[TenTec] Running a Century 21 on external 12V power

[Dukes HiFi]

> On Jun 2, 2017, at 2:09 AM, Jim Brown <k9yc at audiosystemsgroup.com> 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.