So I know where my ground loop is... What is the best way to resolve it?

[Titus]

I just set up a new home theater and ran into what I believe is a ground loop which I can hear in my subwoofer. The loop is between an ultra short throw projector (grounded), a Denon AV receiver (UNgrounded, connected via hdmi), and a Subwoofer (grounded, connected via shielded RCA cable). All components are plugged into the same Furman power conditioner. When the projector is turned on, the hum starts in the subwoofer. If the HDMI or RCA are unplugged, the hum in the subwoofer goes away. I have tried 3 HDMI cables and 2 RCA cables, all of which have carried the hum but interestingly one longer thinner hdmi cable seemed to attenuate it a bit. When the projector is turned off, the hum stops. If I plug the subwoofer into a different outlet, there is no change. If I plug the subwoofer into an outlet on another circuit, the hum is reduced moderately, but still there.

Now, what would be the best way to resolve this? I have heard of ground loop isolators I could put inline between the sub and receiver, but I've heard they reduce quality. I also feel that isn't a true solution to the problem, but a bandaid to treat the symptom.

I have also heard of people "lifting" the ground on the subwoofer, which has been firmly discouraged for safety issues. Though to play devils advocate a bit, I have a Klipsch subwoofer in another room that doesn't have a ground prong. If Klipsch doesn't think they have to ground their subs, why should it be so critical that I don't lift the ground on my other one? Especially if it is already connected to a power conditioner.

But I'd assume the best solution would be to ground the receiver. And why don't the Denon receivers I've owned have ground prongs anyway? How would I ground the receiver? The phono input has a ground post, though I am not sure if that can be used to ground the whole system, or just the phono preamp. I also can't find anything conductive on the outside of my subwoofer, other than the outer ring of the RCA interconnects. If I touch some speaker wire, connected on one end to the phono grounding post on the receiver, to any of those additional interconnects while the LFE is connected, I hear an ever so slight reduction of hum but it is clearly not doing anything useful to resolve the ground loop.

Of these solutions, which would you suggest, and why? Include some details on the "how" if applicable. Thank you!

Note: I know this is not an issue with just my receiver unit. I have tested with two of the same model from the same brand, both brand new. The first did have some unrelated issues that justified a free replacement, which is why I was able to try with two.

 

[everettT]

Remove the sub from the furman and put it on another circuit and see if it disappears. Also, if you have cable or satellite those can be the cause when not properly grounded.

 

[lovinthehd]

Sometimes you need to unplug everything, and connect each extra piece one at a time to see when/where you get hum. When I had some serious hum at my last place temporarily I did lift the ground on the amps to make the problem go away for the time being (was moving soon anyways)....but did track the problem down to the cable provider's connection....they apparently on installation created their own ground separate from the rest of the house. Lifting a ground can be helpful (and a cheater plug is cheap) but does carry a certain liability for long term use (or just don't touch that item while it's plugged in to be safe).

You wouldn't "ground" the receiver, it is double insulated so doesn't need one.

 

[Titus]

Remove the sub from the furman and put it on another circuit and see if it disappears. Also, if you have cable or satellite those can be the cause when not properly grounded.

Hi, thanks for the suggestions. As I mentioned in the OP, "If I plug the subwoofer into an outlet on another circuit, the hum is reduced moderately, but still there." I also don't have cable or satellite. However I do have a wifi router plugged into the same power conditioner, connected to wall with coaxial. It also hardwires with cat5e to the receiver and to the projector, but removing either cat5e's doesn't make a difference to the loop issue and I don't believe the router could be feeding back any ground issue because 1. it isn't grounded, and 2. the buzz happens only when the projector is on.

 

[Titus]

Sometimes you need to unplug everything, and connect each extra piece one at a time to see when/where you get hum. When I had some serious hum at my last place temporarily I did lift the ground on the amps to make the problem go away for the time being (was moving soon anyways)....but did track the problem down to the cable provider's connection....they apparently on installation created their own ground separate from the rest of the house. Lifting a ground can be helpful (and a cheater plug is cheap) but does carry a certain liability for long term use (or just don't touch that item while it's plugged in to be safe).

