[jason]

I installed a pair of bi-amp'd monitors. All seems well
except there is a very faint 60Hz hum present even with the
sound card muted. The computer and monitors are plugged into
the same outlet, though the computer is hooked to a UPS, not
directly to the outlet (as the monitors are). Listening with
headphones I don't hear the hum. I even listened through a
small battery-powered amp I built for another purpose and
there's no hum audible at pretty high gain. So I figure it's
a ground loop. A better quality external audio interface is
in the future, so I'm not losing much sleep over this yet,
but I wonder how I'd go about addressing this since I don't
really have the option of "turning the plug around" in this
configuration. I'm guessing that the UPS is "turning the
plug around" internally somehow. There are not unusued UPS
outlets, else I'd attach the monitors to one. I can narrow
it down to the UPS by removing it from the picture, but
that's quite a hassle. I guess I'll give it a try. I could
also fabricate a pair of 1:1 transformers to isolate the
monitor inputs, but I wonder how badly that would compromise
the sound.

Jason

[soundhaspriority]

"jason" wrote in message
.. .
I installed a pair of bi-amp'd monitors. All seems well
except there is a very faint 60Hz hum present even with the
sound card muted. The computer and monitors are plugged into
the same outlet, though the computer is hooked to a UPS, not
directly to the outlet (as the monitors are).

That's a major risk factor. You have two choices:
1. Plug the speakers into the UPS.
2. Use transformers for isolation.

Listening with
headphones I don't hear the hum. I even listened through a
small battery-powered amp I built for another purpose and
there's no hum audible at pretty high gain. So I figure it's
a ground loop. A better quality external audio interface is
in the future, so I'm not losing much sleep over this yet,
but I wonder how I'd go about addressing this since I don't
really have the option of "turning the plug around" in this
configuration. I'm guessing that the UPS is "turning the
plug around" internally somehow.

It is not "turning the plug around." The inductors in the surge protector
are one cause, though I have found a ground loop to become audible just from
adding the fraction of an ohm of resistance of a relay contact. It certainly
is a recipe for trouble.

There are not unusued UPS
outlets, else I'd attach the monitors to one.

Stick an octopus plug on. $3.00. It may not compromise the UPS backup time,
if the monitors have little no-signal current draw.

I can narrow
it down to the UPS by removing it from the picture, but
that's quite a hassle. I guess I'll give it a try. I could
also fabricate a pair of 1:1 transformers to isolate the
monitor inputs, but I wonder how badly that would compromise
the sound.

Jason

It inevitably does, but in my experience, it still sounds decent.

Bob Morein
(310) 237-6511

[Scott Dorsey]

In article ,
jason wrote:
I installed a pair of bi-amp'd monitors. All seems well
except there is a very faint 60Hz hum present even with the
sound card muted. The computer and monitors are plugged into
the same outlet, though the computer is hooked to a UPS, not
directly to the outlet (as the monitors are). Listening with
headphones I don't hear the hum. I even listened through a
small battery-powered amp I built for another purpose and
there's no hum audible at pretty high gain. So I figure it's
a ground loop. A better quality external audio interface is
in the future, so I'm not losing much sleep over this yet,
but I wonder how I'd go about addressing this since I don't
really have the option of "turning the plug around" in this
configuration. I'm guessing that the UPS is "turning the
plug around" internally somehow. There are not unusued UPS
outlets, else I'd attach the monitors to one. I can narrow
it down to the UPS by removing it from the picture, but
that's quite a hassle. I guess I'll give it a try. I could
also fabricate a pair of 1:1 transformers to isolate the
monitor inputs, but I wonder how badly that would compromise
the sound.

Well, you don't mention what kind of monitors they are, or what
kind of connection you are using. But if you are using a balanced
connection, you effectively have an electronic transformer at each
end, and you can just break the ground connection on the audio
cable at one end and be done with it.

It gets more complicated if one end is balanced and the other is
not, but you can run tip and ring of an unbalanced source to pins
2 and 3 of a balanced destination, leaving pin 1 floating.

