ONHOMETHEATER.COM"Hot Product" Archives

April 1, 2003


Mondial M.A.G.I.C. Cable TV Isolator

The Mondial M.A.G.I.C. isn't a large product, so this won't be a long review. However, if you have a complex home-theater system that's attached to a cable TV provider, it just might be the solution to a huge problem -- one that could destroy your enjoyment of all of your home entertainment. I am speaking of hum.

Actually, not just hum, but HUUUUUUUMMMMMMMMMM!

Boy, that can sorta make the whole expenditure seem moot.

That's the situation my buddy Nigel found himself in when he added broadband cable service recently. Actually, I'm not sure that Nigel didn't already have a problem -- he just didn't know about it because his computers, TV, and hi-fi were all separate entities. However, when he called in the kindly folks from Time Warner Cable, he reckoned that as long as he was disrupting things to get wired up, he'd go whole hog and turn everything into one big wired-house extravaganza. So he finally connected the TV and his DVD player into his hi-fi system and sat back ready to be wowed by the "out of the box" experience his good buddy the A/V reviewer was always raving about.


All the time. With every source. It just about drove him crazy; he thought it was unfair and he blamed me for the whole idea.

Which is why I answered my door to find a red-eyed Nigel insisting I come to his house immediately and fix what I had wrought. I didn't even argue the point -- I've been married over 20 years and I am finally learning that some battles just aren't worth fighting. I hied me hence and turned on the system.


"What's going on?" my friend demanded.

"I think I know what's causing it," I said, and unplugged the cable connection at the wall.



"Ground fault," I explained.

"Well, that certainly stopped the hum, but can you fix it so I can watch TV, too?"

As it so happened, I could. I just happened to have -- somewhere -- a Mondial Antenna Ground Isolation Circuit (M.A.G.I.C.). All I had to do was find it, and insert it between the cable input and the TV. The hum would be gone and Nigel could watch the BBC.

Sometimes a thousand twangling instruments will hum about mine ears

Hum is actually interesting stuff if you can get over the fact that it is a pestilential annoyance. It frequently crops up in audio/video installations when different systems or components, all of which are grounded and noise-free on their own, are joined together. In theory, an earth ground has zero volts AC and DC -- however, there's usually a very small amount of voltage present in a ground. This in itself does not necessarily cause hum, but if two devices are connected to grounds where there's a difference in electrical potential between them, current will flow through one ground wire to the other, developing a voltage whose flow is audible as hum.

When you connect different components to different circuits, you frequently get hum, since each circuit's ground will probably be just a smidge off of zero volts AC and DC -- if everything is connected to a component that is grounded, you can sometimes "cheat" your grounded plugs on everything else and solve your hum problem. (But never, never float everything or you could be in for a heart-stopping shock -- and that's not a figure of speech.)

But that cable TV connection -- that's a tricky one. The coaxial cable that enters your house is usually grounded via its shield -- and that's grounded, not at your house, but at the cable provider's main distribution outlet, which can be miles away. Remember that different circuits in the same house can have ground planes that differ in voltage; and then ask yourself what the chances are that something grounded miles distant from your house has the same potential. Fat chance!

The answer is to "interrupt" the grounded shield on that coaxial cable coming into your house. (Actually, in theory, cable installers are supposed to connect the coax cable's shield to the ground in your circuit box when they do the installation -- in fact, the IEC specifies they do -- but I have never actually seen one who does.) There are ways to "roll your own" hum-blockers, but they require several identical capacitors and some basic knowledge of electronics. If you aren't intimidated by that, feel free to Google "hum + TV" and you'll find instructions on how to proceed.

If, on the other hand, you'd prefer a well-made, easy-to-install, plug'n'play solution to the problem, then Mondial's M.A.G.I.C. is the answer for you.

The oracles are dumb, no voice or hideous hum

The M.A.G.I.C. is a small black die-cast aluminum box with two threaded gold-plated F-connectors mounted on one side and a ground terminal on another. One F-connector is the input, and the other is the output. The unit breaks the coaxial cable's ground connection while passing the signal unabated. It maintains the ground connection on the part of your A/V system, however, so it doesn't compromise safety. Mondial claims it does this with virtually no signal loss, which was reflected in Nigel's and my experiences with the product.

M.A.G.I.C. is a sealed unit, so everything I say about its innards is taken straight from Mondial's literature -- I haven't cracked one open to check their claims. Inside the tiny unit is a double-sided glass-epoxy circuit board with "over 30 surface-mounted components." The unit "also contains a gas discharge lightning suppressor [that] protects your home and equipment from local lightning strikes. It will also eliminate static electricity build-up on the cable line, preventing damage to your system at its most vulnerable point."

If you need to connect multiple sources, Mondial makes a M.A.G.I.C. Splitter, which houses two discrete M.A.G.I.C.s in a single housing.

My ears hum and a cold sweat bathes me

In one sense, there's not a lot to tell. I found the M.A.G.I.C. and an extra few feet of coax and connected them in front of Nigel's TV. We turned on the system and heard . . .

. . . Mishel Husain reading the nightly news. No hum, no hiss, nothing annoying at all. (Nigel would disagree since Manchester United had lost that day -- but you get the idea).

There was an unexpected consequence, however. Nigel couldn't get over how good his picture looked. "It's never been that sharp," he reported happily. Indeed, it was noticeably clearer, sharper, and brighter than it had been earlier in the day.

I asked my pal Tim, who is a techie at a cable provider if he could formulate a reason why that would be so. "It's possible that breaking the ground eliminated voltage on the cable shield," he conjectured. "That could have a huge impact on the video signal-to-noise ratio." He thought for a minute. "At first, I was a little dubious about the claims to eliminate static build-up, but that could be a factor as well. I'm not sure why that might have an effect, but I wouldn't completely dismiss it."

Hey, if you find something that works, stick with it. Nigel agrees -- he refuses to return my M.A.G.I.C.; that's okay, because I borrowed his Fender Champ.

Towered cities please us then, and the busy hum of men

If you don't have cable or you don't have hum, Mondial's M.A.G.I.C. won't do a thing for you. Don't give it a thought.

But if you do have hum or HUUUUUUUUUUMMMMMMMMM, the M.A.G.I.C. is well made and works. It's a simple solution to a noxious problem.

...Wes Phillips

Mondial M.A.G.I.C. Cable TV Isolator
Price: $99.95 USD.
Warranty: Two years parts and labor.

Mondial Designs
3502 Woodview Trace
Suite 200
Indianapolis, IN 46268
Phone: (317) 860-8100
Toll Free: (866) 781-7284

E-mail: support@mondialdesigns.com
Website: http://www.klipsch.com/mondial/

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