Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.

I recently noticed a mild-moderate hum coming from my speakers that is
constant regardless of volume or input. Here are the results of my
attempts to isolate it.

Turn off and unplug pre-amp = hum (no change)
Disconnect pre-amp output cable = no hum
Replace cable connecting pre-amp to amp = hum

Not sure if this is helpful, but my pre-amp has a headphone amp that
produces no hum.

Equipment:
Sonic Frontiers Line 1 Tube Preamp w/ 5-year-old tubes
McCormack DNA-1 Solid State Amplifier
NHT 1.5 speakers.

Thanks a bunch!

John

Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )


"johnelstad" wrote in message
oups.com...
Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.

I recently noticed a mild-moderate hum coming from my speakers that is
constant regardless of volume or input. Here are the results of my
attempts to isolate it.

Turn off and unplug pre-amp = hum (no change)
Disconnect pre-amp output cable = no hum
Replace cable connecting pre-amp to amp = hum

Not sure if this is helpful, but my pre-amp has a headphone amp that
produces no hum.

Equipment:
Sonic Frontiers Line 1 Tube Preamp w/ 5-year-old tubes
McCormack DNA-1 Solid State Amplifier
NHT 1.5 speakers.

Thanks a bunch!

John

"johnelstad" wrote ...
I recently noticed a mild-moderate hum coming from my
speakers that is constant regardless of volume or input.

Does that mean it was always there but you just noticed it?
Or does it mean that it started humming only recently?

He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )

Richard Crowley wrote:

"johnelstad" wrote ...
I recently noticed a mild-moderate hum coming from my
speakers that is constant regardless of volume or input.

Does that mean it was always there but you just noticed it?
Or does it mean that it started humming only recently?

And what did you move ?

Graham

johnelstad wrote:

He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.

Relieved that your equipment is now electrically unsafe ?

They don't fit 3 prongs for no reason.

Graham

johnelstad wrote:
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )


You apparently had multiple ground points at differing potentials
causing current AC leakage current to flow through your input cable
shield, inducing hum. By breaking the power amps chassis-to-house
ground you eliminated the problem. Your power amp chassis is still
most-likely grounded, though now through the interconnect shield
instead of the power cord. If you disconnect all interconnects from
the power amp, then you have a power amp chassis that is not grounded.
So I would keep it grounded via the interconnect that connects to the
preamp to be safe, or even run a ground wire between the preamp ans
power amp chassis if they have external ground posts for that purpose.

On 14 Jun 2006 10:14:27 -0700, johnelstad wrote:


Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.

I recently noticed a mild-moderate hum coming from my speakers that is
constant regardless of volume or input. Here are the results of my
attempts to isolate it.

Turn off and unplug pre-amp = hum (no change)
Disconnect pre-amp output cable = no hum
Replace cable connecting pre-amp to amp = hum

Not sure if this is helpful, but my pre-amp has a headphone amp that
produces no hum.

Equipment:
Sonic Frontiers Line 1 Tube Preamp w/ 5-year-old tubes
McCormack DNA-1 Solid State Amplifier
NHT 1.5 speakers.

Step 1: simplify!

Connect only your amp and speakers. If it hums, then the problem is your
amp. Then connect amp to preamp with no source devices. Still no hum? Then the
problem is with an input source; then connect the source devices one at a
time.

johnelstad wrote:
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )


Be careful that you may have removed the safety ground connection, and
your power amp is grounded only through the audio cable screen to
another piece of grounded equipment. What you have proved is that the
hum is most likely coming from a ground loop. What you now need to do is
to find and eliminate the ground loop whilst still maintaining the
safety ground.

S.

Serge Auckland wrote:
johnelstad wrote:
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )


Be careful that you may have removed the safety ground connection, and
your power amp is grounded only through the audio cable screen to
another piece of grounded equipment. What you have proved is that the
hum is most likely coming from a ground loop. What you now need to do is
to find and eliminate the ground loop whilst still maintaining the
safety ground.

S.

