That has ALWAYS been true -- EU Standards have nothing to do with it,
other than educating (at least partially) on the subject. And there are
elements of design that are not well known (or at least well-practiced)
by the EMC community that have been well known in the pro audio world
for nearly 25 years! Consider "the Pin One Problem," exposed by the
late Neil Muncy, ex-W3WJE in a 1994 AES paper. He also exposed a
manufacturing issue with the shielded twisted pair cable that is still
ubiquitous as "rack wire" in all sorts of studio systems that he dubbed
"shield-current -induced noise" (SCIN). Thanks to the defect, shield
current was converted to a differential voltage on the pair, so that,
for example, mic wring running through the ceiling of a wood frame
church would act as a an RX antenna for a nearby broadcast station and
be detected either as a result of a Pin One Problem or excessive
bandwidth in the audio chain. Mackie, a popular mfr of otherwise good
low cost gear believed that his audio chain should pass at least 2 MHz
to minimize phase shift! These audio mixers and mix desks were unusable
in downtown Chicago, where TV transmitters lit them up, and anywhere
close to an AM station.
The very public stink I raised (and documented) forced the company to
fix both issues. This was late '90s - early '00s. The Pin One issue was
also present in some very top-line microphones.
I published several AES papers on the RFI aspects of both the Pin One
Problem and SCIN.
The power-line equivalent of a Pin One Problem is a green wire that
fails to make contact with the shielding enclosure, and often for the
same reason. It's present in many (most?) Astron power supplies, where
the bonding point is insulated from the enclosure by paint. This is a
VERY common mechanism by which RF is coupled into a victim and out of a
source. There are applications notes on my website about Pin One and
SCIN. k9yc.com I suspect Pin One as the mechanism by which backhaul
signals at HF are coupled out of CATV internet systems.
In bar conversations in the late '90s, Muncy emphatically stated that
Pin One Problems were the primary cause of RFI. A few years later, I did
the research and published it in the form of several AES Papers that
proved him correct. They're on my website -- scroll all the way down.
73, Jim K9YC
On 6/3/2019 2:35 PM, David Eckhardt wrote:
Jim, audio equipment meets its challenge with the immunity
requirements that Europe places on it. Analog circuitry is highly
susceptible to external fields! Design to withstand the EU standards
is no simple task. In addition, even the analog portions of the audio
designs of today employ actives devices that, by themselves, could
operate happily into the VHF and low UHF region (especially your low
noise input stages).
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