[ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner
engineer_bill at verizon.net
Mon Nov 4 10:48:07 EST 2019
Jim mentioned "difference [in potential] is created by IR drops in green wires" as a source of the voltage that drives "ground loop" current. In 2011, I presented an AES paper "Ground Loops: The Rest of the Story" which explains what I'd suspected since about 2007, that the overwhelming majority of this is due to magnetic induction into the green wire in the premises wiring itself - the so-called "conduit transformer". Neil and I disagreed about the origin of this voltage ... but running worst-case numbers (20 devices with UL limit 3.5 mA each leakage current, for example) only results in a few mV IR drop over a 20-foot conduit run ... while peak voltages over 1 volt are often seen over the same length, especially if light dimmers are involved. I'll happily send a pdf copy of that paper to anyone interested.
In my semi-retirement, I have a situation similar to Jim's. Had it not been for a couple of generous sponsors, I couldn't have justified the expense of travel and hotel for AES in NYC. But then I also understand the bind that AES finds itself in.
engineer_bill at verizon.net
From: Jim Brown <jim at audiosystemsgroup.com>
To: proaudio <proaudio at bach.pgm.com>
Sent: Mon, Nov 4, 2019 10:18 am
Subject: Re: [ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner
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
Henry Ott also did a great breakdown on the inductance of a wire as part
of a loop.
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