hum and grounding

[RWG]

This could be a little tricky to explain, so I'll try to be as clear as
possible. I'm getting problems with hum, when connecting my audio system to
my computer system.

I have a conventional stereo system and a PC system (pretty much the usual
Wintel stuff, with PCI sound card). The PC has a three-prong cord, with
ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW
This is North America, 110V.) The PC components all plug into a surge
suppressor. I run the tape output from the stereo into the sound card of the
PC, and I run the sound card output into the aux input of the stereo
receiver. I find that, if I connect all three prongs of the PC equipment
(through the surge suppressor) to the wall outlet, I get hum when I listen
to the sound card.

This seems to happen wherever I plug in the stereo: I can plug it into the
surge suppressor, or the same wall receptacle, or a completely different
receptacle. I still get hum.

The thing that DOES get rid of the hum is to plug the PC system into the
wall, separately from the audio stuff, through a 2-prong adapter, thus
interrupting the ground connection. That's what I've done in the past. But
I've been advised that this offers the PC less protection againsty surges
and other line anomalies than using the ground, which is obviously there for
a reason anyway.

Should I ground the PC case to the stereo case? Will a UPS provide line
isolation and thus eliminate the problem? (I've been planning to get one
anyway for other reasons.)

Or should I just cut out that pecky ground connection, the way I did in the
past?

--Ron Garrison

[CJT]

RWG wrote:

> This could be a little tricky to explain, so I'll try to be as clear as
> possible. I'm getting problems with hum, when connecting my audio system to
> my computer system.
>
> I have a conventional stereo system and a PC system (pretty much the usual
> Wintel stuff, with PCI sound card). The PC has a three-prong cord, with
> ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW
> This is North America, 110V.) The PC components all plug into a surge
> suppressor. I run the tape output from the stereo into the sound card of the
> PC, and I run the sound card output into the aux input of the stereo
> receiver. I find that, if I connect all three prongs of the PC equipment
> (through the surge suppressor) to the wall outlet, I get hum when I listen
> to the sound card.
>
> This seems to happen wherever I plug in the stereo: I can plug it into the
> surge suppressor, or the same wall receptacle, or a completely different
> receptacle. I still get hum.
>
> The thing that DOES get rid of the hum is to plug the PC system into the
> wall, separately from the audio stuff, through a 2-prong adapter, thus
> interrupting the ground connection. That's what I've done in the past. But
> I've been advised that this offers the PC less protection againsty surges
> and other line anomalies than using the ground, which is obviously there for
> a reason anyway.
>
> Should I ground the PC case to the stereo case? Will a UPS provide line
> isolation and thus eliminate the problem? (I've been planning to get one
> anyway for other reasons.)
>
> Or should I just cut out that pecky ground connection, the way I did in the
> past?
>
> --Ron Garrison
>
>

My 2 cents:

Disconnect your cable TV connection from your stereo (assuming they're
connected). If that solves it, get a cable isolator. Cable TV is a
notorious introducer of hum via ground loops.

Strapping the PC case to the stereo case would be a reasonable thing
to try, and generally a good idea (since it introduces a safety ground
to the stereo).

A UPS is overkill, but might also help if you plan to get one anyway.

[Ethan Winer]

Ron,

Agree with Flint: you need an audio isolation transformer. Jenson makes good
ones, but if the highest quality is not important - for example, if the
connection is in the monitor path only - you could probably get away with a
less expensive unit like the EbTech Hum Eliminator.

--Ethan

[RWG]

Thanks to everyone for the quick replies!

The cable TV might be a contributor, and I'll check it out. I really hadn't
thought of that.

I like the idea of the UPS if it will provide isolation, as it won't affect
the stereo (unless I plug that into it too), so I don't have to worry about
it softening the voltage regulation for the power amp. And I'm planning to
get one anyway, so it's the old 2-birds-one-stone thing.

For now, I think the first thing I'll do is strap the PC and receiver cases
together.

BTW don't a lot of receivers have 3-prong cords, at least the bigger ones?

[Barry Mann]

In >, on 08/18/03
at 01:05 PM, "RWG" > said:

>Thanks to everyone for the quick replies!

>The cable TV might be a contributor, and I'll check it out. I really
>hadn't thought of that.

Cable systems are the most likely cause of this sort of problem,
followed closely by PC's. The combination of PC and cable system is
deadly. Actually, it takes two or more to play this game. You need a
unit that is a bad neighbor by polluting the ground and you need a
poorly designed partner that is offended by that ground pollution. (In
the case of the cable system, that bad neighbor could be down the
block.) While there are certainly good and bad designs, home audio
equipment is more susceptible to this sort of problem than professional
gear. Pro gear uses a much more expensive interconnection scheme that
is less prone to this sort of mishap. (And studios are carefully
designed to avoid grounding problems -- home audio systems are mostly
haphazard interconnections.)

