[Dave O'Heare[_2_]]

Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz.
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? Workarounds?

Thanks,

Dave O'Heare

[George's Pro Sound Company]

"Dave O'Heare" dave.oheareATgmail.com wrote in message
.13...
Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

the dimmers are dumping trash back into the ac service
you need better dimmers
or a isolation transformer for the audio circut
dimmers are cheaper
george

[Scott Dorsey]

Dave O'Heare dave.oheareATgmail.com wrote:

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz.
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

And is the basement mixer transformer-isolated or does it have a
bargain-basement solid-state output stage? Have you broken the ground
at the basement mixer?

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

They're all right. It's RF trash coming off the lighting system, getting
into the audio because you have a ground loop in the audio system or because
you have a faulty cable or poorly-designed input stage.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? Workarounds?

Audio isolation transformers are your friend. There is a discussion of
ground loops in the FAQ for this group.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Chris Whealy]

Dave O'Heare wrote:
Argh.

I'm running sound at a series of events in a 120 year old former church, and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from one (basement) fed to the other (main floor) by a couple hundred feet of good quality shielded twisted pair cable, audio never closer than 8 feet to the electrical wiring except at the mixers. Six brand new ETC Smartbars for lighting in the basement. Basement electrical fed from different electrical panel from the main floor, but all the same main building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting is at anything other than off or 100%, I get a very loud buzz in the audio upstairs. Changing the settings on the Smartbars changes the buzz. If I completely disconnect the basement mixer from earth ground (run on batteries, disconnected from grounded powered speakers), the buzz goes away. If I power the main floor audio from the basement electrical panel, *sometimes* the buzz goes away. The audio downstairs is dead quiet always. None of the gear has ever had any problem like this anywhere else.

What I am looking for is help in talking to people about this. One of the owners of the building thinks that it's an audio problem. Another owner thinks that it's "radio waves off the lighting stuff." The lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly bonded neutrals someplace, and that really the whole electrical system ought to be replaced, but that's not going to happen, at least not today.

Suggestions? Workarounds?

Thanks,

Dave O'Heare

The buzz is RF junk created by the switching circuits in the dimmer packs.

Are you sure the building is only single phase? If so, that's a shame
because running the lighting and audio systems from different phases is
always good starting point.

However, whether the building is single phase or not, make sure that
your audio power distribution throughout the building is in a star
arrangement. One common A/C feed and one common earth for all audio
equipment will remove the possibility of an earth loop between the
systems. If this is not possible, then you'll need to buy an audio
isolating transformer for each channel you want connected between the
two desks.

Chris W

--
The voice of ignorance speaks loud and long,
But the words of the wise are quiet and few.
---

[WillStG]

On Apr 27, 10:35 am, "Dave O'Heare" dave.oheareATgmail.com wrote:
Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz.
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? Workarounds?

Thanks,

Dave O'Heare

Sounds like recipe for dirty power to me. You need at minimum a
separate power circuit for everything audio, preferably filtered and
conditioned. This includes the outlets on the stage where the band
plug their amps in. Since this is more of a problem upstairs, perhaps
upstairs a couple of lights are plugged into the same circuit as your
mixer.

You may also have a ground loop between the audio systems on the
two floors. Always good to have a couple isolation transformer
barrels in the kit. An IL-19 isn't the highest quality but does the
job, but there are better quality transformers out there. You might
also try sending your audio between floors digitally, if you suspect
the lines are inducing noise.

Another thing to consider, is your cable run between floors
anywhere near metal air conditioning ducts or waste water pipes? Air
conditioning ducts can become magnetized - at TV Networks I have
observed magnometers installed on them measuring the field strength.
And I have had waste water pipes induce horrible noise into audio
lines. All the crap that lighting and refrigeration/HVAC/everything
else spit into grounds can make a waste water pipe very very bad news
for audio, if you get anywhere near them.

But it's not that, and your audio is clean downstairs and your
power needs modest upstairs, maybe run a long extension cable along
with your audio line between floors. Or some romex. Seems like the
upstairs grounds are your main problem, so there's noise up there, and
downstairs if you have a ground loop that will bring that noise back
into your main system.

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

[Rupert]

On Apr 27, 7:35*am, "Dave O'Heare" dave.oheareATgmail.com wrote:
Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz.
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. *If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? *Workarounds?

Thanks,

Dave O'Heare

At the input to the destination:

http://www.jensen-transformers.com/pb2xx.html

Or at the output of the driver:

http://www.jensen-transformers.com/dm2xx.html

Quickest fix for loop or RF issues and these are top notch
transformers.

Rupert

[Rupert]

On Apr 27, 10:20*am, Rupert wrote:
On Apr 27, 7:35*am, "Dave O'Heare" dave.oheareATgmail.com wrote:



Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz..
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. *If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? *Workarounds?

Thanks,

Dave O'Heare

At the input to the destination:

http://www.jensen-transformers.com/pb2xx.html

Or at the output of the driver:

http://www.jensen-transformers.com/dm2xx.html

Quickest fix for loop or RF issues and these are top notch
transformers.

Rupert

Also a good methodology for tracing down noise problems:

http://www.jensen-transformers.com/an/ts_guide.pdf

[Rupert]

On Apr 27, 8:42*am, WillStG wrote:
On Apr 27, 10:35 am, "Dave O'Heare" dave.oheareATgmail.com wrote:



Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz..
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. *If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? *Workarounds?