Try plugging both power amp and preamp into a power Y adaptor (using
all 3 prongs). This will insure that both chassis are at the same
ground reference, and you have safety ground. If you still have hum
then break the shield on your interconnect at only one end (I'd break
it at the power amp end but shouldn't matter), this should eliminate
the hum loop. The interconnect will still be shielded mind you, but
that shield will only be connected at the preamp side making spurious
current flow in the shield impossible. All signal flow will then be
referenced to the safety ground. You can make a shield breaking
adaptor if you dont want to cut up your interconnect cables.

I install home intercoms as a side job and the first rule is to never
ground a shield at both ends. Because ground references throughout a
typical home are always a few microvolts off. So if you ground a
signal shield at both ends, AC will flow through the shield and make
the system hum every time.

"johnelstad" wrote in message
ups.com...
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from
the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

Does your preamp have an unpolarized two pronged power plug? If so, I'd try
plugging the amp back in *without* the two-prong adapter and try reversing
the preamp's unpolarized power plug to see if that gets rid of the hum. If
it does get rid of the hum, then I'd keep it hooked up that way. Removing
the chassis ground on the amp by using a two-prong adapter isn't the safest
thing to do.

Also, as others have said, I'd make sure the preamp and amp are on the same
circuit. I'd do this by plugging all your audio components into a single
power strip/surge protector/line conditioner.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

"Pooh Bear" wrote ...
Richard Crowley wrote:

"johnelstad" wrote ...
I recently noticed a mild-moderate hum coming from my
speakers that is constant regardless of volume or input.

Does that mean it was always there but you just noticed it?
Or does it mean that it started humming only recently?

And what did you move ?

Don't jump ahead! :-)

OTOH, he seems to think it is solved.

From reading the above I think the problem is a ground earth loop.
What we usually do is open the unit and remove the earth linking the
mains earth to the audio earth. This should clean the noise up.

"kt"

From reading the above I think the problem is a ground earth loop.
What we usually do is open the unit and remove the earth linking the
mains earth to the audio earth. This should clean the noise up.



** Shame it is both dangerous and ILLEGAL to do that.

If it were not - audio gear makers would not have such an internal
connection.






........ Phil

windcrest wrote:
Serge Auckland wrote:
johnelstad wrote:
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )

Be careful that you may have removed the safety ground connection, and
your power amp is grounded only through the audio cable screen to
another piece of grounded equipment. What you have proved is that the
hum is most likely coming from a ground loop. What you now need to do is
to find and eliminate the ground loop whilst still maintaining the
safety ground.

S.

Try plugging both power amp and preamp into a power Y adaptor (using
all 3 prongs). This will insure that both chassis are at the same
ground reference, and you have safety ground. If you still have hum
then break the shield on your interconnect at only one end (I'd break
it at the power amp end but shouldn't matter), this should eliminate
the hum loop. The interconnect will still be shielded mind you, but
that shield will only be connected at the preamp side making spurious
current flow in the shield impossible. All signal flow will then be
referenced to the safety ground. You can make a shield breaking
adaptor if you dont want to cut up your interconnect cables.

I install home intercoms as a side job and the first rule is to never
ground a shield at both ends. Because ground references throughout a
typical home are always a few microvolts off. So if you ground a
signal shield at both ends, AC will flow through the shield and make
the system hum every time.

Sensible advice, but isn't it a pity that consumer electronics rarely
follow professional practice of having a permanent safety ground, and a
separate audio ground which can be bonded to safety ground or lifted.

S.

"Serge Auckland"


Sensible advice, but isn't it a pity that consumer electronics rarely
follow professional practice of having a permanent safety ground, and a
separate audio ground which can be bonded to safety ground or lifted.



** Shame how in very case where that is seen it is VERY unsafe !!

Floating the internal circuitry while grounding the external metalwork of AC
powered audio gear is a recipe for a FATAL accident.

Think it trough.

Humans touch the connectors that link to that floating circuitry.




........ Phil

Phil Allison wrote:
"Serge Auckland"

Sensible advice, but isn't it a pity that consumer electronics rarely
follow professional practice of having a permanent safety ground, and a
separate audio ground which can be bonded to safety ground or lifted.



