?? OK to daisy-chain power conditioners?

[sleepysurf]

I have a challenging "ground loop" issue that has reared it's ugly head. I just took delivery of my "dream" CJ CT-5 preamp (my review will follow, once it's broken in). After initially setting it up, I ended up with a horrible loud background hum, making it impossible to even use, but after hours of trouble-shooting, discovered it's due to a ground loop between my audio gear (all on a dedicated 20A line) and my video gear (all on an adjacent standard 15A line). My previous preamp (Modwright) was apparently immune to this problem. My audio and video gear have multiple interconnections (e.g. my Oppo BDP-83 doubles as my audio transport and DVD/blu-ray player, and I also feed my Denon receiver pre-outs to the CT-5 home theater bypass). The problem is, in order to have enough outlets for all my gear, I need THREE power conditioners-- a 2-outlet Running Springs Duke (for my CJ amp and preamp), and a Belkin PF60 for the rest of my two-channel gear. Both of those are plugged into the 20A dedicated line. All my video gear is fed by a Monster HTS 3500 connected to a 15A outlet. As an experiment, I temporarily plugged my CT-5 into the Belkin (since it draws low power), and then plugged the Monster conditioner into the freed up Duke outlet. That put everything on the same 20A line, and eliminated the hum.

I know it's not ideal to daisy-chain power conditioners, but I need at least 18 outlets for all the electronics in my listening/family room! I suppose I could have an electrician run another 20A line from the same circuit as the first, which (presumably) would prevent a new ground loop. However, at this point, I don't hear (or see) any degradation in my A/V performance, so am thinking to just leave things as is.

What are your thoughts about this? BTW, given the frequency of lightning strikes and power outtages/surges in Tampa, I must have protection for all my gear. I need both the Running Springs and the Belkin for the two-channel side, as only the Belkin offers the Cat5 surge protection needed for my Squeezebox network connection.

 

[Tosh]

Yes, it's fine (and sometimes even helpful). Just watch so you don't overload an upstream outlet. Ask Mike Vans Evers to come over....?

 

[Brad225]

Alan, I would consider adding another 20 amp circuit. Since the electrician has already figured out how to get to there running the first circuit the second should not be as difficult and possibly less cost.
With the considerable investment you have just made in your new preamp and power amp I would think it would be well worth knowing you have plenty of clean power for your system.

Although I'm not the one that has to break the news to Ellen that you now need better wiring to the new equipment. But at least you can let her hear the problem.

 

[sleepysurf]

Well, the plot thickens. I just discovered the hum is BACK when I turn on my HDTV, even though it's now on the same circuit as everything else. That's not a problem for two-channel listening, but becomes a major issue for surround sound TV or video playback. Looks like I'll need to troubleshoot the further, as another dedicated line may NOT prove to be the answer. Bummer!

 

[Beakman]

If you are using any XLR to RCA adapter interconnects, see if the cable crimp on the XLRs are contacting the shield casing. If so, try to remediate that.
Another tack would be to make sure all your RCA cables' shields are only connected to the plug on one end and have all those interconnects "flow" in one direction throughout the entire system.

 

[Speedskater]

Another tack would be to make sure all your RCA cables' shields are only connected to the plug on one end and have all those interconnects "flow" in one direction throughout the entire system.

WOW, that's the exact opposite of what I would do!

Any signal requires two conductors. If you disconnect the shield, the signal will use the power line safety ground (and other chassis and power line paths) as the signal return.

 

[Craig]

Try this as a troubleshooting step. Disconnect the coax cable (as provided by your cable tv/internet service) from the system and see if the humm goes away. If it does then you've confirmed there is a ground source conflict between the cable tv provider's system and your home's grounding system. Very common.

Even though all your devices are plugged into the same outlet and therefore all are plugged into the same ground, your TV cable is not. The coax cable for TV and Internet use their own grounding system which is separate from your home wiring.

JonFo once recommended a ground loop eliminator device that he uses in his system. It's supposed to be very effective. I'm not sure exactly what that was or where to get it.

