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HELP: Have amps on another circuit plugged into my Anthem AVM70 via XLR and causes hum on my subs

xaxxon

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I have a 5.1 system and my surrounds/rears are far in the back so I run 50' (canare cable ) XLR to them and then have an AHB2 amp plugged in to the wall in a different circuit back there. However, when the XLR cables from/to my rear amp is plugged in to my AVM70 (all others are fine) I get the 60hz hum from my subs (connected via RCA - no XLR option on the subs). Unplug the two XLR cables for the surrounds, hum is gone.

I thought XLR made hum not be a thing for stuff like this. Is something defective or do I just have to run a really long extension cord, too? (or wire an outlet in the back on the same circuit)

Thanks.

The XLR cables I'm using are https://www.amazon.com/gp/product/B08YR64JHQ I'm happy to open them up and look at them to see if they're built wrong or something but I'm not sure what I'd be looking for.
 
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HarmonicTHD

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I have a 5.1 system and my surrounds/rears are far in the back so I run 50' (canare cable ) XLR to them and then have an AHB2 amp plugged in to the wall in a different circuit back there. However, when the XLR cables from/to my rear amp is plugged in to my AVM70 (all others are fine) I get the 60hz hum from my subs (connected via RCA - no XLR option on the subs). Unplug the two XLR cables for the surrounds, hum is gone.

I thought XLR made hum not be a thing for stuff like this. Is something defective or do I just have to run a really long extension cord, too? (or wire an outlet in the back on the same circuit)

Thanks.

The XLR cables I'm using are https://www.amazon.com/gp/product/B08YR64JHQ I'm happy to open them up and look at them to see if they're built wrong or something but I'm not sure what I'd be looking for.
Assuming the XLRs are fine. You inadvertently created a ground loop, I would suspect. It is not XLR connection but the RCA which causes trouble. Many subs have a ground lift switch for that reason. If yours has one too, use it and see if that solves the problem.
 

Krusty09

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Hello.

There is a good chance that the circuit breaker that the amp for the rears is not on the same phase in your breaker box. In your breaker find the the two breakers the one for the main stereo and the one for the rear amp and then count from the top of the breaker panel first breaker is A the one beneath that is B then the next is C then it starts over again. If it ends up they are different ones like A and C then it might be your problem . The easy way to check is to take a long extension cord plug into the same outlet the stereo is on and see if the buzz goes away then you know for sure.
Assuming the XLRs are fine. You inadvertently created a ground loop, I would suspect. It is not XLR connection but the RCA which causes trouble. Many subs have a ground lift switch for that reason. If yours has one too, use it and see if that solves the problem.


Hope this helps.
 

DonH56

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XLR cables do not automatically break ground loops; there is still a ground (shield) connection by default. Since the signal does not actually use the ground, you can remove the ground at one end of the XLR cables, and that should break the loop. Professional sounds systems use DI boxes that allow you to do that with a switch, but they are uncommon in home installations. You'd probably have to modify the cables yourself.

I would probably just get an inexpensive RCA ground isolator, e.g. https://www.amazon.com/s?k=ground+l...f=nb_sb_ss_deep-retrain-ln-ops-acceptance_4_9
 
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xaxxon

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I just really don't understand why an XLR connection makes an RCA connection get a hum. The subwoofers are fine unless the amp on the other circuit has its interconnects plugged in.

Also, I noticed my AV processor (AVM70) only has a 2 prong power plug connector. So is it getting the ground for the RCA plugs from the XLR plug?

I'm so confused.

Is this what people are suggesting I use? https://www.sweetwater.com/c812--Ad...fj9qPJ5W-ILjxBBlwb4aAmIhEALw_wcB&gclsrc=aw.ds
 

OldHvyMec

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I usually fix most of the issues by using one or the other of the two hot rails in a 120/220/240vac service. L1 or L2, not both. There is usually
a very slight difference in voltage between the two rails. That difference is the noise you are hearing. You can add all the fancy
explanations you want but that is the problem. The difference between the two circuits and being linked by common ICs.

I have everything on one side or the other in the main. After that some things like Laptop PS and Modems/Routers PS can be noisy.
Our cable company's fix for their modem/router is a ground loop eliminator. LOL Ok! It stopped my noise and I didn't argue.

I had an issue with using 220/240vac power amps and 120vac gear at the same time.
Mcintosh preamp, Cary valves for the mains, Behringer NU12Ks for bass columns and 3-4 Rythmik 370 plate amps. It was a PITA but I have zero noise on
all of my systems. I lifted grounds, used common wires for grounds, ran shielded wire and weaves, used ground loop do-dads and moved breakers from L2 to L1 so
they were all on a common rail. AND the icing on the cake, ROUTING the cables. No cable touches another, EVER. I can hear it when the dog has been back there.
A PC to close to any IC = NOISE!

