Need help with ground loop hum.

[KEW]

I set up my Rythmik E15HP and am frustrated to discover ground loop hum.
I'm no electrical engineer, but I am very good at trial and error!
Here is what I have done/found thus far:

Routed subwoofer cord completely clear of power cords - Hum
Unplugged everything except receiver and sub - Hum
Plugged sub into different circuit - Hum
Use Belkin PF60 power conditioner - Hum
Switch subwoofer to off position - No Hum
Unplug subwoofer line from sub - No Hum

House is 10 years old. Passed routine home inspection "3 light plug" inspection of wiring.
Hum is also coming from receiver/main speakers when it happens, but clearly caused by presence of new sub.

What is next?

Thanks!

 

[tcarcio]

If you have a 3 prong to 2 prong like this http://www.googleadservices.com/pagead/aclk?sa=L&ai=CkY1kg1N3VJvkM4qKpgOuz4IojcPiuQW1x9iYzAGNg5-_6QEIBhACKAhgyZaEiYSk7A-gAaGSqP8DyAEHqgQmT9AlicCCBS2NSpODaa3k3VxxzXW4TqPPc68zLJK3VwNsw0vn_S7ABQWIBgGgBiaAB8ftV5AHA6gHpr4b4BLO3fX59YH0waAB&ohost=www.google.com&cid=5GjBc_dvb74GsvryKrSMIJouJealDopHhDiBU7V2qpmltS0&sig=AOD64_2oaUDTs2ACYOQAMIQ4rX7-42AM9g&ctype=5&rct=j&q=&ved=0CLUBEPQO&adurl=http://www.smarthome.com/avb-cable-u-09-3-prong-to-2-prong-grounding-adapter-gray.html?src=Froogle Put it at the end of the subwoofer power cord and then plug it into the pf-60. Don't just plug it into the wall because it won't be grounded. I did this and it worked for me.

 

[Adam]

Hi Kurt,

Your description took away my go-to suggestions - you certainly know where to start. Unless your PF60 has an issue with its internal grounding, plugging both units into it should have insured that they were on the same ground. Perhaps the Rythmik line input or amp isn't properly grounded internally? Just to troubleshoot, have your tried both line level inputs and/or the speaker level inputs?

 

[KEW]

Thanks for the help! Traveling for T'giving and turned into a puppy rescue mission.
May be a day or two before I get back to this.

 

[Rickster71]

I set up my Rythmik E15HP and am frustrated to discover ground loop hum.
Routed subwoofer cord completely clear of power cords - Hum. That would be a different source of hum, not ground loop.
Unplugged everything except receiver and sub - Hum
Plugged sub into different circuit - Hum. The key here is to get everything onto the same circuit. If you have cable TV, disconnect the coax.
Use Belkin PF60 power conditioner - Hum. Try plugging everything into this conditioner. (This put everything at same ground potential)
Switch subwoofer to off position - No Hum. Does sub and receiver have 2 prong or 3 prong cords?
Unplug subwoofer line from sub - No Hum. When you say 'Line,' do you mean AC power cord or low voltage input?

House is 10 years old. Passed routine home inspection "3 light plug" inspection of wiring.
Hum is also coming from receiver/main speakers when it happens, but clearly caused by presence of new sub.

What is next?

Thanks!

The key to remember is that it's all about different Ground Potentials.
Does all of your equipment have 2 prong plugs or a mix of 2 and 3?
Do it one step at a time so you can have an accurate process of elimination.
First, if you have cable. Disconnect the coax and see if that makes a difference.
I posted my suggestions right next to the steps you posted.

 

[BoredSysAdmin]

one more suggestion if else fails - get a A/C isolating & filtering surge protector like this one: http://www.tripplite.com/audio-video-surge-protector-isobar-6-outlets-6-ft-cord-3330-joules-coax-tel-modem~AVBAR6/

 

[macddmac]

Swap out sub cable?