The UPS is throwing lots of trash on the grounds, because that is
what UPSes do. Unless you spend the money for a serious technical
power UPS, in general UPSes will degrade rather than improve the
line waveform.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger]

"jason" wrote in message

I installed a pair of bi-amp'd monitors. All seems well
except there is a very faint 60Hz hum present even with
the sound card muted. The computer and monitors are
plugged into the same outlet, though the computer is
hooked to a UPS, not directly to the outlet (as the
monitors are). Listening with headphones I don't hear the
hum. I even listened through a small battery-powered amp
I built for another purpose and there's no hum audible at
pretty high gain. So I figure it's a ground loop. A
better quality external audio interface is in the future,
so I'm not losing much sleep over this yet, but I wonder
how I'd go about addressing this since I don't really
have the option of "turning the plug around" in this
configuration. I'm guessing that the UPS is "turning the
plug around" internally somehow. There are not unusued
UPS outlets, else I'd attach the monitors to one. I can
narrow it down to the UPS by removing it from the
picture, but that's quite a hassle. I guess I'll give it
a try. I could also fabricate a pair of 1:1 transformers
to isolate the monitor inputs, but I wonder how badly
that would compromise the sound.

What powered monitors?

Pro or cheap computer speakers?

If your monitors have balanced inputs, you need not provide a balanced
source. Correct wiring can make a lot of hum go away.

[jason]

In article ,
says...


What powered monitors?

Pro or cheap computer speakers?

If your monitors have balanced inputs, you need not provide a balanced
source. Correct wiring can make a lot of hum go away.

They are KRK monitors. They have both balanced & unbalanced
inputs. I am using the unbalanced RCA inputs with my cheap
sound card, but as you and Scott both note, I can use the
balanced inputs and float pin 1. I think I'll give that a
try first.

Thanks!

[David Ballinger]

"jason" wrote in message
.. .
In article ,
says...


What powered monitors?

Pro or cheap computer speakers?

If your monitors have balanced inputs, you need not provide a balanced
source. Correct wiring can make a lot of hum go away.

They are KRK monitors. They have both balanced & unbalanced
inputs. I am using the unbalanced RCA inputs with my cheap
sound card, but as you and Scott both note, I can use the
balanced inputs and float pin 1. I think I'll give that a
try first.

Thanks!


Hi, Jason,
option "B" Radio Shack part # 270-054 Audio System Ground Loop Isolator
$16.99 2 isolation transformers in a little pod, phono males on one end,
females
on the other comes with a mini phone plug Y to phono males.
They are not fantastic, they are inexpensive and they work reasonably well,
always an option "B"
Best Regards,
Dave__________

[Mike Rivers]

On Jan 11, 10:20 pm, jason wrote:

They are KRK monitors. They have both balanced & unbalanced
inputs. I am using the unbalanced RCA inputs with my cheap
sound card, but as you and Scott both note, I can use the
balanced inputs and float pin 1.

I'd bet that your hum isn't (only) a ground problem. When you "mute"
the sound card, all you're doing is muting the audio going to its
analog output stage. The hum is probably coming right in through the
cable to the input of the monitor's amplifier, just like any other
audio signal.

I wrote an article a while back about grounding problems, with some
insight about using transformers (or packaged "isolators") to solve
those problems. I tested a few commercial products and included that
inexpensive Radio Shack unit. It actually had lower distortion and
better frequency response than the next higher priced "hum eliminator"
that I tested, which cost about $100.

If you're in the US, buy one at your neighborhood Radio Shack and try
it. If it improves your situation, keep it. If it doesn't make any
difference, return it and get a refund. They'll take anything back.

http://www.radioshack.com/product/in...ductId=2062214

[jason]

In article 81e1d489-ccec-4e8b-b6e6-b00d57556099
@q30g2000prq.googlegroups.com, says...
On Jan 11, 10:20 pm, jason wrote:

They are KRK monitors. They have both balanced & unbalanced
inputs. I am using the unbalanced RCA inputs with my cheap
sound card, but as you and Scott both note, I can use the
balanced inputs and float pin 1.

