|
|
Post by stormymondays on Sept 15, 2017 2:11:17 GMT -6
My 1-room studio also doubles as a rehearsal room for my band, with a fairly low end PA: a Yamaha MG166c mixer and several Mackie 350v2 floor monitors. Lately a ground loop has been developing, and I'm trying to troubleshoot it. Forunately the studio equipment all works flawlessly, it's just the "Live" equipment that has noise. Here's what I found: - There are potential differences in the ground between outlets. I've learned that this is a fact of life.
- All connections from the desk to the monitors are balanced TRS.
- The desk has a line lump adapter with a 2 prong plug, while the monitors have regular 3-prong schuko plugs (I'm in Spain BTW).
- Plugging all the equipment into the same outlet gets rid of the hum.
So, I do have a cure already, but I want to know what's happening. With a balanced connection, this shouldn't be happening. I've ruled out the power cables, the TRS cables, and the monitors themselves. I have enough of those to swap out every component. The problem only happens when plugging into different outlets. The further away, the worse, as expected. Also, guitar amps are affected too. If I plug the pedalboard into a different outlet than the amp, I get the exact same hum. However, since these are unbalanced connections, that is to be expected. My theories: - For some reason the potential difference in the ground has increased, hence the increased hum that wasn't bothering me before.
- Something has failed in the desk and the outputs are not balanced anymore.
- Or the earth in some of the outlets has gone bad and should be checked ASAP - I might do this right away just in case.
So, any ideas on what should I check/test/look for?
|
|
|
|
Post by Ward on Sept 15, 2017 7:33:54 GMT -6
Run a power conditioner into the wall and plug all PA equipment into it. All guitar amps too, if you can get them connected to it.
Make certain that if you are using a 2 prong adapter/wall-wart for your PA's power-supply, that you have the polarity correct. Other than that... I don't know at this point.
|
|
ericn
Temp
Balance Engineer
Posts: 14,937 
Member is Online
|
Post by ericn on Sept 15, 2017 10:03:05 GMT -6
Welcome to the world of PA !
All you can do is hunt and lift till you find the problem!
I rember a gig where everything was fine unless they ran the dishwasher!
|
|
|
|
Post by spindrift on Sept 15, 2017 10:30:26 GMT -6
Yes, all gear into one outlet...ala star grounding methodology.
|
|
ericn
Temp
Balance Engineer
Posts: 14,937
Member is Online
|
Post by ericn on Sept 15, 2017 10:46:29 GMT -6
Start at the panel and the outlets, tighten everything make sure outlets really are grounded!
|
|
|
|
Post by spindrift on Sept 15, 2017 13:23:45 GMT -6
Start at the panel and the outlets, tighten everything make sure outlets really are grounded! ^^^^^^^^^^^^^^^^^^^ This is EXCELLENT advice! I once chased a noisy ground leaking into my preamps for months before finally un-buttoning the outlet to find that my ground was basic conduit! Once I re-routed my power to a properly grounded (dedicated and isolated copper conductor for ground) and employed the star-ground scheme, my troubles went away. This is a good reference that helped me as well: Rane - Grounding and Shielding Audio DevicesGood science! (because there is no such thing as luck when it comes to these matters)  |
|
|
|
Post by johneppstein on Sept 15, 2017 14:35:43 GMT -6
My 1-room studio also doubles as a rehearsal room for my band, with a fairly low end PA: a Yamaha MG166c mixer and several Mackie 350v2 floor monitors. Lately a ground loop has been developing, and I'm trying to troubleshoot it. Forunately the studio equipment all works flawlessly, it's just the "Live" equipment that has noise. Here's what I found: - There are potential differences in the ground between outlets. I've learned that this is a fact of life.
- All connections from the desk to the monitors are balanced TRS.
- The desk has a line lump adapter with a 2 prong plug, while the monitors have regular 3-prong schuko plugs (I'm in Spain BTW).
- Plugging all the equipment into the same outlet gets rid of the hum.
So, I do have a cure already, but I want to know what's happening. With a balanced connection, this shouldn't be happening. I've ruled out the power cables, the TRS cables, and the monitors themselves. I have enough of those to swap out every component. The problem only happens when plugging into different outlets. The further away, the worse, as expected. Also, guitar amps are affected too. If I plug the pedalboard into a different outlet than the amp, I get the exact same hum. However, since these are unbalanced connections, that is to be expected. My theories: - For some reason the potential difference in the ground has increased, hence the increased hum that wasn't bothering me before.
- Something has failed in the desk and the outputs are not balanced anymore.
- Or the earth in some of the outlets has gone bad and should be checked ASAP - I might do this right away just in case.
So, any ideas on what should I check/test/look for?
