To lift pin 1 or not

[dmp]

Do you connect pin 1 on the output XLR to chassis?

Argument against is that the next piece of equipment will tie the shield to ground, and it breaks potential ground current loops.

Argument for is described in the Rane Grounding and Shielding article as "The Absolutely Best Right Way to Do It"

 

[JohnRoberts]

When in doubt do what's right...  connect pin 1 to chassis ground.

JR

 

[Kingston]

Don't clown around with pin1 on 2013. Connect to chassis always. No exceptions and no hack fixes for broken designs involving pin1.

 

[dmp]

You guys are going to bias the voting!
I'd like to follow the 'right' answer (and have on all my builds so far). But I've run into buzzes when I setup for recording at remote locations.

 

[[silent:arts]]

I always do connect pin1 to chassis and never had any problem with this.
I do not connect the output shields on patch bays.

 

[Kingston]

But I've run into buzzes when I setup for recording at remote locations.

How did you figure out it was a pin1 issue at those places?

I do not connect the output shields on patch bays.

Aww crap I just realised how much time I would have saved with this! I went with the pedantic version: connect to chassis [or connector shield] always.

 

[moamps]

I always do connect pin1 to the audio ground,
audio ground to the chassis (power ground) via GND lift switch.
It works for me.

(Audio cables with pin 1 connected to the chassis form multiple ground loops with the power supply cables. I don't like it. )

 

[dmp]

How did you figure out it was a pin1 issue at those places?

I haven't figured that out. What I meant was I have been following the "The Absolutely Best Right Way to Do It" and had problems.
I don't want to start lifting grounds, but I really don't want to have a buzz when I set up for a recording.
Getting everything to work in a stationary studio would be a dream - setting up as quickly as possible in a rented place (barn, etc) shows that "everything that can go wrong, will go wrong"

 

[JohnRoberts]

You guys are going to bias the voting!
I'd like to follow the 'right' answer (and have on all my builds so far). But I've run into buzzes when I setup for recording at remote locations.

There are problems with some old legacy, or perhaps improperly designed newer DIY builds.

There is only one right way, while exceptions exist.

The shield ground is generally not robust enough to provide a solid safety ground so doing this wrong is generally harmless.

JR

PS: Loops created by shields in unbalanced wiring intersecting a magnetic field can actually corrupt the audio signal. But you can't really open one wire of a two wire circuit.  Proper lead dress can matter for that unbalanced consumer wiring, while it's best avoided entirely for serious audio path integrity.

 

[JohnRoberts]

How did you figure out it was a pin1 issue at those places?

I haven't figured that out. What I meant was I have been following the "The Absolutely Best Right Way to Do It" and had problems.
I don't want to start lifting grounds, but I really don't want to have a buzz when I set up for a recording.
Getting everything to work in a stationary studio would be a dream - setting up as quickly as possible in a rented place (barn, etc) shows that "everything that can go wrong, will go wrong"

That's why when the show must go on no matter what, professionals carry transformers in their tool kit for mitigating problematic interfaces. Some carry transformer isolated DI boxes, mainly for the transformer isolation.

Note; the hum may be caused in the other box, because you have grounded pin1 properly. Not your fault but that is little consolation.

JR

 

[Kingston]

I always do connect pin1 to the audio ground,
audio ground to the chassis (power ground) via GND lift switch.
It works for me.

(Audio cables with pin 1 connected to the chassis form multiple ground loops with the power supply cables. I don't like it. )

It sounds a bit too much based on a belief system. Your method deviates from the standard just enough it's asking for trouble with the outside world. I also consider a ground lift a wildly dangerous proposition in any given situation. A hack at best. Just how much do you trust your electrician? Or the electrician who wired the installation where you are now setting up remote rec.

It helps to think of the whole network of all chassis's, cable shields and safety grounds of a studio as a singular mass of metal that can be connected at random at any point. Technically it isn't, and there are potential differences and resistance. But it's just a shield!
When audio ground is referenced to this mass at singular nodes ground loops don't happen. And we are conveniently shielded from outside RF at all points.

Several great isolation transformers are quite mandatory with any location rec. engineer. Let transformers do what they do best: galvanic isolation. They also leave the shields untouched and let them do what they do best.