You wouldn't "ground" the receiver, it is double insulated so doesn't need one.

Thanks for your reply. I mentioned in my reply to everettT just now that I do have an ungrounded wifi router in the entertainment center, but why I don't believe it would be related to this issue. I would prefer not to resort to lifting ground, but am still curious as to why one of my subwoofers is apparently safe to not ground by design, but another isn't.

 

[lovinthehd]

Thanks for your reply. I mentioned in my reply to everettT just now that I do have an ungrounded wifi router in the entertainment center, but why I don't believe it would be related to this issue. I would prefer not to resort to lifting ground, but am still curious as to why one of my subwoofers is apparently safe to not ground by design, but another isn't.

If there's no wired connection between the router and your gear that wouldn't be it, or is it hardwired?

Don't know why some subs/amps use grounds by design and some not (altho think all my consumer subs use a three prong power cord....and the amps I use on my diy subs definitely use three prong cords, but I have other power amps that do not). You can try an isolator perhaps....but doubt the degradation with a sub would be particularly audible but never used one. Of course it would be best to find the actual reason for the ground loop and take care of it that way....

Thankfully the house I moved to has no ground issues with any of my systems/gear (and I made sure when I had DirecTV installed for a while that they used the house's main ground).

You may have already seen it but here's an article that may help https://www.audioholics.com/home-theater-connection/ground-loops-eliminating-system-hum-and-buzz

 

[Titus]

I have actually read that article. Yes, my router is hardwired to both the projector and the receiver via cat5e cable. But to emphasize, I already know where my ground loop is and it is not related to the cable/internet. Here is a visual aid to make it clear. If any of the connections along the green path are removed, the loop is broken. The subwoofer must obviously be on to hear it, but the loop does not start until I've booted up the projector. It does not matter if the receiver is on or in standby. The loop always carries noise to the subwoofer as soon as the projector turns on, and always stops as soon as the projector turns off, or if either the hdmi or rca cable are removed from the equation.

So unless my fundamental understanding is wrong to which I would welcome correction, diagnosis is complete and I really just need help determining the best fix. I'd prefer not to get into isolators if I can fix it by simply grounding the receiver to something. But I don't know if I can ground the relevant circuitry with the phono grounding post, and I don't know if I will have to open my subwoofer to find a place to ground it to (I have serviced it's capacitors before so I am comfortable with this), or if there is some product that will allow me to run a wire right into the ground hole of an outlet.

I also was hoping for some verification on if this seems like a safe thing to do.

 

[DigitalDawn]

A lot of times the ground loop comes from the Cable TV line. If you remove the coaxial cable from the back of your cable box, and the hum goes away, then this will work.

 

[TLS Guy]

I have actually read that article. Yes, my router is hardwired to both the projector and the receiver via cat5e cable. But to emphasize, I already know where my ground loop is and it is not related to the cable/internet. Here is a visual aid to make it clear. If any of the connections along the green path are removed, the loop is broken. The subwoofer must obviously be on to hear it, but the loop does not start until I've booted up the projector. It does not matter if the receiver is on or in standby. The loop always carries noise to the subwoofer as soon as the projector turns on, and always stops as soon as the projector turns off, or if either the hdmi or rca cable are removed from the equation.

So unless my fundamental understanding is wrong to which I would welcome correction, diagnosis is complete and I really just need help determining the best fix. I'd prefer not to get into isolators if I can fix it by simply grounding the receiver to something. But I don't know if I can ground the relevant circuitry with the phono grounding post, and I don't know if I will have to open my subwoofer to find a place to ground it to (I have serviced it's capacitors before so I am comfortable with this), or if there is some product that will allow me to run a wire right into the ground hole of an outlet.

I also was hoping for some verification on if this seems like a safe thing to do.

The Internet cable may still be the problem. Often installers do not install your entry to the home to code. So see if the hum stops after removing all those Ethernet cables. This also applies to any TV cable systems, so disconnect those also.

Just for a test, take out the Furman, and use a power strip. It is just possible it is not a ground loop, but the Furman not able to support the power of the projector, without sending rough power. I personally have a loathing of units like that. There are unnecessary anyway, as the power from the wall does NOT need conditioning. That is absolute bunk. If the hum goes away get rid of it.

