| Video Noise December 2008
How to Kill a Home Theater
System, Part One: Don’t Use AC Power Conditioning
 Maybe
you’ve heard all the right reasons to use a power-conditioning product. Maybe
you’ve heard some stupid reasons from a young dork at your local electronics store.
If the right reasons for using power protection haven’t convinced you, perhaps you
should reconsider. Maybe you’re convinced, but don’t really understand how to
select a product that’s appropriate for you. I’ve reviewed more than 85
power-related products, and my career as an engineer has included many hours of formal
training in AC power systems and agency compliance (certification). Here are some notes on
the features of power conditioners that I think you should consider using, and how
important I think they are.
Surge and spike protection: Power surges happen
relatively slowly and may last for a while. Spikes are brief but can be severe -- such as
from a bolt of lightning striking nearby. Other sources of spikes aren’t as dramatic,
but can still destroy components if the spike’s energy content is great enough. Surge
and spike protection can save components from damage or death -- to my mind, it’s a
mandatory feature. Many products use metal-oxide varistors (MOVs) for some or all of this
protection, but MOVs are damaged to some degree every time they stop a surge or spike. (If
the type of protection is not specified, it’s almost certainly based on MOVs.) A
single large event can blow out all of a conditioner’s MOVs, but so can hundreds or
thousands of small events. MOV products cost $20 to $2000 USD; some have front-panel
indicator LEDs that tell you if the MOVs are still operating normally. The prices of
non-MOV products whose protection never wears out (though it can still be disabled by a
powerful lightning strike) start at around $500 and go up to many thousands of dollars.
 Noise filtering
removes contamination present in the power line. It’s my experience that this makes
no difference in the image quality of digital video systems. Noise filtering can improve
the sound, but for the best audio performance you pay a lot. For example, the Audience
adeptResponse aR6-T six-outlet power conditioner I recently reviewed
for Ultra Audio sells for $4600. Most such products in the $200-$700 range do
little to improve the sound, and a few actually make it worse, most often because the
components in inexpensive conditioners don’t deliver enough current fast enough even
through their High Current or Amplifier outputs. Noise-filtering gear in the $200-$700
range that does improve the sound tends to have few bells and whistles: no fancy
front-panel displays, no LED arrays, etc.
Auto shutdown for over/undervoltage conditions: This
is included in some power conditioners that may cost a little more, but they’re worth
it -- some good-performing products that have it are available for about $500. Typically,
such conditioners shut down power when the AC voltage is below 90V or higher than 130V,
which can save from destruction any connected components. More advanced versions of Auto
Shutdown delay restoring power to components until a safe voltage level has been restored
for at least a minute or two. This protects gear from the surges that can happen
immediately after a power failure, when power is being restored. More than any other
features, Auto Shutdown and surge/spike protection are likely to save your connected
components from damage.
Balanced power: In this method of delivering AC, a
special transformer delivers 60VAC-60VAC instead of 120VAC-Neutral. This removes more
noise from the power line and tends to improve the sound a little, but does nothing
detectable for digital video displays. With a good sound system, balanced power tends to
reveal more detail more than does filtering alone. Expect to pay more for balanced power,
and a lot more if you want to run your power amps balanced: $1000 to $2000 for
source components and amplifiers that output no more than 50Wpc, and $3000 to $10,000 to
run an entire home-theater system equipped with reasonably powerful amps. Balanced power
tends to decrease the level of background noise, provided your room is quiet enough to
begin with for this to be noticeable. The result can be sound that is more delicate,
spacious, and detailed.
Voltage regulation strives to keep the AC power from
the wall as close as possible to what it’s supposed to be -- 120V -- despite any
changes in the power-line voltage. Again, this is not much of an issue for digital video
displays, or for most solid-state audio components. You might find voltage regulation most
useful for some tube electronics and some analog source components, such as turntables or
tape players. Video displays employing a cathode-ray tube or a projection lamp might also
benefit from voltage regulation. Because voltage regulation requires some sort of active
component(s), and because there may be a need to deliver a fair amount of current, voltage
regulators tend to cost $1500 or more, and may not include some or any of the other useful
power-conditioning tools discussed here.
. . . Doug Blackburn
db@hometheatersound.com |
