[Keith.]

wrote in message
...
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.

Good discussion !..... I just checked the earth pin to ground on my monitors
and they are fine. It should not be difficult to do this to the OP's UPS
too,or better still, for the benefit of the exercise, bypass the UPS.

There seems to be two grounds or two grounds design. One to provide a rapid
current drain through copper wire (low resistance) to trip a circuit breaker
or fuse in case of a short.
The other ground is built into circuit design to provide a potential for
current to flow through resistive components. If two or more of these
circuits are joined in a common ground and there is voltage (AC?) difference
between these circuits then the loop can induce hum.
That is, two different uses for 'ground',and what do they have in common?
Am I on the right path here ?

Keith.

[Ben Bradley]

On Sun, 11 Jan 2009 23:05:57 GMT, 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.

Can you (with your system as originally connected as in this post,
generating the hum in the monitors) turn OFF your computer AND turn
off the UPS, while leaving everything plugged in? You should, of
course, turn off your monitors before switching other things on and
off, so transient pops don't damage the speakers or hurt your ears,
then turn your monitors back on. I suspect you will still hear this
hum from the monitors, though perhaps at a slightly different volume.
If so, this would suggest even more strongly to me that the problem is
as I describe below.

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).

The UPS may well be contributing to the hum, but I doubt it's the
only thing. Turn off the computer, unplug it from the UPS, and plug
both the computer and the monitors into a power strip, so you know
they both go to the "same ground." With the monitors' audio input
connected to the computer soundcard, listen to the monitors

Every computer has a line filter right in line with the plug for
the power cord, meant to keep the computer's switching power supply
noise from going onto the power line and interfering with other
equipment. It has substsntial capacitance between each of the three
power connections (hot, neutral and ground), resulting in a 60 Hz
current being put onto the ground line. As the ground path from the
coomputer to the outlet has something greater than zero resistance
(maybe 1/10th an ohm), a small 60 Hz voltage will appear on the
computer's ground, referenced to the outlet ground.

When you connect your computer's audio to your powered speaker
(with the ground connection as you've done), this voltage will also
appear between your monitor's power ground pin and its audio input
ground connection (or a smaller voltage, as there's low resistance
bwtween the speaker's audio ground input and power ground). This might
or might not cause a problem, depending on whether and how well the
monitor circuitry is designed to handle such a signal through the
ground connection of its audio input. Much equipment, even
"professional" equipment, appears to be designed with little if any
thought to this possible problem.

I recall that Bill Whitlock has suggested a "ground current
immunity" test and specification for audio equipment, which would
indicate how suceptible an audio input's ground is to such a current.
But high immunity wouldn't guarantee equipment doesn't have hum,
especially with unbalanced connections, because the cable grounds and
connections between audio equipment have non-zero resistance, creating
a voltage difference between the equiment that gets superimposed onto
the signal.

The following "white papers" are instructive, specifically AN003
and AN004:

http://www.jensen-transformers.com/apps_wp.html

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,

Unless the new audio interface isolates the audio ground from the
computer ground, I don't see it making any change. If your present
interfaces has balanced I/O (Some that "appear" to have balanced I/O
really don't, specifically the Delta 44 and 66) and you use telescoped
cables between it and the monitor's balanced input as Scott said,
connecting the ground at one end only, then that will solve your
problem without the Radio Shack transformer in the signal path.

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.

The file AN004 talks specifically about "plug reversal" and why it
may reduce the hum, but not eliminate it. But that's just a kludge fix
to the problem, and it's best left alone (there's also the elecric
guitar and guitar amp problem, which deserves its own thread, and that
was also discussed years ago).

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

[David Ballinger]

wrote in message
...
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.

Bill,
You are working too hard here. It is all perfectly normal, maybe not
desirable, but normal.
I am going to set this up as I understand it in a U.S. residential
situation, and most businesses are the same; Power enters the building and
goes through a distribution system, a fuse or circuit breaker panel to be
subdivided to the various paths around your home/office. usually in this box
is a common point, center tap of the 240 volt, Ground and Neutral common on
this one buss. Now arbitrarily I have a duplex receptacle at the end of 100
feet of #14 copper wire, if I put a 10 amp load on this circuit, there will
be a small voltage drop on the wires. a quick look up in the Engineers book
says for hard drawn copper wire 100 feet Equals .25 ohms of resistance, all
normal, all usual, but this voltage drop works out to be 2.5 volts. If I
started out with 120 volts now I only have 118.5 volts, not bad normal. Now
on the neutral return path to the box is now 2.5 volts above ground
potential, still normal, leaves me working with 115 volts at a 10 amp load.
measuring from the safety ground which has no load, and is at ground
potential to the neutral pin of the receptacle 2.5 volts of AC, this only
becomes a problem when I plug in a 2 prong plug that assumes that neutral is
at zero volts and it isn't. no harm no fowl normal but it does hum like the
dickens when you plug in an unbalanced audio with 2.5 volts of hum on the
ground and your amplifier just knows that since it has a grounded 3 wire
plug on it there will be a bit of current flowing on the shield. Balanced
audio is so good because of the common mode rejection that it has. If you
want to go unbalanced the only thing you can do is break the ground loop
circuit by option "A" a line voltage (Mains) isolation/insulation
transformer or option "B" transformer coupling the audio cut. to break the
ground loop. A $100 transformer for the mains or the RadioShack wonder for
$16.99. Like I said all normal, all safe, not a fantastic fix, but
reasonable.
Now if you still want something to worry about, I had a great Aunt that
worried about the electricity leaking out of the unused receptacles, think
about it, have a nice day!
Dave_________

