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.
> >
> >
> >
> >
>
>
>
>
>
>

__._,_.___

Posted by: John Beck <jb30343@windstream.net>
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Re: [Avid-L2] Re: Interesting NAB Discoveries X-Keys

 

Given that the audio is now a single multiplexed stream I wonder how soon we can expect a wireless version - even if it takes a couple of wifi streams to get the speed... No wires appeals to me a lot more than 1 wire.

Mike

On 26 Apr 2015, at 8:41 am, bigfish@pacbell.net [Avid-L2] <Avid-L2@yahoogroups.com> wrote:

 

Good to know.  I was intrigued by the thought of having a Cat 6 Cable take the place of a big mic snake.  Obviously there would be a need on stage to convert everything into the Dante stream of data but I'd bet that equipment isn't as big and bulky as the mic snakes I've had occasion to deal with.  That being said there is a dependability to the old analogue methods that makes troubleshooting easier in my mind.  Also if one cable goes bad in a mic snake it's relatively easy to fix and not catastrophic to the live production whereas losing the Dante stream would mean losing the whole system of audio and that would not be good.  Still very cool technology I was not familiar with.



---In Avid-L2@yahoogroups.com, <jonathansabrams@...> wrote :

---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :

Found several audio transport options with Dante being the most interesting to me.  Over Cat 5e you can control audio devices and send a lot of audio channels bi directionally.

The device control may be proprietary.  While there is a standard for network audio transport (AES67), there is no AES standard for controlling AES67 devices.

__._,_.___

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

 

I checked continuity on all the links of the coax cable for the sync signal and all is good there.  Something about the shields in the machine room having a difference of potential with the shield coming back from the edit bay superimposes a some hum and other nasty distortions.  I'm thinking something in the machine room changed but I would think that would effect all the bays.  Oh well here kitty, kitty time to start rounding up the litter.



---In Avid-L2@yahoogroups.com, <jonathansabrams@...> 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.

__._,_.___

Posted by: bigfish@pacbell.net
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.

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[Avid-L2] Re: Interesting NAB Discoveries X-Keys

 

Good to know.  I was intrigued by the thought of having a Cat 6 Cable take the place of a big mic snake.  Obviously there would be a need on stage to convert everything into the Dante stream of data but I'd bet that equipment isn't as big and bulky as the mic snakes I've had occasion to deal with.  That being said there is a dependability to the old analogue methods that makes troubleshooting easier in my mind.  Also if one cable goes bad in a mic snake it's relatively easy to fix and not catastrophic to the live production whereas losing the Dante stream would mean losing the whole system of audio and that would not be good.  Still very cool technology I was not familiar with.



---In Avid-L2@yahoogroups.com, <jonathansabrams@...> wrote :

---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :

Found several audio transport options with Dante being the most interesting to me.  Over Cat 5e you can control audio devices and send a lot of audio channels bi directionally.

The device control may be proprietary.  While there is a standard for network audio transport (AES67), there is no AES standard for controlling AES67 devices.

__._,_.___

Posted by: bigfish@pacbell.net
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Re: [Avid-L2] Interview Transcription

 

We use 'typing plus'. 

Tina - CC'd above.  Good prices, fast turn around.  

________________________
Greg Huson
Secret Headquarters, Inc
Greg (at) SecretHQ.com

On Apr 25, 2015, at 15:28, David Dodson davidadodson@sbcglobal.net [Avid-L2] <Avid-L2@yahoogroups.com> wrote:

 

I've got several hours of on-camera interviews. I need a transcription done. Does anyone have any advice on who I might contact, and what I might expect to pay for this? I'm assuming I would just provide the QT's with a TC burn, and someone listens and types? Something like that?

I'm in Los Angeles.

Thanks!

DD

David Dodson
davidadodson@sbcglobal.net

__._,_.___

Posted by: Greg Huson <greg@secrethq.com>
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[Avid-L2] Interview Transcription

 

I've got several hours of on-camera interviews. I need a transcription done. Does anyone have any advice on who I might contact, and what I might expect to pay for this? I'm assuming I would just provide the QT's with a TC burn, and someone listens and types? Something like that?

I'm in Los Angeles.

Thanks!