I'd bet that your hum isn't (only) a ground problem. When you "mute"
the sound card, all you're doing is muting the audio going to its
analog output stage. The hum is probably coming right in through the
cable to the input of the monitor's amplifier, just like any other
audio signal.

Can't hear it with headphones, though, even with (battery
powered) amplification. ?


I wrote an article a while back about grounding problems, with some
insight about using transformers (or packaged "isolators") to solve
those problems. I tested a few commercial products and included that
inexpensive Radio Shack unit. It actually had lower distortion and
better frequency response than the next higher priced "hum eliminator"
that I tested, which cost about $100.

If you're in the US, buy one at your neighborhood Radio Shack and try
it. If it improves your situation, keep it. If it doesn't make any
difference, return it and get a refund. They'll take anything back.

http://www.radioshack.com/product/in...ductId=2062214

Excellent advice, Mike and David. I'll give it a try!

[jason]

In article ,
says...


Excellent advice, Mike and David. I'll give it a try!

I picked up the Radio Shack isolation gadget and I can now
turn up the input gain on the monitors way beyond where it
makes sense and *no* hum. I listened to some files I'd been
working on intensively the past few days and I cannot hear
any difference in the audio quality either.

[[email protected]]

On Jan 12, 3:50*pm, jason wrote:
I picked up the Radio Shack isolation gadget and I can now
turn up the input gain on the monitors way beyond where it
makes sense and *no* hum.

Unfortunately, that RS part only confirms that your grounding
problem still exists AND that the ground loop circuit included that
connection. IOW number of reasons for the problem are significantly
reduced. May not (or might) imply a human safety problem. But the
problem does still exist. Keep that in mind to eventually find the
actual defect.

[Frank Vuotto]

If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

[Mike Rivers]

On Jan 12, 3:50 pm, jason wrote:

I picked up the Radio Shack isolation gadget and I can now
turn up the input gain on the monitors way beyond where it
makes sense and *no* hum.

Well, then maybe it was a ground problem. Glad you're happy.

[Keith.]

"Frank Vuotto" wrote in message
...


If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

This made me think......if you don't have a ground ,can you have a ground
loop?.
My monitors are two pronged 'double insulated', my laptop picks up its 19v
DC via the usual transformer......so...no ground and my sound is quiet but
not 'pure'.
Could the transformer be introducing a ripple DC current in my system and
the OP's?.

Keith.

[Chris Hornbeck]

On Wed, 14 Jan 2009 15:02:12 +1100, "Keith."
wrote:

If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

This made me think......if you don't have a ground ,can you have a ground
loop?.
My monitors are two pronged 'double insulated', my laptop picks up its 19v
DC via the usual transformer......so...no ground and my sound is quiet but
not 'pure'.
Could the transformer be introducing a ripple DC current in my system and
the OP's?.

First of all, responding to an earlier post, *never* remove a
safety ground. There's always another solution. Just Say No (in
this case...)

WRT your laptop question: it's such a complex issue that folks
who troubleshoot these kinds of problems regularly *still* see
head-scratchers often. A coupla notes:

Everything has grounds, so everything has ground loops. Sometimes
the fix for an issue is simply to make the loop small enough that
the coupled noise drops down far enough to make you happy enough.

Everything couples to ground(s), in bigger or smaller amounts,
but always some. This seems to be the predominant problem with
many folks' laptop power supplies. They may have no safety
ground, and the whole system may float above safety ground,
yet "ground loop"-like issues are observed. "Ground" contamination.


There really is no such thing as capital-g Ground. (There's a
big ball that we're too weak to jump off of, but ). Electrically,
there's only ever an approximation that has *some* actual,
measurable, probably important, impedance between itself and
some other local (!) definition of Ground.

