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Old 19th June 2013, 02:48 AM   #11
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Yes.
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Old 19th June 2013, 05:59 PM   #12
AndrewT is offline AndrewT  Scotland
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Pin1 does not carry any audio signal.
Pin1 goes to Chassis. Always.
Pin1 must be treated as part of the chassis. That is what makes the screening effective !
The screening becomes a part of the enclosing chassis for all the cables that pass between chassis.
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Old 19th June 2013, 11:40 PM   #13
Enzo is offline Enzo  United States
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I would quibble a bit.

The shell is always chassis. Pin 1 is usually sent to circuit common. You may or may not wire the shell and pin 1 together. Depends upon the rest of the circuit and its needs.

The cable shield only needs to be grounded at one end to be effective, leaving pin 1 vacant at the remaining end.
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Old 20th June 2013, 09:24 AM   #14
AndrewT is offline AndrewT  Scotland
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My understanding of Ott:
Pin1 goes to Chassis, never audio ground.
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Old 20th June 2013, 03:47 PM   #15
fpitas is offline fpitas  United States
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Quote:
Originally Posted by AndrewT View Post
My understanding of Ott:
Pin1 goes to Chassis, never audio ground.
Yes, that is my understanding as well. Shield currents must be confined to the chassis, and never flow through a signal ground path.
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Old 20th June 2013, 04:02 PM   #16
AndrewT is offline AndrewT  Scotland
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and Jensen, Self, Jung & co all agree.
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Old 20th June 2013, 04:58 PM   #17
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Suppose we are talkin patchfield here, rather than devices. Chassis would be the rack in which it would be mounted. So insisting on chassis grounding for all XLRs means (more or less) that the patchfield becomes our central star gounding point, all ground loops are between it and the power grounds of the various mixers, amps and outboard gadgets wired to it. So far, so good, particularly if all inputs and outputs are truly balanced, or all floating. Now, consider a stage system with a FOH set up, desk, equalisers, inserts, patchfield, crossovers etc. Patch reference ground, no problem. Now, on the other end of the tieline multiway we have two amp racks one each side of the stage, also with patches. All the amp signal grounds to the local patch, or signal cables running through.

But I'm not finished. There is another mixer, with the stage mics split into it, running stage monitors. Own equalisers, crossovers, antifeedback gadgets, power amps, in-ear transmitters; needs ground options to optimise performance with FOH system. Doesn't have to be switches, but some form of removable link.

And, just to maintain the interest, there's a mobile recording truck parked in front; own everything, plus intercom (does anyone build a fully balanced intercom, guaranteed not to generate loops?) Cooperating with a video truck, and video thrives on ground loops; they haven't discovered balancing yet. I want all my tracks to be as free of lighting spike as possible (actually I want them a bit cleaner than that), but I challenge anyone to make a diagram indicating ground currents in this system; everything is balanced (except the insert points on the monitor console, for some reason) but it still generally takes a while minimising interference between systems. And that's without my aforementioned keyboard system…
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Old 20th June 2013, 05:21 PM   #18
fpitas is offline fpitas  United States
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Hard to say for sure without a wiring diagram in front of me, but I should think that isolation transformers could be useful where improper grounding would otherwise be inevitable.
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Old 20th June 2013, 05:55 PM   #19
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Andrew ... now don't be so sure, don't be so ready to use words like always...

Pin1 does not carry any audio signal.correct
Pin1 goes to Chassis. Always. also correct while the next of interest is the status of the Chassis IE connected to the electrical ground and or via the ground lift switch to 0 volts ( signal ground ) of the power supply ?


My understanding of Ott:
Pin1 goes to Chassis, never audio ground. WRONG ! this what a ground lift switch does connect 0V of power supply ( signal ground ) to the electrical ground which happens to be the Chassis



in extensive installations as described above the number one reason is that you cannot guarantee that the all set up is in ground lift or not mode ... any of the devices connected that is in Ground on mode rather in a ground lift mode will produce buzz

beyond that there is other distribution of power and signal issues that may produce buzz of any kind

Had to operate a similar setup as described above as head technician of the meeting for the European Ministers of Foreign Affairin Athens 2008 and name it was there every Tom Dick and Harry
20.000 sq meters area with cctv , 120 tv,s broadcasting rooms , tv vans telephone interfaces , audio systems , motorized cameras , multilingual translate systems and multilingual CCTV ...

What i ve done ?
asked my people to follow the rules during the installation and got my self 10 Ground loop isolators cost 12 E each and 2 video ground loop isolators that i never used cost 100 E each .

--asked my people to notify me before doing anything in case of any buzz
--got 6 of them produced from the video modulators (audio part ) that feed the CCTV
--one buzz coming from a TV van of unknown cause ( Azerbaijan i think ) asked the guy if he was ok with unbalanced audio he said yes so i cut him down installing isolator between my audio and his
--And got a video loop from one of my motorized camera due to a BNC broken plug ...

That's about it
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Old 20th June 2013, 07:02 PM   #20
AndrewT is offline AndrewT  Scotland
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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.
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