** Shame how in very case where that is seen it is VERY unsafe !!

Floating the internal circuitry while grounding the external metalwork of AC
powered audio gear is a recipe for a FATAL accident.

Think it trough.

Humans touch the connectors that link to that floating circuitry.




....... Phil




Don't understand the problem. The metal case is permanently connected to
the safety ground. The power supply transformer laminations are also
grounded to the case. The transformer secondary floats, as does all the
audio circuitry. No different to double-insulated appliances where
nothing is grounded. With SMPS, the isolation is done at high switching
frequencies rather than mains frequencies, but in the same way. I have
never come across a problem with lifting the audio ground in pro gear.

S.

Phil Allison wrote:
"Serge Auckland"

Sensible advice, but isn't it a pity that consumer electronics rarely
follow professional practice of having a permanent safety ground, and a
separate audio ground which can be bonded to safety ground or lifted.



** Shame how in very case where that is seen it is VERY unsafe !!

Floating the internal circuitry while grounding the external metalwork of AC
powered audio gear is a recipe for a FATAL accident.

Think it trough.

Humans touch the connectors that link to that floating circuitry.




....... Phil




Further to my post just now, by the way, the XLR shell of pro gear is
normally bonded to safety ground, NOT audio ground, so touching the
connectors puts the user in contact with safety ground only.

S.

Serge Auckland wrote:

Further to my post just now, by the way, the XLR shell of pro gear is
normally bonded to safety ground, NOT audio ground, so touching the
connectors puts the user in contact with safety ground only.

You wanna bet ? !

Graham

"Serge Auckland"

Sensible advice, but isn't it a pity that consumer electronics rarely
follow professional practice of having a permanent safety ground, and a
separate audio ground which can be bonded to safety ground or lifted.


** Shame how in very case where that is seen it is VERY unsafe !!

Floating the internal circuitry while grounding the external metalwork of
AC powered audio gear is a recipe for a FATAL accident.

Think it trough.

Humans touch the connectors that link to that floating circuitry.



Don't understand the problem.


** That was bleeding obvious already.


The metal case is permanently connected to the safety ground. The power
supply transformer laminations are also grounded to the case. The
transformer secondary floats, as does all the audio circuitry. No
different to double-insulated appliances where nothing is grounded.


** OK - so YOU have no *****ing idea* what the safety rules are for
an appliance to qualify as "double insulated" as well as NO idea what the
safety rules are for a fully earthed appliance.

In the latter case - the simple rule is that ALL exposed metalwork
capable of coming into contact with a person must be connected to the safety
ground.


With SMPS,


** Yawn - not one bit relevant.






........ Phil

"Serge Auckland = a ****ing IDIOT "


Further to my post just now, by the way, the XLR shell of pro gear is
normally bonded to safety ground, NOT audio ground, so touching the
connectors puts the user in contact with safety ground only.


** Complete Crapology.

The other end of the SAME lead is not connected to any safety ground.

Shame about the massively WIDESPREAD use of jack plugs connectors !!!

**** OFF - IDIOT .






...... Phil

"kt" wrote ...
From reading the above I think the problem is a ground earth loop.
What we usually do is open the unit and remove the earth linking the
mains earth to the audio earth. This should clean the noise up.

You are only bandaging the symptom, not discovering and
remedying the cause. It is a potentially leathal "solution". It
would not be acceptable to me.

On Thu, 15 Jun 2006 07:53:13 -0700, "Richard Crowley"
wrote:

From reading the above I think the problem is a ground earth loop.
What we usually do is open the unit and remove the earth linking the
mains earth to the audio earth. This should clean the noise up.

You are only bandaging the symptom, not discovering and
remedying the cause. It is a potentially leathal "solution". It
would not be acceptable to me.

Surely a ground loop IS the classic cause of hum? There may indeed be
better ways of curing it.

Laurence Payne wrote:
On Thu, 15 Jun 2006 07:53:13 -0700, "Richard Crowley"
wrote:

From reading the above I think the problem is a ground earth loop.
What we usually do is open the unit and remove the earth linking the
mains earth to the audio earth. This should clean the noise up.

