Apologies to the group if this has been discussed prior:

When I plug my subwoofer into my receiver and turn on the receiver, I
hear a hum. The sound is similar to putting a finger across the
subwoofer cable lead.

I am trying to understand if there is an obvious cause for this hum,
other than a problem with the receiver's subwoofer output jack. I do
not believe this is a ground loop issue.

My equipment is an Onkyo TX-SR500 receiver and Sony SA-WM20 subwoofer.
(I know, not the greatest - but it's what I have.) I tested the
subwoofer on a friend's Onkyo, and it worked properly. I swapped
subwoofer cables and the hum still occurs.

I have disconnected all input/output leads from the receiver other
than the subwoofer cable. When the receiver is not plugged in, there
is a low hum. When the subwoofer is plugged in, the volume of the hum
increases, even with the receiver power off. When the receiver is
powered on, the hum's volume increases more. The receiver and the
subwoofer are configured to plug into different grounded outlets.
Both outlets are properly wired.

The system was working properly before I pulled it apart to install a
wall unit. Other than upgrading some RCA cables and changing the
outlets into which some components plug, no changes were made to the
system. When I disconnected the system, the subwoofer cable was very
difficult to remove from the receiver, In fact, the head came apart
in my hand, and I needed to use needlenose pliers to pull the casing
off the receiver output jack. I am wondering if I somehow damaged
whatever is hooked to the backside of this jack, and whether that
might cause the hum.

Any advice before I cart the receiver off to a shop is gratefully
accepted.

Brian

Any advice before I cart the receiver off to a shop is gratefully
accepted.

Try lifting the ground on the subwoofer. Use a cheater or a cheap extension
cord. If the hum disappears you have found the culprit. If not, ask and
we'll make more suggestions, but this is the first (and simplest) thing to
check.

Alarm and Home Automation System FAQ
http://www.bass-home.com/faq/masterfaq/faq.htm

Regards,
Robert

=============================
Bass Home Electronics
2291 Pine View Circle
Sarasota · Florida · 34231
877-722-8900 Sales & Tech Support
941-925-9747 Fax
941-232-0791 Wireless
Nextel Private ID - 161*21755*1
http://www.bass-home.com
http://www.bassburglaralarms.com
=============================

In , on 02/17/04
at 07:00 PM, (Brian) said:

Apologies to the group if this has been discussed prior:

When I plug my subwoofer into my receiver and turn on the receiver, I
hear a hum. The sound is similar to putting a finger across the
subwoofer cable lead.

I am trying to understand if there is an obvious cause for this hum,
other than a problem with the receiver's subwoofer output jack. I do
not believe this is a ground loop issue.

This seems like a ground loop issue to me. (read on)

My equipment is an Onkyo TX-SR500 receiver and Sony SA-WM20 subwoofer.
(I know, not the greatest - but it's what I have.) I tested the
subwoofer on a friend's Onkyo, and it worked properly. I swapped
subwoofer cables and the hum still occurs.

I have disconnected all input/output leads from the receiver other
than the subwoofer cable. When the receiver is not plugged in, there
is a low hum. When the subwoofer is plugged in, the volume of the hum
increases, even with the receiver power off. When the receiver is
powered on, the hum's volume increases more. The receiver and the
subwoofer are configured to plug into different grounded outlets.
Both outlets are properly wired.

There is always a small amount of hum. It's difficult for us to decide
if it is normal or not unless we hear it or interpret a measurement
that we trust. In a very quiet room, close to the speaker, the hum is
usually audible. In most homes, with all the heaters, appliances,
computers, etc. that are running, the hum is not significant.

The system was working properly before I pulled it apart to install a
wall unit. Other than upgrading some RCA cables and changing the
outlets into which some components plug, no changes were made to the
system. When I disconnected the system, the subwoofer cable was very
difficult to remove from the receiver, In fact, the head came apart
in my hand, and I needed to use needlenose pliers to pull the casing
off the receiver output jack. I am wondering if I somehow damaged
whatever is hooked to the backside of this jack, and whether that
might cause the hum.