 

[TLS Guy]

When ever you have more than one piece of equipment with a three pin grounded plug you will always be prone to this issue, what ever you do.

Personally I would just break the ground on the sub with the 3 to 2 adapter. The sub will still be grounded. If you are worried about a shock, just make sure you unplug your sub before disconnecting the sub signal cable.

In my view domestic equipment should not have three pin plugs, but two pin double insulated systems.

If you really want to avoid the hum, then you will have to link your two AC outlets with copper wire like this.

To avoid having to break grounds, the grounding of my system had to be painstakingly thought out, constructed and tested. No measurable resistance between a ground can be tolerated.

The wire in the AC cords has too high a resistance, so you have to bond the chassis of all equipment to the copper ground plane and the rack.

Recently I had a slight buzz. Despite really wrenching down all the grounds, I had just one connection increase resistance slightly, and it put a slight buzz though out the system. Finding the culprit was a time consuming task.

The ground system I use is one that was published in a paper by the Canadian Broadcasting System.

If you have the problem you are experiencing, the easiest solution is to make sure you have only one piece of equipment grounded. Preferably that should be the receiver, or in the case of a pre/pro power amp system, just the pre/pro.

Still problems will arise with cable connections and Internet connections.

In my case tying the cable system, my FM aerial, the phone/Internet grounds, and house ground was quite a task, but crucial.

My only other observation is that as system complexity increases the more challenging these issues become.

 

[KEW]

Well, I finally had a full day open to really dig into this.

First thing I did was hook up my (ungrounded) SVS-SB12plus, it now had the hum as well. Something inadvertent must have happened when I was hooking up the Rythmik to start the hum!

Pulled everything away from the wall, disconnected every wire (speakers, inputs, etc.) from back of receiver except AC and sub cable - no hum.
Gradually added connections keeping a list of what was added and test result. Now everything is plugged back in and...no hum! Maybe remade a connection that was not whole?
I hate it when stuff like this happens - I must have changed something, but don't know what or if it will return!

For now, there's nothing to do but sit back and enjoy!!!

Thanks for the help, I would likely have procrastinated this another month or more without the assurance of your collective experience!

 

[TLS Guy]

Well congratulations. The fact is that all it takes to get hum is just one RCA plug not properly pushed in, or making poor contact from oxidation to give the problem.

Trust me, I have been there many times. These issues can take hours to sort out. I have just been though one. The culprit turned out to be the aerial connection on the back of the pre/pro not reefed down hard enough. A quarter turn with a wrench and hum gone!

Confronted by this it can be anyone!

 

[djreef]

OMG, TLS.

Someone needs to simplify! The sight of that made the hair on my arms stand up.

You ever thought of going minimalist?

DJ

 

[slipperybidness]

OMG, TLS.

Someone needs to simplify! The sight of that made the hair on my arms stand up.

You ever thought of going minimalist?

DJ

LOL!

TLS probably considers that as his minimalist setup

 

[Irvrobinson]

This is an old thread, but relevant because I've noticed I have a very annoying 60Hz hum on my HT system. It's probably been there since Day 1 and I'm just recently detecting it, but you know how humans are, once trained the subtle becomes obvious.

Everything is plugged into a Tripplite surge protector, and only one component has a three-pronged power plug, the ATI amp. With the exception of the pre-pro outputs to the amp, which are single-ended BJC interconnects, the rest of the system is interconnected with HDMI. The system is moderately complicated, including an Xfinity cable box, a Sony BD player, Roku, Apple TV, cable modem, a Netgear wireless router, and a partridge in a pear tree. I suspect contributors to the issue are the hyper-sensitive Klipsch speakers, as when I swapped in a pair of inefficient JBL mini-monitors the hum was nearly inaudible.

I tried plugging the amp into an isolation transformer - no difference.
I put a Jensen transformer on the CATV coax - no difference. ($70 down the drain.)
I tested all interconnect connections - no difference.

