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post #1 of 29 Old 10-20-2014, 07:13 PM - Thread Starter
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Arrgh! Help with ground loop

Please help me correct, or at least, diagnose, a ground loop problem.

Basically, any time I hook an amp downstream of an AVR I get hum. The amp can be on the same outlet, or on a different circuit.

Amp by itself, no noise.
AVR by itself, no noise. (That's what I'm currently running, but 7.0 isn't very satisfying when you have four subs in the room...)
AVR + amp, noise.

That applies to both my mains amp (an ATI AT2007) on the same circuit, and my multisub amp (an ElectroVoice CPS8.5) on a dedicated 20A circuit I had installed in the basement.

Cable hooked up/not: no difference
Combination of stuff hooked up to the AVR: no difference
Extension cord run up to the basement to run the AVR off the 20A subwoofer circuit: noise

I've swapped out all power cords, used multiple RCA interconnects, etc. Same result.

I've tried multiple amps downstream of the AVR (Parasound Zamp v3, Pro-Ject Amp Box SE, Sonance 875 Mk. II), with the same result. I've also tried two AVRs (an Anthem MRX300 and Sherwood R972), same result.

Here is a setup that did not have noise: AppleTV3 and Comcast cable box as sources both connected by HDMI, Sony TV as DAC/preamp, 3.5mm to RCA analog cable on the headphone jack, Parasound Zamp v3, Soundfield Audio Monitor 1 speakers with the plate amps driving their woofers pulling signal from their high-level inputs.

And another: MacBook powering Meridian Explorer, connected via 3.5mm to RCA analog cable to Pro-Ject Amp Box SE.

I also measured the outlet with a DVM. Here's what I saw:
Hot-neutral: 118V-121V
Neutral-ground: low (tenths to maybe 2V depending on how I jab the probe)
Hot-ground: 118V-121V (same as hot-neutral, basically)

I got the same results on other outlets around the room and in the next room.

Thoughts? At this point I expect I'll have to call an electrician, because I've ruled out equipment issues. But if there's something else I can do, or some direction I could point the electrician that would be very helpful.

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post #2 of 29 Old 10-20-2014, 08:41 PM
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Is the humming equipment powered with a 2-wire power plug?

Look close, I have a disc player that looks like it has 3 wires (the IEC style removable power cord) , but it actually has only two connectors going into the equipment.

I'll be back later...


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post #3 of 29 Old 10-20-2014, 09:34 PM - Thread Starter
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Quote:
Originally Posted by RayDunzl View Post
Is the humming equipment powered with a 2-wire power plug?

Look close, I have a disc player that looks like it has 3 wires (the IEC style removable power cord) , but it actually has only two connectors going into the equipment.
Both AVR's have 2-prong IEC sockets. Both amps have 3-prong IEC sockets.

That's a detail I meant to include above, sorry.

Also, the signal run for the mains is unbalanced (RCA) with no current possibility of running balanced. The signal run for the multisubs comes into my processor (miniDSP 8x8, right above the mains amp in the living room) as unbalanced, but the output to the power amp (in the basement) is balanced.

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post #4 of 29 Old 10-20-2014, 10:03 PM
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Try running an Earth to the AVR...

Find a screw that is in continuity with the ground of the audio jacks, and attach Earth.

Just for grins.

I'll be back later...


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post #5 of 29 Old 10-21-2014, 05:09 AM
 
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post #6 of 29 Old 10-21-2014, 08:09 AM
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Quote:
Originally Posted by RayDunzl View Post
Try running an Earth to the AVR...

Find a screw that is in continuity with the ground of the audio jacks, and attach Earth.

Just for grins.
This is good advice. I use 30" test leads with alligator clips on each end. They are fairly inexpensive and can be purchased in multi-packs from Radio Shack. These are always handy to have on hand when attempting to track down ground loops or grounding issues. I have a Sub with 2-prong power cord (no earth ground) that caused a HUM. In the photo here I simply attached the green test lead from the Sub Amp chassis to the Earth Ground on my power strip. Sub is dead quiet now.

In my case this allowed any Electrical Noise at the Sub chassis to drain directly to Earth Ground. Without the Earth Ground the Electrical Noise was traveling back to my Amp to it's Earth Ground via the Speaker Level connection being used causing the HUM.

issues.
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post #7 of 29 Old 10-21-2014, 10:14 AM - Thread Starter
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As an aside, one of the reasons this problem is so annoying to me (leaving aside that it's there and it's taking time to solve and hasn't yet been solved) is that I literally haven't changed a single piece of gear. I just changed the address at which I plug it in. In my old loft there were no issues at all. Which makes me suspect that something in the house is miswired.

