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zordmaker
Joined: 12 Jun 2010
Location: Temmyson
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 Posted: Sun Jun 20, 2010 9:08 am Post subject: |
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| GL wrote: |
in the *not so old days, mechanical earth on the dimmers/ double coil pickups on the guitars would go to solving that.
I seem to remember something about earth loops as well..
How much metal is in the roof?
*edit |
Earthing on the dimmers is all fine, may as well be superconducted to earth. Double coil pickups and humbuckers all tried with limited success but no overall problem solved.
Roof is all steel, of course.
Lets get something straight here - the coil is doing exactly what it should - registering magnetic flux. The flux however is around all the building and it's cabling (mostly through the roof and floor) and the MDB which is virtually right next to the stage.
I would estimate that at 50% dim, the harmonic current flowing through all this would be several amps. More than enough to create the problem. There's a chance that some of it is flowing through earths but I don't see how. No doubt the harmonic current is also being shunted through other connected loads - one of which (of course) is the backline itself!
ZM |
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GL
Joined: 29 Dec 2009
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| Posted: Sun Jun 20, 2010 11:57 am Post subject: |
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sorry, I said "roof" out of force of habit... I meant how much steel, as in lighting grid, is above the stage?
is the grid at a lowish height?
is the roof/ grid bonded back to the m.e.n.?
if the buzz present in the stage gear but not PA, perhaps (if not dones so already) check each piece of equipment individually.
(I once had a show, some when, where "dimmer buzz" was present. On being hassled by the sound guy and having a reasonable amount of spare time, I thought to check each circuit individually. I tracked the buzz down to one circuit and one circuit only, which was one cell on a pallas 4... the earth had fallen off that cell. That earth was reconnected and there silence.)
Obviously, the stage gear comes off the same feed as the PA?
have earths been ganged together, or individually run?
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"No matter what age we are, some have never quite left the schoolyard" |
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zordmaker
Joined: 12 Jun 2010
Location: Temmyson
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| Posted: Sun Jun 20, 2010 2:00 pm Post subject: |
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| GL wrote: |
if the buzz present in the stage gear but not PA, perhaps (if not dones so already) check each piece of equipment individually.
(I once had a show, some when, where "dimmer buzz" was present. On being hassled by the sound guy and having a reasonable amount of spare time, I thought to check each circuit individually. I tracked the buzz down to one circuit and one circuit only, which was one cell on a pallas 4... the earth had fallen off that cell. That earth was reconnected and there silence.)
Obviously, the stage gear comes off the same feed as the PA?
have earths been ganged together, or individually run? |
Separate circuits. I'm not all familiar with the installation, its just that the customer called us after exhausting their options with the original installer I think. Its pretty much a standard private high school set up, the "grid" (as it were, because it's not really a grid just 50mm pipes everywhere) is about 4.5m up.
Short of that I guess I could go out there and go over the place for the standard fees. Im sure it could be fixed, but somehow I think the "fix" would probably be 30m of 3 phase extension between the rack and the 3 phase sockets..
ZM |
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GL
Joined: 29 Dec 2009
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| Posted: Sun Jun 20, 2010 2:48 pm Post subject: |
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another thing which comes to mind as well, considering the PA is quiet... could be unbalanced/ unshielded cables being used where they shouldn't be.
4.5 m, shouldn't be that much of a bother
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"No matter what age we are, some have never quite left the schoolyard" |
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zordmaker
Joined: 12 Jun 2010
Location: Temmyson
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| Posted: Sun Jun 20, 2010 8:41 pm Post subject: |
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| GL wrote: |
another thing which comes to mind as well, considering the PA is quiet... could be unbalanced/ unshielded cables being used where they shouldn't be.
4.5 m, shouldn't be that much of a bother |
Naah first thing I thought of was the leads. They've tried multitudes, and in every case the noise only happens when the guitar is actually attached i.e. the noise is being induced in the pick up coils.
In the end I just told them in that venue they would have to live with it and that the guitar player needs to learn to use his pedal properly. Have it properly adjusted for Lead / Rhythm and keep it on Rhythm, only hitting up lead when he's actually playing a screaming lead break and then hitting back seconds before he finishes so nobody notices the noise under the lead break.
(I think these guys were leaving it sit there on full gain all the time, and then hearing the worst of the noise at the end of scenes when the dimmers were on their way up or down.
This is by far the most common way of dealing with this "problem" and one that most seasoned guitar players soon learn. But of course I imagine they would be few and far between in a school..
ZM |
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GL
Joined: 29 Dec 2009
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David Ashton
Joined: 26 Jan 2006
Location: perth
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| Posted: Tue Jan 25, 2011 12:35 am Post subject: |
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| Most noise problems in PA's are caused by a total ignorance of gain structure by audio guys, they have the power amps at "full" and have to reduce gain in the path from the mixer, this stuffs up the signal/noise ratio,[as well as the dynamic range], and as the main source of noise is the dimmers, it becomes "our" fault.90+% of noise problems are solved or significantly reduced with correct gain structure, but don't waste your breath argueing with most audio guys, thy know better than Rane, Yamaha, Mackie or any of the other manufacturers instructions on how gain structure should be set.Even students straight out of tertiary instutions have not been taught the basics. |
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zordmaker
Joined: 12 Jun 2010
Location: Temmyson
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| Posted: Thu Jan 27, 2011 7:11 am Post subject: |
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<<Finding and eliminating troublesome ground loops in complex electronic systems can be a difficult and frustrating task; it requires an expertise gained largely through experience. This is why grounding, in many cases, is referred to as a " black magic art ". >>
No arguments there. Likewise the solutions are not always "vanilla" ones too, you can't just go thinking that you can use the same theory on your next problem that worked on the last one. Each situation is unique and changes depending on loads imposed on the electrical system.
"Agreed" too on the last post about total lack of knowledge in audio circles but hey.. you get what you pay for. And nowadays show budgets seem to say "cost one box of peanuts" under the audio production cost category.
"You don't tell how good someone is by what they do right. It's what they do when something goes wrong that sorts the men from the boys"...
ZM |
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