[sdiy] Mysterious ground noise

[harry]

Hi Tom... Inline

Tom May wrote:

> 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?

Arrgh ya got me. You have to put the circuit under test on the isolation
transformer, and float any other grounds that might be present...

>
>
> > 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.

Well... two things IMHO.
1) The power flowing in a USA zip cord now has the AC out of phase relative
to ground... the AC will tend to cancel out. How well ?  That depends on your
studio. If you have good wiring practice, you will probably not notice a
difference.

2) It establishes a secondary ground, just for ther studio. A lot of noise comes
from
the ground drop when the refrigerator or HVAC comes on or off... and a lot of
basebord AC outlets are poorly grounded.  Running all the gear from one single
grounded point gets rid of a lot of noise.

Now our good friend, Larry Hendry... will give us some National Electic Code
violations about grounding systems at two points.   ;^)
(we've done this before... but rather than say go look in the archives, then you
say
what archives ?...   ;^)

Both grounds must be bonded together... but you could CHOOSE where to do that...

You should also use the orange AC outlets with the Isolated Ground terminals
(and the symbols) so everyone knows what's what.

You just NOT mix normal hot / neutral 120VAC with the 60/60 balanced AC...
the signal wires can become funny conductors... especially with a tube
(yeah...tube) amp with a hot chassis (yeah... shitty tube amp...).  The results
range from MASSIVE speaker eating hum to pyrotechnics !!!

I think the biggest use of the 60/60 is Isolated Power and separate (but equal ;^)

grounds !!!

H^) harry

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

--
Jihad Terrorism Conspiracy New World Order
Revolution Black Helicopters Freedom of
Speech First Amendment Rights: Carnivore Bait
go ahead and READ my e-mail I have nothing to
hide... how about YOU ???