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Old 20th June 2013, 09:37 PM   #21
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02:13 PM malsackj thanks for the PM w/ the links. I remember those, but they've been improved!
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Old 21st June 2013, 12:06 AM   #22
Enzo is offline Enzo  United States
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Andrew, without me looking up the cited references, are you talking about the equipment or the cables between them?

I was talking about the cables. After all this thread was opened by asking how to wire cables.
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Old 21st June 2013, 07:07 AM   #23
AndrewT is online now AndrewT  Scotland
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The cables connect between equipment enclosures.
If the cables are screened then those screens are an extension of the chassis.
Pin1 goes to chassis.
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Old 21st June 2013, 07:11 AM   #24
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This ART DI box has a ground lift. It works I have one.
ART ARTcessories Xdirect Professional Active Direct Box | Musician's Friend
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Old 21st June 2013, 10:10 AM   #25
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Quote:
Originally Posted by AndrewT View Post
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.
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Old 21st June 2013, 10:13 AM   #26
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...... then Andrew just explain to us in one pro amplifier what use and connection of the ground lift switch ...
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Old 21st June 2013, 10:32 AM   #27
AndrewT is online now AndrewT  Scotland
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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.
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Old 21st June 2013, 10:33 AM   #28
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by chrispenycate View Post
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, ........
Looks like you are describing the "Pin1 problem".
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Old 21st June 2013, 01:13 PM   #29
fpitas is offline fpitas  United States
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Quote:
Originally Posted by chrispenycate View Post
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.
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Old 21st June 2013, 01:26 PM   #30
AndrewT is online now AndrewT  Scotland
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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.
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