Audio Hmm from AC lines what do I do?

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Stinger208

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Sylmar, California
Hello, I am doing some work on a studio and they have a large amount of hum on the A/C lines. Now I know grounding is an issue as the the studio is in a detached garage and the fed comes off the main 200 amp panel that is located on the side of the garage. This is very load EMF wise so they put an Isolation transformer on the feeder that feeds the garage/studio panel. This helped a lot but there still is a fair amount coming in. Now I had them check the sound/hum level and I shut off the 2 150amp breakers that feed the house and this cut the hum down a lot!! Now I looked in the feeder conduits that travel about 80' underground to feed the 2 150amp panels in the basement and there is no ground cable in these at all!! SO I thought that if I was to put a ground rod in the basement and connect these panels up to it (not the neutral bus just the grounding bars etc) the this might cancel out that hum coming back to the panel. Also I see that the main panel does not seem to have a ground rod also. It might but I can't find it. It does have a #4 going to the water pipe but that is it.

Have any of you guys worked with ground loops or know what I should do or have any pointers on sorting this out? There is a major celeb coming in a week so I have to fix this fast. I am going to run an above ground wire from these basement panels to the main service panel and connect it up to see if this helps before I go pulling out the feeders and pulling in a new ground etc.

Help :blink:
 
Stinger208 said:
Hello, I am doing some work on a studio and they have a large amount of hum on the A/C lines. Now I know grounding is an issue as the the studio is in a detached garage and the fed comes off the main 200 amp panel that is located on the side of the garage. This is very load EMF wise so they put an Isolation transformer on the feeder that feeds the garage/studio panel. This helped a lot but there still is a fair amount coming in. Now I had them check the sound/hum level and I shut off the 2 150amp breakers that feed the house and this cut the hum down a lot!! Now I looked in the feeder conduits that travel about 80' underground to feed the 2 150amp panels in the basement and there is no ground cable in these at all!! SO I thought that if I was to put a ground rod in the basement and connect these panels up to it (not the neutral bus just the grounding bars etc) the this might cancel out that hum coming back to the panel. Also I see that the main panel does not seem to have a ground rod also. It might but I can't find it. It does have a #4 going to the water pipe but that is it.

Have any of you guys worked with ground loops or know what I should do or have any pointers on sorting this out? There is a major celeb coming in a week so I have to fix this fast. I am going to run an above ground wire from these basement panels to the main service panel and connect it up to see if this helps before I go pulling out the feeders and pulling in a new ground etc.

Help :blink:
Click to expand...
I have a home studio, and I can't do recording for film because of the medium voltage transmission lines that run alongside my property. There is a 60Hz noise floor that I can never totally eliminate. If I play a guitar with a single coil pickup into a high gain amp and I stand facing toward or directly away from where those power lines are, the noise is horrendous. If I turn 90 degrees it gets a lot better. No amount of filtering, rewiring, power conditioning, or grounding would get rid of this. Maybe if I wrapped my house in foil and grounded it... :D
 
Stinger208 said:
Hello, I am doing some work on a studio and they have a large amount of hum on the A/C lines. Now I know grounding is an issue as the the studio is in a detached garage and the fed comes off the main 200 amp panel that is located on the side of the garage. This is very load EMF wise so they put an Isolation transformer on the feeder that feeds the garage/studio panel. This helped a lot but there still is a fair amount coming in. Now I had them check the sound/hum level and I shut off the 2 150amp breakers that feed the house and this cut the hum down a lot!! Now I looked in the feeder conduits that travel about 80' underground to feed the 2 150amp panels in the basement and there is no ground cable in these at all!! SO I thought that if I was to put a ground rod in the basement and connect these panels up to it (not the neutral bus just the grounding bars etc) the this might cancel out that hum coming back to the panel. Also I see that the main panel does not seem to have a ground rod also. It might but I can't find it. It does have a #4 going to the water pipe but that is it.

Have any of you guys worked with ground loops or know what I should do or have any pointers on sorting this out? There is a major celeb coming in a week so I have to fix this fast. I am going to run an above ground wire from these basement panels to the main service panel and connect it up to see if this helps before I go pulling out the feeders and pulling in a new ground etc.

Help :blink:
Click to expand...

Before you spend too much effort in trying to fix the problem, you should invest some time in figuring out where the hum is originating and how it is getting into the audio.