If the hum stays then the grounding plan needs changing. The most reliable grounding plan is the "starburst" layout. This is where there is one ground and the other units are grounded back to a central point with stout wire. Remember a ground loop is a resistance between grounds and wires also have resistance.

So, if removing the Furman does not solve the problem, then ground the receiver from the chassis with stout wire via a terminal block at the receiver, and run low resistance grounding wires back to all units to that block.

I have to ground my theater AVP to the metal rack. That is a two prong AC plug. In more complex systems racks are a big advantage and everything bonds to a rack. and then the rack system can be grounded back to the panel. Obviously in most systems that is not possible, but you get the idea.

 

[highfigh]

The Internet cable may still be the problem. Often installers do not install your entry to the home to code. So see if the hum stops after removing all those Ethernet cables. This also applies to any TV cable systems, so disconnect those also.

Just for a test, take out the Furman, and use a power strip. It is just possible it is not a ground loop, but the Furman not able to support the power of the projector, without sending rough power. I personally have a loathing of units like that. There are unnecessary anyway, as the power from the wall does NOT need conditioning. That is absolute bunk. If the hum goes away get rid of it.

If the hum stays then the grounding plan needs changing. The most reliable grounding plan is the "starburst" layout. This is where there is one ground and the other units are grounded back to a central point with stout wire. Remember a ground loop is a resistance between grounds and wires also have resistance.

So, if removing the Furman does not solve the problem, then ground the receiver from the chassis with stout wire via a terminal block at the receiver, and run low resistance grounding wires back to all units to that block.

I have to ground my theater AVP to the metal rack. That is a two prong AC plug. In more complex systems racks are a big advantage and everything bonds to a rack. and then the rack system can be grounded back to the panel. Obviously in most systems that is not possible, but you get the idea.

I agree that cable installers don't always ground their feed properly, but I don't remember having these problems with many DSL installations. Not that it can't happen, but it's not as common.

Furman products can handle 15A without a problem- don't jump to conclusions without knowing which unit is being used. I have used Furman and they all performed extremely well, but in the large systems I also had a new circuit to work with. I have posted several times that lightning struck outside of the room where a system was located, while I was in that room- the system was operating at that time and I heard a loud 'snap' sound in the corner where ADT had placed their cellular transponder. The Furman AND the AV system are still working, after more than 15 years and that rack is full, but I have never had any problems from the Furman.

All systems are supposed to be grounded at the rack, not just yours. NEC articles 725 and 800 cover many low voltage issues that are often unknown to installers and their companies don't train them on these. Article 800 deals with grounding and bonding.

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However, while I agree that removing the Furman should be done, in order to eliminate all possible causes, surges can and do reach AV components from inside of the house- every time the HVAC starts, the induction motor/blower and possibly the AC compressor creates a voltage spike and these can damage sensitive electronics, over time. I strongly disagree with the way most of these are marketed, though- it's all rainbows and unicorns.

A ground loop is often caused purely by resistance between pieces of equipment, but it can also be caused by voltage 'leaking' from one piece of equipment and interacting with something else in the building- a loose grounding screw inside of one piece of equipment can cause all kinds of annoying problems that make people want to weave baskets for a living.

 

[highfigh]

I have actually read that article. Yes, my router is hardwired to both the projector and the receiver via cat5e cable. But to emphasize, I already know where my ground loop is and it is not related to the cable/internet. Here is a visual aid to make it clear. If any of the connections along the green path are removed, the loop is broken. The subwoofer must obviously be on to hear it, but the loop does not start until I've booted up the projector. It does not matter if the receiver is on or in standby. The loop always carries noise to the subwoofer as soon as the projector turns on, and always stops as soon as the projector turns off, or if either the hdmi or rca cable are removed from the equation.

So unless my fundamental understanding is wrong to which I would welcome correction, diagnosis is complete and I really just need help determining the best fix. I'd prefer not to get into isolators if I can fix it by simply grounding the receiver to something. But I don't know if I can ground the relevant circuitry with the phono grounding post, and I don't know if I will have to open my subwoofer to find a place to ground it to (I have serviced it's capacitors before so I am comfortable with this), or if there is some product that will allow me to run a wire right into the ground hole of an outlet.