Quote:
Originally Posted by RayDunzl View Post
Try running an Earth to the AVR...

Find a screw that is in continuity with the ground of the audio jacks, and attach Earth.

Just for grins.
Thanks for the idea! I'll test the screws on the back for continuity with the RCA shields (that's what you mean by "ground of the audio jacks,' right?) and try that.

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Originally Posted by D-Shark View Post
This is good advice. I use 30" test leads with alligator clips on each end. They are fairly inexpensive and can be purchased in multi-packs from Radio Shack. These are always handy to have on hand when attempting to track down ground loops or grounding issues. I have a Sub with 2-prong power cord (no earth ground) that caused a HUM. In the photo here I simply attached the green test lead from the Sub Amp chassis to the Earth Ground on my power strip. Sub is dead quiet now.
Neat idea. Thanks, I'll try it! There's a Rat Shack on the way home from work, so I'll stop by today. One thing interesting here is when I was running speaker-level to plate amps on monitors I didn't have an issue. Then I think the TV and Parasound Zamp were 3-prong and the plate amps were 2-prong.

I see you clipped one end to a coax on your power strip. I can't quite tell what on the sub plate you clipped to.

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post #8 of 29 Old 10-21-2014, 01:32 PM
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If you are going to Radio Shack then pick up an Outlet Tester something like this:

http://www.amazon.com/GE-3-Wire-Rece...+outlet+tester

This will tell you if all your electrical outlets are wired properly and the same (Hot, Neutral, Earth Ground).

On my Sub I simply clipped one end of the test lead to one of the metal toggle switches which has continuity to the Sub Amp chassis (I could have clipped anywhere on the Sub Amp Chassis, the toggle just happened to be easy). The Chassis of my power strip is tied to my homes Earth Ground via the power strip 3-prong cord. I clipped to the unused Coax simply because it was convenient and tied to the power cord Earth Ground.

Ground Loops come in all different flavors. If you are using two separate power circuits to power you system, One Circuit might have an Earth Ground and the other Circuit might not (the outlet tester should catch this). Polarity of the Hot & Neutral my be different on different power Circuits (the outlet tester should catch this).
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post #9 of 29 Old 10-21-2014, 08:34 PM - Thread Starter
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Quote:
Originally Posted by D-Shark View Post
If you are going to Radio Shack
Ended up billing until after they were closed. Boo. Going tomorrow during lunch to make sure I get there...

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Originally Posted by D-Shark View Post
Ground Loops come in all different flavors. If you are using two separate power circuits to power you system, One Circuit might have an Earth Ground and the other Circuit might not (the outlet tester should catch this). Polarity of the Hot & Neutral my be different on different power Circuits (the outlet tester should catch this).
Here, I have the hum when the gear is on the same circuit, i.e. when just mains amp and AVR are connected, or when I ran an extension cord up from the basement to put the AVR on the 20A sub amp circuit.

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post #10 of 29 Old 10-22-2014, 01:41 PM
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DS-21,

It's good that you tried powering the AVR, Amp & Mains from each dedicated 120 Volt circuit. Just to rule out the unlikely possibility that both 120 Volt circuits are wired incorrectly (causing the Hum) check each Circuit with the Outlet tester I recommended earlier. This should help to rule out any wiring issues between your wall outlet and home circuit breaker box.

Since you have two separate 120 Volt circuits feeding different components within your system it is important that the Voltage Potential between the two Earth Grounds be 00.00 Volts AC. Set your Digital Volt Meter to a range of 0 to 20 Volts AC. Touch one Meter lead to the Earth Ground of 120 Volt Circuit #1 and the other Meter lead to the Earth Ground of 120 Volt Circuit #2 and your reading should be 00.00 Volts AC.

Next remove any interconnects or other cables connected between your AVR & Amp. Power up your AVR & Amp and I assume you have no Hum at this point Correct? Now with your Digital Volt Meter set to a range of 0 to 20 Volts AC touch one Meter lead to a Chassis screw on your Amp and the other Meter lead to a Chassis screw on your AVR. If both components are properly grounded to Earth Ground you should get 00.00 Volts AC. My bet is you are going to read a couple Volts or more because as you stated your AVR has a two prong power cord and is not connected to Earth Ground. If there is a Voltage Potential between the AVR & Amp then current will flow between the two devices via interconnecting audio cables causing the Hum.