DD

David Dodson
davidadodson@sbcglobal.net

__._,_.___

Posted by: David Dodson <davidadodson@sbcglobal.net>
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Re: [Avid-L2] Ground Loop if you hum a few bars...?

 

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.
>
>
>
>



__._,_.___

Posted by: Dave Hogan <mactvman@yahoo.com>
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Re: [Avid-L2] Ground Loop if you hum a few bars...?

 

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.
>
>
>
>

__._,_.___

Posted by: John Beck <jb30343@windstream.net>
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[Avid-L2] Re: Ground Loop if you hum a few bars...?

 

---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :


Chasing a sync issue in one bay out of 10 or more.  We have it localized to some sort of ground loop that is distorting the ntsc ref black and tri-leve sync signals.  If the problematic bay is the only thing connected to the AJA gen-10 all is well.  As soon as any of the other sync connections shield in the machine room touch the shield of any connector on the Gen-10 the noisy kicks in and Avid loses sync lock.  A tek rasterizer scope wfr-7000 will still accept the sync signal as ntsc ref and lock to it but the Nitris won't.  The NitrisDX has been swapped along with the HBP card and interconnect cable.  This is a bay that has worked for years and in fact after replacing a broken off bnc connector on the sync line from MCR last year there was nothing like the noise I see in 2 field mode on a Tek 1750.

If you compare a good sync signal on a WFR-7000 with the bad sync signal on a WFR-7000, do you only see a difference between the two when looking at both fields?

All the power is tech power with isolated grounds.  I can only guess something changed in the machine room or the edit bay that is causing the hum/distortion on the black signal to be to much for NitrisDX to lock to.

I'm adding ground loops to a close number two to the things I hate most right after fonts.  Could additional equipment added in MCR somehow unbalance the isolated tech power that comes from several 20 amp isolated ground circuits to the racks and raise the isolated ground to create an issue.

First, a point about terminology.  Any company who claims their power is balanced (ahem, Furman) is not really telling the truth.  The power is symmetrical, not balanced.  Symmetrical power involves having 60V on each leg relative to ground.  Conversely, the regular power you have otherwise is 120V on one leg, with the second leg at 0V, and the third pin is ground/safety.

I know this is a lot like herding cats but figure this group might have some of their own experiences that might shed some light.  I have seen at my regular gig an intermittent hum pop on and off on my online bay sync signal, that I post about here, come and go and now it's gone after I replaced the batteries in a UPS and the engineer replaced some in a few other ups units.  I'm assuming that had something to do with it because those aging battery units would kick into battery mode when the power hadn't even gone out for some reason and I think that was contributing to the sync issue I was having.  I have been told some of the ups units in this machine room have been serviced or replaced in the recent past so maybe there's something there.  I'm thinking of trying my video humbucking isolation transformer if I can find it, but that didn't resolve anything at my regular gig so I'm not holding my breath.

A humbucker might help if the hum is at 60Hz.  If you connect the sync signal to a composite video input, do you see a rolling bar from bottom to top that takes about 17 seconds to cycle off of the display?

Next maybe 3 to 2 ground lifters on the power cords to tech power in the edit bay.

Please don't do this.  It's not safe.

Then maybe start turning off equipment in the bay and or machine room to see if there is any effect on the noise.

This would be the safer way to troubleshoot.  Start with as little equipment as possible and figure out at which point the hum returns.

The one thing I haven't had a chance to do is look at the black ref signal in the other bays that are not experiencing the sync issue. 

This would be good for comparison purposes.

So someone be my Ground Loop Fairy.  If I leave a tweaker under my pillow will you come by and make this problem go away?  I won't even expect a quarter.  ;-)

I live too far away to be your Ground Loop Fairy.  Good luck!

__._,_.___

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

 

---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.

__._,_.___

Posted by: jonathansabrams@yahoo.com
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.

__,_._,___

[Avid-L2] Re: Interesting NAB Discoveries X-Keys

 

---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :

Found several audio transport options with Dante being the most interesting to me.  Over Cat 5e you can control audio devices and send a lot of audio channels bi directionally.

The device control may be proprietary.  While there is a standard for network audio transport (AES67), there is no AES standard for controlling AES67 devices.

__._,_.___

Posted by: jonathansabrams@yahoo.com
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