I also was hoping for some verification on if this seems like a safe thing to do.

This might be easier if you post the brand and model of ALL of your equipment, including the Furman. Also, your photo is too small to read.

Who installed the electrical wiring?

Where is your router WRT the AV system? If it's on a different circuit and in a different room, the ground loop can be caused by the location.

DO NOT lift any ground, unless it's only done as a test. If that proves to eliminate the hum, buy an isolation transformer and do it right- lifted grounds are dangerous and the equipment is grounded as it is because code requires it, not to cause problems in buildings where wiring is faulty or the cable feed wasn't installed correctly.

If you use a Cable TV provider, disconnect the cable feed from the building- if the hum stops (and it's likely), call them to schedule an appointment so they can fix their problem. Hand them a copy of NEC Articles 725 and 800, if they want to argue.

Have you made sure all outlets were wired correctly? If you don't have a circuit tester, I would recommend buying one and checking for reversed Hot & Neutral, lifted Neutral or Ground. You can also plug an extension cord into an outlet AT the Furman and plug the projector into that cord- if the hum stops, it won't necessarily be easy to correct. When I can, I have the electrician install a separate piece of Romex (or separate wires when they install conduit), so a power inlet can be installed but ONLY for the TV or projector. That way, it can be powered through the Furman or whatever is used for surge protection- it's the part at the bottom- the outlet at the top is for installations where the low voltage cabling has been run to the equipment location during the prewire, not as a retro installation.

http://www.metraonline.com/images/products/full/IECWP.jpg

If you disconnect the sub OR the PJ, it's possible that the problem is between those two and the AVR is only in the middle.

 

[everettT]

I have actually read that article. Yes, my router is hardwired to both the projector and the receiver via cat5e cable. But to emphasize, I already know where my ground loop is and it is not related to the cable/internet. Here is a visual aid to make it clear. If any of the connections along the green path are removed, the loop is broken. The subwoofer must obviously be on to hear it, but the loop does not start until I've booted up the projector. It does not matter if the receiver is on or in standby. The loop always carries noise to the subwoofer as soon as the projector turns on, and always stops as soon as the projector turns off, or if either the hdmi or rca cable are removed from the equation.

So unless my fundamental understanding is wrong to which I would welcome correction, diagnosis is complete and I really just need help determining the best fix. I'd prefer not to get into isolators if I can fix it by simply grounding the receiver to something. But I don't know if I can ground the relevant circuitry with the phono grounding post, and I don't know if I will have to open my subwoofer to find a place to ground it to (I have serviced it's capacitors before so I am comfortable with this), or if there is some product that will allow me to run a wire right into the ground hole of an outlet.

I also was hoping for some verification on if this seems like a safe thing to do.

It's definitely a component as moving the didn't eliminate, thanks for clarifying. The AVR itself isn't going to be the fix, it's one the components. One at a time, turn them on till the hum comes, including your network connection, it matke completely disconnecting every connection and doing them that way one by one also.

 

[Titus]

The Internet cable may still be the problem. Often installers do not install your entry to the home to code. So see if the hum stops after removing all those Ethernet cables. This also applies to any TV cable systems, so disconnect those also.

Just for a test, take out the Furman, and use a power strip. It is just possible it is not a ground loop, but the Furman not able to support the power of the projector, without sending rough power. I personally have a loathing of units like that. There are unnecessary anyway, as the power from the wall does NOT need conditioning. That is absolute bunk. If the hum goes away get rid of it.

If the hum stays then the grounding plan needs changing. The most reliable grounding plan is the "starburst" layout. This is where there is one ground and the other units are grounded back to a central point with stout wire. Remember a ground loop is a resistance between grounds and wires also have resistance.

So, if removing the Furman does not solve the problem, then ground the receiver from the chassis with stout wire via a terminal block at the receiver, and run low resistance grounding wires back to all units to that block.