[[email protected]]

On Jan 18, 6:43*pm, "David Ballinger" wrote:
I am going to set this up as I understand it in a U.S. *residential
situation, and most businesses are the same; Power enters the
building .. *Now on the neutral return path to the box is now 2.5
volts above ground potential, still normal, leaves me working with
115 volts at a 10 amp load.measuring from the safety ground which
has no load, and is at ground potential to the neutral pin of the
receptacle 2.5 volts of AC,

With basic electrical knowledge, one would know earth ground (maybe
100 feet away) is irrelevant. Voltages from electronics to earth are
irrelevant. The poster has naively confused earth ground with other
grounds.

Even if audio components are all at 300 volts (relative to earth)
and if all are properly grounded (bonded) together at the power strip
(only feet away), then voltage difference is zero. Then no current
flows through that signal wire; no hum exists. Earth ground or ground
inside a neighbor’s TV have no relevance.

It is naive to assume all grounds are same. Earth ground is
irrelevance to a common safety ground (only feet away) and shared by
all audio components. Defect in that common safety ground would
explain ground loop currents on a signal cable.

[Scott Dorsey]

Frank Vuotto wrote:
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.

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

If they have no AC ground, the cheater won't do any good anyway.

But they could still be illegal, too. I have encountered plenty of Asian
consumer gear that did not pass basic UL specifications for grounding and
insulation.

Still, at this point I think it's clear that the problem is the UPS waveform,
which also could very well be illegal. I see a lot of consumer grade UPS
systems that don't meet FCC part 15, or even come close.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Peter Larsen[_3_]]

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.

First suspect: the powered monitor. Rule that out prior to using a lot of
time on the other options. Perhaps it simply hums, perhaps you need to look
at its input sensitivity setting. Not telling us what apparatus it is about
makes it an unanswerable question.

Jason

Kind regards

Peter Larsen

[jason]

In article ,
says...


First suspect: the powered monitor. Rule that out prior to using a lot of
time on the other options. Perhaps it simply hums, perhaps you need to look
at its input sensitivity setting. Not telling us what apparatus it is about
makes it an unanswerable question.

Kind regards

Peter Larsen

They are Rokit 8 monitors. They don't hum on their own. The
input gain is a stepped control with 31 steps.. I find that
a setting of 7 is plenty for the room where I'm using them,
but even cranking them up all the way produces no hum (with
just a resistor bridging the input). Mike Rivers said good
things about the inexpensive Radio Shack ground loop
isolation gadget..two transformers, I presume.. so I bought
one and the hum vanished. Everything is hooked to a UPS
except the monitors. They are attached to the same outlet,
bypassing the UPS. Others have reported that UPS's are
seriously dirty..perhaps non-compliant with FCC rules. Next
time I feel like uprooting everything, I will try hooking
the monitors to the UPS, too--without the isolation
transformers--to see if that makes a difference.

[Laurence Payne[_2_]]

On Mon, 02 Feb 2009 03:58:43 GMT, jason wrote:

They are Rokit 8 monitors. They don't hum on their own. The
input gain is a stepped control with 31 steps.. I find that
a setting of 7 is plenty for the room where I'm using them,
but even cranking them up all the way produces no hum (with
just a resistor bridging the input). Mike Rivers said good
things about the inexpensive Radio Shack ground loop
isolation gadget..two transformers, I presume.. so I bought
one and the hum vanished. Everything is hooked to a UPS
except the monitors. They are attached to the same outlet,
bypassing the UPS. Others have reported that UPS's are
seriously dirty..perhaps non-compliant with FCC rules. Next
time I feel like uprooting everything, I will try hooking
the monitors to the UPS, too--without the isolation
transformers--to see if that makes a difference.

Yes. It seems a no-brainer to perform the simple and easy experiment
of trying everything connected (a) through the UPS and (b) not through
the UPS.