Among the possibilities are
1. 60 Hz magnetic fields being coupled into audio wiring with poor grounding or poor wire pair twisting.
2. 60 Hz voltages on the ECG going to different equipment causing ground current to flow over the signal grounds.
3. Complex waveforms such as SCR/Triac switching which has a 120 Hz fundamental frequency but lots of higher harmonics which can couple more easily past transformers and power supplies causing "buzz" at 60 or 120 Hz rather than a pure looking 60Hz hum.

Also you need to find out where in the signal path the hum is being introduced.
A. Is it present at the mixing board output even when all input signals are potted down completely or muted?
B. If not, what signal lines is the hum coming in through?
C. If the loudness of the hum is independent of the level of signal being sent toward the input, the problem is most likely being introduced by problems with that particular signal line. Either the type of wire used, the routing of the wire, or severe ground voltage offsets between the equipment at one end of the line and the other.
D. You can shield cables against electric fields very effectively. But magnetic fields pass right through electrostatic shielding. Using balanced signal feeds and twisted pair wiring is the only want to go, short of reducing the magnetic fields in the first place. (Tightly twisted power wiring can help a lot with this kind of coupling.)

Shielded balanced line cables for all low level signals and for a many high level signal wires as possible can reduce the hum coming into preamps and amplifiers along with the signal.
Using three wire low impedance shielded cable with a balanced-to-unbalanced transformer at each end can cut down tremendously on ground offset noise.
And last but not least, keep audio wiring as far separated as possible from power wiring, having the two cross at right angles if they have to cross.
 
As a short term fix for your major celeb:

1.Turn off all house power and rent a generator or borrow power from your next door neighbour to power up the studio.

2.I have done lots of studio hum work--trust me you have a major problem to sort out.Good Luck:D
 
hum issues

hum issues

Ya it is a B*&^#% but we will figure it out! So the house is causing all of the problem as when you shut off the 2 125amp beakers that feed the house sub panels the hum is gone. We went one by one to try to locate the worst offenders breaker wise but there are a lot and they just keep adding up. We out a 10kva iso transformer on line and this cut the hum in half which was good but still a problem. I might get another iso xfmr and put this in series and see if i can cut it down even more. Do any of you have any ideas on how to isolate the house from the studio. The main service panel is on the studio and then feeds the house underground which is about 40' away. Once again when you turn off the house 125 sub feeds the hum is handled but we can't leave the house off :D I could put a Pillar Gen/set ups system on line but that is way to pricy for this job.

Any ideas? Do you think this other iso xfmr, in series, will help or what do you recommend?

Thanks,
 
Stinger208 said:
Any ideas? Do you think this other iso xfmr, in series, will help or what do you recommend?

Thanks,
Click to expand...

Once again, if you can figure out how the hum is getting into the equipment, you might have a better idea of what is going wrong and where it is originating from.

Since it appears to be cumulative with load in the house, one quick experiment would be to turn off all the house breakers on one phase only. If the hum increases beyond what you get with them all on, then excessive (for audio purposes anyway) voltage drop on the neutral (or worse on the EGC) may be the culprit.
As a test, (and NOT for regular use!) you can try connecting the neutral from the isolation transformer not to the primary EGC but only to a local ground. I hope they have wired up the isolation transformer as a separately derived system so that you do not have to connect the secondary neutral to the primary neutral.
Also confirm that there is no neutral to EGC bond at any subpanels in the studio. Your description says that the service is physically located at the studio, so that is where the neutral to EGC bond is located. Is that correct? There should not be a neutral to EGC bond at the house panels either.
 
Eliminating "loops" solves loop problems. Driving ground rods and attaching at somewhat random locations just creates more potential "loops". Do not even consider using a ground rod only for an equipment grounding conductor, this can be very dangerous.

If your feeders to other buildings do not have a separate equipment grounding conductor you could have some potential problems as the neutral was likely bonded to to the equipment grounding conductor at the load end, but that used to be allowed, and still is for existing installations.