The plug on the end of the cable fell apart? The jack on the receiver
separated?

It is possible that you damaged the jack on the receiver. Obviously,
replacing the subwoofer cable will cure a damaged cable issue. You can
quickly check for a damaged jack by using a screwdriver to short the
shield (outside) of the subwoofer cable to the shield on a nearby jack.
If the problem cures, the the jack must be replaced.

Plugging the subwoofer into another outlet can easily cause ground
loops. You can test for this situation by using a power extension cord
to temporarily use the same outlet for everything in the system.

Also, disconnect the cable TV feed if you have one.

-----------------------------------------------------------
spam:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

When the receiver is
powered on, the hum's volume increases more. The receiver and the
subwoofer are configured to plug into different grounded outlets.
Both outlets are properly wired.

just sticking the 3 light tester into an outlet doesnt mean the GROUNDS are
connected correctly. in a perfect world, all the grounds only make contact
with the neutral at one point, and that is in the panel OUTSIDE YOUR HOUSE.
often electritians connect the neutral to the ground inside the panel, and
its also contacting inside the meter box. depending on how far this is and
other circumstances this alone can create a hum. and this is just one
example of where the tester says yes, but its not quite right. you may not
have proper ground rods installed, there may be a water meter that breakes
the electrical connection in the plumbing which was being used for the
ground. etc...

but i would first try this. disconnect any cable tv sources you have and
see if it goes away. if that doesnt work, do what robert bass said. either
isolate the ground plug, or put em both in the same exact outlet and see
what happens. you also didnt say if the different outlets are on the same
circuit..

lastly, before taking it back to the shop, take it down to bare bones, and i
mean bare. just plug in the sub, and use the radio on the receiver and
disconnect everything else. if this fixes it, bring it up one at a time
until the hum returns.

randy

"Brian" wrote in message
om

Apologies to the group if this has been discussed prior:

No problem, if you keep an open mind. Grounding problems with subwoofers are
very common, and have been discussed many times. Try searching using words
like subwoofer and hum at www.google.com .

When I plug my subwoofer into my receiver and turn on the receiver, I
hear a hum. The sound is similar to putting a finger across the
subwoofer cable lead.

I am trying to understand if there is an obvious cause for this hum,
other than a problem with the receiver's subwoofer output jack. I do
not believe this is a ground loop issue.

That makes about as much sense as having a short-term cough and sniffles and
not suspecting that you might have a cold.

It's probably a ground loop issue or another kind of grounding issue called
a "grounding potential difference".

Probably, the first thing to do is to eliminate the fact that you have the
sub and the receiver grounded at separate points as a potential source of
problem. IOW plug the receiver and the subwoofer into the same outlet or
plug strip, and see what happens.

Also, eliminate the rest of your system as a potential source of problems.
Remove all connections from your receiver but power, speakers, and the
connection to the subwoofer.

Once you get reasonably hum-free operation, add things back one at a time
and see if any of them are causing grounding problems.

(Brian) writes:

When I plug my subwoofer into my receiver and turn on the receiver, I
hear a hum.

The receiver and the subwoofer are configured to plug into different
grounded outlets. Both outlets are properly wired.

Other than upgrading some RCA cables and changing the
outlets into which some components plug, no changes were made to the
system.

You appear to have every symptom of a ground loop problem. If
possible, plug the receiver and subwoofer into the same outlet, and
I'll betcha a quarter the issue goes away. :-)

If plugging them into the same outlet is not feasible, seek out an
audio isolation transformer for the line level signal that feeds your
subwoofer. This isolates the grounds of the two affected component
and often eliminates the hum.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."

