Best method for XLR cable construction? pin1 to shell or no?
Derek
I'll be making some new cable soon, particularly short jumpers for use
in mic-to-boom, boom-to mixer connections and want to see if I can
find a consensus on the best way to do solder these up. Obviously
pin1-ground, pin2-hot, pin3-reverse, but I wanted to see where you all
stand on the more optional connection of pin1(cable shield) to the XLR
shell lug, as well as the idea of using ferrite beads and capacitors
to soak up extra RF/EMI. If anyone has been implementing these kinds
of "extras" into their audio cable with success I'd love to hear about
it.
I've heard many opinions and positions on these oft-overlooked
details. Some people firmly believe that the shell should never be
connected (to avoid ground loops), whereas some seem to believe that
connecting the shell provides a more complete level of shielding (both
Ron of PSC, and Jon Tatooles of SD were in this camp). One tech I
talked to (an amp designer) thought that the ideal situation would be
to connect the ground to shell but use caps and ferrite beads to ward
off any ground loops that you may encounter.
I get the feeling that the answer depends on the purpose of the cable
as well as the connected equipment's relationship to mains ground.
eg.. maybe a mic jumper should be fully shielded, whereas a 100' cable
operating at line-level used for patching one panel mixer to another
on AC should not have a link to the shell (ground issues)... ??
For my purposes, all of this cable will live in an OTS rig powered by
batteries 99% of the time, and occasionally tethered to cameras that
may be plugged into AC about 5% of the time... if that helps
btw, I'll be using L-4E6S as well as some cloth Neumann hose (for
shock-mount jumpers), and standard (silver-colored) Neutrik NC3FX/MX
parts.
Thanks,
-d
Richard Crowley
> I get the feeling that the answer depends on the purpose of the cable
> as well as the connected equipment's relationship to mains ground.
Yikes. Making up special cables for such purposes that otherwise
look identical to "normal" cables sounds like asking for trouble.
My observation of "common practice" is to leave the shell "floating"
at both ends unless you run in to trouble with RFI (in high radio-field
environments like near broadcast transmitters, etc.) And then the
solution is to use a capacitor (something low impedance at the RFI
frequency) to bond the male-end shell to pin 1 shield/screen/ground.
I've made something over 500 mic, snake and jumper XLR cable
ends and I've never had to connect anything to the shell (except
for a snake stage box.)
Douglas Tourtelot
any problems in that method and I HAVE had problems with the other way,
fixed by merely clipping the connection from the shell-lug at both ends.
If you are having RF issues, I highly recommend the Neutrik RF resistant
XLR connectors ( EMC-XLR Series). They really work well.
D.
On 2/10/09 5:11 PM, in article 6vemuhF...@mid.individual.net, "Richard
Rainman
pre DAT) have the pin 1 connected to the shell. I always unwire pin 1
and never connect it to the shell when making new cables. Never had
any problems with cables I make.
Jason
I agree with Douglas regarding the Neutrik EMC connectors:
http://www.neutrik.com/uk/en/audio/210_1111665835/NC3MXX-EMC_detail.aspx
It's a slightly more expensive route than you're suggesting, but
certainly keeps things simple & avoids introducing any worry about
ground-loop possibilities.
All the best,
Jason
beech...@gmail.com
First of all, I want to clarify that floating the shell (almost never
helpful in our line of work) should not be confused with lifting the
cable's shield from Pin-1, which is sometimes helpful.
For the type of work most on this group do (remote film/video
production sound), the standard absolutely should be to ground the XLR
shells (connect them to Pin-1). Some of the reasons for this:
1) Grounding the shell shields the conductors within the shell
(particularly important for mic level signals). The advantage of this
can often be noticed by crossing a noisy lighting cable with the
mating connectors of an XLR extension. No one would want a mic cable
that has a couple of inches of unshielded conductors, but this what is
taking place when two XLR cables with ungrounded shells are connected
together. In this scenario, and grounded shell is often helpful, but
never harmful.