You are only bandaging the symptom, not discovering and
remedying the cause. It is a potentially leathal "solution". It
would not be acceptable to me.

Surely a ground loop IS the classic cause of hum? There may indeed be
better ways of curing it.

Gound lifts on signal cables is a very common to-do in pro audio, less
so in home audio, it poses no danger, (as long as the connected chassis
are all on 3 prong power).

Other posters were correct in that there is no reason to open the
chassis and mess with the power ground, even if the references between
2 chassis are off a little (due to separate outlets, ground binding
corrosion, the fit of the plugs in the power strip, currents induced
into one chassis by its own circuit, etc).

If all else fails, just find out what signal interconnect has the
current flow in it's shield, and break it, and reference it to one
ground (side) or the other by trial.

Safety grounds should never depend on the audio interconnects (by using
a 2 prong adapter on one of the chassis), nor should there ever be a
reason to eliminate a safety ground. A pre-amp connected to a power
amp is easy. Whereas finding a hum loop in a pro rack with 10
processing devices, a 32 channel board, with all the aux buses and
inserts going is much harder. But flipping the ground lift switch at
one end or the other, or using a ground lift adaptor on an interconnect
is often the cure. Sometimes re-binding the chassis togeter, by wire,
in the rack is the cure. Sometimes isolating a chassis from the rack
with nylon shoulder washers is the cure.

Ground current in the audio path is pure voodoo and defies logic and
require seemingly unlogical cures.

But I think adhering to not breaking a power ground is always a good
rule, as well as adding a chassis ground to older equipment along with
removal of the death cap from same.

"johnelstad" wrote in message
ups.com...
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from
the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )

Do you own a fairly sensitive AC voltmeter? If so you might measure the AC
voltage on the common side of the preamp to the (now disconnected) ground
pin of the amplifier. If it's in the low millivolts region you can restore
the safety ground without restoring the hum by wiring a rectifier diode in
each direction between the 2 grounds. What this does is connect the 2
grounds for any voltage above 0.5v.

Norm

Sorry to disappear on you guys. I thought the issue was resolved and
didn't expect further comments. Thanks to all who have contributed
helpfully. I think I've found the real cause of the problem.

I'll try to address the questions or suggestions you've offered:

Jeff Findley: My pre-amp doesn't have an unpolarized two pronged power
plug, so I can't plug it in flipped around. Also, all components are
attached to the same power strip.

: I don't have a voltmeter, sorry.

windcrest: I don't have a power Y adaptor, but I'll buy one if others
think this is the best solution.

Richard Crowley: I noticed the hum a couple weeks ago.

AZ Nomad: A ha! By doing this, I isolated the new coax cable directly
connect to my tv as the cause of the hum. See reply to Pooh Bear below
for more info.

Pooh Bear: At first I thought I hadn't moved anything, but now I
realize that two weeks ago I signed up for cable to watch the World
Cup. I now have a splitter that goes to my cable modem and directly to
my tv. Disconnecting the coax cable from my tv kills the hum.

Any suggestions? Thanks again!


Jeff Findley wrote:
"johnelstad" wrote in message
ups.com...
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from
the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

Does your preamp have an unpolarized two pronged power plug? If so, I'd try
plugging the amp back in *without* the two-prong adapter and try reversing
the preamp's unpolarized power plug to see if that gets rid of the hum. If
it does get rid of the hum, then I'd keep it hooked up that way. Removing
the chassis ground on the amp by using a two-prong adapter isn't the safest
thing to do.

Also, as others have said, I'd make sure the preamp and amp are on the same
circuit. I'd do this by plugging all your audio components into a single
power strip/surge protector/line conditioner.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

"johnelstad" wrote ...
Pooh Bear: At first I thought I hadn't moved anything, but now I
realize that two weeks ago I signed up for cable to watch the World
Cup. I now have a splitter that goes to my cable modem and directly to
my tv. Disconnecting the coax cable from my tv kills the hum.

Any suggestions? Thanks again!

That is a very common problem. The cable system uses a different
ground reference than your power/mains system uses. There is
always some voltage difference between these grounds. This is what
you hear as "hum". In some cases the difference has been reported in
the mid-50 volt range(!)

