Infernal Ground Loop Hum!!! - Page 2 - AVS Forum
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post #31 of 59 Old 12-17-2013, 07:49 AM
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Good find arny, $120 for 10 feet ain't cheap but looks like a solution.


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post #32 of 59 Old 12-17-2013, 08:42 AM - Thread Starter
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Originally Posted by arnyk View Post

It probably won't.

For obtaining ground isolation of HDMI lines you need something like this:

Rainbow Fish Fiber Optic HDMI Cable

http://www.ebay.com/itm/20-6m-Rainbow-Fish-Fiber-Optic-HDMI-Cable-Best-Picture-Sound-Quality-/281159562297

http://store.rainbowfishcorp.com/c/home-series - minimal length suffices for your purposes.


Now there we go! Thanks! biggrin.gif
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post #33 of 59 Old 12-17-2013, 09:37 AM
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Originally Posted by Blackdevil77 View Post

Now there we go! Thanks! biggrin.gif
Careful. That is another Forrest Gump type of solution: "life is like a box of chocolate, you never know what you are going to get!" biggrin.gif That optical solution may or may not resolve your problem. Indeed, the Oppo may not the issue but rather the trigger. Yes, I know the hum went away when you unplugged the HDMI cable but does not mean it was the problematic component. Here is the theory.

Consumer audio products by definition are broken. Yes, let me repeat: consumer audio products are fundamentally broken. This is why you get hum randomly and in many instances solutions don't seem to exist. The problem occurs because the ground is used as part of the communication channel. All audio products will cause some amount of leakage into the ground of the product. This is also by design. So you can try all you want with outlets and such but the devices themselves will create voltage differentials by their very nature. Have you ever felt a slight buzzing/shock when you touch the case of an electronic device, especially with the back of your hand? If you so, you are experiencing that leakage from the hot lead to the enclosure of the device. The current is low enough that won't kill you and hence the reason it passes UL certification and such. But it is pretty high with respect to small audio signals. Standard unbalanced audio interconnects unfortunately use that ground as one leg of their signal and hence, will interconnect the two pieces of electronics and different voltages and cause the current to flow and cause the hum.

The HDMI interface among its other ills also has a ground connection. Indeed, the source provides a 5 volt signal to enable plug-and play. So when you connect that HDMI you wind up changing the ground potential of your processor since it is now coupled to the Oppo. That change may actually be then causing a ground loop between the processor and amplifier to be elevated. The optical product will change this situation but not necessarily fix anything. The optical interface has electronics at both ends together with power supplies of their own. That power supply yet again will supply its own ground potential. Maybe you get lucky and that changes things for the better. Maybe not. So my advice is if you are going to try that, make sure to buy it from the local best buy so that you can return it easily. Alternatively, if Arny is so sure this will fix your problem, have him buy it for you and if it doesn't work, make it his problem. biggrin.gif

Importantly, all HDMI repeaters like the optical device recommended, have the potential to cause HDMI incompatibilities. The cable is mostly used for the display/projector so likely has had little to no testing between your sources. If you can at all avoid these repeaters, you should. Speaking of display, that may also be causing your ground loop even though it is down stream.

The solutions I would offer would be the following:

1. Just live with it smile.gif. Don't put you ear next to the speaker. I know once you are aware of the noise it is hard to get it out of your mind but it is the cheapest and easiest solution. You don't listen to your speakers point blank so it may not be an audible problem.

2. Make sure it is hum. It might be buzz and noise. And if so, it has other causes. Many amps for example will have some residual amount of buzz/noise that become more or less audible depending on your speaker's sensitivity. They will not be dead silent. This noise will often come about when you turn on one of the inputs, i.e. select the Oppo, etc.

3. Try using a balanced transformer between the Integra and your amps. You can buy the cheap Rat Shack unit for a quick test. But if this is the fix, I highly recommend getting the Jensen isolators: http://www.jensen-transformers.com/iso_aud.html. Remember, in this situation the transformer will be in the loop for all audio so you want it to be absolutely neutral, not kind of, not sort, not "good enough," not "this guy tested it on the Internet using his PC and thought it was good," and not, "let me ignore what the manufacturer says and assume it is much better." Get the right product for the problem and the industry standard is Jensen. What is also great that Jensen will provide free technical consulting. Call them and explain the problem and they will give you far better analysis than anything you have been told in this thread smile.gif.