I have to ground my theater AVP to the metal rack. That is a two prong AC plug. In more complex systems racks are a big advantage and everything bonds to a rack. and then the rack system can be grounded back to the panel. Obviously in most systems that is not possible, but you get the idea.

Removing the cat5e cables does not fix the issue. I had already tested just the devices in the diagram in isolation and just now I tried with them disconnected just to be sure.

I had the issue on power strips before deciding to buy the Furman this week, so the power conditioner didn't introduce the problem. I also got the power conditioner because it was neater than the two power strips I was using previously, has it's own 15A breaker, and I don't trust the power in this apartment because we just moved in and my TrippLite in another room picked up on a line fault that was resolved by maintenance changing the breaker. Respectfully, I don't really buy the argument that power never needs conditioning without more evidence against it, as I have seen the voltage fluctuations in the last couple places I've lived throughout the day, to say nothing of the flickers when AC starts or when a vacuum is turned on, and I'd prefer to not leave the balancing of that solely to the power supplies in my expensive devices.

This grounding advice is excellent. Especially the points on resistance. The PJ and Sub are all nonconductive on their exteriors though, with the obvious exception of connections for cables. There is a metal backplate to the sub, but it appears to be nonconductive because if I touch a couple leads of a multimeter to it to check resistance, I can't get any continuity. Given that the PJ and Sub are already grounded via three prong plugs, couldn't I just run a wire from the receiver chassis to a ground hole on one of the outlets of the power conditioner and then everything would be grounded to the same point? If so, I just wonder if there are any special plugs that allow me to secure the wire to the ground of that outlet.

 

[TLS Guy]

Removing the cat5e cables does not fix the issue. I had already tested just the devices in the diagram in isolation and just now I tried with them disconnected just to be sure.

I had the issue on power strips before deciding to buy the Furman this week, so the power conditioner didn't introduce the problem. I also got the power conditioner because it was neater than the two power strips I was using previously, has it's own 15A breaker, and I don't trust the power in this apartment because we just moved in and my TrippLite in another room picked up on a line fault that was resolved by maintenance changing the breaker. Respectfully, I don't really buy the argument that power never needs conditioning without more evidence against it, as I have seen the voltage fluctuations in the last couple places I've lived throughout the day, to say nothing of the flickers when AC starts or when a vacuum is turned on, and I'd prefer to not leave the balancing of that solely to the power supplies in my expensive devices.

This grounding advice is excellent. Especially the points on resistance. The PJ and Sub are all nonconductive on their exteriors though, with the obvious exception of connections for cables. There is a metal backplate to the sub, but it appears to be nonconductive because if I touch a couple leads of a multimeter to it to check resistance, I can't get any continuity. Given that the PJ and Sub are already grounded via three prong plugs, couldn't I just run a wire from the receiver chassis to a ground hole on one of the outlets of the power conditioner and then everything would be grounded to the same point? If so, I just wonder if there are any special plugs that allow me to secure the wire to the ground of that outlet.

Does you receiver have a turntable grounding terminal? If it does, you can use that, and run a heavy gauge copper wire to the Furman. The spec. of the AC wave is set by Federal Law, and its distortion levels are always in legal limits in my measurements with scope and HP distortion analyzer. However you can get voltage fluctuation is adverse weather events, especially surges from lightening strikes. The best way to deal with that is to have whole house surge protector, and a beefy one.
I do use UPS units on everything except the power amps. These units will support and shave voltage, and let you know when this is happening, which is not frequent except in thunderstorms or icing conditions. However, in the event of a power cut, the units will support from the batteries. I have an auto start generator, and the UPS will keep supply until the generator starts, and if it didn't would do a soft shut down.

It occurs to me that this may not be a ground loop, but a fault in your projector. You can decide this by having only the projector and sub connected to the receiver, and see if you have the hum. During this test use a ground break on the sub, which is also known as a cheater plug. If you have hum then, the projector is a POS.

 

[Titus]

This might be easier if you post the brand and model of ALL of your equipment, including the Furman. Also, your photo is too small to read.

Who installed the electrical wiring?

Where is your router WRT the AV system? If it's on a different circuit and in a different room, the ground loop can be caused by the location.

