Subwoofer hum with no grounds?

On Jan 6, 1:37 pm, "severian" wrote:
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.

Ouch. But this is the second subwoofer we got, and it only hums when
it's plugged in to the receiver. If it were the power, wouldn't it hum
from the moment it's turned on? And it seems unlikely that we would
have gotten 2 subwoofers with backwards plugs.

It's nice to get a suggestion that doesn't include the word 'ground' in
it, though.

On Jan 6, 5:01 pm, "Italo" wrote:
Does your sub have a 2 prong power plug or a 3 prong power plug?

It's a 2 prong polarized plug. And the only noise it makes is the
buzzing, so I don't think it's the amp, because wouldn't it make the
bass noises if the amp was working?

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


On Jan 6, 1:37 pm, "severian" wrote:
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.

Ouch. But this is the second subwoofer we got, and it only hums when
it's plugged in to the receiver. If it were the power, wouldn't it hum
from the moment it's turned on? And it seems unlikely that we would
have gotten 2 subwoofers with backwards plugs.

It's nice to get a suggestion that doesn't include the word 'ground' in
it, though.


This sub hummed no matter if it was hooked up to a signal source or not, it
was directly out of the power supply. Doesn't sound like yours is the same
cause then, if it goes away when you unplug the signal wires. But my
experience shows that all sorts of gremlins can lurk there that you might
not think of.

Chasing hum can be a tough job, I wish you luck with it, as it is also a
really annoying problem.

"Loth" wrote in message
oups.com...


On Jan 6, 5:01 pm, "Italo" wrote:
Does your sub have a 2 prong power plug or a 3 prong power plug?

It's a 2 prong polarized plug. And the only noise it makes is the
buzzing, so I don't think it's the amp, because wouldn't it make the
bass noises if the amp was working?

Well if you've got a 2 prong plug already then you're sub is not picking up
noise transferred through the power cable. I'm also guessing that it's
probably not a 'closed' sub i.e. it's a sub with a tuned port/s etc... which
will probably aggravate the problem since the buzzing will be more clearly
heard.

It's highly likely that it's the internal amp buzzing and getting amplified
by the subs enclosure, not that rare I've had 3 subs and all have 'buzzed',
the first one very loudly. If the noise is that bad that you can notice it,
the only solution is to change sub.

--
Italo

wrote:
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.


Hi Loth.

Let me get this straight...

Neither subwoofer produced any audio, just hum?
You tried a different cable to no avail?
The hum increases with the level control?

Assuming you didn't get two bad subwoofers [unlikely], the problem
is originating in the receiver. Groundloop notwithstanding, you'd have
audio regardless.

Plug the subwoofer into another output on the receiver.
It doesn't matter which one...center, left front, etc.

Either L or R of the tape monitor output will also work if the receiver
doesn't have any other line outputs.
However, ensure the gain control is off @ the SW first before turning
anything on as the tape monitor hookup will put full signal into it as
the receiver's volume control will be bypassed. Control the volume with
the SW's gain control.

If you get sound from the subwoofer, there's something wrong with
the Onkyo's sub outs.

If you still don't get any audio and the hum persists, you've got
something too bizarre for newsgroup help, requiring in-person technical
help, or something is missing from your description.

--
-Gandalf

Never meddle in the affairs of a dragon for you are crunchy and taste
good with ketchup!

In article . com,
"Loth" writes:


On Jan 6, 1:37 pm, "severian" wrote:
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.

Ouch. But this is the second subwoofer we got, and it only hums when
it's plugged in to the receiver. If it were the power, wouldn't it hum
from the moment it's turned on? And it seems unlikely that we would
have gotten 2 subwoofers with backwards plugs.

It's nice to get a suggestion that doesn't include the word 'ground' in
it, though.

We had a problem where one outlet had the hot and common wires (the 2
wires) reversed from the correct way. It caused all kinds of problems.
I'm assuming the subwoofer is not plugged into the outlet as the amp.
Try plugging into the same outlet of if not possible, a different one.
There are tester devices available that can test if the wires are
correct. A volt meter can also be used, the wide slot should be
120VAC when measured to the screw holding the outlet cover.

David E. Bath wrote:

We had a problem where one outlet had the hot and common wires (the 2
wires) reversed from the correct way. It caused all kinds of problems.
I'm assuming the subwoofer is not plugged into the outlet as the amp.
Try plugging into the same outlet of if not possible, a different one.
There are tester devices available that can test if the wires are
correct. A volt meter can also be used, the wide slot should be
120VAC when measured to the screw holding the outlet cover.

OP already stated plugging into the same outlet strip as the receiver
afforded no cure.

I think the key lies in the original post.
No audio. Just hum.

Barring incorrect and/or incomplete symptoms described initially, the
problem is almost certainly in the Onkyo.

--
-Gandalf

Never meddle in the affairs of a dragon for you are crunchy and taste
good with ketchup!

"Gandalf" wrote in message
m...
David E. Bath wrote:

We had a problem where one outlet had the hot and common wires (the 2
wires) reversed from the correct way. It caused all kinds of problems.
I'm assuming the subwoofer is not plugged into the outlet as the amp.
Try plugging into the same outlet of if not possible, a different one.
There are tester devices available that can test if the wires are
correct. A volt meter can also be used, the wide slot should be
120VAC when measured to the screw holding the outlet cover.

OP already stated plugging into the same outlet strip as the receiver
afforded no cure.

I think the key lies in the original post.
No audio. Just hum.

Barring incorrect and/or incomplete symptoms described initially, the
problem is almost certainly in the Onkyo.

--
-Gandalf

Never meddle in the affairs of a dragon for you are crunchy and taste good
with ketchup!

Can't remember if this has been tried yet, but has the cable to the sub been
tested? Could be a bad cable, or a bad Onkyo, but it's starting to sound
suspiciously like a source problem.

Plug the subwoofer into another output on the receiver.
It doesn't matter which one...center, left front, etc.

Either L or R of the tape monitor output will also work if the receiver
doesn't have any other line outputs.
However, ensure the gain control is off @ the SW first before turning
anything on as the tape monitor hookup will put full signal into it as
the receiver's volume control will be bypassed. Control the volume with
the SW's gain control.

If you get sound from the subwoofer, there's something wrong with
the Onkyo's sub outs.


You were right, I plugged it into the tape output and it started
playing music. So the sub outs are just bad - it's so strange to me
that both of them went bad together.

I guess we'll just have to save up and get a new receiver to use the
subwoofer. Not the best news, but something we were probably going to
do someday anyway.

By the way, I love your sig. I've always liked that quote.

"Loth" wrote in message
oups.com...

If you get sound from the subwoofer, there's something wrong with
the Onkyo's sub outs.

You were right, I plugged it into the tape output and it started
playing music. So the sub outs are just bad - it's so strange to me
that both of them went bad together.

I guess we'll just have to save up and get a new receiver to use the
subwoofer. Not the best news, but something we were probably going to
do someday anyway.

If your receiver has pre-amp outputs, you can use one of them for the
sub. The mid and high frequencies will be filtered and ignored by the
sub, but the bass will be passed along to the sub. It usually won't
really matter if you use left or right main because both will have the
same bass frequencies in most tracks, but to be sure you can buy a $5
Y-cable and blend the left/right signals into the sub.