While it is now accepted by many that a poor mains supply can have an adverse effect on the sound of an audio system, it is less commonly acknowledged that the same holds true of video. Think about it, if your source, A/V receiver and processor and display are all taking power from the same mains supply, and that supply is dirty or noisy, then it stands to reason that this will affect all aspects of system performance.
Given this, very few companies have even attempted to tackle the issue of protecting video devices from mains pollution. So far, the only company to make a serious attempt at resolving this is mains filtration specialist Isotek with its new Mira.
The Mira has two mains sockets along with a video loop (to protect your system from lightning strikes on the aerial) all mounted in a steel extrusion. One end of the extrusion is sealed while the other end has a fused IEC mains inlet and an LED to show power is applied.
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Price: £150
More info: Isotek
Size (WHL): 90 X 82 X 150 mm
Weight: 900g
Connectivity: IEC mains inlet, 2 13A mains outlets (video and component), 'F' type aerial sockets (1 X input, 1 X output)
Features: Triple resonant absorbing filter plus shunt filter on video outlet, Delta configuration filter on component outlet. 2,200W capacity at 230V (1,100W on each outlet), lightning strike protection on aerial loop, soft start and voltage spike protection.
Plus points:
Protects connected components from mains noise and voltage spikes, protects other components from noise generated by connected components, improves both video and audio performance of components
Minus points:
None to speak of
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The video outlet filter circuit, while loosely based on that in the Vision mains filter, (itself a product based on the Minisub GII audio mains filter, but with a dedicated video filter), is claimed by Isotek to be six times more effective at removing mains noise than the Vision's at the frequencies which adversely affect video displays, and is a self-adjusting circuit which allows the filter to reconfigure itself to the power demands of any display device connected.
The topology is described by Isotek as a 'Triple Resonance Filter', the idea being that the noise which can harm the display device, and the noise produced by the display device, are both predictable, so this filter is designed to absorb both inbound and outbound noise, while a separate 'Shunt' filter absorbs sudden spikes and surges which are random in nature. To give you some idea of this filter's abilities, independent lab tests have shown that mains-borne noise leaving the Mira is at 1/10,000th of the noise level going in.
The audio 'component' outlet uses a 'Delta' filter circuit very closely related to that used in Isotek's MiniSub GII mains filter for high-end audio systems, which protects the connected component on all three legs positive, negative, and, critically, the earth. While most mains filtration products take great pains to protect the obvious positive and negative legs of the mains, most completely miss out on the earth. This is a pity, since much of the mains noise present actually rides the earth line as this is where switch mode power supplies found in wall wart transformers, PCs, set-top boxes and games consoles tend to dump all the noise and rubbish they generate during normal operation.
The Delta filter is like several filters in one, taking care of both 'differential mode' noise, such as sudden spikes from switches and surges, and 'common mode' noise, such as the insidious RFI noise which is present from radio transmitter, mobile phone masts and Wi-Fi access points, not to mention switch mode power supplies such as those you'll find in mobile phone chargers and set top boxes.
The Mira also features a soft start circuit which prevents mains surges at switch on and prevents voltage spikes from reaching connected components. While these two problems are usually not enough to do any lasting damage to electronics components, they can, over time, damage power supplies and shorten the operational life of components.
Performance
I tried the Mira with a Sony KDL-32U2000 720p 32in LCD screen, a Sony KDF-E50A12U 720p 50in rear projection display and Sony VPL-VW50 1080p front projector being fed from a HTPC and Sony PS3 via HDMI. On the audio side, surround sound was fed to my Denon AVR-3805 AV receiver via S/PDIF, which in turn fed a pair of Bryston 3B-SST and a 14B-SST power amps driving Martin Logan Vantage L/R speakers, a Martin Logan Cinema centre and a pair of Martin Logan Fresco surround speakers, while subwoofer duties were performed via a Rocket UFW-10.
The Mira's effect was immediately noticeable on all displays, with more shadow detail and low level information being easily discernable, removing chroma noise in solid colour blocks (especially when using analogue inputs), improving colour saturation, and on analogue feeds it sharpened edges and prevented overshoot (the slight ghosting you see in high contrast areas on screen).
Up until now the second audio component outlet on the Mira was unused, so I connected the AVR-3805 to this and tried the system again. Running the AV receiver from the audio outlet of the Mira brought about further improvements in bass control, and also gave a little more extension with a touch more slam. But it was in dialogue intelligibility where the big gains were heard - very low level dialogue almost uttered under the breath or by characters in the background now became clearly discernable while the main dialogue channel showed substantial gains with dialogue gaining more presence and sounding more natural. This was echoed musically where vocals gained greater weight and presence in my system, bringing out subtleties in the vocal performance which were simply lost when the receiver was plugged straight into the wall.
Images were more precisely placed throughout the surround sound channels with greater continuity between the front and surround channels, it was as though you had moved the surround speaker closer to the front speakers while simultaneously improving their dispersion, the overall effect was to completely envelop the listener in a 360-degree sound field.
There is no doubt that mains-borne interference is only going to get worse as we all have increasing amounts of electrical gadgets in our homes, all generating noise from their power supplies. The Mira tackles not just the noise being generated by the display devices themselves, but also prevents them from being adversely affected by mains pollution already present. 