Thanks,

Dave O'Heare

* * *Sounds like recipe for dirty power to me. *You need at minimum a
separate power circuit for everything audio, preferably filtered and
conditioned. This includes the outlets on the stage where the band
plug their amps in. *Since this is more of a problem upstairs, perhaps
upstairs a couple of lights are plugged into the same circuit as your
mixer.

* * You may also have a ground loop between the audio systems on the
two floors. *Always good to have a couple isolation transformer
barrels in the kit. *An IL-19 isn't the highest quality but does the
job, but there are better quality transformers out there. *You might
also try sending your audio between floors digitally, if you suspect
the lines are inducing noise.

* * Another thing to consider, *is your cable run between floors
anywhere near metal air conditioning ducts or waste water pipes? *Air
conditioning ducts can become magnetized - at TV Networks I have
observed magnometers installed on them measuring the field strength.
And I have had waste water pipes induce horrible noise into audio
lines. *All the crap that lighting and refrigeration/HVAC/everything
else spit into grounds can make a waste water pipe very very bad news
for audio, if you get anywhere near them.

* * But it's not that, and your audio is clean downstairs and your
power needs modest upstairs, maybe run a long extension cable along
with your audio line between floors. *Or some romex. *Seems like the
upstairs grounds are your main problem, so there's noise up there, and
downstairs if you have a ground loop that will bring that noise back
into your main system.

"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

Rupert

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

[[email protected]]

On Apr 27, 10:20*am, Rupert wrote:
On Apr 27, 7:35*am, "Dave O'Heare" dave.oheareATgmail.com wrote:



Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz..
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. *If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

What I am looking for is help in talking to people about this. One of
the owners of the building thinks that it's an audio problem. Another
owner thinks that it's "radio waves off the lighting stuff." The
lighting designer says "I dunno, never seen that before." The
electrician is experienced, but not with theatrical and lighting stuff.

Personally, I think that it's a ground problem, possibly with improperly
bonded neutrals someplace, and that really the whole electrical system
ought to be replaced, but that's not going to happen, at least not
today.

Suggestions? *Workarounds?

Thanks,

Dave O'Heare

At the input to the destination:

http://www.jensen-transformers.com/pb2xx.html

Or at the output of the driver:

http://www.jensen-transformers.com/dm2xx.html

Quickest fix for loop or RF issues and these are top notch
transformers.

Rupert

Those are great. I use their XLR inline transformers on any video
playback because video is usually plugged in to the same AC as
projection which causes the same interference as lighting dimmers.

[George's Pro Sound Company]

"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

dimmer noise has nothing to do with ground loops or grounding
it is the function of how the dimmer chops wave forms and dumps significant
hash back into the ac supply
no amount of grounding will resolve this, as it is not a grounding issue
one needs isolation or better dimmers that do not chop the wave form and
dump in back into the service.
better dimmers will not throw rf either
george

[George's Pro Sound Company]

instead of looking at all the bandaids to try to work around your issue why
not fix it with some proper dimmers?
George

[DougD]

In article , "Dave O'Heare" dave.oheareATgmail.com wrote:

When I feed audio from the basement to the main floor AND the lighting
is at anything other than off or 100%, I get a very loud buzz in the
audio upstairs. Changing the settings on the Smartbars changes the buzz.
If I completely disconnect the basement mixer from earth ground (run on
batteries, disconnected from grounded powered speakers), the buzz goes
away. If I power the main floor audio from the basement electrical
panel, *sometimes* the buzz goes away. The audio downstairs is dead
quiet always. None of the gear has ever had any problem like this
anywhere else.

Sounds like you're picking up dimmer noise on the shield of your
twisted pair that's feeding the upstairs mixer. Or the dimmer noise
is showing up on your downstairs AC ground lines and not being
properly drained to ground, so it's finding a better path along your
audio shielding. IF both AC supplies where your electronics are
powered from were connected to the same AC ground, this should
not happen, so somewhere you probably have a bad ground line.
A quick fix is to somewhat single point ground the system.
In your case, disconnect the shield of the twisted pair at the source
end in the basement and make sure it's isolated from any earth
connections at the source. You still want to make sure that the
basement mixer is plugged in to a grounded outlet and don't lift
the AC ground! Doing it this way, the grounded
amp inputs upstairs will provide the noise drain via the twisted
pair shielding, but because it's not connected to the ground down
stairs, there's no path for the dimmer noise via your mixer. The
basic rule is "always shield your inputs" when leaving one end
of shield off of a line.
This is common studio practice, but in those cases, each
piece of equipment has it's own seperate earth ground run to
it which homes back to a master ground point. This works very
well when you have lots of patch bays to feed with aux. gear
into the main desk, tape transports, etc. In some cases depending
on the type of noise that's showing up, a cap can be wired from
the floating end to the ground pin of the source, this provides
a bypassed kinda virtual ground, but this is more for dealing
with high freq. RF noise from radio stations, etc.

Good luck!
d.

[WillStG]

On Apr 27, 4:00 pm, "George's Pro Sound Company"
wrote:
"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

dimmer noise has nothing to do with ground loops or grounding
it is the function of how the dimmer chops wave forms and dumps significant
hash back into the ac supply
no amount of grounding will resolve this, as it is not a grounding issue
one needs isolation or better dimmers that do not chop the wave form and
dump in back into the service.
better dimmers will not throw rf either
george

Well my point George was if he has dimmer noise in his upstairs
room's power, that could possibly be introduced into his downstair
room system through the audio ground. A lot of hash may be making it
hard to hear what else is going on. He can try lifting the electrical
ground upstairs, condition his power, use isolation transformers on
his audio lines, try a different power circuit entirely upstairs, do
them all. Blaming the gear like Rupert suggests could work with
management, I guess he could just blame it on Herr Behringer - right
George? g

Perhaps the reason I have experienced waste water pipes sometimes
being a problem for audio has more to do with magnetic potential than
actual dimmer or HVAC noise in the grounds, but fact is they can be a
problem if an audio line gets near to them sometimes. But something
is causing those pipes to become magnetized. I do work in NYC and
both cases I experienced were tall buildings, but who knows why? But
demagnetizing a 40 story building's waste lines would take a huge
degausser. Someone mentioned here once seeing pictures of lighting
between girders during demolitions in NYC.

