| Video Noise January 2009
How to Kill a Home Theater
System, Part Two: Use the Wrong AC Power Conditioner
 Use a cheap UPS
(uninterruptible power supply)
An uninterruptible power supply (UPS) supplies AC power for
a short period of time from an onboard battery. A UPS makes sense for a home-theater
system only when your video display has a projection lamp. When such displays are shut
down, their cooling fans continue to run for a few minutes to cool the lamp and thus
protect the optical-system components from the heat produced by the lamp. If you have such
a display, a UPS will let the fans run long enough after a power failure to do their work.
The output of a "true sinewave" UPS emulates the
smooth sinewave of the AC power delivered to your home. But "true sinewave"
products cost more than UPS systems designed for computers, and many people think
it’s OK to use the latter. But cheap UPS products cost less because fewer and less
expensive components are used to produce, from a DC battery, a waveform that is often a
jagged squarewave, triangle wave, or sawtooth wave, not a true sinewave with nice, smooth
curves. The sharp corners of jagged waveforms cause extreme levels of high-frequency
distortion that can damage power supplies, or pass through them to damage other
components.
 Which components or parts are damaged
and how quickly the damage occurs are difficult to gauge because there’s a wide range
of tolerance for poor-quality AC power. More than likely, products with switching power
supplies, such as are common in newer video displays and disc players, will survive a
poor-quality UPS’s low-quality AC power. But products with analog power supplies --
many power amplifiers, A/V receivers, preamplifiers, DACs, surround-sound processors,
VCRs, cassette decks, etc. -- can be damaged by the high levels of distortion present in
poor-quality AC waveforms, as the high-frequency energy reaches electronic components not
designed to accept them or such high levels of distortion. Some products with switching
power supplies may have secondary analog supplies; you can never be sure about what
components won’t be damaged by poor-quality AC from a cheap UPS. Desktop
computers are generally safe, but that’s about all I’d ever connect to one of
them.
Use inadequate power protection
An inadequate power-protection product, or power strip,
will suck the life right out of your system by not being able to deliver the current peaks
amplifiers need to deliver all the dynamics present in film soundtracks. In inadequate
products, the "grippers" that hold the prongs of your components’ AC plugs
are made of thin stamped brass, formed together in a single strip with no wire connecting
them to each other -- they’re connected only by strips of brass so thin, and such
poor conductors, that your amplifiers may not be able to draw all the current they need.
Internal wires are riveted to the ends of the formed brass grippers. This quickens
assembly, but more current is delivered by copper wire of moderately large gauge connected
to the more substantial brass grippers present in even inexpensive AC sockets. Using one
of these inadequate power strips is like using a garden hose to fight a three-alarm fire.
 If your power conditioner has a plastic
housing with molded slots for the AC plugs, and a list price of $150 USD or less, it
probably has the construction described above, and will be OK to use so long as your
system is modest and your amplifiers not too powerful. But the more power-hungry (i.e.,
larger) the video display and amplifiers, the less likely it is that such a product will
be good enough. There’s nothing worse than being sold a $50 power conditioner with
your $2000 video display, only to have the display look better when it’s plugged into
the wall.
Good power-conditioning products start at around $80. The
Tripp-Lite Isobar shown in the photo costs $85. Its housing is of metal, the outlets are
separate from the housing, and the internal wiring is of large enough gauge that you
won’t have to worry about enough current getting to your components. You probably
won’t find Tripp-Lite products where you bought your TV or A/V receiver; you’re
more likely to find them at more serious electronics stores, or online.
 The Monster Power Home Theater
PowerCenter ($199.95) is an example of a well-made whole-system power conditioner with
extras like protection circuits for a telephone line, Ethernet (network) connection, TV
antenna, and cable or satellite connections. Again, the AC outlets look similar to the
ones in your house: separate from the housing, though in your house the outlets are
probably white or ivory. Power-conditioner outlets are usually brown, black, or orange.
Some excellent companies that sell good products in the +$200 range also sell lower-cost
products that aren’t good enough for many systems. You have to look at the
construction to get a feel for the worthiness of any power-conditioning product.
 At least one good company, APC, uses
a flat molded panel over good-quality outlets and wiring; APC products designed to sit on
a shelf or be mounted in a rack are just fine, quality-wise. The photo shows the APC H10
($349). You can see that its AC outlets don’t appear to be individual outlets, as in
the photos above, and a look under the hood reveals that the internal construction is very
good. APC also sells an inexpensive line of power-conditioning products that are only OK
for fairly simple and lower-powered systems with video displays that don’t need a lot
of power. This APC model regulates (stabilizes) the AC power-line voltage -- a nice
feature, but not common among home-theater power conditioners. If I had to choose between
a product with voltage regulation and one without, but that shuts off power to all
components if the AC goes above 130VAC or below 90VAC, I’d pick the latter. Most
home-theater products aren’t noticeably bothered if the AC voltage drifts up or down
by 5V -- a common range for many areas. But removing high or low voltages from connected
components is automatically more likely to protect them from damage than having voltage
regulation.
Picking your power conditioner
I recommend getting a power conditioner that includes an
indicator that lets you know that its surge/spike protection is still working -- but you
still need to look at that indicator regularly. I also recommend using a power product
that removes power from all connected components if the AC voltage goes above 130VAC or
below 90VAC, as discussed last month. This is why I recommend spending no less than $200
to $300 on such a product. But within that range, you have to make sure you’re
getting your money’s worth.
Ultralink’s Ultrapower PowerGrid models ($300-$500)
have most everything you might want in a power conditioner, including over/undervoltage
protection. APC’s products, such as the H10, also offer good value. Belkin makes two
models ($400-$600) with overvoltage shutdown, as well as a comprehensive array of
features. Monster Power offers many products, from $200 to over $1500, with complete sets
of features (though over/undervoltage shutdown is not listed). Panamax sells several
M-series models ($300-$700) that include over/undervoltage shutdown, along with all the
other features you’d want.
Getting something good for under $100 takes the most work,
and the most investigation into how the product is constructed. If you have a fairly
powerful system -- say, a 50" or larger plasma display and +100Wx5 worth of
amplification, plus a powered subwoofer of 150W or more, you’ll want a product rated
for at least 15A or 1700W (or 1700VA). This will cost a little more than products rated
for less current or fewer watts, but you really need the higher power rating. The $85
Tripp-Lite is your safest bet, but there may be other brands with similar construction and
capabilities at similar prices.
But there’s only so much any company can deliver for
less than $80 retail. Unless your system doesn’t need a lot of power, inexpensive
power products can reduce, rather than support, your system’s performance.
. . . Doug Blackburn
db@hometheatersound.com |
