[ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner
Steve.Lampen at belden.com
Mon Nov 4 20:25:07 EST 2019
Having retired two years ago, I am no longer giving presentations for Belden. When I was speaking, one quote that I could recite from memory was that “a balanced line was where the two wires and all passive pieces attached to them are at the same impedance in reference to ground” (with your name attached!). In other words, electrically identical. Since R-C-L make up impedance, I would imagine these should be identical as well, right? In the cable portion, the resistance is the size (AWG) of the wires. (This also affects inductance). It always amazed me to see data on competitors cables where one wire was considerably larger or smaller than the other, or where the motor on the drawing machine would make the conductor variably larger or smaller. Capacitance is predominantly the insulation (dielectric) and its consistency. This is much harder to do than people think and again, many cables had variations of dielectric that could be easily seen by the naked eye! This resulted in impedance that was all over the map with CMRR equally unpredictable.
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steve.lampen at belden.com<mailto:steve.lampen at belden.com>
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From: ProAudio [mailto:proaudio-bounces at bach.pgm.com] On Behalf Of Bill Whitlock
Sent: Monday, November 04, 2019 5:58 PM
To: proaudio at bach.pgm.com
Subject: [EXTERNAL] Re: [ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner
Corey and Steve (and others who might be interested), here is a link to one of my presentations in pdf format:
Cory, note the section on AC power and the example of just what you proposed.
Steve, note the explanation of how a balanced interface rejects noise - it has nothing whatsoever to do with equal and opposite signal swings.
From: Corey Bailey Audio Engineering <proaudio at baileyzone.net>
To: proaudio <proaudio at bach.pgm.com>
Sent: Mon, Nov 4, 2019 4:10 pm
Subject: Re: [ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner
Jim Brown, Bill Whitlock & David Josephson:
All great advice,
For equipment that I want to be truly ground isolated, I use a driven stake (Grounding Rod) and avoid AC ground if at all possible (local electrical codes be damned!). Then, follow the advice of someone who's knowledgeable on the subject of proper grounding. (Like, any of the three mentioned above.)
Corey Bailey Audio Engineering
On 11/4/2019 10:18 AM, Jim Brown wrote:
On 11/3/2019 7:38 PM, David Josephson wrote:
For instance as Jim Brown says, every conductor is an antenna.
My favorite quote on this topic is from Henry Ott, who in his lectures spoke of the hidden schematic lurking behind the ground symbol. Since my retirement, I've been devoting my energies to ham radio, teaching fundamentals to folks with a wide variety of technical backgrounds. No surprise, the Pin One Problem is a hot topic -- Neil Muncy repeatedly told me that it was the primary mechanism behind RFI, and work for a paper that David and I co-authored in 2003 proved it. Fast forward to today, Pin One in CATV and DSL systems is the cause of EGRESS of RF noise that pollutes the radio spectrum.
I do, however, strongly object to the phrase "ground loop," instead using Bill's excellent model showing the mechanism as a difference in potential chassis-to-chassis between interconnected equipment (or chassis to ground) t as the cause of shield current, whether that difference is created by IR drops in green wires or antenna action. The reason I so strongly object is the that solution, especially in small very local systems, is so often proper bonding, which visually creates a loop with signal conductor shields. I'm thinking here of a home entertainment system or a ham station. I use a drawing of Bill's model in my talks and on-sine tutorials.
I stopped teaching at trade shows several years ago because I was unwilling to participate in one held in Florida, in protest of the acquittal of that vigilante murder and the law that allowed it.
As to our conventions -- my interest has always been in the papers and workshops, and hanging out with colleagues. In retirement, I can no longer justify the cost of a convention that requires a hotel stay in an expensive city.
Henry Ott also did a great breakdown on the inductance of a wire as part of a loop.
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