 

[Cherian]

I had the same issue with my systems. At the time I had a 2 channel system and a 5.1 channel system. However, both systems used the same sub. I had the 5.1 system going to the LFE input of the Depth and the L and R line level inputs from my 2 channel pre amp going to the L and R in of the depth. As soon as I switched on the system the humm was out of control. The only fix I could find was to isolate the two systems. No RCA cables between the 2 systems. Both systems are still plugged into the same Power conditioner. I now have Subs for 2 channel and another sub for 5.1.

 

[Brad225]

Try this as a troubleshooting step. Disconnect the coax cable (as provided by your cable tv/internet service) from the system and see if the humm goes away. If it does then you've confirmed there is a ground source conflict between the cable tv provider's system and your home's grounding system. Very common.

Even though all your devices are plugged into the same outlet and therefore all are plugged into the same ground, your TV cable is not. The coax cable for TV and Internet use their own grounding system which is separate from your home wiring.

JonFo once recommended a ground loop eliminator device that he uses in his system. It's supposed to be very effective. I'm not sure exactly what that was or where to get it.

Craig is correct. This is often the problem you are having. I have used this type of grounding block with antenna's. Would it work for coaxial of TV.



Thinking about it Alan has Fios fiber optic coming to the house. Could it be a grounding problem in the OLN box on the house. The only metal in the fiber optic cable is just enough to be able to locate it underground. There is no grounding to the house with the cable according to our Fios tech.

 

[JMAUSGP]

You know, this is one of those threads that makes you go HMMMMM.

O'crap now I have a HMMMM in my system.

If it comes to it, you can always switch to Dish or DirectTV, HMMMMM,
no it's still there.

 

[Craig]

Craig is correct. This is often the problem you are having. I have used this type of grounding block with antenna's. Would it work for coaxial of TV.

Thinking about it Alan has Fios fiber optic coming to the house. Could it be a grounding problem in the OLN box on the house. The only metal in the fiber optic cable is just enough to be able to locate it underground. There is no grounding to the house with the cable according to our Fios tech.

Is there no grounding to the house because they use their own ground system separate from the house? Let me disclaim that I'm no electrician and this is just my theory on ground loop.

Only the signal to the house is fiber optic. Once it gets to the house it's converted to electrical coax but suspect that it's grounded at that point. Fiber optic comes to the house, then goes into a complex electronic box attached to the house which converts the signal to a coax cable. That coax cable comes out of the wall into a router which outputs to another coax cable into the DVR/Cable box. At that point it outputs via HDMI, RGB, SPDIF, Analog or coax cable which then goes into your TV and/or receiver. In addition to all that, this same coax system is connected to your internet router. So there are plenty of sources for a ground loop problem or otherwise induced hum in a system that is connected to cable TV/Internet.

 

[Brad225]

Is there no grounding to the house because they use their own ground system separate from the house? Let me disclaim that I'm no electrician and this is just my theory on ground loop.

Only the signal to the house is fiber optic. Once it gets to the house it's converted to electrical coax but suspect that it's grounded at that point. Fiber optic comes to the house, then goes into a complex electronic box attached to the house which converts the signal to a coax cable. That coax cable comes out of the wall into a router which outputs to another coax cable into the DVR/Cable box. At that point it outputs via HDMI, RGB, SPDIF, Analog or coax cable which then goes into your TV and/or receiver. In addition to all that, this same coax system is connected to your internet router. So there are plenty of sources for a ground loop problem or otherwise induced hum in a system that is connected to cable TV/Internet.

My thought was, (although I didn't explain it that way) that the grounding for the circuitry of the OLN box may need to be grounded at the same point the rest of the system is. If there are multiple grounds this could be the source.

I just looked at our OLN box and it has its own ground and it is connected with a split bolt to the main ground wire for the house electrical system.

It is possible that depending on where Verizon located the OLN box connecting to that same ground as the electrical system may be difficult. Unless you can achieve this the ground loop eliminator device Craig mentioned may be your solution.

I believe it was in Jim Smith's "Getting Better Sound" he talked about grounding situations. He referred to multiple grounds working in areas that were less densely populated than in city's or tightly built subdivisions. I could only draw from that the grounding current or signal could interact with each other in the ground.

