Ground lift switches

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If I had the ability and the Author's permission I would show you the diagrams and the text where H.Ott tells us repeatedly that the screen is never connected to audio ground.
The Pin1 problem is an explanation of exactly the same thing.
Pin1 does not go to Audio Ground, it goes to Chassis.

And I have repaired any number of professional rack units where the XLRs are pc mounting, and pin one is soldered directly to the ground plane, or to a convenient (and, I trust calculated) signal ground, from the same network as feeds DC volts for opamps, and reference zero for pots. And remarcably few which run a separate link to the chassis – that complicates the wiring, and increases production costs; and, after all, there's always a link between the two, so there's no potential difference, is there? (that last phrase was said with irony, in case anyone might think I believed it). Mind you, I've lived through an age where the chassis was almost invariable used as part of the ground current circuit, with a sort of 'if the impedance is low enough, eddy currents won't be able to develop enough voltage to interfere' philosophy, and, apart from being impossible to repair (my opinions of surface mounting components would not be suitable for a family friendly forum) new stuff is better conceived.
 
The screen is an extension of the chassis.
All the components inside that chassis AND inside the screen are "protected" to some extent from outside interference fields.

In many situations the Screen is connected at both ends to the terminating chassis/equipment.

In some arrangements it is helpful to have only the source Chassis hardwired to the existing cable screen. At the Receiving end the Screen to Chassis connection can be a capacitor. With this style of screen termination there is advantage in offering a hard wired bypass across the cap connection, so that the operator can have a screen connected to Chassis at both ends of the screened cable.

This could be what some are calling a ground lift switch. But, even in this situation the screen is connected to the CHASSIS not to the Audio Ground.
The cores carry the audio signal and they alone connect to the audio circuitry inside the screening enclosure.
 
And I have repaired any number of professional rack units where the XLRs are pc mounting, and pin one is soldered directly to the ground plane, or to a convenient (and, I trust calculated) signal ground, from the same network as feeds DC volts for opamps, and reference zero for pots. And remarcably few which run a separate link to the chassis – that complicates the wiring, and increases production costs; and, after all, there's always a link between the two, so there's no potential difference, is there? (that last phrase was said with irony, in case anyone might think I believed it). Mind you, I've lived through an age where the chassis was almost invariable used as part of the ground current circuit, with a sort of 'if the impedance is low enough, eddy currents won't be able to develop enough voltage to interfere' philosophy, and, apart from being impossible to repair (my opinions of surface mounting components would not be suitable for a family friendly forum) new stuff is better conceived.

In my experience, all engineers are not in agreement about grounding practices. This is often a hotly debated subject during the design phase of a project.
 
fpi and anyone else that wants to listen,
the examples being given for ground lift switches connecting to audio ground are probably all related to badly designed Balanced Impedance equipment.

We have known about the Pin1 problem for years. All the accepted experts agree. I count Self + Jung + Whitlock + Ott as the experts who we should all be following.
 
Anybody got a nice link to standards on how to wire XLR connectors in cables for balanced lines for microphones and between equipment, and how to wire a ground lift switch on a patchbay, etc.?

In response to your original query, I would say that David Davenport's article on this very site is the best primer I have read on earthing and pin 1 problems:
http://www.diyaudio.com/forums/diyaudio-com-articles/163575-audio-component-grounding-interconnection.html

In the article he reference a good number of external links, which I would recommend reading up on. In particular one of the reference articles by Rod Elliott specifically addresses earth lift switches and safety:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

Best of luck
Simon
 
fpi and anyone else that wants to listen,
the examples being given for ground lift switches connecting to audio ground are probably all related to badly designed Balanced Impedance equipment.

We have known about the Pin1 problem for years. All the accepted experts agree. I count Self + Jung + Whitlock + Ott as the experts who we should all be following.

You're preaching to the choir here. When I'm put in charge of system grounding I follow Ott, and he has never let me down. Ralph Morrison also wrote a useful book on the subject (Grounding and Shielding Techniques in Instrumentation), that states the same principles.
 
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The XLR pin 1 connects to the chassis with a short wire (1 inch, 2 cm)
The phantom power supply ( 0 Volt) connects at the chassis & pin 1 juncture.

The audio circuit also makes one connection to the chassis but this connection is not related to the shield.

***********************
Old Jim Brown articles on the subject:

Pin 1 Revisited
http://www.audiosystemsgroup.com/Pin_1_Revisited.pdf

Pin 1 Revisited -- Part 2
http://www.audiosystemsgroup.com/Pin_1_Revisited_Part_2.pdf

***********************

A new Jim Brown paper on this subject. Don't let the title fool you. It started as an audio system paper, then he added lots of Ham content. See Chapter 1.

A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing
Revision 5a 5 Jun 2010

by Jim Brown K9YC
Audio Systems Group, Inc.
Audio Systems Group, Inc. Home Page

http://www.audiosystemsgroup.com/RFI-Ham.pdf
 
AndrewT said:
fpi and anyone else that wants to listen,
the examples being given for ground lift switches connecting to audio ground are probably all related to badly designed Balanced Impedance equipment.

We have known about the Pin1 problem for years. All the accepted experts agree. I count Self + Jung + Whitlock + Ott as the experts who we should all be following.

Fair enough i have nothing ta say against the above but then one has to explain to me why do the 99% of pro amps available in the market have a ground lift switch that actually selects pin 1 connection from the audio ground ( 0V ) or to the electrical ground /chassis ?

Can be all these manufacturers wrong ?
Is there other practical reasons make them do so ?
 
Andrew, it is all well and good to cite proper practice and what everyone ought to do. But in the real world we encounter every day things like ground loops, where two pieces of equipment simply have a different ground potential at their chassis. That creates a real world need for a ground lift. What shall we do, accept hum as a fact of life? Or break the "proper" ground wiring in order to solve the problem? Chanting Ott, Ott, Ott over and over doesn't stop the hum. We can decry the equipment maker for causing the problem, we can decry the electricians who wire the venues, we can point fingers all we like, but right or wrong, that is the gear that shows up to the performance in the equipment trucks, and is what we have to wire together so there is sound. And that is why professional soundmen always have available various ground lifting solutions.
 
All I was interested in was a ground lift for intermediate cable or patch bay; whether to even connect incoming pin 1 to outgoing pin1. That's probably to accommodate some piece of equipment that established pin 1 reference differently than some other piece of equipment, which I really hadn't intended to discuss. I guess one subject brings up the other. Yes, in an ideal world maybe you'd never need a ground lift switch. But that's not where we live. That said, the patch bay is completed...without any ground lift switches for pin any pin 1.
 
Jim Brown often comments in his papers about how slow some equipment manufactures are to catch on. The first pin #1 problem papers were published in 1994.

Audio Systems Group, Inc. Publications

Pin 1 Revisited Neil Muncy called our attention to the Pin 1 problem (the improper termination of the shield of audio wiring to the circuit board rather than to the shielding enclosure) in his classic 1994 paper, reprinted in the June 1995 Journal of the AES. When he wrote his paper, most commercially available audio gear had pin 1 problems. It was, indeed, difficult to find equipment without it -- even the most prestigeous consoles had serious pin 1 problems! Over the next decade, the better manufacturers redesigned their products to correct their mistake, but sadly, many have not done so.

http://www.audiosystemsgroup.com/Pin_1_Revisited.pdf
 
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