Several vendors make isolation transformers for the cable connection.
Highly recommend that solution in preference to any others.

"Lots of people talking, but few of them know..."
The real story behind the most common source of hum in unbalanced audio
systems (common impedance coupling and inter-chassis current) and how to
properly treat it is well covered in Bill Whitlock's paper for Jensen
transformers:
http://www.jensentransformers.com/an/an004.pdf

The "ground loop" explanation may lead one to eliminate the hum, but it is
not usually the real culprit.

Stuart Welwood
6 sigma


"johnelstad" wrote in message
oups.com...
Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.

I recently noticed a mild-moderate hum coming from my speakers that is
constant regardless of volume or input. Here are the results of my
attempts to isolate it.

Turn off and unplug pre-amp = hum (no change)
Disconnect pre-amp output cable = no hum
Replace cable connecting pre-amp to amp = hum

Not sure if this is helpful, but my pre-amp has a headphone amp that
produces no hum.

Equipment:
Sonic Frontiers Line 1 Tube Preamp w/ 5-year-old tubes
McCormack DNA-1 Solid State Amplifier
NHT 1.5 speakers.

Thanks a bunch!

John

"Lots of people talking, but few of them know..."
The real story behind the most common source of hum in unbalanced audio
systems (common impedance coupling and inter-chassis current) and how to
properly treat it is well covered in Bill Whitlock's paper for Jensen
transformers:
http://www.jensentransformers.com/an/an004.pdf

The "ground loop" explanation may lead one to eliminate the hum, but it is
not usually the real culprit.

Stuart Welwood
6 sigma


"johnelstad" wrote in message
oups.com...
Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.

I recently noticed a mild-moderate hum coming from my speakers that is
constant regardless of volume or input. Here are the results of my
attempts to isolate it.

Turn off and unplug pre-amp = hum (no change)
Disconnect pre-amp output cable = no hum
Replace cable connecting pre-amp to amp = hum

Not sure if this is helpful, but my pre-amp has a headphone amp that
produces no hum.

Equipment:
Sonic Frontiers Line 1 Tube Preamp w/ 5-year-old tubes
McCormack DNA-1 Solid State Amplifier
NHT 1.5 speakers.

Thanks a bunch!

John

Stuart Welwood wrote:
"Lots of people talking, but few of them know..."
The real story behind the most common source of hum in unbalanced audio
systems (common impedance coupling and inter-chassis current) and how to
properly treat it is well covered in Bill Whitlock's paper for Jensen
transformers:
http://www.jensentransformers.com/an/an004.pdf

The "ground loop" explanation may lead one to eliminate the hum, but it is
not usually the real culprit.

Stuart Welwood
6 sigma


"johnelstad" wrote in message
oups.com...
Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.

I recently noticed a mild-moderate hum coming from my speakers that is
constant regardless of volume or input. Here are the results of my
attempts to isolate it.

Turn off and unplug pre-amp = hum (no change)
Disconnect pre-amp output cable = no hum
Replace cable connecting pre-amp to amp = hum

Not sure if this is helpful, but my pre-amp has a headphone amp that
produces no hum.

Equipment:
Sonic Frontiers Line 1 Tube Preamp w/ 5-year-old tubes
McCormack DNA-1 Solid State Amplifier
NHT 1.5 speakers.

Thanks a bunch!

John


Transformers are another alternative, but you need to get good ones,
I've got some sitting in my junkbox that simply sound awful and I have
not touched them for years. (garbled midrange, weakend bass)

These transformers were always marketed in the pro audio world so most
consumers would not even be aware of them.

Thats why I'll usually prefer a ground lift of the interconnect, or
re-binding / isolating the chassis (assuming everything is already
safety grounded).

As for the OP's issue with the cable TV shield, I would suggest first
trying a power strip that has CATV protectors on the strip. This will
put the local cable at the same potential as the safety ground. These
protectors usually have your typical power outlets as well as F
connectors and telephone connectors for grounding phones and cable
boxes from lightening damage. A nice by-product is that they will put
the cable shield down, usually these are placed at entry to the house
but there are models for branch circuit use too.