A good way of looking at the issue of grounds is to remember
that all "grounds" are local. And that these local grounds
all have their turf wars. Between any pair of "grounds" is
some geography, noisily fought over, perfect access impeded.


Electronic equipment has *internal* grounds that are internally
contaminated by internal ground loop issues. (Laptops are so
difficult to build that they seem especially prey, and are
the current hot topic, but it's true everywhere and always).

But also, all "grounds" are contaminated both by noise and
by signal.



Way more than anybody cares to read, sorry, but maybe useful as
a framework someday for a head-scratcher,
Chris Hornbeck

[Richard Crowley]

"Keith." wrote ...
"Frank Vuotto" wrote ...
If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

This made me think......if you don't have a ground ,can you have a ground
loop?.
My monitors are two pronged 'double insulated', my laptop picks up its 19v
DC via the usual transformer......so...no ground and my sound is quiet but
not 'pure'.
Could the transformer be introducing a ripple DC current in my system and
the OP's?.

Many (most?) of those laptop 19V "brick" power supplies are
horribly noisy. It is rather common to require isolation transformers
coming out of a laptop (or else run it isolated on battery.)

If you have a quiet 19V brick, then you are in the fortunate
minority.

[William Sommerwerck]

This made me think... if you don't have a ground,
can you have a ground loop?

Perhaps.

"Ground loops" occur when the "ground" sides (that is, the sides with the
lowest potential) are at different AC voltages.

This is theoretically impossible in a balanced circuit, but perhaps there's
some quirky situation that can cause a shift in AC potential...

[GregS[_3_]]

In article , "Keith." wrote:

"Frank Vuotto" wrote in message
.. .


If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

This made me think......if you don't have a ground ,can you have a ground
loop?.
My monitors are two pronged 'double insulated', my laptop picks up its 19v
DC via the usual transformer......so...no ground and my sound is quiet but
not 'pure'.
Could the transformer be introducing a ripple DC current in my system and
the OP's?.


Most laptops ARE grounded.

greg

[Scott Dorsey]

Frank Vuotto wrote:

If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

No. This is not only stupid and hazardous, but also illegal. Safety
grounds are there for a reason. Don't ever lift the safety ground, lift
the audio ground.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Keith. wrote:
"Frank Vuotto" wrote in message
.. .


If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

This made me think......if you don't have a ground ,can you have a ground
loop?.

No. A ground loop is caused when there is more than one ground path between
two pieces of equipment.

My monitors are two pronged 'double insulated', my laptop picks up its 19v
DC via the usual transformer......so...no ground and my sound is quiet but
not 'pure'.
Could the transformer be introducing a ripple DC current in my system and
the OP's?.

Your laptop power supply is spewing out huge amounts of RF trash and
contaminating the ground on the laptop. Many of them are like this.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

William Sommerwerck wrote:

"Ground loops" occur when the "ground" sides (that is, the sides with the
lowest potential) are at different AC voltages.

Yes.

This is theoretically impossible in a balanced circuit, but perhaps there's
some quirky situation that can cause a shift in AC potential...

It is quite readily possible in a balanced circuit. Once you have currents
circulating through your ground system, all bets are off. Balanced circuits
just reduce the problems.... but if the ground is contaminated, everything
else bundled with the ground wire will eventually be contaminated by induction
or capacitive coupling, cables being what they are. Current should never
circulate through signal grounds if you can help it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

x-no-archive:
On Jan 13, 11:02*pm, "Keith." wrote:
"Frank Vuotto" wrote in message

...



If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

This can be hazardous to your health!


This made me think......if you don't have a ground ,can you have a ground
loop?.

A device with a two wire power plug and that is not electrically
connected to anything else and not bolted into a rack and not
internally miswired can be considered electrically floating and
balanced (at audio frequencies) and normally cannot create an audio
ground loop. Notice there are a lot of conditions there that have to
be met.