2) Some microphones have resistors that give isolation between Pin 1
and the microphone chassis (Schoeps and Neumann come to mind, 10 ohms
I believe). Therefore, if only Pin-1 is relied on for shielding,
proper noise draining is hindered and susceptibility will increase.
This is why it is important to ground the shell of the female XLR on
the cable that plugs into the microphone.
3) In permanent installations that have a lot of complex hook-ups and
long runs that do not change (such as broadcast facilities, studios,
and remote trucks), it can make sense to have a grounding scheme that
keeps chassis grounds and audio grounds of some connections separate.
This which is why XLR connectors have the option of being grounded or
not. But for remote film/video production sound, it is impossible to
adhere strictly to a grounding/floating scheme because our setups
often change (several times a day), and the use of our XLR cables
change.
4) In remote film/video production sound, the odds of a grounded shell
causing more problems than it prevents are about 157563 to 1. But even
if the odds were only 3 to 1, odds are, the shells should be grounded.
For those really wanting to embrace a heady grounding scheme: Since it
is always best to ground the female connector that plugs into a
microphone it could conceivably make sense to float the male connector
of an XLR cable. The thought here being that only outputs would be
grounded to chassis (input grounds would float to interrupt ground
loops), and, when XLR cables are extended with other XLR connections,
the grounded female shell would also ground the mating male shell. But
the chances are much better that an XLR cable that also has a grounded
male chassis will one day save the day by connecting to one of Doug's
ungrounded female shells that could eventually find its way into your
kit.
If, in the course of remote film/video production sound, you ever have
problems that ungrounding the XLR shell fixes, explain what happened
and I'll send you a replacement.
Ground 'em if you got 'em.
Glen Trew
Douglas Tourtelot
I, personally, in 25 years or making, using, repairing, and re-making xlr
cables, have had far more problems with grounded shells than un-grounded
shells. I clip every one that comes my way.
Just my $.02 but I'm stickin' with it<g>.
D.
On 2/11/09 2:19 PM, in article
d44b7c69-7cc3-46ba...@h16g2000yqj.googlegroups.com,
Jason
Out of interest, what would you recommend (re' grounding the shell)
for the interconnects between a 442 & 744T for example, particularly
if they're sharing the same battery-based power supply?
Thanks,
Jason
Gtrew
Doug, I'm afraid you might get a green violation fine for all of
those buss wire clippings needlessly going into Seattle's landfills.
First, I want to clarify the topic of Pin-1 and chassis as relates to
Schoeps microphones. The current version of the CMC-6 body does have
Pin-1 directly grounded to the chassis. In fact, it is the most
directly ground Pin-1 I've ever seen. Those who have them can see the
gold waffer at the base of the XLR connector that is pressed into
Pin-1 and the chassis. This means that the comment about the
importance of grounding Pin-1 to the shell of the female XLR plugging
into that mic is not as vital I earlier indicated. However, it should
still be done so that shielding properties of the shell do not rely
solely on casual contact with the body of the mic. On some other
condenser mics, however, Pin-1 is isolated from the chassis, in which
case, it is vital that the shell of the female XLR going into the mic
be grounded.
Now, Jason, to your Sound Devices question:
As mentioned earlier, if XLR cables will have just one specific
purpose, then consideration can be given to the possibility of audio
ground loops, power ground loops, etc. But XLR cables are so, uh,
ubiquitous (I learned that word from Jon Tatooles) that they will
likely end up somewhere else soon where you would want them grounded.
That said, since the audio grounds and chassis grounds are shared in
both the 442 and the 744T, the XLR connector shells become grounded
anyway by virtue of both ends of the XLR cables being plugged into the
744T and 442. Though the power ground of the 442 is isolated from its
chassis, the 744T power ground is shared by its chassis. So if the
744T and 442 are connected directly to the same power supply, and
Pin-1 of both devices are connected by a straight-thru XLR cable (or
even if shiny parts of the chassis come in contact with each other),
then the chassis grounds, audio grounds, power grounds, and XLR shells
become one in the same ground.