The only real hints I found is that when I switch inputs on the Outlaw pre-pro it mutes the outputs, and the hum goes away. That probably means the hum is in the pre-pro or earlier in the signal path. When I did that test the BD player and the Xfinity box were turned off. Switching the input selection on the pre-pro makes no difference; the hum is present on all selections, including the internal FM tuner.

I'd pull my hair out, if I had any.

 

[djreef]

My bet - Xfinity cable box. Try disconnecting everything from the box, then the router, then the modem. All of these devices are notorious for allowing stray noise into the system.

DJ

 

[KEW]

DJ probably has it. I remember reading several instances where the cable box was the guilty party.
Otherwise, I'd suggest simply disconnecting each source (and TV) one at a time and see when the hum disappears to identify the culprit.

 

[Irvrobinson]

My bet - Xfinity cable box. Try disconnecting everything from the box, then the router, then the modem. All of these devices are notorious for allowing stray noise into the system.

DJ

I'll try that today and let you know if your bet was correct. But if you're right that means the cable box is injecting power supply noise into the HDMI ground path. The designers couldn't be that stupid... We'll see.

 

[Irvrobinson]

I'd suggest simply disconnecting each source (and TV) one at a time and see when the hum disappears to identify the culprit.

Yeah, I know, I've just been avoiding that because in my cabinet that will be a very annoying process.

 

[TLS Guy]

I agree, the most likely source of the noise is from your cable Internet system.

First of all disconnect your cable system and Internet cables from your system.

If the hum goes that is your problem.

If it does not then there is a resistance to ground someplace else.

Cable company and Direct TV installers know nothing usually, and next to nothing if you are lucky. The latter means they have heard of the problem. The upshot is that their installations are pretty much universally improper. Every time one of these guys turn up I have a hum and I'm redoing at least part of their work.

The big point about these systems is that must enter close to the panel and the cable/satellite grounds be bonded to the house ground with stout copper at entry.

Last time was interesting. When the Genie system was installed for some reason he put on a new grounding block. First step was improvement after I got the paint off the grounding screws.

The next issue was that there was slight hum if the Direct TV Genie unit was connected via HDMI cable to the pre/pro. It turned out the main unit must have an internal ground loop, as I had to remove the shield ground from one end of the HDMI cable so only the grounding pin had a unit to unit ground connection. Total silence after that.

These issues are complicated. Units can have internal ground plane issues which are especially troublesome. This is where buying good stuff helps. Unfortunately we do not have a say in satellite/cable boxes.

The other issue is that now a lot of HDMI cables are pretty puny. It does not take much of a resistance between grounds to have an issue. Some of these smaller cables have too much resistance in the shield and ground wires. Hefty cables are more likely to be free of this than the skinny ones.

It always pays to at least look at the home grounding system. I like at least three large grounding rods, as close as possible to the panel. Then use very heavy gauge copper from panel to rods, and make sure the house neutrals and ground are soundly bonded with stout copper.
Make sure the rods are in an area that gets plenty of rain. If not you need to water them like plants. The soil is sandy here and I do have to water my rods in dry spells.

Lastly your system is may be getting complex enough you might have to consider constructing a star cluster grounding system like I had to do.

 

[Irvrobinson]

My bet - Xfinity cable box. Try disconnecting everything from the box, then the router, then the modem. All of these devices are notorious for allowing stray noise into the system.

Unfortunately, DJ, your guess wasn't correct. Completely disconnecting the Xfinity box didn't change the hum at all.

Now I have to do the unplug-one-input-at-a-time method, which will be a PITA. My suspicion is that the problem is rooted in the Outlaw 975 pre-pro.

 

[Irvrobinson]

Just did a Google search... the Outlaw 975 and 60Hz hum is the subject of many threads on several forums. Ugh. Of course, I also did a search on Marantz pre-pros, and got some similar results, though fewer. Hmmm.