This IS the Avid L2: Re: [Avid-L2] Ground Loop if you hum a few bars...?

Sunday, April 26, 2015

Re: [Avid-L2] Ground Loop if you hum a few bars...?

No problem. It didn't hurt a bit. --J.B.

Dave Hogan mactvman@yahoo.com [Avid-L2] wrote:
>
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> John Beck, my sincere apologies. My response should have been
> directed to John S Abrams comments.
>
> Dave Hogan
> Burbank, CA
>
>
>
> On Saturday, April 25, 2015 8:44 PM, "John Beck jb30343@windstream.net
> [Avid-L2]" <Avid-L2@yahoogroups.com> wrote:
>
>
> I think you have the wrong John. I'm not opposed to occasional use of
> cheaters to solve a hum problem. I'm the John who suggested using a
> volt meter to check the voltage between grounds and neutrals on the
> various circuits powering your system. It's not uncommon to see 2 or 3
> volts floating on things that should be at ground. --J.B.
>
> Dave Hogan mactvman@yahoo.com [Avid-L2] wrote:
> >
> >
> > Hello John Beck,
> >
> > While your concerns about safety are well noted, I am describing a
> > very common practice in the analog audio and video days, for decades.
> > I never got shocked, and to the best of my knowledge, neither did any
> > of my colleagues. I will repeat that your concerns about safety are
> > notable and not to be taken lightly. However, there are thousands of
> > safe devices manufactured and sold every year even in todays markets
> > that do not have 3 prong plugs. They have 2 prong polarized plugs.
> >
> > I have an electrician's 3 prong tester in my kit of tools, to ensure,
> > first off, that the wiring in a room has correctly wired plugs. It is
> > not all that uncommon for an electrician to get it wrong, which can
> > also be quite dangerous.
> >
> > I am not advocating removing ALL paths to ground, just duplicative
> > ones which create loops that can cause interference.
> >
> > I love audio optical and network fiber interfaces due to the lack of
> > any electrical connection between equipment, and the elimination of
> > noise through digital encoding.
> >
> > There are some converters/extenders that transmit HD video over Fiber,
> > that would be a great way to electronically isolate a problematic bay.
> > I don't have personal experience with one to make recommendations, or
> > an idea of cost, but it is an uber-safe way to solve the issue of
> > ground loops.
> >
> > Also, I have seen broken shields on coaxial wires still work, due to
> > common grounds via devices interconnects or power, already creating a
> > common ground. The cable with a broken shield still passes a signal
> > due to multiple common grounds. It just allows injection of noise and
> > hum, due to the lack of a complete shield on the center wire. I have
> > also seen RF and high frequency digital signals still pass in a cable
> > with a broken shield as well, just less reliably.
> >
> > YMMV
> >
> > Dave Hogan
> > Burbank, CA
> >
> >
> >
> > On Saturday, April 25, 2015 10:44 AM, "John Beck
> > jb30343@windstream.net [Avid-L2]" <Avid-L2@yahoogroups.com> wrote:
> >
> >
> > Sometimes it's enlightening to use an AC voltmeter to check the
> > potential between various grounds. Ideally, any two chassis grounds,
> > any two neutrals and any neutral to ground in your entire system will
> > have 0V between them. Often, this is not the case. --J.B.
> >
> > jonathansabrams@yahoo.com [Avid-L2] wrote:
> > >
> > >
> > > ---In Avid-L2@yahoogroups.com, <mactvman@...> wrote :
> > >
> > > A ground loop is simply an added path to ground, which creates an
> > > antenna loop, and you get noise generated from any electrical signal
> > > in the vicinity, mostly the AC mains. You probably already know this.
> > >
> > > John - The above text is fine.
> > >
> > > Get a bucket of those old adapters that take a 3 prong grounded plug
> > > and allow it to be plugged into a 2 prong plug. Put those on all your
> > > gear, except for a primary component, and they all share the same
> > > ground, through the wires connecting the equipment. (better than just
> > > cutting off all the ground plugs on your power cords).
> > >
> > > John - Please do not do what Dave wrote above! This is dangerous.
> > > Devices that have 3 prong plugs have them for a reason. What is that
> > > reason? Safety! If you lift the third prong (ground), you have just
> > > defeated the electrical safety mechanism of the device in question.
> > > For those of you thinking, "The device has a fuse", I counter withe
> > > question "Which device will die first? You or the fuse?" The answer
> > > is you.
> > >
> > > Used to have to chase this in audio studios when they were all analog.
> > > Just put ground lift plugs on everything except a primary piece of
> > > gear, like the Switcher or Audio console. I use the ones that have
> > > polarity blades, so that I don't end up pumping full power down to
> > > ground....You'll know when that happens when the lights go out, and
> > > things go spark!
> > >
> > > Dave - Did anyone using that equipment ever get injured from a shock?
> > > Consider yourself lucky if they did not. This is not the proper way
> > > to solve the problem you described.
> > >
> > > You also have to make sure that nobody made bum cables (Audio XLR
> > > mostly) which swap the ground and hot leads.
> > >
> > > John - This is true and easy enough to check with either a continuity
> > > tester or by opening the connector shell and seeing which leads are
> > > connected to which pins.
> > >
> > > Only other thing that can cause an issue is if your have a shield
> > > loose on a video cable. Check continuity on the shields.
> > >
> > > Dave - If the shield on a coax cable was compromised, would you have
> > > any signal at all? The circuit wouldn't be completed with a broken
> > > shield.
> > >
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