Even expensive dimmers on 3 phase power can cause noise in audio
though, especially if you have a noisy smoke machine, robot lights and
other stuff on the same circuit. I used get noise sometimes because
people would plug heaters and refrigerators into my audio power.

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"THe large print giveth and the small print taketh away..." Tom Waits

[George's Pro Sound Company]

Will you are I are basically on the same page
as well as Rupert was correct in saying significant ground loops can exist
silently if one has enough isolation inthe system
the isolation could be as simple as lifting sheild IN THE GEAR at the
destination
I have seen "lots " of building that upgrade to all grounding edision
outlets, but did not upgrade the wiring sothe ground on the outlet was
simply left unconnected

you shouldn't be pushing the boat out into the bay until there is water in
the bay
you should not be bandaiding.a system without first determining if there is
a non cobbed together solution
simple test
hard wire around the dimmers, if the noise goes away, replace the dimmers
with Lutons they have a line of noise free dimmers
or determine if "dimmers" are actually needed, perhaps a simple on/off is
all that is really needed
and outfit the fixtures with proper wattage lamps for the brightness desired
george

[Scott Dorsey]

In article ,
George's Pro Sound Company wrote:
instead of looking at all the bandaids to try to work around your issue why
not fix it with some proper dimmers?

Nobody EVER wants to put the money into proper dimmers.

Noise problems like this are a combination of two problems: a noise source,
and an audio system that picks up the noise. You can fix one of the
problems or both of them, but sadly fixing the source is usually the more
expensive of the two, while doing the RIGHT thing and fixing both of them
is usually given the thumbs down from the people with the money.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Rupert]

On Apr 27, 1:15*pm, (DougD) wrote:
A quick fix is to somewhat single point ground the system.
In your case, disconnect the shield of the twisted pair at the source
end in the basement and make sure it's isolated from any earth
connections at the source. You still want to make sure that the
basement mixer is plugged in to a grounded outlet and don't lift
the AC ground! Doing it this way, the grounded
amp inputs upstairs will provide the noise drain via the twisted
pair shielding, but because it's not connected to the ground down
stairs, there's no path for the dimmer noise via your mixer. The
basic rule is "always shield your inputs" when leaving one end
of shield off of a line.
* * * * This is common studio practice, but in those cases, each
piece of equipment has it's own seperate earth ground run to
it which homes back to a master ground point.

From Whitlock's grounding tutorial:

Ground Only at Receiver (input) = Bad
- Forms pair of low-pass filtersfor common-mode noise
- Driver Z imbalances and 4% to 6% typical cable C imbalances create
mismatched filters
- Mismatched filters cause conversion of common-mode noise to
differential, degrading CMRR

Ground Only at Driver (output) = Good
- Grounding only at driver completely ELIMINATES FILTERS!
- All filter elements move together (with driver ground)

Connections and Crosstalk
- Signal asymmetry and capacitance mismatch cause signal currentflow
in the shield
- Grounding only at receiver forces current to return to the driver
via an undefined path; can result in crosstalk, distortion, or
oscillation
- Grounding only at driver allows current to return directly to the
driver –NO PROBLEMS

The driver end of a balanced cable should always be grounded, whether
or not the receiver end is grounded

------

Rupert

[George's Pro Sound Company]

"Rupert" wrote in message
...
On Apr 27, 1:15 pm, (DougD) wrote:
A quick fix is to somewhat single point ground the system.
In your case, disconnect the shield of the twisted pair at the source
end in the basement and make sure it's isolated from any earth
connections at the source. You still want to make sure that the
basement mixer is plugged in to a grounded outlet and don't lift
the AC ground! Doing it this way, the grounded
amp inputs upstairs will provide the noise drain via the twisted
pair shielding, but because it's not connected to the ground down
stairs, there's no path for the dimmer noise via your mixer. The
basic rule is "always shield your inputs" when leaving one end
of shield off of a line.
This is common studio practice, but in those cases, each
piece of equipment has it's own seperate earth ground run to
it which homes back to a master ground point.

From Whitlock's grounding tutorial:

Ground Only at Receiver (input) = Bad
- Forms pair of low-pass filtersfor common-mode noise
- Driver Z imbalances and 4% to 6% typical cable C imbalances create
mismatched filters
- Mismatched filters cause conversion of common-mode noise to
differential, degrading CMRR

Ground Only at Driver (output) = Good
- Grounding only at driver completely ELIMINATES FILTERS!
- All filter elements move together (with driver ground)

Connections and Crosstalk
- Signal asymmetry and capacitance mismatch cause signal currentflow
in the shield
- Grounding only at receiver forces current to return to the driver
via an undefined path; can result in crosstalk, distortion, or
oscillation
- Grounding only at driver allows current to return directly to the
driver –NO PROBLEMS

The driver end of a balanced cable should always be grounded, whether
or not the receiver end is grounded

------

Rupert

it is distracting to talk of a noise problems as if it were a grounding
problem.
noise is rarely a ground issue
george

