patchbay grounding question...

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

strat

New member
Joined
Feb 21, 2005
Messages
1
Hello!
I'm a tech. with a grounding question for Keith. [EDIT: For anyone, I would have hoped... -After all, asking only one person's opinion doesn't give a full picture, after all! -Keith]
I've seen several different ways that shields are terminated to/from a patchbay, and I was wondering what type of ground/shield configuration that you use?
One studio I worked at had the shields lifted at the signal wire's point of entry , and the system would develop the "creeping hum".(This phenomenon would start as an almost immeasurable 120Hz noise, then over a period of days would become intolerable. Powercycling the power on all equipment would solve it temporarily--until it became audible again.) I verified the problem as ground currents on the shields, but the studio owner didn't want to pay to rewire the studio. It was cheaper to powercycle the equipment everyday... ::) (I probably should mention that this studio had electronically balanced gear--no transformers, and an improper residential type electrical service with redundant grounds and no clean technical ground.)
A similar setup had CB radio rip everybody's head off whenever a trucker that was passing by flipped the switch. I spun the wheel, gambled, and rewired that studio per AES recommendations,had the power service rewired,and the CB radios went away.I guess I got it right... :-\
There seems to be so many camps of grounding procedures, and you have obviously been in the field  getting it right, I would really like to hear your thoughts and  recommendations regarding shield termination at and to/from the patchbay.
Thank you for your help!
 
Personally, I don't think that any one approach works perfectly in EVERY single situation.

However, I do believe most strongly that this does NOT mean things can be done haphazardly; on the contrary a careful, consistent approach should be adopted, then adapted if required.

For patchbays, I prefer ALL shields to be connected at the patchbay, and lifted remotely. -That way if a change has to be made (such as a ground ADDED, or a change to the cold/ground arrangement in unbalanced equipment), there's never ANY guessing about which end is lifted. -It's also usually less disturbing to open up XLRs or ¼" connectors in order to make a change, rather than tugging on a huge 'gator' of cable (or -worse yet- a TANGLE if the wiring has been improperly managed!) to make a single change whihc may or may not require revisiting.

Sometimes the choice is between connecting a ground and having a hum, or lifting the ground and allowing the floating shield to pick up RF... in these cases, a 0.01-0.1µF capacitor link to ground can effectively 'kill' the antenna, while still sufficiently hindering 50Hz/60Hz current flow, thus relieving the hum problem.

Some people ground at source and lift-at-destination, others do the exact opposite... Me? -I "star-ground-at-the-patch" and lift elsewhere.

Usually.

Keith
 
Related discussion.

http://www.groupdiy.com/index.php?topic=40291.0

My take on the topic is that ground is never lifted or combined anywhere with any cables. That's just asking for confusion. It is the function of all electrical equipment to handle grounding correctly. Doing that with cables (hence patchbays) is salvequick.

Running a true "pin1" implemented and mostly fully balanced studio, and there will never be any need for lifting or combining etc. tricks. That of course assumes that all gear in the studio is implemented correctly. Sometimes that means fixing commercial gear that has design errors, even balancing them for added security. "Pin1" goes to chassis star ground point or directly to chassis, never touches anything in any audio paths, and always has the shortest possible path to IEC safety ground as well. This concerns each and every electrical device in the studio.

The above is the view point of a small studio owner, who has complete control of all gear ever entering or leaving the studio. No experience with TV-station size installations so take it with a grain of salt.
 
Back
Top