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

Saturday, April 25, 2015

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

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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