A couple other things that can cause hum are cheap cable (or a cable gone
bad),and speaker cables tangled in power cables.Try another cable of high
quality and clean up around the back of your system.Have all power cables
away from speaker cables.Make sure you are running everything out of one
outlet,if needed buy a good power bar.

Good Luck




Brian wrote in message
om...
Apologies to the group if this has been discussed prior:

When I plug my subwoofer into my receiver and turn on the receiver, I
hear a hum. The sound is similar to putting a finger across the
subwoofer cable lead.

I am trying to understand if there is an obvious cause for this hum,
other than a problem with the receiver's subwoofer output jack. I do
not believe this is a ground loop issue.

My equipment is an Onkyo TX-SR500 receiver and Sony SA-WM20 subwoofer.
(I know, not the greatest - but it's what I have.) I tested the
subwoofer on a friend's Onkyo, and it worked properly. I swapped
subwoofer cables and the hum still occurs.

I have disconnected all input/output leads from the receiver other
than the subwoofer cable. When the receiver is not plugged in, there
is a low hum. When the subwoofer is plugged in, the volume of the hum
increases, even with the receiver power off. When the receiver is
powered on, the hum's volume increases more. The receiver and the
subwoofer are configured to plug into different grounded outlets.
Both outlets are properly wired.

The system was working properly before I pulled it apart to install a
wall unit. Other than upgrading some RCA cables and changing the
outlets into which some components plug, no changes were made to the
system. When I disconnected the system, the subwoofer cable was very
difficult to remove from the receiver, In fact, the head came apart
in my hand, and I needed to use needlenose pliers to pull the casing
off the receiver output jack. I am wondering if I somehow damaged
whatever is hooked to the backside of this jack, and whether that
might cause the hum.

Any advice before I cart the receiver off to a shop is gratefully
accepted.

Brian

"xrongor" wrote in message news:HeDYb.212095$U%5.1223717@attbi_s03...
When the receiver is
powered on, the hum's volume increases more. The receiver and the
subwoofer are configured to plug into different grounded outlets.
Both outlets are properly wired.

(snip)

but i would first try this. disconnect any cable tv sources you have and
see if it goes away.

A cable TV connection somewhere in the system (such as connected to
your TV or VCR) is often the problem, although other posts in this
thread may also be useful.

If you have cable TV, try disconnecting the cable from your system. If
that solves the problem, then go to www.google.com and search web and
newsgroups for fixes. Search terms such as:

cable TV
hum
ground loop
subwoofer

A few searches will probably lead you to more info and simple fixes.
Fixes for this sort of problem are often cheap or free.

If the cable TV is the problem, also call cable TV company and ask for
advice.

If you can't fix the problem, here's another resource:

rec.audio.tech

But I think your problem should be easy to fix, although it may
involve a little trial and error and plugging in your gear a few
different ways until you find something that makes the hum go away.

if that doesnt work, do what robert bass said. either
isolate the ground plug, or put em both in the same exact outlet and see
what happens. you also didnt say if the different outlets are on the same
circuit..

lastly, before taking it back to the shop, take it down to bare bones, and i
mean bare. just plug in the sub, and use the radio on the receiver and
disconnect everything else. if this fixes it, bring it up one at a time
until the hum returns.

randy

A couple other things that can cause hum are
cheap cable (or a cable gone bad),and speaker
cables tangled in power cables...

I disagree. You will not get audible hum from defective speaker cables.
You also will not get it from wrapping them around power cables. Defective
interconnect cables can allow noise to enter the system but the SNR on the
speaker cables -- after all of the amplification -- is so great that any
induced AC there will not be audible.

In all probability this is a ground loop problem.
--
Alarm and Home Automation System FAQ
http://www.bass-home.com/faq/masterfaq/faq.htm

Regards,
Robert

=============================
Bass Home Electronics
2291 Pine View Circle
Sarasota · Florida · 34231
877-722-8900 Sales & Tech Support
941-925-9747 Fax
941-232-0791 Wireless
Nextel Private ID - 161*21755*1
http://www.bass-home.com
http://www.bassburglaralarms.com
=============================

"Robert L. Bass" said:

I disagree. You will not get audible hum from defective speaker cables.