Balanced outputs in the desk won't have anything to do with it - it's a grounding problem. Since you say that the problem has increased over time I would guess that the culprit is probably corrosion in your building wiring, either where individual runs of wire connect together or where the wire connects to the wall sockets and/or power panel - most likely both. The corrosion increases the resistance of thr connection and ground connection of different resistance create voltage differences which manifest as noise. Is there a lot of humidity in your area? |
|
|
|
Post by EmRR on Sept 15, 2017 18:37:48 GMT -6
Start at the panel and the outlets, tighten everything make sure outlets really are grounded! Oh boy...there are a few rooms I work on a yearly basis, and for at least 5 running the outlets are all so worn out you have to tape the AC plugs to the outlet face to keep them in, then the cable itself to the wall to keep the plugs from moving. Then use either side of the outlet as case storage so there's a physical barrier to keep people away from them. We file a report/complaint with house engineering every year...... |
|
ericn
Temp
Balance Engineer
Posts: 14,937
Member is Online
|
Post by ericn on Sept 15, 2017 19:02:54 GMT -6
Start at the panel and the outlets, tighten everything make sure outlets really are grounded! Oh boy...there are a few rooms I work on a yearly basis, and for at least 5 running the outlets are all so worn out you have to tape the AC plugs to the outlet face to keep them in, then the cable itself to the wall to keep the plugs from moving. Then use either side of the outlet as case storage so there's a physical barrier to keep people away from them. We file a report/complaint with house engineering every year...... Only thing scarier than some outlets is the box you might have to tap into! |
|
|
|
Post by stormymondays on Sept 16, 2017 3:17:12 GMT -6
Balanced outputs in the desk won't have anything to do with it - it's a grounding problem. Since you say that the problem has increased over time I would guess that the culprit is probably corrosion in your building wiring, either where individual runs of wire connect together or where the wire connects to the wall sockets and/or power panel - most likely both. The corrosion increases the resistance of thr connection and ground connection of different resistance create voltage differences which manifest as noise. Is there a lot of humidity in your area? Good call! There is a LOT of humidity in my area, and since the studio was built from scratch, the walls were shedding humidity for quite a few years. So that explains the change for the worse. I've been reading the fantastic paper on grounding by Bill Whitlock ( centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf ) and I think the balanced connection should cancel the ground noise. I'll have to do some further reading. Well, I have a plan now. Check the outlets/grounding, and accept the fact of life that different outlets will have a different ground potential. Thanks everyone! |
|
|
|
Post by stratboy on Sept 16, 2017 19:41:00 GMT -6
Oh boy...there are a few rooms I work on a yearly basis, and for at least 5 running the outlets are all so worn out you have to tape the AC plugs to the outlet face to keep them in, then the cable itself to the wall to keep the plugs from moving. Then use either side of the outlet as case storage so there's a physical barrier to keep people away from them. We file a report/complaint with house engineering every year...... Only thing scarier than some outlets is the box you might have to tap into! I've tapped into some mains where it was so scary I had another crew member holding on to a towel run through the back of my belt to pull me off in case I got cooked. One of the worst jobs in touring sound. |
|
ericn
Temp
Balance Engineer
Posts: 14,937
Member is Online
|
Post by ericn on Sept 16, 2017 21:10:47 GMT -6
Only thing scarier than some outlets is the box you might have to tap into! I've tapped into some mains where it was so scary I had another crew member holding on to a towel run through the back of my belt to pull me off in case I got cooked. One of the worst jobs in touring sound. Yep as I lay in a hospital after a insane man set me on fire more than one old road hand " I' m suprised he didn't end up here years ago with electrical burns" |
|
|
|
Post by keymod on Sept 17, 2017 6:52:27 GMT -6
Only thing scarier than some outlets is the box you might have to tap into! I've tapped into some mains where it was so scary I had another crew member holding on to a towel run through the back of my belt to pull me off in case I got cooked. One of the worst jobs in touring sound. So why aren't licensed electricians called in to do this? ( it's even scary to us sometimes ) |
|
|
|
Post by stratboy on Sept 17, 2017 13:37:37 GMT -6
In smaller venues, especially non union,
$$$$$$$$
|
|
ericn
Temp
Balance Engineer
Posts: 14,937
Member is Online
|
Post by ericn on Sept 17, 2017 14:09:02 GMT -6
I've tapped into some mains where it was so scary I had another crew member holding on to a towel run through the back of my belt to pull me off in case I got cooked. One of the worst jobs in touring sound. So why aren't licensed electricians called in to do this? ( it's even scary to us sometimes ) Lots of places would not want anybody who has any idea what code is near their building!! |
|
|
|
Post by EmRR on Sept 17, 2017 18:19:29 GMT -6
So why aren't licensed electricians called in to do this? ( it's even scary to us sometimes ) Lots of places would not want anybody who has any idea what code is near their building!! Yep, on top of the number of times it's not even a place licensed for public gathering on the scale of the event, or it's a party in a frat house basement, etc. I've been in the bid conversation a few times for things like an outdoor band at a church/etc, ends when I mention an electrician to pull a dedicated line outside for the event. |
|