And it kind of has been mentioned - if you are turning things off and it still doesn't go away maybe it is not coming from the premises wiring. You mentioned water pipe ground - make sure there isn't excessive stray current on this, maybe either your place or a neighbors place has a bad neutral and the water pipe is carrying all the neutral current of either place. Be careful opening the connection to the water pipe cause if it is carrying full neutral current you will A- be exposed to the difference in potential when the connection is opened and B- you will open the neutral path potentially causing unstable line to neutral voltages for 120 equipment if this connection completely or even partially opens any or all neutral paths back to the source.
 
kwired said:
Do not even consider using a ground rod only for an equipment grounding conductor, this can be very dangerous.
Click to expand...
Which was definitely not what I suggested, given that the isolation transformer could be configured to make this an SDS.
But if there was other interconnected equipment in the studio which was not powered from the isolation transformer, there could be problems.
 
Dear Guys, Thanks!

Now I did go through and turn breakers off oone by one and marked the ones that created the loudest hum in the studio but this was about 11 of them. But they seemed to fluctuate a bit and some just added a little but once you have a lot turned on then it was buzzing pretty loud. Now I can try to go thorugh this whole house and fix all the probelms to quite the house but that is a ton of work and may not pay off. But like I said tha service panel is on the studio which is about 40' away from the house. This service panel feeds an ISO xfmr that feeds a small sub panel in the studio. The service pabel has 2 125amp breakers that feed the subs in the basement of the house. When we turn off the 125 amp breakers the hum is gone!! So it seams like if I could find a way to isolate the studio from the house then I want to do that.

The house sub panes do not have a ground wire running to them from the main service so somehow they are grounding out through the steel in the house and possibly the water lines but I can not find this in the house. we cant really find the grounding rod either (there is a #4 running to the water pipe going in the ground) So I ran a 2/0 ground wire (I had in stock) on the ground and connect this to the service panel ground and then ran it to the house panel grounds. This really did not make any change in the hum. I also checked voltage on this and it really did not read anything. I did the same with the copper water pipe that I saw in the basement but this did not really do anything either. The main thing was just turning off the house feeder breakers which killed the hum.

So any ideas on how to isolate the house from the studio power? Like I said we did install an ISO transformer and this helped a ton!! and this is a separately derived system and the neutrals do not tie together.

And I did not lift any grounds or neutrals as this house does have MW circuits through out and I do not want to burn anything up id these are not well balanced.

So Like I said I thought about putting another ISO transformer in line with the feeder that powers the studio sub to see if this can knock it down to a usable level.

Any ideas here as with out the house it is really quite?

Tks!!
 
Now I did go through and turn breakers off oone by one and marked the ones that created the loudest hum in the studio but this was about 11 of them.
Click to expand...

What do you suppose those 11 have in common? Plus you said those were the loudest, meaning others were still contributing. I still think you are looking for something on the distribution side of things and not in each branch circuit. Apparently the more load you add the worse it seems to get, no matter which circuits the load is added to. Could simply be a connection going bad somewhere in the supply.
 
Stinger208 said:
The house sub panes do not have a ground wire running to them from the main service so somehow they are grounding out through the steel in the house and possibly the water lines but I can not find this in the house. we cant really find the grounding rod either (there is a #4 running to the water pipe going in the ground) So I ran a 2/0 ground wire (I had in stock) on the ground and connect this to the service panel ground and then ran it to the house panel grounds. This really did not make any change in the hum. I also checked voltage on this and it really did not read anything. I did the same with the copper water pipe that I saw in the basement but this did not really do anything either. The main thing was just turning off the house feeder breakers which killed the hum.

So any ideas on how to isolate the house from the studio power? Like I said we did install an ISO transformer and this helped a ton!! and this is a separately derived system and the neutrals do not tie together.

And I did not lift any grounds or neutrals as this house does have MW circuits through out and I do not want to burn anything up id these are not well balanced.

So Like I said I thought about putting another ISO transformer in line with the feeder that powers the studio sub to see if this can knock it down to a usable level
Click to expand...

You say that there is no "ground" wire running from the "main service" to the house subpanels. If there is a ground-neutral bond at the main, then you are required under current code to bring an EGC and a neutral from the service to those sub panels. This could be contributing to the problem, even though you tried running a separate ground (EGC) from the service to the house with no effect. Is that feeder from garage to house in conduit? That could be serving as a proper ECG. And, as a separate building the house will need its own separate grounding electrode(s) even though the EGC is connecting it to ground at the service panel.
Instead of just adding the extra ground wire, confirm that there is NOT a ground to neutral bond at either of the house subpanels.

One more question: Is this a relatively clean 60 Hz hum, or is it a buzz with lots of "sharp edged" harmonics on a 60 Hz. fundamental?
 