[Rupert]

On Apr 27, 3:59*pm, "George's Pro Sound Company"
wrote:
"Rupert" wrote in message

...
On Apr 27, 1:15 pm, (DougD) wrote:

A quick fix is to somewhat single point ground the system.
In your case, disconnect the shield of the twisted pair at the source
end in the basement and make sure it's isolated from any earth
connections at the source. You still want to make sure that the
basement mixer is plugged in to a grounded outlet and don't lift
the AC ground! Doing it this way, the grounded
amp inputs upstairs will provide the noise drain via the twisted
pair shielding, but because it's not connected to the ground down
stairs, there's no path for the dimmer noise via your mixer. The
basic rule is "always shield your inputs" when leaving one end
of shield off of a line.
This is common studio practice, but in those cases, each
piece of equipment has it's own seperate earth ground run to
it which homes back to a master ground point.

From Whitlock's grounding tutorial:

Ground Only at Receiver (input) = Bad
- Forms pair of low-pass filtersfor common-mode noise
- Driver Z imbalances and 4% to 6% typical cable C imbalances create
mismatched filters
- Mismatched filters cause conversion of common-mode noise to
differential, degrading CMRR

Ground Only at Driver (output) = Good
- Grounding only at driver completely ELIMINATES FILTERS!
- All filter elements move together (with driver ground)

Connections and Crosstalk
- Signal asymmetry and capacitance mismatch *cause signal currentflow
in the shield
- Grounding only at receiver forces current to return *to the driver
via an undefined path; can result in *crosstalk, distortion, or
oscillation
- Grounding only at driver allows current to return *directly to the
driver –NO PROBLEMS

The driver end of a balanced cable should always be grounded, whether
or not the receiver end is grounded

------

Rupert

it is distracting to talk of a noise problems as if it were a grounding
problem.
noise is rarely a ground issue
george

I agree about the dimmer noise vs. ground loop problem in this case,
though there's plenty of noise problems that are ground related due to
poor interface implementation. The point about this post is to point
out that grounding only from the receiver as the poster I replied to
suggests is an incorrect method prone to various problems, that's all.

Rupert

[Rupert]

On Apr 27, 1:00*pm, "George's Pro Sound Company"
wrote:
"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

dimmer noise has nothing to do with ground loops or grounding
it is *the function of how the dimmer chops wave forms and dumps significant
hash *back into the ac supply
no amount of grounding will resolve this, as it is not a grounding issue
one needs isolation or better dimmers that do not chop the wave form and
dump in back into the service.
better dimmers will not throw rf either
george

Actually the dimmer noise is RF generated by the SCR type dimmers and
gets into the signal lines of the audio gear. It doesn't infiltrate
via the AC supply per se though the AC lines attached to the dimmer
can act as an antenna to a point and enlarge the affected area.
Dimmer noise is proportional to the proximity of the audio gear to the
dimmer(s). Direct coupled audio inputs can be efficient at converting
this RF into audio spectrum noise. Using high quality isolation
transformers at the input of the receiving device having problems can
greatly increase the CMRR and attenuate the noise to acceptable
levels.

Rupert

[George's Pro Sound Company]

"Rupert" wrote in message
...
On Apr 27, 1:00 pm, "George's Pro Sound Company"
wrote:
"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

dimmer noise has nothing to do with ground loops or grounding
it is the function of how the dimmer chops wave forms and dumps
significant
hash back into the ac supply
no amount of grounding will resolve this, as it is not a grounding issue
one needs isolation or better dimmers that do not chop the wave form and
dump in back into the service.
better dimmers will not throw rf either
george

Actually the dimmer noise is RF generated by the SCR type dimmers and
gets into the signal lines of the audio gear. It doesn't infiltrate
via the AC supply per se though the AC lines attached to the dimmer
can act as an antenna to a point and enlarge the affected area.
Dimmer noise is proportional to the proximity of the audio gear to the
dimmer(s). Direct coupled audio inputs can be efficient at converting
this RF into audio spectrum noise. Using high quality isolation
transformers at the input of the receiving device having problems can
greatly increase the CMRR and attenuate the noise to acceptable
levels.

the use of quality dimmers makes the isolation transformer bandaid a
needless expense
george

Rupert

[Rupert]

On Apr 27, 4:54*pm, "George's Pro Sound Company"
wrote:
"Rupert" wrote in message

...
On Apr 27, 1:00 pm, "George's Pro Sound Company"
wrote:



"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

dimmer noise has nothing to do with ground loops or grounding
it is the function of how the dimmer chops wave forms and dumps
significant
hash back into the ac supply
no amount of grounding will resolve this, as it is not a grounding issue
one needs isolation or better dimmers that do not chop the wave form and
dump in back into the service.
better dimmers will not throw rf either
george

Actually the dimmer noise is RF generated by the SCR type dimmers and
gets into the signal lines of the audio gear. It doesn't infiltrate
via the AC supply per se though the AC lines attached to the dimmer
can act as an antenna to a point and enlarge the affected area.
Dimmer noise is proportional to the proximity of the audio gear to the
dimmer(s). Direct coupled audio inputs can be efficient at converting
this RF into audio spectrum noise. Using high quality isolation
transformers at the input of the receiving device having problems can
greatly increase the CMRR and attenuate the noise to acceptable
levels.

the use of quality dimmers makes the isolation transformer bandaid *a
needless expense
george

Rupert

Very true indeed - at least in a fixed install situation. Of course as
I'm sure you're well aware, those who do portable PA don't have that
luxury as most venues won't avail themselves or us to using quality
noise free dimmers. So having some quality isolation transformers in
the toolbox is a good idea - IMHO.