Good luck smile.gif. Sadly, you need that in this broken audio architecture....

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post #34 of 59 Old 12-17-2013, 10:23 AM - Thread Starter
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Thanks for the response, it was a good read. My biggest concern is damage caused by a ground loop. I remember reading that the voltage that causes a ground loop hum can damage electronic equipment. At this point, it's only audible if you put your ear up to the speaker and it's not even out of every speaker. I can live with it as long as it won't damage my stuff.
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post #35 of 59 Old 12-17-2013, 12:20 PM
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Ground loops rarely cause damage, especially in audio equipment. The trade bodies (UL etc.) limit the amount of current that can flow through a safety ground. The only time I can recall causing damage is when I didn't watch the gain controls before powering up the system in a new venue and took out a driver (speaker). Helper didn't hear anything after turning on the mixer (I always turned it on first, then power amps) and left it wide-open. Aaarrggghhhh...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #36 of 59 Old 12-17-2013, 12:21 PM
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As a test, remove the HDMI and connect the Oppo to the pre/pro using standard optical. If the hum persists, you may have have other issues with the Oppo or who knows what.

If no hum using optical, move on to coax. No hum: may be an HDMI issue in the Oppo.

Just a suggestion to test/isolate before spending $100+

http://www.overstock.com/Electronics/Rainbow-Fish-Fiber-Optic-HDMI-Cable-Home-20-White/6812909/product.html
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post #37 of 59 Old 12-17-2013, 12:27 PM - Thread Starter
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Okay, that puts me at ease. I'll do that with the Oppo. Thanks everybody for the help
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post #38 of 59 Old 12-18-2013, 05:12 AM
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Quote:
Originally Posted by DonH50 View Post

Ground loops rarely cause damage, especially in audio equipment. The trade bodies (UL etc.) limit the amount of current that can flow through a safety ground. The only time I can recall causing damage is when I didn't watch the gain controls before powering up the system in a new venue and took out a driver (speaker). Helper didn't hear anything after turning on the mixer (I always turned it on first, then power amps) and left it wide-open. Aaarrggghhhh...

I'm not sure that I've ever seen damage due to ground loops, but they are related to safety ground potential differences which under fault conditions can reach damaging levels as high as the power line voltage. I remember that some friends who once (and only once!) made the mistake of moving some mainframe computer cabinets without disconnecting them from the power. Two metal cabinets brushed and flash!, bang!, biff!, boom!, boff! they welded themselves together. oops! ;-)

One can only imagine what would have happened if there was a person in the way. The equipment was on 230 volt 200 amp circuits...

We live in wonderful times where most AV signals can be transported optically with minimal costs. Another friend had the task of moving audio signals between two rooms, one of which was several thousand volts above the other, and he collected a nice fat fee for engineering an audio link between the two with a custom designed optical link. The context was testing automotive equipment.
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post #39 of 59 Old 12-18-2013, 08:45 AM
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Note in my example the damage was secondary due to the sound board max'd out so when I powered on the amp stack the full-amplitude hum took out a driver. The way my "helper" set the board it probably wouldn't have mattered if there was a ground loop or not; a whisper on any channel probably would have done the trick.

That's a scary story about the racks, Arny! I think the most damage I have done is connecting a HS 'scope probe to an isolated ground circuit without thinking that the probe's ground went to chassis ground which the scope tied to the safety ground. The potential difference melted the probe while I was trying to figure out what was going on with the signal. Scratch one $10k active RF probe, ouch.