DO NOT lift any ground, unless it's only done as a test. If that proves to eliminate the hum, buy an isolation transformer and do it right- lifted grounds are dangerous and the equipment is grounded as it is because code requires it, not to cause problems in buildings where wiring is faulty or the cable feed wasn't installed correctly.

If you use a Cable TV provider, disconnect the cable feed from the building- if the hum stops (and it's likely), call them to schedule an appointment so they can fix their problem. Hand them a copy of NEC Articles 725 and 800, if they want to argue.

Have you made sure all outlets were wired correctly? If you don't have a circuit tester, I would recommend buying one and checking for reversed Hot & Neutral, lifted Neutral or Ground. You can also plug an extension cord into an outlet AT the Furman and plug the projector into that cord- if the hum stops, it won't necessarily be easy to correct. When I can, I have the electrician install a separate piece of Romex (or separate wires when they install conduit), so a power inlet can be installed but ONLY for the TV or projector. That way, it can be powered through the Furman or whatever is used for surge protection- it's the part at the bottom- the outlet at the top is for installations where the low voltage cabling has been run to the equipment location during the prewire, not as a retro installation.

http://www.metraonline.com/images/products/full/IECWP.jpg

If you disconnect the sub OR the PJ, it's possible that the problem is between those two and the AVR is only in the middle.

I don't understand how in one comment you can say it's uncommon for cable providers to not properly ground their feed, and in the next say that it is likely that disconnecting it will make the hum go away. To humor the presumption that this issue is cable related one last time, I have fully disconnected the power and coax from our wifi router which is the only cable provided device in the unit. No surprise to me, it did not resolve the problem.

My photo is 2k pixels wide, you can click on it to blow it up.

I don't know who installed the electrical, I didn't build the place. It is also an apartment.

I don't have a circuit tester but I have a Tripp Lite power conditioner in another room that I checked all outlets with before moving in. It has a light that turns red if it picks up a line fault, and detects a handful of kinds but doesn't specify which has triggered. On one circuit it did detect a fault which was resolved by maintenance changing the breaker. That was resolved weeks ago.

Now I'd really like to focus on the most likely and simplest solution, which is simply that the three components pictured need a mutual grounding point, and how best to achieve that.

 

[Titus]

Does you receiver have a turntable grounding terminal? If it does, you can use that, and run a heavy gauge copper wire to the Furman. The spec. of the AC wave is set by Federal Law, and its distortion levels are always in legal limits in my measurements with scope and HP distortion analyzer. However you can get voltage fluctuation is adverse weather events, especially surges from lightening strikes. The best way to deal with that is to have whole house surge protector, and a beefy one.
I do use UPS units on everything except the power amps. These units will support and shave voltage, and let you know when this is happening, which is not frequent except in thunderstorms or icing conditions. However, in the event of a power cut, the units will support from the batteries. I have an auto start generator, and the UPS will keep supply until the generator starts, and if it didn't would do a soft shut down.

It occurs to me that this may not be a ground loop, but a fault in your projector. You can decide this by having only the projector and sub connected to the receiver, and see if you have the hum. During this test use a ground break on the sub, which is also known as a cheater plug. If you have hum then, the projector is a POS.

Yes, there's a turntable grounding terminal. I'll try that with some 16 gauge copper wire straight to the Furman. The potential for a projector issue is noted and I may get a ground lifter to test that theory. I think these are the most promising paths forward, in that order.

 

[Titus]

Progress! I cut a length of 16 gauge speaker wire and ran it from the phono grounding post on the receiver to the Furman power conditioner. I pinched it in the ground hole in the same outlet the sub was plugged into. This reduced the noise to around a third of what it was previously, but it was still there. I wondered if a thicker gauge would improve it further, or if I just need to make a better connection with that wire that's just pinched in between the sub's ground prong and the side wall of the ground plug on the Furman. I could also try running a second ground wire. So I resat the first ground wire to make sure it was making good contact, and ran a second one to the plug where the projector was. I also cut a few inches off of both lengths so they were still long enough to work with but with as little resistance as possible. In the end, the hum has been reduced by 95% or so and I am satisfied with that. It does seem awfully inelegant, all these ground wires. But, the issue seems to be resolved.