Rupert

[Phil Allison]

"Rupert"

Actually the dimmer noise is RF generated by the SCR type dimmers ..

** Absolute nonsense !!!!

The switching noise ( buzz) generated by triac/SCR dimmers IS in the
AUDIO frequency range.

Multi channel lighting dimmers all include RF filtering at each output -
but these filters have little of no effect on the audio frequency part of
the noise.


It doesn't infiltrate via the AC supply per se

** Fraid it can and it does.

The current levels involved are large and so can resistively and inductively
couple into AC supply ground wiring.

Because active an neutral conductors carry equal currents in opposite
directions in any cable, inductive coupling to the ground conductor is
almost ( but not completely) cancelled. Dimmer buzz problems would be *
horrendous * if this were not the case.


though the AC lines attached to the dimmer
can act as an antenna to a point and enlarge the affected area.


** Because the chopped AC wave appears as a high voltage on only ONE of the
two conductors * going from the dimmer to a lamp * - that conductor
radiates an *electric field* that will inject a buzzing noise into any
poorly shielded piece of audio gear that happen to be in range.

This is however normally only a problem for stage equipment like electric
guitars and keyboards housed in plastic cases. Unbalanced, high impedance
( ie musical instrument) cables that are not well shielded will also pick up
buzzing noise this way.


Dimmer noise is proportional to the proximity of the audio gear to
the dimmer(s).

** Only in the cases above, where the injection of noise is due to the
electric field coming from lamp cables and the audio gear is NOT inside a
grounded metal box.


Direct coupled audio inputs can be efficient at converting
this RF into audio spectrum noise.

** The noise ** IS ** audio band - no RF to audio conversion is
necessary nor present, as all lighting dimmers have RF filtering.


Using high quality isolation
transformers at the input of the receiving device having problems can
greatly increase the CMRR and attenuate the noise to acceptable levels.


** If an audio system has even a minor level of AC supply hum from the
existence of ground loops - then it will ALSO be prone to dimmer buzz.



...... Phil

[DougD]

In article , Rupert wrote:

it is distracting to talk of a noise problems as if it were a grounding
problem.
noise is rarely a ground issue
george

I agree about the dimmer noise vs. ground loop problem in this case,
though there's plenty of noise problems that are ground related due to
poor interface implementation. The point about this post is to point
out that grounding only from the receiver as the poster I replied to
suggests is an incorrect method prone to various problems, that's all.

Rupert

In reality and practical application, you can't always observe a set
rule. In some single point ground patch systems, the shields are
only attached at the patch, which is tied to the main audio ground,
and both in's and out's are floated. This is how we installed all of
NPR's studio's as per Neve's instructions. And many, many others
as well. In practical non-patch situations, you would tend to want to
always shield the inputs, as you never know when someone is going
to unplug the other end on you. If you only grounded at the source,
unplugging that you turn your un-shielded input into one really good
antenna.. Again, no two installations or projects are always the same,
and different methods have to be used as called for.

$.0002
d.

[Scott Dorsey]

George's Pro Sound Company wrote:

The driver end of a balanced cable should always be grounded, whether
or not the receiver end is grounded

it is distracting to talk of a noise problems as if it were a grounding
problem.
noise is rarely a ground issue
george

Induced noise (QRM) is two problems together: a thing that makes noise
and a thing that accepts noise. You need to fix both of them.

Proper layout of audio system grounds is important for all KINDS of
reasons. In the modern age of electronic balancing, you don't want
equipment damaged by noise induced in the ground system during a
thunderstorm, for instance.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[George's Pro Sound Company]

"Rupert" wrote in message
...
On Apr 27, 4:54 pm, "George's Pro Sound Company"
wrote:
"Rupert" wrote in message

...
On Apr 27, 1:00 pm, "George's Pro Sound Company"
wrote:



"Dirty Power" is a misnomer at best and a myth at worst. Check out
page 29 on this:

http://www.campuspa.com/downloads/gr...g_tutorial.pdf

In fact, the whole article is well worth a read. There's a ton of
misconceptions about grounding and power. This paper debunks most if
not all the myths. The summary would be that ground noise is a problem
of poorly designed signal interfaces. In most cases, even with
substantial ground loops, well designed interface should prevent the
injection of noise into the audio circuit.

dimmer noise has nothing to do with ground loops or grounding
it is the function of how the dimmer chops wave forms and dumps
significant
hash back into the ac supply
no amount of grounding will resolve this, as it is not a grounding issue
one needs isolation or better dimmers that do not chop the wave form and
dump in back into the service.
better dimmers will not throw rf either
george

Actually the dimmer noise is RF generated by the SCR type dimmers and
gets into the signal lines of the audio gear. It doesn't infiltrate
via the AC supply per se though the AC lines attached to the dimmer
can act as an antenna to a point and enlarge the affected area.
Dimmer noise is proportional to the proximity of the audio gear to the
dimmer(s). Direct coupled audio inputs can be efficient at converting
this RF into audio spectrum noise. Using high quality isolation
transformers at the input of the receiving device having problems can
greatly increase the CMRR and attenuate the noise to acceptable
levels.

the use of quality dimmers makes the isolation transformer bandaid a
needless expense
george

Rupert

Very true indeed - at least in a fixed install situation. Of course as
I'm sure you're well aware, those who do portable PA don't have that
luxury as most venues won't avail themselves or us to using quality
noise free dimmers. So having some quality isolation transformers in
the toolbox is a good idea - IMHO.