My monitors are two pronged 'double insulated', my laptop picks up its 19v
DC via the usual transformer......so...no ground and my sound is quiet but
not 'pure'.
Could the transformer be introducing a ripple DC current in my system and
the OP's?.


Yes, there are many other ways to inject hum and noise besides ground
loops.

Mark

[William Sommerwerck]

A ground loop is caused when there is more than one ground path
between two pieces of equipment.

Actually, you can have multiple ground paths without having a ground loop.
Any system in which the devices are plugged into different outlets -- even
on the same circuit -- have a ground loop.

The issue is the difference in AC potential between the grounds.

It would be more-correct to say... When the ground paths are not
electrically "equivalent".

[GregS[_3_]]

In article , "William Sommerwerck" wrote:
A ground loop is caused when there is more than one ground path
between two pieces of equipment.

Actually, you can have multiple ground paths without having a ground loop.
Any system in which the devices are plugged into different outlets -- even
on the same circuit -- have a ground loop.

The issue is the difference in AC potential between the grounds.

It would be more-correct to say... When the ground paths are not
electrically "equivalent".

You can have loops caused by the capacitance between the power
line and the equipment. Its almost always referenced to ground.
That would be common mode noise, primarily 60 Hz. In
sensitive circuits there can be a need for less than 30 pF leakage
from AC to the circuit or use battery. If the switching power supplies
are well above the used frequencies, they are often not noticed, but
they still leak AC 60 Hz which must be tied to ground or isolated.

greg

[Scott Dorsey]

William Sommerwerck wrote:
A ground loop is caused when there is more than one ground path
between two pieces of equipment.


Actually, you can have multiple ground paths without having a ground loop.

No, you cannot. You can have small and quiet ground loops, rather than
big and noisy ones. But if there are multiple ground paths between any
two pieces of equipment, by definition there is a ground loop.

Any system in which the devices are plugged into different outlets -- even
on the same circuit -- have a ground loop.

ONLY if the devices have safety grounds AND if the devices have additional
signal grounds being shared between them. If all the devices have balanced
connections with signal grounds telescoped at one end, there are no ground
loops.

The issue is the difference in AC potential between the grounds.

Yes, this is true. But once you have a ground loop, sooner or later you
will be in some situation in which noise is induced in it. The vast
majority of ground loops are small and harmless, but that doesn't mean
that they will always stay that way.

It would be more-correct to say... When the ground paths are not
electrically "equivalent".

For them to be electrically equivalent they have to be located in the
same point in space. Once two wires are located at different points in
space and connected at the ends, a shorted turn is formed and circulating
currents can be induced.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

GregS wrote:

You can have loops caused by the capacitance between the power
line and the equipment. Its almost always referenced to ground.

No. The LOOP is caused by the physical configuration. The induced current
in the loop is caused by capacitive coupling.

That would be common mode noise, primarily 60 Hz. In
sensitive circuits there can be a need for less than 30 pF leakage
from AC to the circuit or use battery. If the switching power supplies
are well above the used frequencies, they are often not noticed, but
they still leak AC 60 Hz which must be tied to ground or isolated.

Yes.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger]

"Scott Dorsey" wrote in message


Once two wires are located at
different points in space and connected at the ends, a
shorted turn is formed and circulating currents can be
induced.

It's good that someone finally outed the real cause of the problem.

The modern world is full of all kinds of conductive loops carrying all sorts
of currents. The power line is usually the 500 pound gorilla, but it may not
be the only monkey flying around. ;-)

Make a conductive loop, and magnetic induction will make sure that there is
a noisy current circulating in that loop.

The bigger the area of the loop, likely the larger the current that will
flow. The smaller the area of the loop, usually the less current. Twisted
pair is a common means for reducing the area of the loop.

There are some interesting twists. For example if you have a loop going from
A to B to C and then back to A:

Then the voltage flowing between A and B will be due to the induced current
flowing through the resistance between A and B.

Reduce the resistance between A and B, and you will decrease the voltage A
and B - common sense and intuitive. Trouble is, this is often hard to do.