I think one of the ARC preamps used optoisolators, can't recall if they were in the signal path or not. Would have been long ago, like the SP-6 series.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #40 of 59 Old 12-29-2013, 08:34 AM - Thread Starter
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Okay, now I'm at a loss. The ground loop hum is back and louder than ever. I had an electrician come over, and he can't figure out why it's happening. I disconnected the cable, it still happens. I turned off and disconnected every piece of electronic equipment from the Integra DHC 80.3. As soon as the processor powers up, the hum comes blaring through the speakers, with absolutely nothing else connected to it. I had the cable guy here AND an electrician for hours and neither could figure it out so I'm just completely at a loss right now. I have no idea what to do.
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post #41 of 59 Old 12-29-2013, 09:54 AM - Thread Starter
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I need a new electrician. I've been playing around and turning different things on and off throughout the house makes differences in the amount of hum coming through the speakers. There appears to be no rhyme or reason to it which is making it so hard to pinpoint. It's not the cable, it's none of the source components, it seems like it's simply the electricity in house. Like the houses ground is just bad.
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post #42 of 59 Old 12-29-2013, 10:38 AM
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As soon as the processor powers up, the hum comes blaring through the speakers, with absolutely nothing else connected to it.

You still have the power amp connected, isolate that to see if the hum is coming from that or the integra
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Like the houses ground is just bad.

The integra doesn't have a ground, so I don't see why you're looking at safety ground being an issue.
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post #43 of 59 Old 12-29-2013, 10:49 AM
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Quote:
Originally Posted by Blackdevil77 View Post

Like the houses ground is just bad.
The main purpose of the ground is for safety. It is designed to trip the circuit breaker should the hot lead in the appliance connect to the case. It doesn't play a role in hum in consumer gear. Think of equipment in cars or airplanes. They don't have a "ground" at all. Yet they perform without hum (assuming well designed). Whether you have a hum or not is a function of how your specific equipment is designed. Some combinations in your home will just do that.

As Sam says and I mentioned earlier, you need to isolate the equipment from each other with the transformer if you have the hum. Or alternatively replace the gear with another. No electrician will be able to help you with this.

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post #44 of 59 Old 12-29-2013, 11:02 AM
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Originally Posted by amirm View Post

...... Think of equipment in cars or airplanes. They don't have a "ground" at all. Yet they perform without hum (assuming well designed).......

Hah!

I sat on many coast to coast flights in the 1980s when the in flight entertainment was a aircraft grade VHS and the monitor was 3 tube CTR projector. People think 60hz is bad, try 400hz! The ever present whine in the audio and the waterfall ripple on the picture!

All of you over 40 have all experienced this, now you know why!

Of course fortunately today with digital servers feeding in seat monitors over Ethernet, that is all a thing of the past.

This however further reinforces Amirm's point that a ground loop has nothing to do with the Earth as a ground.

Note: For those who may not be aware, large aircraft uses standard 120v AC for the utility systems but it is generated at 400hz rather than 60hz. The reason is the higher the frequency, smaller generators, motors, and transformers can be used for the same capacity as 60hz. 400hz is a good compromise versus the problems of going even higher in frequency. The critical power buss on all aircraft small and large is 28v DC with a 24v battery.

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post #45 of 59 Old 12-29-2013, 11:38 AM - Thread Starter
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You still have the power amp connected, isolate that to see if the hum is coming from that or the integra
The integra doesn't have a ground, so I don't see why you're looking at safety ground being an issue.

How would I do that? The amps are in the speakers. They are powered Seaton Catalyst 12C's. With the Integra off and the speakers/amps on, no hum. It's when the Integra powers on that the hum starts. This morning someone was on the treadmill in the other room. With the treadmill on, the hum was audible on the opposite end of the room. After the treadmill was turned off, the hum dramatically lessened. I'll turn the Integra off and back on and each time, the volume of the hum may be slightly different, and once in a while, there is no hum. It's different every time, there is no rhyme or reason like I said which is making it so hard to pinpoint.
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post #46 of 59 Old 12-29-2013, 11:41 AM
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How would I do that?

Disconnect the speakers from the preamp.
Do they have balanced inputs?
Lift the ground on the XLR's?

Is the hum being induced into the interconnects, the speakers amps or the integra?
Are the power supplies in these devices so poorly designed that they're passing AC through to the output?
You need to do some troubleshooting, an electrician won't help here.
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post #47 of 59 Old 12-29-2013, 11:51 AM - Thread Starter
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Originally Posted by SAM64 View Post

Disconnect the speakers from the preamp.
Do they have balanced inputs?
Lift the ground on the XLR's?

