I recently bought a 422/S-8 system. I also bought a Yamaha HTR-5860 receiver. Just a few days ago, I noticed a hum from the subwoofer. The hum seems to wax/wane in a 2 second cycle. Would appreciate any help/suggestions.

 

Thanks

It is possible that the incomming power from the electric company is noisy, or another device on the same circuit is adding EMI noise to the line. Even DVD players have been known to do this.

Try removing anything plugged into the same circuit except the sub and receiver and see if the noise goes away.

Also, you could try plugging everything into a line-conditioner. There are some affordable units from PureAV (Belkin - http://www.pureav.com/power/) available at most B&M stores, as well as upper end units from companies like APC (http://www.apc.com/products/apcav/) designed with home theater in mind.

From the Blue Jeans Cable website:

"There are two primary reasons why an otherwise healthy subwoofer may hum, and cables can deal only with one of these: EMI. The other possibility, a ground loop, is something your cables can't fix, and has to do with differences in ground potential in your system's power wiring. Although the best and most permanent way to eliminate ground loop hum is by fixing the underlying grounding problem, another simpler way to resolve the problem is to insert an isolation transformer in your subwoofer line to break the ground connection between your source and your subwoofer."

A couple of sites that discuss ground loops:

http://www.epanorama.net/documents/groundloop/
http://www.smr-home-theatre.org/Ground-Loops/index.html

 

Assuming your sub is hooked-up using the usual RCA or XLR line-level cables (instead of amplified high-level speaker cables), I recommend that you use a Hum Eliminator from EB Tech (this is an audiophile quality isolation transformer).  You can look up "Hum Eliminator" on froogle.com and find them for a good price, they simply work wonders with the problem you are describing.

Ok, I in no way recommend you do this, because I read somewhere that you shouldn't, (but then I also got told not to take candy from strangers too, but hey, free candy..)... I was experiencing grounding hum on my S12 sub from my Pioneer receiver and solved it by getting a 79 cent 3 pin to 2 pin adaptor from Home Depot that I plonked on the end of my subs power lead. Hum gone.

while I've never taken candy from strangers....oh, wait, forgot about Halloween....

anyway, I used the same solution as Adam. It worked without any problems.

Just remember, people have died by lifiting the ground on equipment...

 

 

Well, that's what people have told me, but I'm not quite sure how they managed to do that to themselves, nor have I heard of an actual real life example. Can someone explain how, in real life, my sub is going to shock me by not having a connected ground ?

If your house is from the 1970's or older, it is very likely that the neutral connection was designed to carry the ground as well.

My house has a mix, (though not on the same breaker), My cooktop, oven etc are grounded to neutral, later remodelling work has a dedicated ground. Anyway as far as safety goes, the sub is still grounded, via the RCA cable to the reciever's chassis and on to earth. In the unlikely event of the live wire flailing inside the sub and coming in contact with the chassis of the sub, that errant current would still be whizzed to earth, tripping your breaker.

In my house, there is a bridge connection in the main that combines the neutral and ground. So even though all the outlets have a dedicated ground copper connection to the main, it is basically just another neutral connection.

While unlikely, it could happen...  If your wiring in your house was incorrect AND your ground was lifted, YOU could become the path to ground for the current.

It's all about safety.

Hmm, but I know my house wiring is in good shape, so in risk assessment terms it's about on par with getting hit by a small chunk of french person whilst playing golf on a thursday... Anyhooo.. as I said originally, just 'cos I do it doesn't mean anybody else has to... Back to the original post, and possibly wondering about other causes, Neela mentioned that it wasn't constant, but cyclic, so maybe after all that, it's not ground related...?