 

[Beakman]

WOW, that's the exact opposite of what I would do!

Any signal requires two conductors. If you disconnect the shield, the signal will use the power line safety ground (and other chassis and power line paths) as the signal return.

Yea, I'm getting a little mixed up here. Never mind the second half, but the isolation of the body's cable crimp does wonders on the xlr-rca cables.

 

[Craig]

If you are using any XLR to RCA adapter interconnects, see if the cable crimp on the XLRs are contacting the shield casing. If so, try to remediate that.
Another tack would be to make sure all your RCA cables' shields are only connected to the plug on one end and have all those interconnects "flow" in one direction throughout the entire system.

I think that's the reason why some manufacturers put directional arrows on RCA cables. The shielding is connected at one end and isolated at the other. Therefore, I pay attention to the cable direction when it's labeled as such. Certainly can't hurt.

 

[Speedskater]

Yea, I'm getting a little mixed up here. Never mind the second half, but the isolation of the body's cable crimp does wonders on the xlr-rca cables.

Maybe we are talking about too many things at the same time.

a) RCA Phono to RCA Phono co-ax: always connect the shield.
b) RCA Phono to RCA Phono 2 conductor plus shield: the shied may be connected at only one end. (but I prefer co-ax).
c) 1/4inch RCA Phone (note the "e") similar wiring to an XLR connector.
d) XLR connector have 4 contacts:
#1 Shield/Ground connects to the unit's chassis - cable may be connected at only one end.
#2 and #3 audio signal conductors.
Shell/Case - typically not connected.

XLR to Phono adapters - these are special animals and some wiring methods may work with some units but not others.

 

[sleepysurf]

I appreciate all the advice thus far.

FYI, I'm using only RCA connections, with Blue Jeans shielded (Belden) cables. Never had the noise issue with my Modwright preamp, so it's clearly something unique to the CT-5. The CT-5 owners manual specifically mentions it's design uses minimal RF shielding (ostensibly to improve fidelity) but at the risk of possible increased RFI.

Of note, I disconnected the cable coax, with no improvement, so the problem is NOT a ground loop from that source. There is minimal hum with the TV off, and moderate hum with it on, so it might be the TV's power supply creating RFI +/- additional RFI from one of the numerous other electronic/network devices in my family/listening room (Sprint AIRave home cell phone extender, or network switch with ethernet cables to my Receiver, Oppo, and Squeezebox).

I'll need to isolate every device individually to try and pinpoint the culprit, but won't be able to do that till next week.

 

[Speedskater]

What I do when trying to solve a problem, is simplify it as much as possible.
Start with only one power conditioner (the one with the most outlets) disconnect everything (power, audio, video and other wires).
Connect the speaker wires and plug in the amp AC - does it hum?
If not connect the pre-amp - does it hum?
If not connect one unit or one external communications cable at a time until it does hum.
Then when it hums, the problem is at one end or the other of the last connection.

 

[sleepysurf]

Yep, that's my plan! Also, I hope to enlist fellow MLOC member Craig and his special "noise sniffing device" to help sort it out. I think he's also training his dog Kona to sniff out RFI!

 

[sleepysurf]

I've spent 8+ hrs so far troubleshooting this. I've tried every conceivable permutation of disconnecting/rearranging cables, power conditioners- even totally disconnecting all my cable/video/non-audio gear. I was able to reduce the "hum" by 50% by daisy-chaining everything off my (single) 20A dedicated line, but it's still clearly audible from my listening position. None of my video gear or ethernet/network devices is responsible. However, ANY audio input to the CT5 (Oppo player, Benchmark, Squeezebox, or Denon) causes the "hum" to varying degrees. Some folks have suggested employing isolation transformers or other "humbusting" devices, but I really don't have space for additional components (and cables), and for the $$$ I spent on the CT5, I really shouldn't have to do that! Next step will be to call C-J and see what they have to say.

 

[Spike]

Here's a long shot

Try disconnecting power cords from your cable/video/non-audio devices just to rule out the possibility that these devices are contaminating on the AC power side. Go down to the minimum configuration of 1 source, CJ combo and your Summits to see whether the hum still exist, and go from there.

Spike