Is the hum being induced into the interconnects, the speakers amps or the integra?
Are the power supplies in these devices so poorly designed that they're passing AC through to the output?
You need to do some troubleshooting, an electrician won't help here.

Yes, everything is hooked up with balanced XLR cables.

Forgive me but, how would I lift the ground on the XLR's?

Something I forgot to mention, a lot of the time, it's not even out of all the speakers. Sometimes it's all of them, sometimes it's only the front speakers, sometimes it's only the right surround speaker and not any of the other ones.
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post #48 of 59 Old 12-29-2013, 11:52 AM
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Forgive me but, how would I lift the ground on the XLR's?
Cut the wire on pin 1
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post #49 of 59 Old 12-29-2013, 12:00 PM - Thread Starter
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Originally Posted by SAM64 View Post

Cut the wire on pin 1

That's what I thought. There's no other way of doing this without damaging the XLR cables? They're in my walls so replacing them would involve breaking my walls and ceiling open.
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post #50 of 59 Old 12-29-2013, 12:00 PM
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Originally Posted by Blackdevil77 View Post

Yes, everything is hooked up with balanced XLR cables.

Forgive me but, how would I lift the ground on the XLR's?

Something I forgot to mention, a lot of the time, it's not even out of all the speakers. Sometimes it's all of them, sometimes it's only the front speakers, sometimes it's only the right surround speaker and not any of the other ones.

Pin 1 is always the ground in audio XLR connections. However the infamous "PIN 1 problem" is usually only found in large systems with long cables - and with stage setups. Lifting pin 1 in a home system with cables 10 feet or less should not have any effect. If it does, then you have a problem elsewhere.

I would ask is all the equipment connected with XLR cables true balanced? I have seen some low cost pro "band" gear that uses unbalanced XLR connections. And I wouldn't put it past one of these high end Tiffany audio manufactures to install an XLR connector because it looks high end but just wire it to the RCA connector so it is still really -10db unbalanced.

An XLR cable and/or connector does not automatically indicate a true balanced connection. It should and was intended to but there are many cheats floating around. And using an XLR to RCA cable or adapter destroys any benefits of a balanced connection.

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post #51 of 59 Old 12-29-2013, 12:06 PM
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Originally Posted by Blackdevil77 View Post

That's what I thought. There's no other way of doing this without damaging the XLR cables? They're in my walls so replacing them would involve breaking my walls and ceiling open.

I have never seen a molded XLR connector in the past 30 years and I have seen thousands. There is a set screw on some the allow the connector to be opened. Neutrik has a screwed on back end. In any case you can pull the connector apart and desolder pin 1. And then re-solder it back so you won't really damage the cable.

Another idea and probably better is to buy or make a pin 1 breaker XLR male to female adapter. You could make one with two connectors and a short 6 inch piece of plain old lamp cord. Just wire pin2 to pin2 and pin3 to pin3 leaving pin1 open. Then insert this adaptor to check for pin1 problems.

Don't worry about the additional connectors in line or the short piece of lamp cord causing problems. That's audiophile bunk! I would not leave this in line however because like I said above, if a pin1 breaker fixes the hum, it means there is a problem elsewhere.

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post #52 of 59 Old 12-29-2013, 12:41 PM
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That's what I thought. There's no other way of doing this without damaging the XLR cables? They're in my walls so replacing them would involve breaking my walls and ceiling open.

Cut it at the connector ....this isn't in the wall is it?
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post #53 of 59 Old 12-29-2013, 12:54 PM - Thread Starter
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I have never seen a molded XLR connector in the past 30 years and I have seen thousands. There is a set screw on some the allow the connector to be opened. Neutrik has a screwed on back end. In any case you can pull the connector apart and desolder pin 1. And then re-solder it back so you won't really damage the cable.

Another idea and probably better is to buy or make a pin 1 breaker XLR male to female adapter. You could make one with two connectors and a short 6 inch piece of plain old lamp cord. Just wire pin2 to pin2 and pin3 to pin3 leaving pin1 open. Then insert this adaptor to check for pin1 problems.