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I know you are not permitted to install a balanced power system for this application per the code rules. (Article 647) That being said I believe that there are stand alone cord and plug connected units that could be used for this purpose.

You could rewire a transformer to make a balanced power system as a test to see if that would solve the problem before buying the stand alone units.
A transformer wired for 240 in and 120/240 out, but fed with 120 on the primary side would create a balanced power system. I think the ones made for this application may have a metallic shield between the primary and secondary.
 
Forgive me if this is a stupid question, but I am inferring that the owner of the property has plenty of money and the studio is important to him. Can you move the service to the house so that the studio is on a subpanel from the house rather than the other way round?
 
Yes I know code wise and I was going to do this but I first need to handle the hum they have as they have some recording sessions scheduled really soon. And they are going to do a full house fix up latter. When I hooked up the ground wire to the ground bar in the panels the audio guys said it sounded like it slowed down the changed directions and sped back up to the original sound. I looked to see if the ground and neutral were bonded but I just found this at the service. This hum is pretty clean and there are about 11 breakers that when turned off clean it up pretty well. But when the full panel is turned off it is really really quite. This is a large house and possible cloth wire etc as it has had different renos over time and I do not want to go outlet by outlet trying to find each problem as this will cost the client a lot of money as it will be very time consuming so that is why I am trying to see if I can handle it at the studio side by some how splitting them up or correcting the problem at the panels. But when I checked the grounding by running an above ground ground this did not do it so I am still searching :(
GoldDigger said:
You say that there is no "ground" wire running from the "main service" to the house subpanels. If there is a ground-neutral bond at the main, then you are required under current code to bring an EGC and a neutral from the service to those sub panels. This could be contributing to the problem, even though you tried running a separate ground (EGC) from the service to the house with no effect. Is that feeder from garage to house in conduit? That could be serving as a proper ECG. And, as a separate building the house will need its own separate grounding electrode(s) even though the EGC is connecting it to ground at the service panel.
Instead of just adding the extra ground wire, confirm that there is NOT a ground to neutral bond at either of the house subpanels.

One more question: Is this a relatively clean 60 Hz hum, or is it a buzz with lots of "sharp edged" harmonics on a 60 Hz. fundamental?
Click to expand...
 
Balanced power system

Balanced power system

How do I wire this up? ie. if the normal input is 240 and I then wire it for 120 wont the secondary side be half the voltage? I am not used to this type of transformer. Do you think if I put another ISO xfmr in series this would help the issue?;)
don_resqcapt19 said:
I know you are not permitted to install a balanced power system for this application per the code rules. (Article 647) That being said I believe that there are stand alone cord and plug connected units that could be used for this purpose.

You could rewire a transformer to make a balanced power system as a test to see if that would solve the problem before buying the stand alone units.
A transformer wired for 240 in and 120/240 out, but fed with 120 on the primary side would create a balanced power system. I think the ones made for this application may have a metallic shield between the primary and secondary.
Click to expand...
 
That's a lot of money as it is an underground service that goes across roads and stairs and a pool deck and right now money they do not quite have. So I am just trying to work out a handling that could isolate the studio from the house noise.
ggunn said:
Forgive me if this is a stupid question, but I am inferring that the owner of the property has plenty of money and the studio is important to him. Can you move the service to the house so that the studio is on a subpanel from the house rather than the other way round?
Click to expand...
 
You end up with two ungrounded conductors that have 120 volts between them and they each have 60 volts to ground.
It looks like this. If the primary is designed for 240 and you feed it with 120 each of the secondary coils will have 60 volts.

As I said the use of a balanced power system is not permitted by the NEC for your application, but I am suggesting that if you have a transformer you can do a temporary set up to test and see if a balanced power system will solve the problem. If so you can purchase a plug-in stand alone balanced power system and plug all of the studio loads into that system.
 
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Start by reading this troubleshooting paper:

UNDERSTANDING, FINDING, & ELIMINATING GROUND LOOPS IN AUDIO & VIDEO SYSTEMS

Instructor - Bill Whitlock - president
Jensen Transformers, Inc.
Chatsworth, CA

http://www.jensen-transformers.com/an/generic seminar.pdf

or his recent PowerPoint with added notes:

An Overview of Audio System Grounding and Interfacing

by Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers

http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
 
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