Big thanks to TLS Guy who really helped me understand the resistance concept, and confirmed that the phono ground post would work, and gave some assurance that I could safely run a wire right to the ground hole of an outlet.

 

[lovinthehd]

Progress! I cut a length of 16 gauge speaker wire and ran it from the phono grounding post on the receiver to the Furman power conditioner. I pinched it in the ground hole in the same outlet the sub was plugged into. This reduced the noise to around a third of what it was previously, but it was still there. I wondered if a thicker gauge would improve it further, or if I just need to make a better connection with that wire that's just pinched in between the sub's ground prong and the side wall of the ground plug on the Furman. I could also try running a second ground wire. So I resat the first ground wire to make sure it was making good contact, and ran a second one to the plug where the projector was. I also cut a few inches off of both lengths so they were still long enough to work with but with as little resistance as possible. In the end, the hum has been reduced by 95% or so and I am satisfied with that. It does seem awfully inelegant, all these ground wires. But, the issue seems to be resolved.

Big thanks to TLS Guy who really helped me understand the resistance concept, and confirmed that the phono ground post would work, and gave some assurance that I could safely run a wire right to the ground hole of an outlet.

Hopefully you find the magic combo of what you want to use/connect the way you want with the additional grounding scheme, good luck!

 

[Titus]

Someone was telling me very confidently elsewhere that as long as one of the three end components was grounded, then it doesn't matter if I lift the grounds to the others. As long as they are interconnected via the HDMI and RCA. If this is true, it would rationalize a more elegant solution.

I could ground the receiver manually with heavy gauge wire, and break the ground (only via the power cable) to both the sub and projector with cheater plugs like loveinthehd and TLS Guy told me about. The projector is then grounded only via the HDMI to the AVR, and the sub is then grounded only via the RCA to the AVR. That way there's no spiderweb of grounds of various resistances, no looping.

But I've been told adamantly by others to never lift the direct ground of a device as more than a test. And while, yes, the RCA and HDMI cables clearly carry ground, I imagine they do so with a higher resistance than the direct path to the wall and may not be suitable for safety. This same person egged me on, saying it's safe, that I know the solution, but am scared to do it. It's true. I may know just enough to be dangerous but I've never dealt with ground issues before, which is why I'm looking for some confirmation or denial of my theories.

Thoughts on that as an alternate solution?

 

[TLS Guy]

Progress! I cut a length of 16 gauge speaker wire and ran it from the phono grounding post on the receiver to the Furman power conditioner. I pinched it in the ground hole in the same outlet the sub was plugged into. This reduced the noise to around a third of what it was previously, but it was still there. I wondered if a thicker gauge would improve it further, or if I just need to make a better connection with that wire that's just pinched in between the sub's ground prong and the side wall of the ground plug on the Furman. I could also try running a second ground wire. So I resat the first ground wire to make sure it was making good contact, and ran a second one to the plug where the projector was. I also cut a few inches off of both lengths so they were still long enough to work with but with as little resistance as possible. In the end, the hum has been reduced by 95% or so and I am satisfied with that. It does seem awfully inelegant, all these ground wires. But, the issue seems to be resolved.

Big thanks to TLS Guy who really helped me understand the resistance concept, and confirmed that the phono ground post would work, and gave some assurance that I could safely run a wire right to the ground hole of an outlet.

Good, now we can solve this. Order this two pack of cheater plugs. Now run at least 12 G wires between your receiver grounding pin and the screw on these cheater plugs at the projector AND the sub. Also run a 12 G grounding wire between the grounding pin and one of the screws holding the cover plate on the receptacle your receiver is plugged into. That will cure your problem, as you will have created a classic star burst grounding system. There will be one ground were it should be, coupled by low resistance cable to the peripherals. Your system will be dead silent after that, unless your cable/Ethernet system is an issue as well.

There really is not a more elegant solution. A big part of the issue is the grounding plane of your apartment. When I built this home three and a half years ago, I was with the electrician most of the time, to make sure the whole house grounding plane was the way I wanted. Everything is silent here.

So your only option is to have ONLY ONE ground for your whole system. The plan above will achieve that.