 

[moamps]

.....It sounds a bit too much based on a belief system. Your method deviates from the standard just enough it's asking for trouble with the outside world. I also consider a ground lift a wildly dangerous proposition in any given situation. A hack at best. Just how much do you trust your electrician? Or the electrician who wired the installation where you are now setting up remote rec...

You should reread my post. The chassis of the gears is always permanently connected to the power (safety) ground in my grounding scheme.

 

[Andy Peters]

I always do connect pin1 to the audio ground,

Which is the wrong place to connect it ... pins 1 go to the CHASSIS.

If you consider that the cable shield is an extension of the chassis, you're getting the right idea.

Now if you do it this way, noise collected on the shield ends up on the chassis, and not in your audio common.

audio ground to the chassis (power ground) via GND lift switch.

We assume you're not lifting the safety ground ever, but lifting the pins 1 in a properly-wired system makes the shielding less effective.

(Audio cables with pin 1 connected to the chassis form multiple ground loops with the power supply cables. I don't like it. )

Except ... it doesn't matter, because you've keep the grounded enclosure separate from the audio common, so the ground loop currents don't get into the audio.

-a

 

[moamps]

I always do connect pin1 to the audio ground,

Which is the wrong place to connect it ... pins 1 go to the CHASSIS.

AES48 is just a recommendation. I'm member there, here is the part:

"An AES standard implies a consensus of those directly and materially affected by its scope and provisions
and is intended as a guide to aid the manufacturer, the consumer, and the general public.  The existence of
an AES standard does not in any respect preclude anyone, whether or not he or she has approved the
document, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in
agreement with the standard."

If you consider that the cable shield is an extension of the chassis, you're getting the right idea.

Nope. I see the shield as a weak link between two racks full of gears in separate rooms.

audio ground to the chassis (power ground) via GND lift switch.

We assume you're not lifting the safety ground ever, but lifting the pins 1 in a properly-wired system makes the shielding less effective.

It is connected to the power ground - chassis on one or both side, so the shielding is fully effective. 

I did once wireing for audio part of a one big international TV company using their standard project (about 10000 analog and AES wires in several rooms). The shields was connected only on one side, only in rack grounding bars.  I'm not trying to reinvent the wheel here. 

 

[Andy Peters]

I always do connect pin1 to the audio ground,

Which is the wrong place to connect it ... pins 1 go to the CHASSIS.

AES48 is just a recommendation.

This has nothing to do with AES recommendations.

It's about foundational engineering principles. Outside of audio systems, the notion of bonding a shield to the chassis isn't controversial, it is standard design practice.

-a

 

[moamps]

(Audio cables with pin 1 connected to the chassis form multiple ground loops with the power supply cables. I don't like it. )

Except ... it doesn't matter, because you've keep the grounded enclosure separate from the audio common, so the ground loop currents don't get into the audio.

http://www.audiosystemsgroup.com/Shield_Current_Induced_Noise.pdf
http://www.audiosystemsgroup.com/SCIN-2.pdf

 

[Speedskater]

Tony Waldron's thoughts on the subject, especially for large installations. Unfortunately the photos & diagrams are blurry.

http://www.fragrantsword.com/twaudio/

 

[keefaz]

I like Tony Waldron's approach to tie shield both ways but I haven't experienced cable management across different rooms

 

[dmp]

Seems like there is some confusion from using shield and pin 1 interchangeably.

The shield of a properly made XLR cable is connected to the connector housing on both ends, which will be connected to the jack on chassis, and always have a chassis ground connection on both ends. The XLR pin1 will not be connected to the shield in a properly made xlr cable (although you will find it in some).
This poll was about lifting pin1 from chassis, which will not lift the shield. 
Or maybe I'm missing something?

 

[Ethan]

Neil Muncy, Bill Whitlock, and Henry Ott (more generally) have all written extensively about this issue.
Google the "Pin 1 Problem" and you're sure to be busy for a while. Henry Ott is an ex Bell labs brain and Noise/EMC expert that has done extensive work investigating Noise issues in system integration scenarios and meticulously backs up his findings with data.

Pin1 == Shield == Chassis.

I've heard Bill Whitlock say that if you get better noise performance tying pin1 to audio common, you've got bigger issues.