> On Jun 2, 2017, at 2:09 AM, Jim Brown <k9yc@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Electrical codes (like NEC) are written by a bunch of EXCELLENT electrical
> engineers, and are based on solid engineering. Codes are written to take a
> VERY wide variety of conditions into account -- everything from lightning
> protection, electrical safety, to the interconnection of all sorts of low
> voltage systems (like home entertainment systems, telephone, CATV, alarm and
> security systems, etc.). Anyone who thinks they're wrong needs to learn some
> more engineering, or to learn more about those multiple systems types. And
> anyone who thinks there is a difference between theory and practice needs to
> learn more about one or the other.
Codes regarding my bathroom project were also written by a bunch of EXCELLENT
engineers. These codes forbid me from building my bathroom without a sit-down
tub as opposed to what I want, a large standup shower… Codes are well-meaning,
but, as you yourself state, are the result of trying to address every possible
situation. My suggestion of TEMPORARILY opening the ground on the C21 to
determine if this affected hum was intended as a diagnostic. Had this corrected
the problem, I would have suggested such possible things as an isolation
transformer (fully legal and safe) as a permanent corrective action.
As far as ground loops versus what you call “bonding” goes, the end result is
the same. Improper grounding in electronics does cause hum. It is ALWAY 60 Hz
(in USA and Canada, 50 Hz elsewhere) and no amount of added filter capacitance
in a power supply will reduce it.
Now that it appears that the actual problem might be magnetic coupling from the
transformer to circuit wiring (i said MAY be, it’s not a done deal yet), the
cure is simple, magnetic shielding. I assume you believe in magnetic shielding…
No amount of ground alteration will correct for magnetic coupling - different
origin, different cure.
I am fully aware of double insulation and the relaxation of the ground
requirement. Again, the REASON these audio products use double insulation is
exactly hum elimination by elimination of ground loops and the associated hum
thereto.
Call it what you like, bonding or ground loop elimination, the outcome is the
same, hum reduction.
My cable isolators are Jensen…
Without them, I get very strong hum in my A/V system. With them, the hum goes
away.
73
Gary
W0DVN
PS: You have strong knowledge of codes and reasons therefor. I have personal
experience in hum elimination spanning 40+ years. I am not an electrical
engineer and I do not know everything. I am an applied physicist with good
observational skills and may use an incorrect term to describe what I see (from
an EE perspective), but, as I said, the outcome is the same. I use diagnostic
methods to determine root causes and then try various means to correct problems
safely and permanently (such as legal and safe isolation devices and magnetic
shielding where appropriate). Operation of a radio with the ground pin
disconnected for 5 minutes as a diagnostic is not going start a fire or harm
anyone, nor will it result in lightening damage, unless done during a
lightening storm. Every principle that a applies to hum elimination in high end
audio equipment applies to ham radio equipment as well, since the causes are
exactly the same, regardless of what name you give them.
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