Depends on the circuit.
There's a feedback loop in most amps from output to input, and said
input is out of phase with the source signal.
Hence, there's no attenuation from feedback for signals intruding in
the feedback loop. Because of the high open loop gain in that case,
hum and other undesired rubble may well be audible.
It can even be demodulated, in case of strong RF signals.

I've actually seen amps humming and even oscillating due to
interference that came in through the speaker outputs.

Some small caps across the outputs and gnd, as well as chokes in the
output circuit may well prevent this, shielded speaker cables may help
too.

--
Sander deWaal
Vacuum Audio Consultancy

(Brian) wrote in message . com...
Thanks to the group for all the excellent advice. I am clearly
trolling in the right waters.

This is an update on my progress: I disconnected ALL leads from the
receiver other than the subwoofer cable. I unplugged the receiver's
powercord from the AC outlet. I removed the receiver to a new room,
away from all other wires and hardware. I place the receiver in the
middle of the floor (still not plugged to AC), connected the subwoofer
and turned on the subwoofer. Hmmm? Hummm! Touching the receiver's
case slightly altered the pitch of the hum. When I plugged the
received into the same outlet as the subwoofer, the hum increased in
volume, and loudened again when I powered on the receiver.

(All: Is it possible that a ground loop is being set up between the
receiver's subwoofer output jack and the receiver's case? With a
receiver that isn't even plugged into an electrical outlet?)
(Robert B: Wish I knew how to lift the ground using an extension
cord. You all are too smart for me.)
(Troy: hope its not speaker wire interference, because the speaker
wires are 30 feet away.)
(Todd, Neil and Arny: I am using same outlet. I've removed about all
I can remove from the system, including tv cable in. What I have
configured is: electric
outlet-to-power-cord-to-subwooder-to-cable-to-receiver to an electric
cord either (a)laying on the floor or (b) plugged back into the same
outlet as the subwoofer.
(Randy: I take your meaning about the 3 light tester not being the
end-all. Beyond that, you're beyond me. But I stripped down pretty
much to my skivvies here.)
(Barry: this is more than a little hum. It overpowers the other 5
speakers, even with the gain on the subwoofer fairly low. The jack of
the receiver didn't separate, but the plug end of the connecting cable
came apart. The sheath, pin and some plastic stayed on the receiver
jack, while a small metallic clip and some more plastic stayed on the
wire. And yes, I am thinking that maybe I did damage the receiver
jack. I'm trying the eliminate other potentials before taking my
Onkyo into the shop.)

Sometimes sniffles and a cough aren't a cold. Sometimes it's an
pneumonia.

Brian

You may just have a ground off inside the unit.When you took it apart there
may have been a ground wire grounded to the case that got removed.Have a
look inside.



Brian wrote in message
om...
(Brian) wrote in message
. com...
Thanks to the group for all the excellent advice. I am clearly
trolling in the right waters.

This is an update on my progress: I disconnected ALL leads from the
receiver other than the subwoofer cable. I unplugged the receiver's
powercord from the AC outlet. I removed the receiver to a new room,
away from all other wires and hardware. I place the receiver in the
middle of the floor (still not plugged to AC), connected the subwoofer
and turned on the subwoofer. Hmmm? Hummm! Touching the receiver's
case slightly altered the pitch of the hum. When I plugged the
received into the same outlet as the subwoofer, the hum increased in
volume, and loudened again when I powered on the receiver.