>I like the idea of the UPS if it will provide isolation, as it won't
>affect the stereo (unless I plug that into it too), so I don't have to
>worry about it softening the voltage regulation for the power amp. And
>I'm planning to get one anyway, so it's the old 2-birds-one-stone
>thing.

You will compromise your protection somewhat if you plug signal cables
from an unprotected device into a protected device. "Device" includes
PC, stereo, phone line, cable system, TV, external TV antenna,
Satellite dish, etc.

>For now, I think the first thing I'll do is strap the PC and receiver
>cases together.

>BTW don't a lot of receivers have 3-prong cords, at least the bigger
>ones?

Some do, but as you've found out, that 3rd prong can cause heartburn.

-----------------------------------------------------------
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, SPAMers are ruining my mailbox]
-----------------------------------------------------------

[RWG]

Sounds like there are more aspects to this than I had guessed, particuarly
the cable TV element. And the cable TV part sounds like it has no easy cure,
if I want to run its sound into my stereo.

The idea of digital interconnections, using fiber optics, also looks better
all the time. (-;

[Dave Platt]

>Sounds like there are more aspects to this than I had guessed, particuarly
>the cable TV element. And the cable TV part sounds like it has no easy cure,
>if I want to run its sound into my stereo.

Actually, it probably does.

You can buy, or built, an isolation-transformer for the cable-TV feed.
Installing this between your cable TV line and your TV (or A/V
receiver) will break the ground loop.

For a commercially-built device, check out part #180-075 at
www.partsexpress.com (type "isolation" in the keyword search box, and
scroll down to the "CATV Misc" section).

Attached below is one possible approach for a homemade isolator,
courtesy of Jamie Hanrahan and my USENET-snippings archive. I don't
know if the Radio Shack baluns he specifies are still available - they
may have changed designs in the ten years since this article was
written.

Another thing which you could do, is examine your cable-TV
installation. In most areas, cable-TV installers are required by the
local electrical code to "bond" the cable to the house's grounding
system at the point where it enters the building - the cable-TV
coaxial shield is connected to the building ground. If this was not
done when your cable feed was installed, it could exacerbate the hum
problem, because the cable's idea of "ground" would be whatever ground
voltage is present back at the pole, or at your neighbor's house, or
some combination thereof. If you find that your cable-TV line wasn't
properly grounded on entry to your building, you could call your cable
TV company and complain about the defective installation, and request
that they bring it "up to code".

###############################

From:
Newsgroups: sci.electronics,rec.audio,rec.video
Subject: Revisited: CATV baluns for eliminating AC hum
Date: 1 Nov 93 20:15:24 PST

Some time ago, someone in one of these groups had a question about eliminating
AC hum from their stereo system. The problem started when they connected
a VCR into the system, the VCR being connected to cable TV.

I suggested (as I and others have done in the past) using a pair of 75/300
baluns back-to-back in series in the CATV lead, in order to isolate the
stereo system from the cable's connection to earth ground. The problem is
especially bad if there's another earth ground connection in the system (like a
unit with a three-prong plug).

Recently, someone objected to this, stating that a balun has a common
connection between its two "sides", and hence offers no isolation.

And of course, he's right. Most of the diagrams of baluns that I've seen
show the "bottoms" of the two transformer windings connected together.

But, I've used this trick of two back-to-back baluns several times to
eliminate these CATV-induced ground loops, and it's always worked.

Well, today I had to do it again. I went to Rat Shack and bought two baluns --
an "inline" one with a female F-connector and pigtails for the 300-ohm lead,
and a compact one with a push-on male F connector and screw terminals for the
300-ohm side. (This type is often supplied with TV sets.) Before hooking
things up, I got out my trusty Fluke and measured the baluns. (Gasp, what a
concept!)

It turns out that the in-line one is a true transformer -- there's no common
connection between the 300 ohm and 75 ohm sides. The compact one does have a
common connection, but of course any single break in the "ground" chain is
sufficient.

So there you have it. I don't know *why* RS makes their in-line baluns this
way, but I'm glad that they do...

--- Jamie Hanrahan, Kernel Mode Systems, San Diego CA
Internet: (JH645) Uucp: uunet!cmkrnl!jeh CIS: 74140,2055

###############################

--
Dave Platt > AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[flint]

I use the Jensen CATV isolation product. Works perfectly.

Also, I have yet to see anyone hook up a PC to a stereo without getting a
serious hum problem that can be easily fixed with an audio isolation
transformer. I have several spares in my house for testing and in case a
visiting friend wants to hook his notebook to my audio system.

