Subwoofer hum with no grounds?

As a christmas present for ourselves, my husband and I bought a new set
of speakers - nothing fancy, but nicer than our stereo setup. We got
the yamaha NS-SP5700 5.1 surround sound system from Best Buy and hooked
it up to our hand-me-down Onkyo TX-DS939 receiver.

All the speakers work fine, but the subwoofer produced a humming noise
and no other sound. We returned it, but the new one has the same
problem, so we're assuming now that it's something other than the
woofer.

Here's what I know so far: the humming goes up and down when I turn the
volume knob on the subwoofer, stops when I unplug it from the back of
the receiver, but doesn't when the receiver is turned off. It's a
louder buzzing than the buzzing that happens when I touch the wire with
my finger. I tried using a different cable for the subwoofer but it
still buzzed. There's only one input on the back of the subwoofer, and
the receiver is capable of handling 2 subwoofers but switching the cord
from one to the other made no difference.

Neither the subwoofer nor the receiver have a grounded plug, and the
outlets in our house aren't grounded(except for the computer room).
The rest of our setup includes a TV, VCR, Tivo with cable, PS2 and
Gamecube. Everything but the subwoofer is plugged into a power strip,
the woofer is plugged into a different outlet but plugging it into the
power strip didn't fix it. The room has dimmer lights, but I'm not
sure exactly why that's a problem except that a few troubleshooting
guides mentioned that that might make a difference.

All the guides I've seen for people with my problem say that it's
almost positively a grounding feedback thing, but since nothing in this
setup has grounded plugs I'm at a loss. The only option that sounds
feasible is that maybe my cable connection is doing something, but how
would I test for that or fix it? I tried moving all my speaker cables
and power cords away from the cable but it still buzzed.

We'd really like to use the .1 of our new system, so if anybody has any
ideas we're all ears.

wrote in message
ups.com...

All the speakers work fine, but the subwoofer produced a humming
noise
and no other sound. We returned it, but the new one has the same
problem, so we're assuming now that it's something other than the
woofer.


This sounds like a typical ground-loop hum.

Try this page for help:

http://forum.ecoustics.com/bbs/messa...79/180767.html

--
Happy New Year!

this is a very common problem caused by the cable
TV provider, its a ground loop. the easiest way to get rid
of it is to hook ALL cable TV connections to your system
through a CATV isolation transformer.
this prevents the CATV ground from entering your system, but
also lets the cable TV signal come through as usual.
disconnect the main cable TV feed to your system and Ill
bet you a dollar the hum goes away! (disconnect ALL cable TV
from your system)
also if you look carefully at your TV picture, there is a faint
horizontal bar floating through your screen, this is also caused
by the cable TV ground loop.
here are the options:
1. contact the cable TV provider and tell them you need your
cable ground lifted with an isolation transformer. most providers
are too stupid to understand this and will claim the problem is in
your system, (which its not) or they will charge you a fortune to
screw around until they accidentally fix it. Lets face the fact that
CATV companies dont understand home theater, ground loops or
audio quality, and dont care either!
2. buy a cable TV isolation transformer from a supplier and install
it so that ALL of your equipment is on the isolated side of the
transformer.
3. buy two 75-300 ohm transformers from radio shack (about $12)
and make your own isolation transformer. it works perfect...
i have made and installed this setup lots of times with 100% success.
ok Ill draw you a picture and post it here today if i can later this
afternoon...
anyone can make their own isolation tranny, its easy!
then enjoy HUM FREE subwoofing.

http://www.partsexpress.com/pe/showd...number=180-075

I tried disconnecting the cable from the wall, but it only made the hum
louder. I also disconnected the RCA inputs going to my receiver from
my Tivo and that didn't change anything. Surely one of those would
have broken the ground loop? I'm really confused.

"Loth" wrote in message
ups.com...

I tried disconnecting the cable from the wall, but it only made the hum
louder. I also disconnected the RCA inputs going to my receiver from
my Tivo and that didn't change anything. Surely one of those would
have broken the ground loop? I'm really confused.


I once had a powered subwoofer that had the polarized plug installed on it
the wrong way. Nothing would get rid of the hum, no matter what I did, until
out of curiousity I got desperate and filed the wide spots off the one plug
tab and plugged it into the wall "backwards." Hum gone. It wasn't the house
wiring, as it was the only piece of electronic gear that I've ever had that
problem with, but it sure took forever to find the problem.

"Loth" wrote in message
ups.com...

I tried disconnecting the cable from the wall, but it only made the hum
louder. I also disconnected the RCA inputs going to my receiver from
my Tivo and that didn't change anything. Surely one of those would
have broken the ground loop? I'm really confused.

Does your sub have a 2 prong power plug or a 3 prong power plug? Try a 2
prong plug instead, that will cut out the possibility of the ground loop
being picked up by the earth in the power cable. Don't worry subs are triple
insulated and the earth connection is superfluous.

If the sub still produces an audible hum then it's not a ground loop but the
noisy internal amplifier of the sub. Unfortunately a lot of subs do not have
sufficient shielding around the internal amp and any hum produced by these
is amplified by the sub's interior. If it is very loud only changing sub
will help.

--
Italo

Loth wrote:
I tried disconnecting the cable from the wall, but it only made the hum
louder. I also disconnected the RCA inputs going to my receiver from
my Tivo and that didn't change anything. Surely one of those would
have broken the ground loop? I'm really confused.

a groundloop is caused by ANY device in the system which
has more than ONE ground connected to it.
stop being confused, step by step testing will locate
the groundloop.

don't despair, we will solve this, stand by for instructions
and part numbers. patience will win the day.
need to know is this a mono subwoofer input?
(one RCA patchcord from receiver to subwoofer)
is this one patchcord connected from receiver SUB out
to sub woofer input?
how many devices have a three prong AC plug:
does receiver have one? does subwoofer have one?
Does TV have one? Does cable box have one?

jump to my e mail and i will walk you through this
step by step
professional AV installer.

wrote in message
ups.com...
stop being confused,

Why, it works so well for you?

On Jan 7, 8:17 am, wrote:


need to know is this a mono subwoofer input?
(one RCA patchcord from receiver to subwoofer)
is this one patchcord connected from receiver SUB out
to sub woofer input?
how many devices have a three prong AC plug:
does receiver have one? does subwoofer have one?
Does TV have one? Does cable box have one?

I thought I said all this in my first post? Nothing on my system has a
ground, subwoofer/receiver/TV/Tivo/VCR/PS2/Gamecube all just have
polarized plugs and (except for the woofer) are all plugged into the
same powerstrip(I plugged the subwoofer into the power strip earlier,
no effect). There is one mono connection from the reciever to the
subwoofer, and it's connected to subwoofer pre out, which is what the
manual says to do.

It's a hand-me-down receiver, which we got from my husband's brother,
who got it from their dad, who was the last person to have a subwoofer
attached to it, and his worked. Of course, that was something like 6
years ago.