(All: Is it possible that a ground loop is being set up between the
receiver's subwoofer output jack and the receiver's case? With a
receiver that isn't even plugged into an electrical outlet?)
(Robert B: Wish I knew how to lift the ground using an extension
cord. You all are too smart for me.)
(Troy: hope its not speaker wire interference, because the speaker
wires are 30 feet away.)
(Todd, Neil and Arny: I am using same outlet. I've removed about all
I can remove from the system, including tv cable in. What I have
configured is: electric
outlet-to-power-cord-to-subwooder-to-cable-to-receiver to an electric
cord either (a)laying on the floor or (b) plugged back into the same
outlet as the subwoofer.
(Randy: I take your meaning about the 3 light tester not being the
end-all. Beyond that, you're beyond me. But I stripped down pretty
much to my skivvies here.)
(Barry: this is more than a little hum. It overpowers the other 5
speakers, even with the gain on the subwoofer fairly low. The jack of
the receiver didn't separate, but the plug end of the connecting cable
came apart. The sheath, pin and some plastic stayed on the receiver
jack, while a small metallic clip and some more plastic stayed on the
wire. And yes, I am thinking that maybe I did damage the receiver
jack. I'm trying the eliminate other potentials before taking my
Onkyo into the shop.)

Sometimes sniffles and a cough aren't a cold. Sometimes it's an
pneumonia.

Brian

if at all possible, try the receiver on a friends sub, and/or your sub on a
friends receiver. take your stuff to their house where you know there isnt
hum and use the same exact connections.

randy

(Brian) wrote in message . com...

---snip---

Not trying to be snarky towards you but if you don't understand what
the other poster was talking about concerning (temporarily) lifting
the house wiring ground, you probably know just enough to get into
trouble fire and/or injury/death wise.
Also, you don't seem to know exactly what you danmaged or whether you
got it all put back together correctly, so you don't know whether
you've introduced another variable or not.
Find a good shop to resolve the situation and then enjoy the music in
good health.

In , on 02/19/04
at 12:48 PM, (Brian) said:

(Brian) wrote in message
.com... Thanks to
the group for all the excellent advice. I am clearly trolling in the
right waters.

This is an update on my progress: I disconnected ALL leads from the
receiver other than the subwoofer cable. I unplugged the receiver's
powercord from the AC outlet. I removed the receiver to a new room,
away from all other wire and hardware. I place the receiver in the
middle of the floor (still not plugged to AC), connected the subwoofer
and turned on the subwoofer. Hmmm? Hummm! Touching the receiver's
case slightly altered the pitch of the hum. When I plugged the
received into the same outlet as the subwoofer, the hum increased in
volume, and loudened again when I powered on the receiver.


(All: Is it possible that a ground loop is being set up between the
receiver's subwoofer output jack and the receiver's case? With a
receiver that isn't even plugged into an electrical outlet?)

"Ground" is a relative thing, usually implying "zero" potential, but
"zero" is not an absolute. Think of a chair. You can measure the height
of a chair by sitting it on the ground and measuring the distance
between the ground and the top of the chair seat. Now move the chair to
the 10th floor of a building. What is the chair height now? How would
you measure it? Generally, we would measure chair height from the
surface the chair sits on and everything works out. However if the
surface is not level or not flat, there could be some unwanted chair
movement. Because I want to use the concept below, consider what could
happen to our chair if our perfectly flat floor is distorted by a
nearby heavy appliance.

The electrical "ground" in your home is usually a metal rod driven into
the earth near the electrical panel. Each piece of your audio equipment
keeps an eye on that ground so that it knows what "zero" means in the
context of your home. (Your next door neighbor could have a slightly
different ground.) When you connect units together in your stereo, each
unit assumes that it and all the other units reference the same ground.
If the ground in your home is stressed by a large appliance, the units
in your stereo might see different grounds. This will cause unexpected
current to flow in the ground and trouble is likely.

Consider what could happen if your receiver is sending out zero (the
output voltage of the receiver is the same as the receiver's ground).
If the subwoofer's ground is the same as the receiver's, the the
subwoofer agrees that the input is zero and there should be no sound.
If the subwoofer's ground is different from the receiver's ground by
0.05, then the subwoofer will think the receiver is sending 0.05 when
the receiver thinks it is sending 0.00. The subwoofer will amplify that
0.05 and you'll hear whatever trash is circulating in the ground.