Rupert

I can't vouch for that, I have thousands of events under my belt and have
never had a issue that required a iso to resolve
not saying there never will be one
but they a very rare and the expesne , at this point could not be justified
by something that in 20 years of live sound I have never needed

and this thread is specifically about a fixed instal and should be addressed
as so
george

[George's Pro Sound Company]

"Scott Dorsey" wrote in message
...
George's Pro Sound Company wrote:

The driver end of a balanced cable should always be grounded, whether
or not the receiver end is grounded

it is distracting to talk of a noise problems as if it were a grounding
problem.
noise is rarely a ground issue
george

Induced noise (QRM) is two problems together: a thing that makes noise
and a thing that accepts noise. You need to fix both of them.

Proper layout of audio system grounds is important for all KINDS of
reasons. In the modern age of electronic balancing, you don't want
equipment damaged by noise induced in the ground system during a
thunderstorm, for instance.

now it comes down to the quality/protection Vs the expense, there is ALWAYS
another level up one can go
one can go to ac service iso's, whole building surges, encaseing the
electronics room in a copper net
where is the balance?
good dimmers most likely can be warrentted into the building with the EC
picking up the costs, unless the (ac)instal is REALLY OLD
I would look at just running the dimmers full on, adust lumination with
proper sized lamps and calling it a day.
cheap, effective, and can be implimented while other solutions are budgeted
george

[Scott Dorsey]

George's Pro Sound Company wrote:

now it comes down to the quality/protection Vs the expense, there is ALWAYS
another level up one can go
one can go to ac service iso's, whole building surges, encaseing the
electronics room in a copper net
where is the balance?

Well, that's the rub, isn't it?

I always carry a couple nice Pomona boxes with 600:600 transformers
around, and when working in the field I try and use equipment with
transformer inputs and outputs for good noise rejection.

But usually cleaning up grounding configurations doesn't actually
cost any money at all, and just involves sitting down and drawing
out the system, figuring out where the grounds go, and breaking them
at the connector body as needed to make a system where there is one
and only one ground path between every two devices.

good dimmers most likely can be warrentted into the building with the EC
picking up the costs, unless the (ac)instal is REALLY OLD
I would look at just running the dimmers full on, adust lumination with
proper sized lamps and calling it a day.
cheap, effective, and can be implimented while other solutions are budgeted

Proper audio grounding is usually free, though, and it is _always_ a
good idea. Yes, sometimes you can't get away with electronic balancing
and you need a transformer, but much of the time you can.

There's a simple rule for ground configuration and if you follow it,
90% of these noise problems just disappear.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[George's Pro Sound Company]

Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the inputs
of a graphic EQ and I/O of a Lexicon mpx 500.
do you use nylon isolators on your rack mounts
I fi nd often one defective design creates a defective rack through the rack
rail
george

[WillStG]

On Apr 27, 8:42 pm, (DougD) wrote:
In reality and practical application, you can't always observe a set
rule. In some single point ground patch systems, the shields are
only attached at the patch, which is tied to the main audio ground,
and both in's and out's are floated. This is how we installed all of
NPR's studio's as per Neve's instructions. And many, many others
as well. In practical non-patch situations, you would tend to want to
always shield the inputs, as you never know when someone is going
to unplug the other end on you. If you only grounded at the source,
unplugging that you turn your un-shielded input into one really good
antenna..

I remember one particular Neve VR with an elusive RF buzz, turned
out to be a cable acting as an antenna between the desk's talkbackmic
and the patchbay.

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

[Dave O'Heare[_2_]]

"George's Pro Sound Company" wrote in
m:

instead of looking at all the bandaids to try to work around your
issue why not fix it with some proper dimmers?

That'd be a good idea -- save that the Smartbars are brand new (installed
fresh out of the box on Wednesday), and there will be a large pushback from
the people that installed said Smartbars. They're brand new, so they must
be good, right?

Funny, I'd always had the impression that ETC was pretty good stuff.

Dave, too tired to think right now.

[DougD]

In article , WillStG wrote:

I remember one particular Neve VR with an elusive RF buzz, turned
out to be a cable acting as an antenna between the desk's talkbackmic
and the patchbay.

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

Neve installs were always kind of a "challange" to be polite. They were
the only console supplier at that time (80's) that would only allow us as
the systems vendor to wire up as far as the desk, they did the rest. I
guess I can't blame them, however they would go away after blessing
their work. In some cases like the Mpls. NPR, we had 3000+ patch
points/tie lines to debug after the fact so one had to trust that there were
no problems coming from their side of the wiring... But we had a hell of
a good eng. staff (3 ex mil eng's) that were grounding fanatics and we
had to learn real quick to do it their way or else. I think they would have
had us salute them if they could have gotten away with it..

d.

[Scott Dorsey]

George's Pro Sound Company wrote:

Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the inputs
of a graphic EQ and I/O of a Lexicon mpx 500.
do you use nylon isolators on your rack mounts
I fi nd often one defective design creates a defective rack through the rack
rail

Actually, grounding through the rack rails is a _good_ thing. Break your
signal grounds, not your power line grounds or chassis grounds.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[George's Pro Sound Company]

"Scott Dorsey" wrote in message
...
George's Pro Sound Company wrote:

Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the
inputs
of a graphic EQ and I/O of a Lexicon mpx 500.
do you use nylon isolators on your rack mounts
I fi nd often one defective design creates a defective rack through the
rack
rail

Actually, grounding through the rack rails is a _good_ thing. Break your
signal grounds, not your power line grounds or chassis grounds.
--scott

the devices are all grounded, but several manufactures tie signal and earths
together
so
without re-engineering the device is question isolating from rack rail is
effective to break the signal ground loop between racked units

but again this is wandering pretty far from the OP's issue
which should be addressed at the point of origin, the dimmers
george

[George's Pro Sound Company]

"George's Pro Sound Company" wrote in message
...

