[Amps] Amp causing RFI

[Jim Brown]

On 2/4/2020 7:23 PM, MU 4CX250B wrote:
> There’s no such thing as a ground loop?That is not correct, Jim! Of 
> course, ground loops exist, along with substantial documentation on how 
> to minimize them. I first encountered ground loops in grad school at 
> Cornell, when part of my dissertation involved measuring nanovolt DC 
> voltages in ultra pure metals at liquid helium temperatures. I’m sure 
> you know that ground loops are a major and common source of hum in low 
> level audio signals.

What you're describing are instrumentation systems, not radio systems.

> A few years ago I wrote up some notes on ground loops for builders of my 
> StationPro controller kits. Here’s a link to my writeup which explains 
> what they are, what causes them, and how to minimize them. They can be 
> nasty little buggers.

Jim,

What you're calling ground loops in this context is part of trying to 
fix failures caused by improper bonding. BTW -- I spent much of my 
professional life in pro audio, which regularly works with 30-40 
microphones where 120 dB or more of dynamic range is required, and where 
mics produce a signal that's often in the low nanovolt range. To 
appreciate how difficult this can be, any noise that is coherent (for 
example, hum, buzz, RFI that's the same on each mic line) will sum as 
the square of the number of those coherent signals, while signal, which 
is different at each mic, sum in proportion to the number of mics (6 
dB/doubling). This means that signal to noise degrades in proportion to 
the number of mics in use (3 dB/doubling).

I suggest that you take a look at my analysisof the problem, which is 
really caused by leakage currents in the power system. And I first saw 
this analysis by Bill Whitlock, who by analyzing noise in a balanced 
circuit as a balanced Wheatstone Bridge, caused the IEC Standard for 
CMRR to be revised. Bill, Neil Muncy, and I were elected Fellows of the 
AES, in part on the basis of this work.

The false concept of of a "ground loop" has caused thousands of hams and 
high futility nuts to do the absolute wrong thing to kill noise that is 
the result of power line leakage currents.

A detailed analysis is beyond the scope of an email reflector, but it's 
in that link I posted.

73, Jim K9YC