Note the above discussion is a small tip of the iceberg. Whole books
are written about grounding.

(Robert B: Wish I knew how to lift the ground using an extension cord. You
all are too smart for me.)

Use one of those "cheater" adaptors designed for connecting a three
prong plug to a two prong outlet and don't connect the green wire to
annything. Some high end audio components have a switch designed to
accomplish this.

(Troy: hope its not speaker wire interference, because the speaker
wires are 30 feet away.)
(Todd, Neil and Arny: I am using same outlet. I've removed about all
I can remove from the system, including tv cable in. What I have
configured is: electric
outlet-to-power-cord-to-subwooder-to-cable-to-receiver to an electric
cord either (a)laying on the floor or (b) plugged back into the same
outlet as the subwoofer.

Good. This minimizes (but does not eliminate) the possibility of a
ground loop. (Poor design can create ground loops inside a unit) (an
improperly designed unit may pollute the ground and cause trouble for
other units in the system)

(Randy: I take your meaning about the 3 light tester not being the
end-all. Beyond that, you're beyond me. But I stripped down pretty
much to my skivvies here.)

This is a good start. (Don't stand near the window in your skivvies or
we'll be seeing you on the news.)

(Barry: this is more than a little hum. It overpowers the other 5
speakers, even with the gain on the subwoofer fairly low. The jack of
the receiver didn't separate, but the plug end of the connecting cable
came apart. The sheath, pin and some plastic stayed on the receiver
jack, while a small metallic clip and some more plastic stayed on the
wire. And yes, I am thinking that maybe I did damage the receiver
jack. I'm trying the eliminate other potentials before taking my
Onkyo into the shop.)

It is very likely that you broke the outer part of the subwoofer jack
on your receiver. If this is so, then you will probably pick-up some
noise.

I am not surprised that you hear some noise when the receiver is turned
off or not plugged in to the power outlet. This is another issue and we
can deal with it separately (if necessary) after we solve the more
urgent problem of the loud hum.

For a test, pick another output jack on your receiver that is not
adjacent to your subwoofer jack (adjacent jacks could also have been
damaged by the same event). Make sure that the subwoofer is turned off
and its level control is turned down when you do this. You can use REC
OUT if you like (if you do use REC OUT, turn the selector switch to CD
and make sure your CD player is ON and in the STOP mode) If the
subwoofer hum is now gone (don't forget to turn the subwoofer ON and
turn up its level control), then you have a damaged subwoofer output
jack.

Sometimes sniffles and a cough aren't a cold. Sometimes it's an
pneumonia.

Or allergies and someone will claim it's a government plot.

-----------------------------------------------------------
spam:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

(Robert B: Wish I knew how to lift the ground
using an extension cord. You all are too smart
for me.)

Two-conductor extension cords have no ground lug. This suggestion was only
for a temporary means of lifting the ground to see if that's the problem.

(Barry: this is more than a little hum. It overpowers
the other 5 speakers, even with the gain on the subwoofer
fairly low.

Did you say something about having opened and worked on the inside of the
powered sub? I must have missed that but someone else made a comment to
that effect. If so, it's beginning to sound as though you've accidentally
shorted (or opened) something inside. This might be a good time to trundle
on down to your local electronics repair shop.

Alarm and Home Automation System FAQ
http://www.bass-home.com/faq/masterfaq/faq.htm

Regards,
Robert

=============================
Bass Home Electronics
2291 Pine View Circle
Sarasota · Florida · 34231
877-722-8900 Sales & Tech Support
941-925-9747 Fax
941-232-0791 Wireless
Nextel Private ID - 161*21755*1
http://www.bass-home.com
http://www.bassburglaralarms.com
=============================