The NU12Ks are quiet AFTER I fixed everything else noise wise. Magic I guess. :)

All of the sub/bass drivers I use are above 89% efficient @ 8ohms. 92% or > for the mids and as high as 105% for tweeters. They reveal every single flaw
in a systems electrical supply and my routing skills. :)

BTW 101 cable routing is a fine art to learn too.

Regards
 

DonH56

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I just really don't understand why an XLR connection makes an RCA connection get a hum. The subwoofers are fine unless the amp on the other circuit has its interconnects plugged in.

Also, I noticed my AV processor (AVM70) only has a 2 prong power plug connector. So is it getting the ground for the RCA plugs from the XLR plug?

I'm so confused.
The XLR cables are adding another ground path, and that is causing a loop. It is a different ground path than the one the RCA cables use and the net effect is a great big ground loop. XLR allows balanced signals so the XLR path is OK, but the ground through the shield (ground, "third wire") is creating a loop in your system. An XLR cable typically has two signal cables plus an outer shield (ground).

Here is a a thread on ground loops: https://www.audiosciencereview.com/forum/index.php?threads/ground-loops-101.7162/ There are many other references.

That should help. Get one for each XLR cable; you only need to lift the ground at one end. Common practice is to lift the ground at the load (end away from the preamp).
 
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xaxxon

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@DonH56 Is this a deficiency in the avm70 that allows the XLR cables to establish what is the "ground" for the RCA cables? It doesn't seem like an XLR cable should be "allowed" to define the ground on an RCA jack.

It seems like the signal should just be "received" by the amp and interpreted by the amp, not defined by the amp. I thought that was what XLR cables were for. a baseline "null" and two opposite signals. It doesn't matter what the "null" is.

I guess I'm just really confused. I've ordered ground lifters for my surround XLR cables - hopefully that's enough since those are the ones causing the problems.
 

DonH56

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@DonH56 Is this a deficiency in the avm70 that allows the XLR cables to establish what is the "ground" for the RCA cables? It doesn't seem like an XLR cable should be "allowed" to define the ground on an RCA jack.

It seems like the signal should just be "received" by the amp and interpreted by the amp, not defined by the amp. I thought that was what XLR cables were for. a baseline "null" and two opposite signals. It doesn't matter what the "null" is.

I guess I'm just really confused. I've ordered ground lifters for my surround XLR cables - hopefully that's enough since those are the ones causing the problems.
No, it is normal, and not uncommon. The AVR has essentially a single "ground" that all paths share. The cables do not "define" the ground but do connect to different grounds on different components, along with the safety ground from the wall outlet for any components that use that. The XLR balanced signal is inside the cable, surround by an outer ground shield to guard against things like EMI/RFI. That ground is often common with other grounds, like the shield of your RCA cable. Signals need a send and return path, current is a loop, so for an RCA cable the "send" is inside the cable and the return is the ground. Anytime you mix balanced and single-ended signals there is potential for a ground loop, and for that matter whenever you have multiple ground paths no matter the cable. The fact that the extra cables are XLR does not really matter; you probably would have had the same problem or worse if they were RCA.

Look at the post I linked above and notice how ground loops are formed whenever you have multiple cables in a system. It is a system-level problem.

https://www.audiosciencereview.com/forum/index.php?threads/ground-loops-101.7162/

There are many online articles about ground loops as it is a very common problem. It is not the "fault" of any one cable or component, just something that happens and must be dealt with.

HTH - Don
 

Chrispy

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Why not just run high gauge speaker wire to the surrounds and locate your amp on the same circuit as the other gear?
 

sam_adams

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I usually fix most of the issues by using one or the other of the two hot rails in a 120/220/240vac service. L1 or L2, not both. There is usually
a very slight difference in voltage between the two rails. That difference is the noise you are hearing.

Residential AC power delivery in the US is from a split-phase system. Basically a 240 VAC center-tapped transformer that has the neutral line referenced to the center tap of the transformer. The EGC (Equipment Grounding Conductor) or 'safety ground' for all three-wire circuits terminates back at the service entry or breaker panel. It is then connected to either a cold water pipe—or most commonly—to a grounding rod driven into the ground outside the building. The neutral line is bonded to the EGC at one place only—at the breaker panel. All load current flows back to the source—the transformer.

branchcir.png


Any 'ground noise' that is present is caused by small differences in currents that flow through the EGC of the different branch circuits for equipment that has an EGC. For equipment that has no EGC—double-insulated—parasitic capacitance in the power supply will cause unavoidable circulating currents in the chassis of the ungrounded equipment with a voltage potential of up to 70 VAC. These currents will flow through the shields of interconnects when connected to devices with an EGC and induce a voltage in the signal conductor that will present as hum/buzz. Equipment that is on the other "phase" is still referenced to the UPT (Utility Power Transformer) CT and has no effect on ground-loop conditions.