Increase the resistance between B and C, or C and A, and the voltage between
A and B will usually also drop. Not so intuitive.

[Don Pearce[_2_]]

On 14 Jan 2009 11:13:21 -0500, (Scott Dorsey) wrote:

GregS wrote:

You can have loops caused by the capacitance between the power
line and the equipment. Its almost always referenced to ground.

No. The LOOP is caused by the physical configuration. The induced current
in the loop is caused by capacitive coupling.


Or very often for 50/60Hz, inductive coupling. The loop can form a
mighty large area as the secondary of a transformer to whatever fields
are hanging around.

d

[William Sommerwerck]

"Scott Dorsey" wrote in message
...
William Sommerwerck wrote:

A ground loop is caused when there is more than one ground path
between two pieces of equipment.

Actually, you can have multiple ground paths without having a ground
loop.

No, you cannot. You can have small and quiet ground loops, rather than
big and noisy ones. But if there are multiple ground paths between any
two pieces of equipment, by definition there is a ground loop.

I meant to say (really!) an _audible_ ground loop. (Really.)

[fuzznuts]

On Jan 13, 7:31*pm, Soundhaspriority wrote:
In article , "jason"

wrote:
In article ,
says...

Excellent advice, Mike and David. I'll give it a try!

I picked up the Radio Shack isolation gadget and I can now
turn up the input gain on the monitors way beyond where it
makes sense and *no* hum. I listened to some files I'd been
working on intensively the past few days and I cannot hear
any difference in the audio quality either.

You shouldn't follow Arny's "simple" non-engineer solutions. *You're aware
Arny is a liar, aren't you? I'm a degreed engineer, and I gave you much more
expensive and reliable solutions to choose from.

If you've ignored my advice, I can only wish a pox on your house.
Oh,
You're a "degreed engineer" huh? Let us know which window at
McDonalds you're working at,
and we'll all stop by for fries.
Jerry
www.boskolives.wordpress.com


"I don't really have a replacement career," Morein said. "It's a very
gnawing thing."

http://robertmorein.blogspot.com/

Bob Morein
(310) 237-6511

[Scott Dorsey]

Arny Krueger wrote:
"Scott Dorsey" wrote in message


Once two wires are located at
different points in space and connected at the ends, a
shorted turn is formed and circulating currents can be
induced.

It's good that someone finally outed the real cause of the problem.

A Mr. Black at Bell Telephone did that nearly a century ago.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger]

"Scott Dorsey" wrote in message

Arny Krueger wrote:
"Scott Dorsey" wrote in message


Once two wires are located at
different points in space and connected at the ends, a
shorted turn is formed and circulating currents can be
induced.

It's good that someone finally outed the real cause of
the problem.

A Mr. Black at Bell Telephone did that nearly a century
ago. --scott

How so? I know he invented negative feedback, but can find nothing about him
in connection with grounding problems and/or techniques.

[Scott Dorsey]

Arny Krueger wrote:
"Scott Dorsey" wrote in message

A Mr. Black at Bell Telephone did that nearly a century
ago. --scott

How so? I know he invented negative feedback, but can find nothing about him
in connection with grounding problems and/or techniques.

I think it was a different Black, actually. Let me see if I can dig up
a cite... it actually predates the BSTJ by by more than a decade and I
think it was in the IEE Journal.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[jason]

In article 48dbb751-2b4a-49ac-9771-24da428e7125
@z6g2000pre.googlegroups.com, says...
On Jan 12, 3:50*pm, jason wrote:
I picked up the Radio Shack isolation gadget and I can now
turn up the input gain on the monitors way beyond where it
makes sense and *no* hum.

Unfortunately, that RS part only confirms that your grounding
problem still exists AND that the ground loop circuit included that
connection. IOW number of reasons for the problem are significantly
reduced. May not (or might) imply a human safety problem. But the
problem does still exist. Keep that in mind to eventually find the
actual defect.

