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Re: [Amps] Pin 1

To: amps@contesting.com
Subject: Re: [Amps] Pin 1
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sat, 08 Jun 2013 21:50:42 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
On 6/8/2013 5:14 PM, Ed K0KL wrote:
When I was a young broadcast engineer I learned that audio shielding should only be at one end of the cable.

Yes. The reason for that was that much equipment at that time had Pin One Problems, but we didn't know what it was, so we opened the shield and it solved the problem. It wasn't until Neil Muncy's landmark paper (1994) that we learned the actual cause.

AES54-1, the AES Standard for balanced interconnection of Line Level equipment calls for the shield to always be connected at the sending end, and allows for an interruption at the sending end when needed for compatibility with legacy equipment with Pin One Problems AES48, which addresses termination of external wiring inside equipment calls for the cable shield to go to the "shielding enclosure."

Bill Whitlock's landmark paper on balanced interfaces, on the same session as Neil Muncy's, showed that a balanced interface is properly analyzed as a Wheatstone bridge, and quite convincing showed that when a shield is connected at one end only, the point of connection must be at the sending end.

Whitlock owns Jensen Transformers, and his excellent tutorials are on the Jensen Transformers website.

73, Jim K9YC
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