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I'm trying to figure out which jacks on my PA amp are shielded and which aren't. To this end, I was looking at the block diagram in the manual. I'm new to reading block diagrams, but it's obviously a useful skill to have for understanding signal flow in a pro audio environment.

Can anyone tell me what the symbol below means? (Just in case the image ever gets separated from this text, it's the one that looks like a wide, slanted triple-tined fork pointing down, under both the hi Z and low Z input jacks.)

enter image description here

Even better, could anyone point me at a resource of pro audio block diagram symbols? I was surprised to not be able to find this online.

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There are block symbol standards in both BSOL (British Standards) and in IEC. If you're affiliated with a university you might have access to either (or both). –  jodles May 10 '13 at 16:20
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1 Answer

That appears to be a chassis common ground.

Update: After re-reading your question, I'm confused by what you mean by "which jacks are shielded?" The circuit diagram says nothing about whether the jacks are shielded or not. It does say that the grounds are connected to chassis ground. Most mixers have a metal body that acts as a shield for the entire device, so individual jacks don't need their own individual shields.

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Does that mean I can use a shielded/TRS cable for the Hi-Z connection? –  neilfein May 5 '13 at 5:31
    
@NeilFein Can you please emphasize what is your question? Why do you think you might not be able to use a TRS cable here? –  Eugene S May 5 '13 at 10:38
    
If I use a TRS cable here will it be shielded? Or am I misunderstanding the situation? –  neilfein May 5 '13 at 13:03
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TRS cables are generally shielded. The circuit diagram indicates that the shield portion of the TRS plug (which should be connected to the shield of the cable) is grounded to the chassis common ground of the mixer. –  ObscureRobot May 5 '13 at 16:14
    
@ObscureRobot - Thanks, I thought that was the case but needed to verify. –  neilfein May 7 '13 at 18:36
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