- Flint

"RWG" > wrote in message
...
> Sounds like there are more aspects to this than I had guessed, particuarly
> the cable TV element. And the cable TV part sounds like it has no easy
cure,
> if I want to run its sound into my stereo.
>
> The idea of digital interconnections, using fiber optics, also looks
better
> all the time. (-;
>
>

[flint]

I have never found that a UPS can cure a hum problem.

The only AC power device I know if that cures hum issues is a "Balanced
Power" conditioner. These are expensive, and everything in your rig needs to
be plugged into the power conditioner. Not simple, but very effective.

- FLINT

"RWG" > wrote in message
...
> Thanks to everyone for the quick replies!
>
> The cable TV might be a contributor, and I'll check it out. I really
hadn't
> thought of that.
>
> I like the idea of the UPS if it will provide isolation, as it won't
affect
> the stereo (unless I plug that into it too), so I don't have to worry
about
> it softening the voltage regulation for the power amp. And I'm planning to
> get one anyway, so it's the old 2-birds-one-stone thing.
>
> For now, I think the first thing I'll do is strap the PC and receiver
cases
> together.
>
> BTW don't a lot of receivers have 3-prong cords, at least the bigger ones?
>
>

[CJT]

Geoff Wood wrote:

> "RWG" > wrote in message news:bhr0um$7j2$
>
>>For now, I think the first thing I'll do is strap the PC and receiver
>
> cases
>
>>together.
>
>
>
> Do that and yyou'll introduce yet *another* ground loop. But give it a
> try - the best result can be found empirically.

Ground loops are only problematic when they have a voltage drop across
them. Brute force can sometimes be effective to decrease that drop to
an insignificant amount.

>
> Disconnecting anything electrically connected to the computer that is
> plugged into the mains from a different outlet is usually the first place to
> look.
>
> geoff
>
>

[Barry Mann]

In >, on 08/18/03
at 06:35 PM, (Dave Platt) said:

[ ... ]

>Well, today I had to do it again. I went to Rat Shack and bought two
>baluns --
>an "inline" one with a female F-connector and pigtails for the 300-ohm
>lead, and a compact one with a push-on male F connector and screw
>terminals for the 300-ohm side. (This type is often supplied with TV
>sets.) Before hooking things up, I got out my trusty Fluke and
>measured the baluns. (Gasp, what a concept!)

>It turns out that the in-line one is a true transformer -- there's no
>common connection between the 300 ohm and 75 ohm sides. The compact
>one does have a common connection, but of course any single break in
>the "ground" chain is sufficient.

[ ... ]

Years ago, I had to make my own cable TV isolators. Rather than trying
to explain to the electronics store counter person what I was
attempting to accomplish, I asked for them to fetch a pile of baluns,
which I then sorted through with my Ohmmeter. To them, all baluns were
alike (a mystery) and they could not understand why I only wanted
certain ones.

-----------------------------------------------------------
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, SPAMers are ruining my mailbox]
-----------------------------------------------------------

[Tomi Holger Engdahl]

"RWG" > writes:

> This could be a little tricky to explain, so I'll try to be as clear as
> possible. I'm getting problems with hum, when connecting my audio system to
> my computer system.
>
> I have a conventional stereo system and a PC system (pretty much the usual
> Wintel stuff, with PCI sound card). The PC has a three-prong cord, with
> ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW
> This is North America, 110V.) The PC components all plug into a surge
> suppressor. I run the tape output from the stereo into the sound card of the
> PC, and I run the sound card output into the aux input of the stereo
> receiver. I find that, if I connect all three prongs of the PC equipment
> (through the surge suppressor) to the wall outlet, I get hum when I listen
> to the sound card.
>
> This seems to happen wherever I plug in the stereo: I can plug it into the
> surge suppressor, or the same wall receptacle, or a completely different
> receptacle. I still get hum.
>
> The thing that DOES get rid of the hum is to plug the PC system into the
> wall, separately from the audio stuff, through a 2-prong adapter, thus
> interrupting the ground connection. That's what I've done in the past. But
> I've been advised that this offers the PC less protection againsty surges
> and other line anomalies than using the ground, which is obviously there for
> a reason anyway.

The PC shoudl be grounded. Do not use those 2-prong adapters,
beacause it cuts thr ground. Without the ground the surge suppressor
does not work well and the whole ungrounded PC is potential
electrical safety risk.

> Should I ground the PC case to the stereo case?

Extra grounding wire from PC to stereo case can help sometimes
soemwhat, but usually it does not remove the problem.

The problem is elsewhere.
http://www.epanorama.net/documents/groundloop/index.html

> Will a UPS provide line
> isolation and thus eliminate the problem?

Generally UPS does not help in this.
The ground connection is continuous through the UPS.
It does not change the grounding of the system.

> (I've been planning to get one
> anyway for other reasons.)

UPS might be OK for those other reasons and a good idea
to get it.

