[sdiy] Mysterious ground noise

[Tom May]

harry <harrybissell at prodigy.net> writes:

> Hi Antti:
> 
> In the USA this noise could be from having safety ground connected in
> two places.  One on the circuit, from some point... the other from the
> scope case.
> 
> The answer here is to run the scope from an isolated power supply (isolation
> transformer).

I don't entirely get this.  What happens to the safety ground on the
other side of the isolation transformer?  Is the scope chassis still
connected to safety ground?  If yes, what has been solved?  If not,
how is this better than the 3-to-2 adapter method?

> The other way is to temporarily defeat the safety ground... 3 to 2
> wire adapter.

This, I get :-)

I also don't understand exactly what the balanced 60V/60V system
solves, and how it solves it.

This all leads somewhat into the grounding question I'm about to ask
in my next post.

Tom.