Of course I'm willing to stand corrected by Jon Tatooles on the issue
of Sound Devices grounding and the use of the word ubiquitous.
Until then, ground 'em if you got 'em.
Glen Trew
Steve House
....
>
>If, in the course of remote film/video production sound, you ever have
>problems that ungrounding the XLR shell fixes, explain what happened
>and I'll send you a replacement.
>
>Ground 'em if you got 'em.
>
>Glen Trew
Just curious ... do your Remote Audio pre-made cables come grounded or
ungrounded?
Steve
beech...@gmail.com
> On Wed, 11 Feb 2009 14:19:54 -0800 (PST), beechba...@gmail.com wrote:
>
> ....
>
>
>
> >If, in the course of remote film/video production sound, you ever have
> >problems that ungrounding the XLR shell fixes, explain what happened
> >and I'll send you a replacement.
>
> >Ground 'em if you got 'em.
>
> >Glen Trew
>
> Just curious ... do your Remote Audio pre-made cables come grounded or
> ungrounded?
>
> Steve
3-pin XLR cables have the grounding tab jumped to pin 1.
Gtrew
> On Feb 12, 4:46 am, Steve House <filmma...@nospam.cogeco.ca> wrote:
>
>
>
> > On Wed, 11 Feb 2009 14:19:54 -0800 (PST), beechba...@gmail.com wrote:
>
> > ....
>
> > >If, in the course of remote film/video production sound, you ever have
> > >problems that ungrounding the XLR shell fixes, explain what happened
> > >and I'll send you a replacement.
>
> > >Ground 'em if you got 'em.
>
> > >Glen Trew
>
> > Just curious ... do your Remote Audio pre-made cables come grounded or
> > ungrounded?
>
> > Steve
The standard for XLR audio cables (3-pin and 5-pin) made by Remote
Audio is to ground the shells to pin-1.
Glen Trew
oniro
For system interconnection between audio gears, I used this paper from
Rane engineering to solve problems with pin. 1 2 3 and ground lift.
http://www.rane.com/pdf/ranenotes/Sound%20System%20Interconnection.pdf
Jeff Linteau
Boomboom
>
> For system interconnection between audio gears, I used this paper from
> Rane engineering to solve problems with pin. 1 2 3 and ground lift.http://www.rane.com/pdf/ranenotes/Sound%20System%20Interconnection.pdf
>
>
So for a mic input cable, you'd lift the ground, according to this
exapmle ? (Rane ex. #1)
Boomboom
Gtrew
> Oh, never mind previous post, not for mic, only for gear...
The Rane article has some interesting and useful information, and much
of it is based on the AES48 standard which says that shields of
balanced lines should be grounded at both ends. But it assumes that
balanced cables are used only to connect one piece of equipment to
another, and that the equipment being connected has pin 1 tied to
chassis ground internally. So, do not be misled by the part of the
article that suggests the shells of XLR connectors need not be tied to
pin 1, because it does not take into account several things that we,
as remote production Sound Mixers, often encounter in our line of
work.
For example, the Rane acticle it does not consider that we often
connect XLR cables together as extensions (as they were designed to be
able to do), and that we sometimes plug them into condenser
microphones that have an isolated chassis, both of which require a
grounded shell for proper shielding. Also, the article assumes that
the spring contact of the XLR shell with the chassis will give
sufficient grounding, which, as we've discovered recently with digital
transmitters, is sometimes insufficient in shielding microphones
against AM radio (this is why Zaxcom recommends the use of Switchcraft
XLR connectors that use a positive screw contact for grounding the
shell).
Jason
(It's interesting that you & Douglas have such opposing views on the
subject though!)
J
Derek
Glenn, thanks for taking the time to lay out your train of thought on
this as well. If anyone else would like to chime in, I think it's
interesting to see where everyone stands, and see how and why people
make their cables the way they do. I think in a lot of cases it goes
back to advice that was given by a mentor/supervisor. My generation
learns a lot of tricks like this from the internet (in some cases)
these days whereas older generation's knowledge almost always has a
story to go along with it.