"Scott Dorsey" wrote in message
...
George's Pro Sound Company wrote:

Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the
inputs
of a graphic EQ and I/O of a Lexicon mpx 500.
do you use nylon isolators on your rack mounts
I fi nd often one defective design creates a defective rack through the
rack
rail

Actually, grounding through the rack rails is a _good_ thing. Break your
signal grounds, not your power line grounds or chassis grounds.
--scott

I owned several Korg units, a gp8, a rack tuner thaat I recall just simply
would not play with other gear when racked without isolation
george

[GregS[_3_]]

In article , (Scott Dorsey) wrote:
George's Pro Sound Company wrote:

Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the inputs
of a graphic EQ and I/O of a Lexicon mpx 500.
do you use nylon isolators on your rack mounts
I fi nd often one defective design creates a defective rack through the rack
rail

Actually, grounding through the rack rails is a _good_ thing. Break your
signal grounds, not your power line grounds or chassis grounds.

Grounding is a good thing. The better rack grounding method
is using a big copper rail from top to bottom. about 1/4 " by 1 inch. All equipment
chassis are then tied to this, and other racks. Standard in the NASA equipment I worked on.
Even then there were problems.

greg

[bob[_4_]]

GregS wrote:
In article , (Scott Dorsey) wrote:
George's Pro Sound Company wrote:
Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the inputs
of a graphic EQ and I/O of a Lexicon mpx 500.

do you use nylon isolators on your rack mounts
I find often one defective design creates a defective rack through the rack
rail
Actually, grounding through the rack rails is a _good_ thing. Break your
signal grounds, not your power line grounds or chassis grounds.

Grounding is a good thing. The better rack grounding method
is using a big copper rail from top to bottom. about 1/4 " by 1 inch. All equipment
chassis are then tied to this, and other racks. Standard in the NASA equipment I worked on.
Even then there were problems.

greg

In a perfect world, all should be securely grounded at every point and
all should be quiet. The neutral and ground should be securely bonded
together at the service entrance point.

In the real world, it does not always work out this way.

In the concert hall i work at, we have some Clearcom 220 rack mount com
stations. depending on where we put them, there is noise in the com from
grounding these units to the audio racks. The solution? not have the
Clearcom station ground at the audio racks (not bolted in to the racks).
Obviously, there is some ground differential difference between the com
system and the audio at some given point.

I had a new church once that i was called in to consult on that another
contractor has installed. The church usually ran the lights at 70% or so
on a dimmer system spec'ed for the building. As usual, every body was
blaming everyone else. Lights 100% WAS no issue. Dimmed, it was.

Dimmed, there was noise in the audio. There was a feeder from the light
dimmer running under the stage area buried under concrete. The mikes on
the stage and music system were picking up this noise. I used a 58 as a
"witching stick" and could find the areas of the stage where this was
worse by the buried feeder. Dynamic mikes were inducing this magnetic
hash from the dimmers. Of course, no one was game for moving the feeder
or changing the dimmers. The ultimate work around was to use condenser
mikes and active DI boxes that did not have transformers in them to
act as "pick ups". The original contractor on the system said i was
full of crap. But, they tried everything and could not make the system
any better....

Non linear loads put all sorts of crap into the ac distribution lines.
Anything with a switching power supply can be a suspect. Large motors,
florescent lights, refrigerators, copy machines and a host of others can
add to the pollution. And put all this on a three phase power
distribution that is not well balanced and its a brew for noisy
power with high harmonic distortion.

Another issue sometimes is the power supply in one rack mounted unit
affecting the unit above it or below it. sometimes you have to move
units around to see if the symptom changes.

When working in audio, we usually don't have the luxury of telling 3rd
parties they have to reworked there electrical system or change there
dimmers. We have to work around the issues the best we can.

You always try to have all the audio on the same electrical panel if
possible. Isolated ground in a permanent systems takes the conduit out
of the equation.

When sending signals from two areas where there are issues, you always
want to send the signal balanced if possible. Then try floating the
ground on the shield. Or try transformer isolation.

Optical or cat five distribution are options also if available.

It takes some one with the experience to work through and around issues
to sometimes make systems function acceptably.

When in the trenches, sometimes you don't have time to fix the problem
and have to work around it. I did a three tenors pops show last month
where one of my leads condenser mikes developed a hash 1/2 way through
the first half. With a short intermission, there was no time to figure
out why. I just moved the mike to another unused line and all was well.
There are times you don't need to know WHY, just solve the problem
any way you can.


bob

[GregS[_3_]]

In article , bob wrote:
GregS wrote:
In article , (Scott Dorsey)
wrote:
George's Pro Sound Company wrote:
Ya know... I get the feeling that Rupert is talking about 1:1 audio
transformers and George is talking about power line isolation
transformers.

I had my share of hum problem this week. It required transformer
balancing/isolation between the aux outputs of an LX7 mixer and the inputs

of a graphic EQ and I/O of a Lexicon mpx 500.

do you use nylon isolators on your rack mounts
I find often one defective design creates a defective rack through the rack

rail
Actually, grounding through the rack rails is a _good_ thing. Break your
signal grounds, not your power line grounds or chassis grounds.