Agreed. A new (external Firewire or USB) box is in the near-
I-hope future. I think Scott has it right, namely that the
UPS does funky things to the power. I don't know if the APC
unit I have now works like the Belkin USP it replaced, but
when I took the Belkin apart to try to fix it (gave up) it
looked as if it -always- powered the AC ports from its
inverter whether batteries were providing the juice or not.
A full-wave bridge rectifier was the first thing the
incoming AC encountered (after a transformer), and there was
a skinny little wire between the transformer and the
rectifier that wandered off to a little patch of circuity
that I presume was the sensor for mains failure.

[Frank Vuotto]

Give it a break, his speakers have NO AC grounds. Are they illegal?


On 14 Jan 2009 09:33:48 -0500, (Scott Dorsey) wrote:

Frank Vuotto wrote:

If both speakers have 3 prong plugs, use an ac ground lift adapter
from Walmarts.

No. This is not only stupid and hazardous, but also illegal. Safety
grounds are there for a reason. Don't ever lift the safety ground, lift
the audio ground.
--scott

[[email protected]]

On Jan 15, 6:26 pm, jason wrote:
Agreed. A new (external Firewire or USB) box is in the near-
I-hope future. I think Scott has it right, namely that the
UPS does funky things to the power.

First appreciate what you have. You have a low frequency AC current
flowing down that signal cable from one box to the other. The Radio
Shack isolation transformer blocked that current - broke the ground
loop.

Second, that current must have never existed. Safety ground on both
units means there is no ground voltage difference - therefore no
ground loop current. But as you have proven, you have a low frequency
ground loop current. Why? Safety grounds mean there should be no
such voltage difference; therefore no current.

Third, UPSes must connect that safety ground to the third (safety
ground) prong without anything (even a filter) in that connection.
Then all grounds have shortest and single point connections - no
reason for current to flow thought that signal wire.

Implied is a missing safety ground inside that UPS or a safety
ground with filter circuits. Either way, a violation or the failure
you are looking for.

Of course, UPSes output much 'dirtier' electricity. The UPS itself
could be culpriut. Popular myths hype UPS as 'cleaner' electricity.
Only true when a UPS connects a load directly to AC mains.

But again, you have a tool - the Radio Shack filter - to identify
part of that ground loop current path; to help identify the still
existing failure. Of course, you don't know which wire in that cable
is carry current. But when the failure is found and corrected,
install nothing or less hardware to have no hum.

[Mike Rivers]

wrote:

First appreciate what you have. You have a low frequency AC current
flowing down that signal cable from one box to the other. The Radio
Shack isolation transformer blocked that current - broke the ground
loop.

Second, that current must have never existed. Safety ground on both
units means there is no ground voltage difference - therefore no
ground loop current. But as you have proven, you have a low frequency
ground loop current. Why? Safety grounds mean there should be no
such voltage difference; therefore no current.

The problem is that safety grounds are just that - for SAFETY. There
shouldn't be
enough potential difference between "grounds" to kill you, but that's as
far as the
guarantee goes. It doesn't assure that there won't be enough current to
get in to
the audio path of poorly designed equipment. Therein lies the problem,
and the
Radio Shack Ground Isolator corrects, or more accurately, masks the design
deficiency.

[[email protected]]

* Second, that current must have never existed. *Safety ground on both
units means there is no ground voltage difference - therefore no
ground loop current. *But as you have proven, you have a low frequency
ground loop current. *Why? *Safety grounds mean there should be no
such voltage difference; therefore no current.

That is not true.

If you take a piece of wire, form it into a loop connecting the two
ends, there is NOMINALLY no voltage diff between the ends but if the
loop is in a magenttic field there can be a small difference and when
you connect the ends together, the small voltage can create a large
current because the resistance is so low. There are other ways for
rather large currents to flow in saftey grounds that are "nominally
the same voltage". A voltage diff of only 1 volt would be considered
the "same voltage" from the point of view of a saftey ground, you
would never get a shock from 1 Volt, but from the point of view of the
audio, that 1 Volt can be a hugh difference.