It's worth a try and he'll get some lightening protection to boot.

Phil Allison wrote:
"Serge Auckland = a ****ing IDIOT "

Further to my post just now, by the way, the XLR shell of pro gear is
normally bonded to safety ground, NOT audio ground, so touching the
connectors puts the user in contact with safety ground only.


** Complete Crapology.

The other end of the SAME lead is not connected to any safety ground.

Of course it is, if it follows decent professional practice.

Shame about the massively WIDESPREAD use of jack plugs connectors !!!

So, what's your point? The barrel of a jack plug should be connected to
safety ground, and the equipment, if fitted with jack sockets shouldn't
offer a ground-lift option. Alternatively, jack sockets where the barrel
is insulated from safety ground, and connected to audio ground only. In
this case, a ground-lift can be provided.

**** OFF - IDIOT .






..... Phil





I was interested in a serious debate until you went to personal abuse.

S.

"Stuart Welwood" wrote ...
"Lots of people talking, but few of them know..."

Au coutraire, now that the OP has revealed his recent
cable-TV addition we know exactly what is causing his
ground-loop induced hum. Many have been there before
him and solved the problem with an RF isolation transformer.
Several vendors of these things because it is a rather
common problem.

On 14 Jun 2006 10:14:27 -0700, "johnelstad" wrote:

Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.


Do you have vcr or tv tuner that's connected to CATV running into the
pre-amp ? I had a similar problem and ended up connecting 2 75ohm
baluns back to back inline with the cable.

Pancake

On Thu, 15 Jun 2006 18:21:38 -0400, pancake wrote:


On 14 Jun 2006 10:14:27 -0700, "johnelstad" wrote:

Well, I'm at my wit's end, but I'm hoping this will be obvious to
someone with more experience. Please help if you can.


Do you have vcr or tv tuner that's connected to CATV running into the
pre-amp ? I had a similar problem and ended up connecting 2 75ohm
baluns back to back inline with the cable.

Keep in mind that most 75300 ohm "transformers" are actually
autotransformers do not have isolation between input and output.

"Serge Auckland = a ****ing IDIOT "


Further to my post just now, by the way, the XLR shell of pro gear is
normally bonded to safety ground, NOT audio ground, so touching the
connectors puts the user in contact with safety ground only.


** Complete Crapology.

The other end of the SAME lead is not connected to any safety ground.

Of course it is, if it follows decent professional practice.


** Utter bull****.



Shame about the massively WIDESPREAD use of jack plugs connectors !!!

So, what's your point?


** Mainly, that YOU are a complete ****WIT.


**** OFF - IDIOT .



I was interested in a serious debate


** YOU are not capable of holding one with anybody.

YOU are a dangerous IDIOT !!!!

**** OFF - IDIOT .




........ Phil

"Serge Auckland" wrote in message
...
Further to my post just now, by the way, the XLR shell of pro gear is
normally bonded to safety ground, NOT audio ground,

Not true at all in most cases.

so touching the
connectors puts the user in contact with safety ground only.

Of course all those TRS connectors may be another matter eh?

Anyhow, whenever a ground lift is used, the device must be earthed via some
connection for it to work. This is usually via the screen to the mixer
earth. So the problem arises in the case of a faulty cable screen
connection. With multiple connections for most devices, this is probably
more unlikely than the mains earth connection coming loose. And just because
the earth *IS* missing doesn't mean it's automatically deadly, another fault
has to occur as well for mains to get on the case/connectors.

The answer is that all such equipment must be regularly tested, and an earth
leakage breaker used, something which is unfortunately not always the case.
And the chance of being killed getting to a gig Vs being electrocuted at a
gig is about 10 million to one.


MrT.

"Phil Allison" wrote in message
...
Unless you want to blame Masseurs Ohm and Maxwell personally ??

Ohm and Maxwell moonlighted as masseurs? Or just a hobby maybe.

MrT.

"Mr.T"


Ohm and Maxwell moonlighted as masseurs? Or just a hobby maybe.



** MSWord's spellchecker has a wicked sense of humour ...






...... Phil