Grounding is a good thing. The better rack grounding method
is using a big copper rail from top to bottom. about 1/4 " by 1 inch. All
equipment
chassis are then tied to this, and other racks. Standard in the NASA
equipment I worked on.
Even then there were problems.

greg

In a perfect world, all should be securely grounded at every point and
all should be quiet. The neutral and ground should be securely bonded
together at the service entrance point.

In the real world, it does not always work out this way.


You can install an isolation transformer away from the box and form
a new neutral. That sometimes helps things with some equipment
if the ground has noise in relation to neutral.

I was sitting at a wedding once, and the DJ's had a problem with the amp
kept shutting down. It was the dimmer circuit. I forget what the fix
was. Probably use another outlet. Hey they were using my amplifier
with my fault detection circuit. Good for protection, but bad for
music.

greg


In the concert hall i work at, we have some Clearcom 220 rack mount com
stations. depending on where we put them, there is noise in the com from
grounding these units to the audio racks. The solution? not have the
Clearcom station ground at the audio racks (not bolted in to the racks).
Obviously, there is some ground differential difference between the com
system and the audio at some given point.

I had a new church once that i was called in to consult on that another
contractor has installed. The church usually ran the lights at 70% or so
on a dimmer system spec'ed for the building. As usual, every body was
blaming everyone else. Lights 100% WAS no issue. Dimmed, it was.

Dimmed, there was noise in the audio. There was a feeder from the light
dimmer running under the stage area buried under concrete. The mikes on
the stage and music system were picking up this noise. I used a 58 as a
"witching stick" and could find the areas of the stage where this was
worse by the buried feeder. Dynamic mikes were inducing this magnetic
hash from the dimmers. Of course, no one was game for moving the feeder
or changing the dimmers. The ultimate work around was to use condenser
mikes and active DI boxes that did not have transformers in them to
act as "pick ups". The original contractor on the system said i was
full of crap. But, they tried everything and could not make the system
any better....

Non linear loads put all sorts of crap into the ac distribution lines.
Anything with a switching power supply can be a suspect. Large motors,
florescent lights, refrigerators, copy machines and a host of others can
add to the pollution. And put all this on a three phase power
distribution that is not well balanced and its a brew for noisy
power with high harmonic distortion.

Another issue sometimes is the power supply in one rack mounted unit
affecting the unit above it or below it. sometimes you have to move
units around to see if the symptom changes.

When working in audio, we usually don't have the luxury of telling 3rd
parties they have to reworked there electrical system or change there
dimmers. We have to work around the issues the best we can.

You always try to have all the audio on the same electrical panel if
possible. Isolated ground in a permanent systems takes the conduit out
of the equation.

When sending signals from two areas where there are issues, you always
want to send the signal balanced if possible. Then try floating the
ground on the shield. Or try transformer isolation.

Optical or cat five distribution are options also if available.

It takes some one with the experience to work through and around issues
to sometimes make systems function acceptably.

When in the trenches, sometimes you don't have time to fix the problem
and have to work around it. I did a three tenors pops show last month
where one of my leads condenser mikes developed a hash 1/2 way through
the first half. With a short intermission, there was no time to figure
out why. I just moved the mike to another unused line and all was well.
There are times you don't need to know WHY, just solve the problem
any way you can.


bob

[Mike Dobony]

On Mon, 27 Apr 2009 14:35:26 +0000, Dave O'Heare wrote:

Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.


By twisted pair, do you mean unbalanced? You are not running close to
exectrical wiring, but are you running it along any metal pipes or beams?
I would be following Geroge's advice and get quality dimmers and possibly a
digital cable (ethernet) for connecting the two mixers.

Mike D.

[Rupert]

On Apr 28, 11:36*am, Mike Dobony wrote:
On Mon, 27 Apr 2009 14:35:26 +0000, Dave O'Heare wrote:
Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.

By twisted pair, do you mean unbalanced? *You are not running close to
exectrical wiring, but are you running it along any metal pipes or beams?
I would be following Geroge's advice and get quality dimmers and possibly a
digital cable (ethernet) for connecting the two mixers.

Mike D.

'Twisted pair' is by definition a balanced signal line. In fact it's
one of the oldest and is used for telephone wiring which is why
telephone wire works over the long distances that does:

http://en.wikipedia.org/wiki/Twisted_pair

Ethernet cable is also twister pair(s).

Rupert

[George's Pro Sound Company]

"Mike Dobony" wrote in message
. ..
On Mon, 27 Apr 2009 14:35:26 +0000, Dave O'Heare wrote:

Argh.

I'm running sound at a series of events in a 120 year old former church,
and have run into a peculiar problem.

The scenario: two separate sound systems on different floors. Audio from
one (basement) fed to the other (main floor) by a couple hundred feet of
good quality shielded twisted pair cable, audio never closer than 8 feet
to the electrical wiring except at the mixers. Six brand new ETC
Smartbars for lighting in the basement. Basement electrical fed from
different electrical panel from the main floor, but all the same main
building feed. I'm told that the building is fed single-phase.


By twisted pair, do you mean unbalanced? You are not running close to
exectrical wiring, but are you running it along any metal pipes or beams?
I would be following Geroge's advice and get quality dimmers and possibly
a
digital cable (ethernet) for connecting the two mixers.

Mike D.
Mike a quick dirty way to check is walk around with a AM radio and listen
for a buzz to appear, it can help you find trouble spots
and as far as dimmers, talk to your supplier, voice your concerns, make them
warentte what they recommend, and replace them with quieter ones if they do
not live up to your expectations
george