Often posted and quoted materials from Bill Whitlock that should be studied to gain a better understanding of grounding, shielding, and interconnecting balanced and unbalanced systems:

Bill Whitlock - Interconnection of Balanced and Unbalanced Equipment - Jensen AN-003

Bill Whitlock - Hum And Buzz In Unbalanced Interconnect Systems - Jensen AN-004

Jensen Transformers Application Notes

Bill Whitlock - An Overview of Audio System Grounding and Interfacing - Indy-AES-2012

Bill Whitlock - The Myth and Mystery of Analog Signal Interfaces - AES Detroit -2021

Bill Whitlock - Understanding, Finding, And Eliminating Ground Loops - CEDIA Class EST016
 
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xaxxon

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Why not just run high gauge speaker wire to the surrounds and locate your amp on the same circuit as the other gear?
noise and damping. it runs through my attic and there are a bunch of power lines up there too.
 

OldHvyMec

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WOW, sam_adams that was a lot to sort through for a guy like me. Did you agree or not? It really doesn't matter.
I'm not a scientist. I do believe in science though. My problem is keeping my EYES OPEN with exactly the type of
information you just posted. Can you condense whatever it was you were trying to impress me with. I'll still be
impressed, if that helps! :)

I understood almost everything Einstein said. Tesla, not so much. I think it's a left handed thing for me or the fact
I don't give a crap. You made my brain hurt. On the right side mostly, towards the back.
I tried the read it again, my head is throbbing now. I'm kidding, sort of. :cool: Sunglasses help.

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

"noise and damping. it runs through my attic and there are a bunch of power lines up there too."

You need to ROUTE your cables carefully. You just identified the potential problem, now route the cables correctly.
Cable routing 101, is the only way to get rid of noise period. Once you understand that, you will have a quiet system.
A pile of cables will be noisy and it looks like crap too boot.

50% of all the systems I have quieted down was due to cable routing. Cables plugged and dropped or bundled are asking
for noise issues. I never leave cable on the floor either. To hard to clean. I have a rabbit, a dog and a goat. Rabbit hair sucks.
The rabbit is two ears UP for Tube gear too. Great tool his ears.
He actually flops on his back and plays dead If I say Yoko Ono is up next!

Regards
 
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xaxxon

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No, it is normal, and not uncommon. The AVR has essentially a single "ground" that all paths share. The cables do not "define" the ground but do connect to different grounds on different components, along with the safety ground from the wall outlet for any components that use that. The XLR balanced signal is inside the cable, surround by an outer ground shield to guard against things like EMI/RFI. That ground is often common with other grounds, like the shield of your RCA cable. Signals need a send and return path, current is a loop, so for an RCA cable the "send" is inside the cable and the return is the ground. Anytime you mix balanced and single-ended signals there is potential for a ground loop, and for that matter whenever you have multiple ground paths no matter the cable. The fact that the extra cables are XLR does not really matter; you probably would have had the same problem or worse if they were RCA.

Look at the post I linked above and notice how ground loops are formed whenever you have multiple cables in a system. It is a system-level problem.

https://www.audiosciencereview.com/forum/index.php?threads/ground-loops-101.7162/

There are many online articles about ground loops as it is a very common problem. It is not the "fault" of any one cable or component, just something that happens and must be dealt with.

HTH - Don
Thank you so much
 

OldHvyMec

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What effect would the "phase" of a residential AC branch circuit have on the DC voltage produced by any competently designed power supply in any audio device?
Well, I suppose it wouldn't be an issue with your scenario, BUT that hasn't always been my experience, weather by my own choice or someone else's.
I know you CAN get what you pay for or make what you want. I'm way past building equipment with my worn out hands.
If I can maintain what I have I'll be happy. I'm glad I know a couple of good repair people. :)

I like perfect, great, better and all the other things that improve other things. I'm just not sure I can afford it. LOL

Speakers, I have one set left in me. I've never done stand mounts. The prices I see, holy cow, I'll give it a shot.
 
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xaxxon

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Something to think about:

What effect would the "phase" of a residential AC branch circuit have on the DC voltage produced by any competently designed power supply in any audio device?
Really good point.
 

OldHvyMec

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Really good point.
It's a good point but it's not what most people can afford or can do themselves. So there is a work around that works for those that do make mistakes.
The world is full of people making mistakes, 100% to be accurate. I found it's best to understand perfection is not an option, but satisfaction can be.

Respectfully a Retired HD Master Mechanic.
 
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xaxxon

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It's a good point but it's not what most people can afford or can do themselves. So there is a work around that works for those that do make mistakes.
The world is full of people making mistakes, 100% to be accurate. I found it's best to understand perfection is not an option, but satisfaction can be.

Respectfully a Retired HD Master Mechanic.
I'm not actually clear what you're talking about.

How would AC phase affect DC ground differentials in any design?
 
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