieved that by using audiophile grade plugs and connectors and an often over looked item, the mains fuse which we up-grade.

The final pieces in the jigsaw are mains cable with 4mm sq conductors housed in a special carbon infused braiding to prevent pick up of RFI.

David Brook

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