Mark

[William Sommerwerck]

wrote in message
...

Second, that current must have never existed. Safety ground on
both units means there is no ground voltage difference - therefore
no ground loop current. But as you have proven, you have a low
frequency ground loop current. Why? Safety grounds mean there
should be no such voltage difference; therefore no current.


That is not true.
If you take a piece of wire, form it into a loop connecting the two
ends, there is NOMINALLY no voltage diff between the ends...

You're assuming the wire has literally zero resistance and thus can "force"
both ends to the same potentional. This is not necessarily the case.

[[email protected]]

On Jan 17, 12:28*pm, wrote:
If you take a piece of wire, form it into a loop connecting the two
ends, there is NOMINALLY no voltage *diff between the ends but if the
loop is in a magenttic field there can be a small difference and when
you connect the ends together, the small voltage can create a large
current because the resistance is so low. *

Now calculate how much current is created by that magnetic field.
Once numbers are provided in that post (and that also comes from
experience), then the few feet of wire must never create that kind of
voltage. Nothing even approaching 1 volt should exist. Even more
than two volts between electronics and the mains breaker box is
completely unacceptable for human safety. Magnetic fields on short AC
cords create 1 volt. Nonsense.

Properly noted is that wire is an electronic component - which is
why the safety ground must join at a common point nearby all
components.

Safety ground performs many functions beyond protecting human life.
Safety ground between two adjacent components at 1 volt? Complete
nonsense or an indication of a serious problem that is also a major
human safety threat. If both components are properly safety grounded
to a common point, then voltage differences created by massive
magnetic fields are so low as to not cause measureable hum.

First, safety ground serves many functions beyond human safety - if
properly connected.

Second, magnetic fields do create such currents. Current that must
be so trivial as to be virtually zero. Furthermore, no such massive
magnetic fields should exist there anyway. Two reasons why magnetic
fields do not create as speculated without numbers. Remove the
hypothetical massive magnetic field generator that is drawing maybe
100 watts if those hypothetical fields exist. Another example of
curing the problem rather than its symptoms.

Meanwhile, if the safety grounds are properly connected (and that
includes how grounds connect inside each component), then no
significant voltage difference should exist on that signal cable. The
Radio Shack transformer is blocking currents due to a design
deficiency that must never exist if all safety grounds are properly
connected (ie not compromised by a UPS) and if a design or component
defect does not exist inside one component.

Fix the problem. Do not invent excuses or cure symptoms. Magnetic
fields creating such currents on short wires is only speculation not
supported by numbers or cured by removing a defective massive field
generator that should never exist. Safety ground serves many
functions beyond human safety - including no hum on signal wires.
That is why safety grounds meet at an adjacent and common point -
which is clearly not required for human safety - which is clearly done
to make those currents blocked by the Radio Shack isolator not
possible.

Maybe safety ground is perverted by the UPS as the OP suggests.
Therefore the RS isolator is curing a symptom. Instead, cure the
problem. No such noise currents should exist if all components are
properly safety grounded to a common and nearby point.

[[email protected]]

On Jan 17, 12:30*pm, "William Sommerwerck"
wrote:
You're assuming the wire has literally zero resistance and thus can "force"
both ends to the same potentional. This is not necessarily the case.

If I was assuming (ignoring 40 years of design experience), then
safety grounding all components to a common point inside the mains
breaker box would eliminate that hum. I said otherwise. Wire is an
electronic component which is why safety grounds must meet a common
point AT electronics. That common point is necessary so that ground
loop current need not flow through that signal cable.

Further implied was defective safety grounding in one UPS. If
safety ground is properly wired, then nothing but wire - not even a
noise filter - exists between all safety ground connectors.

A Radio Shack isolator may mask a design deficiency or an internal
part failure. But again, for some reason, safety ground did not put
both components at a common potential. No ground loop currents should
be flowing between components on that signal wire. Cure the problem;
not its symptoms.