> Or should I just cut out that pecky ground connection, the way I did in the
> past?

No.

Read the document http://www.epanorama.net/documents/groundloop/index.html
instead. When you understand what is happening, pick a safe
method from there to solve this problem.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

[Tomi Holger Engdahl]

CJT > writes:

> RWG wrote:
>
> > This could be a little tricky to explain, so I'll try to be as clear as
> > possible. I'm getting problems with hum, when connecting my audio system to
> > my computer system.
> > I have a conventional stereo system and a PC system (pretty much the
> > usual
> > Wintel stuff, with PCI sound card). The PC has a three-prong cord, with
> > ground. The stereo equipment has the typical polarized 2-prong plugs. (BTW
> > This is North America, 110V.) The PC components all plug into a surge
> > suppressor. I run the tape output from the stereo into the sound card of the
> > PC, and I run the sound card output into the aux input of the stereo
> > receiver. I find that, if I connect all three prongs of the PC equipment
> > (through the surge suppressor) to the wall outlet, I get hum when I listen
> > to the sound card.
> > This seems to happen wherever I plug in the stereo: I can plug it
> > into the
> > surge suppressor, or the same wall receptacle, or a completely different
> > receptacle. I still get hum.
> > The thing that DOES get rid of the hum is to plug the PC system into
> > the
> > wall, separately from the audio stuff, through a 2-prong adapter, thus
> > interrupting the ground connection. That's what I've done in the past. But
> > I've been advised that this offers the PC less protection againsty surges
> > and other line anomalies than using the ground, which is obviously there for
> > a reason anyway.
> > Should I ground the PC case to the stereo case? Will a UPS provide
> > line
> > isolation and thus eliminate the problem? (I've been planning to get one
> > anyway for other reasons.)
> > Or should I just cut out that pecky ground connection, the way I did
> > in the
> > past?
> > --Ron Garrison
> >
>
> My 2 cents:
>
> Disconnect your cable TV connection from your stereo (assuming they're
> connected). If that solves it, get a cable isolator. Cable TV is a
> notorious introducer of hum via ground loops.

This is the most common problem in this kind of systems.

If you still need the cable TV connection, buy a suitable
signal isolator for the cable TV signal, so you get the
cable signal through without causing the humming.

What applies to the cable TV connection applies to all
common antenna systems, because they tend to be all
grounded, and usually at some different place where your
PC is (and this causes potential difference that is heard as humming).

> Strapping the PC case to the stereo case would be a reasonable thing
> to try, and generally a good idea (since it introduces a safety ground
> to the stereo).

Usually this does not help in solving the hummign problem.

> A UPS is overkill, but might also help if you plan to get one anyway.

UPS does not generally help in any this kind of ground loop problems.


--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

[Tomi Holger Engdahl]

"RWG" > writes:

> Thanks to everyone for the quick replies!
>
> The cable TV might be a contributor, and I'll check it out. I really hadn't
> thought of that.
>
> I like the idea of the UPS if it will provide isolation, as it won't affect
> the stereo (unless I plug that into it too), so I don't have to worry about
> it softening the voltage regulation for the power amp. And I'm planning to
> get one anyway, so it's the old 2-birds-one-stone thing.

UPS systems generally do not provide the ground isolation you need.

> For now, I think the first thing I'll do is strap the PC and receiver cases
> together.

Did it help ?

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

[RWG]

"Tomi Holger Engdahl" > wrote in message
...
..
..
..
> The problem is elsewhere.
> http://www.epanorama.net/documents/groundloop/index.html

Thanks for the URL. I have not read it just yet, but it looks very
informative.

GOOD NEWS: I disconnected the cable TV/cable Internet connection, and the
problem went away completely. (Looking back, I guess the fact that the hum
appeared only on the sound card and cable TV inputs to the stereo was a
pretty good clue!)

My sincere thanks to all those who promoted that theory. I guess I know what
I need to do now...

--Ron

[Curious Cat]

> I use the Jensen CATV isolation product. Works perfectly.

I tried hooking my laptop up to my receiver today to play RealOne Rhapsody
over my audio system.

Of course, I experienced hum.

What specific Jensen CATV isolation product would you recommend?

Does the isolator go between the laptop and the receiver?

BTW, I do have audio from my cable box connected to my receiver.

[CJT]

Curious Cat wrote:

>>I use the Jensen CATV isolation product. Works perfectly.
>
>
> I tried hooking my laptop up to my receiver today to play RealOne Rhapsody
> over my audio system.
>
> Of course, I experienced hum.
>
> What specific Jensen CATV isolation product would you recommend?
>
> Does the isolator go between the laptop and the receiver?
>
> BTW, I do have audio from my cable box connected to my receiver.
>
>
The isolator goes on the cable input to the cable box.