I think we need to conduct a poll on this.. maybe on jwsound (where
this topic is cross-threaded btw)
Thanks again!
-derek
Derek
posted a poll on this topic over on jwsound [url]http://
www.jwsound.net/SMF/index.php?topic=3662.0[/url][/url]
Rock the vote!
-d
camp...@yahoo.ca
Very interesting post .Question for Glen and everybody else :I found
this below phrase in the archives of another forum ,can you please
tell me if this is correct as it is a important safety issue for all
us on a set .
<<One good reason for NOT grounding the shell is this; if you grab the
XLR which is grounded and are about to plug into a piece of gear
that's NOT grounded and it's AC cord is plugged in with it's AC ground
cut off then YOU are the ground path until its path is complete. An
XLR shell is grounded when its plugged into a piece of gear, but not
before...>>
Thanks .
Richard Crowley
> Very interesting post .Question for Glen and everybody else :I found
> this below phrase in the archives of another forum ,can you please
> tell me if this is correct as it is a important safety issue for all
> us on a set .
> <<One good reason for NOT grounding the shell is this; if you grab the
> XLR which is grounded and are about to plug into a piece of gear
> that's NOT grounded and it's AC cord is plugged in with it's AC ground
> cut off then YOU are the ground path until its path is complete. An
> XLR shell is grounded when its plugged into a piece of gear, but not
> before...>>
And a similar problem if an inline XLR shell touches some other
source of current, even a "dirty" ground, etc. it becomes a ground-
loop problem (or worse).
Gtrew
The potential of electrical shock described above would also exist in
the typical scenario of plugging one end of an XLR cable into PA
mixing console (front-of-house feed, for example) and the other end
into an ENG audio rig (where the chassis is never connected to earth),
which is something many of us are expected to do routinely. This
hazard (small as it may be) exists as soon as you touch your ENG rig,
whether the shell was connected to pin-1 or not.
As mentioned a while back in the is thread, most on this group use the
XLR cables one day in a different way then they'll be used the next
day. Therefore, since the odds are far greater that grounded shells
will prevent more problems than the cause, the standard for remote
film/video production sound should be to ground the XLR shells to
pin-1.
Glen Trew
camp...@yahoo.ca
>
> - Show quoted text -
Ok thanks Glen and Richard . Im a production mixer with little
electrical knowledge.I want to learn more to be able to protect myself
and my fellow co-workers on set ....so what do I do ! What can I read
on the internet thats easy to understand ..any suggestions.I already
began reading the Rane doc and other related docs..just want to know
if anybody has any other interesting educational links .
Thanks .
0jun...@bellsouth.net
On 2009-02-15 camp...@yahoo.ca said:
>Ok thanks Glen and Richard . Im a production mixer with little
>electrical knowledge.I want to learn more to be able to protect
>myself and my fellow co-workers on set ....so what do I do ! What
>can I read on the internet thats easy to understand ..any
>suggestions.I already began reading the Rane doc and other related
>docs..just want to know if anybody has any other interesting
>educational links . Thanks .
try the faq for the newsgroup rec.audio.pro. Last I knew it
was at
www.recordist.com/rap-faq/current/
Regards,
Richard webb,
replace anything before at with elspider
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
--- Benjamin Franklin, NOvember 1755 from the
Historical review of Pennsylvania
Richard Crowley
> The potential of electrical shock described above would also exist in
> the typical scenario of plugging one end of an XLR cable into PA
> mixing console (front-of-house feed, for example) and the other end
> into an ENG audio rig (where the chassis is never connected to earth),
> which is something many of us are expected to do routinely. This
> hazard (small as it may be) exists as soon as you touch your ENG rig,
> whether the shell was connected to pin-1 or not.
No, that is a different hazard. I was refering to the *unintentional*
(accidental) interconnection from casual contact of an XLR shell
with some other metalic object.