Don't worry about the additional connectors in line or the short piece of lamp cord causing problems. That's audiophile bunk! I would not leave this in line however because like I said above, if a pin1 breaker fixes the hum, it means there is a problem elsewhere.

Okay I'll look for the adapter. I don't want to start cutting the pins off or doing something irreversible. Especially as an experiment to see IF it fixes the problem.
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post #54 of 59 Old 12-29-2013, 12:57 PM
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You don't cut the pin, you cut the wire that's connected to it, solder it back if you want,
Ground is not part of the circuit, unless it's unbalanced.
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post #55 of 59 Old 12-29-2013, 01:03 PM
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Okay I'll look for the adapter. I don't want to start cutting the pins off or doing something irreversible. Especially as an experiment to see IF it fixes the problem.

Well if you don't have the soldering tools or experience (XLR's are very easy for a novice to solder btw) you could buy a cheap M/F three foot XLR cable and make your own pin1 breaker. Just cut the cable in half and reconnect the two internal wires color to color, making sure the shields do not touch each other. Hand twist and electrical tape is fine. This is just a test cable.

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post #56 of 59 Old 12-29-2013, 01:28 PM
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Originally Posted by Blackdevil77 View Post

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Originally Posted by SAM64 View Post

Cut the wire on pin 1

That's what I thought. There's no other way of doing this without damaging the XLR cables? They're in my walls so replacing them would involve breaking my walls and ceiling open.

Get some short male-female XLR extension cable and do the ground lifting in them.

Here's an example: http://www.ebay.com/itm/3FT-PREMIUM-XLR-3-Pin-Male-to-Female-Mic-Microphone-Audio-Shielded-Cable-Cord-/261342851035

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post #57 of 59 Old 12-29-2013, 03:18 PM - Thread Starter
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Thanks, just ordered them.
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post #58 of 59 Old 12-31-2013, 03:46 AM
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I came across this article in the QR dude page on making DIY diffusers
"Minimising hum caused by earth loops. - learn how to bury these little mongrels, and check out some links to other sites on the issue. "
http://www.subwoofer-builder.com/earth-loop.htm
Its a really simple read and makes loops easy to grasp, lots of visual's also, below is example.
Quote:
Earthed vs Double Insulated Equipment

If you are not sure how to classify a piece of equipment, use a multimeter or continuity tester (battery plus lightbulb) to check if the cable sheath is connected to the earth pin on the power plug - not plugged in of course!
Many modern devices are Double Insulated where there is no connection to the household earth. These devices have a symbol indicating that they are double insulated, and often (but not always) come with a power cable that only has two pins.

There are still plenty of devices that are earthed - where the chassis is connected to the household earth.
The purpose of this is to make sure that in the event of a failure of the mains level circuitry within the box, any lethal voltage is shunted to earth, thus blowing the fuse rather than you!
You must never disconnect the earth on such equipment.
Doing so would remove this safety feature and could result in someone's death.


From an audio perspective, earthed equipment will provide a connection between the cable shield and household earth.
If there is a second item of earthed equipment in your setup, there can be a second audio path between your gear which will produce hum.
If you have a hum problem, and only have one item that is earthed, then the problem is not due to an earth loop, and you need to look at other causes.
Quote:
Simple Earth Loop

Consider the following drawing of two pieces of equipment, both earthed. The signal wire is shown in red and the signal return via the sheath is shown in blue. Note that the sheath is connected to the chassis, which in turn, is connected to the household earth.
The green loop indicates that a current can be induced in the closed earth loop. Because this current flows in part of the audio circuit ( the sheath ), it is audible and becomes the demon known as hum




To stop the hum, we must break the loop. For safety reasons we can't break the connection between the chassis and household earth. Nor can we break the household earth connection between the two pieces of equipment. This just leaves the sheath between the two pieces of gear. Of course, there are several ways to do it:

  • Use optical fibre interconnects - outside the scope of this article
  • Switch to balanced cabling - buy new gear or convert selected runs using a Cleanbox
  • Use isolating transformers - some possible signal loss
  • Disconnect one end of the shield
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post #59 of 59 Old 12-31-2013, 03:46 AM
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Originally Posted by Blackdevil77 View Post

Thanks, just ordered them.

Lets us know if your issue is solved.
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