Clip one of the Radio Shack test leads from a Chassis screw on the AVR to Earth Ground at your power strip or wall outlet. At this point if you still have a Voltage Potential between the AVR & Amp then clip a second test lead from a Chassis screw on the Amp to the same Earth Ground as the AVR. Doing one or both of these Should eliminate any Voltage Potential between the AVR Chassis and Amp Chassis and eliminate the Hum once re-connecting cables between the two devices.

Checking all of the above should solve the problem or at least provide added information that will allow us to proceed further. Good Luck.
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post #11 of 29 Old 10-22-2014, 07:02 PM - Thread Starter
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Update: went to RS today. They didn't have the outlet tester in stock, but I picked up the alligator leads one of their isolation transformers. I ordered the outlet tester from Amazon and with Prime I should have it Friday at the latest.

In rooting around for another IEC power cord I also found a cheater plug I had bought when I first hooked everything up, but then promptly lost.

The isolation transformer, if anything, made things worse. Admittedly, I only tried it with the R972. Would've been nice to find a legitimate solution, but on the plus side that little thing is very ugly. I built a nice 8 channel RCA snake cut to size with ends color-coded per CEA-863B. And the Rat Shack part has male RCAs on both ends, while not being long enough to reach across my equipment rack from AVR to amp. So part of me is glad the transformers

The cheater plug worked like a charm on the mains amp. Deep black noise floor with all sources connected to the AVR. (Except for my TT, which I haven't unpacked yet.) I haven't tried the cheater plug on the sub amp yet.

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Originally Posted by D-Shark View Post
Since you have two separate 120 Volt circuits feeding different components within your system it is important that the Voltage Potential between the two Earth Grounds be 00.00 Volts AC. Set your Digital Volt Meter to a range of 0 to 20 Volts AC. Touch one Meter lead to the Earth Ground of 120 Volt Circuit #1 and the other Meter lead to the Earth Ground of 120 Volt Circuit #2 and your reading should be 00.00 Volts AC.
Will do, along with the steps you mentioned that I didn't quote, and report back. Who knew a 100' extension cord I bought so I could blow/vacuum leaves would come in so handy!

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Next remove any interconnects or other cables connected between your AVR & Amp. Power up your AVR & Amp and I assume you have no Hum at this point Correct?
Right. Either one independently, I'm good. Hook up any amp (mains or sub) to an RCA plug on the AVR, and noise. And now, apparently, plug the ATI AT2007 into a cheater plug temporarily, and I'm good too.

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post #12 of 29 Old 10-23-2014, 07:11 AM
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Right. Either one independently, I'm good. Hook up any amp (mains or sub) to an RCA plug on the AVR, and noise. And now, apparently, plug the ATI AT2007 into a cheater plug temporarily, and I'm good too.
As suspected it sounds as though unwanted AC current (noise) is flowing from your AVR Chassis through interconnects to the Amp Chassis and to Earth Ground via the Amp's 3-prong power cord. When you install a 2-prong Cheater Plug at the Amp power Cord you are lifting the Amp's Earth Ground which interrupts the flow of current (electrons) to Earth Ground from your AVR, thus no Hum.

Go back to the original recommendation. Clip one end of a test lead to the AVR Chassis, Clip the other end of the test lead to the same Earth Ground as the Amp and ditch the cheater plug on the Amp. AC current (noise) that was flowing from your AVR across interconnects to your Amp should now take path of least resistance through the test lead directly to Earth Ground eliminating you Hum.
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post #13 of 29 Old 10-23-2014, 01:40 PM
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if everything else fails try this toy:

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

it is the only thing that worked for my studio set up helping with both ground loop and motherboard RFI issues.
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post #14 of 29 Old 10-23-2014, 02:20 PM
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Quote:
Originally Posted by DS-21 View Post
Cable hooked up/not: no difference.
Did you sever the actual incoming RF feed to the cable box? That outer shield is quite often the alternate ground potential which causes the overall system's ground loop.

In A/V reproduction accuracy, there IS no concept of "accounting for personal taste/preference". As art consumers we don't "pick" the level of bass, nor the tint/brightness of a scene's sky, any more than we pick the ending of a novel or Mona Lisa's type of smile. "High fidelity" means "high truthfulness", faithful to the original artist's intent: an unmodified, neutral, accurate copy of the original master, ideally being exact and with no discernable alterations, aka "transparency".
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post #15 of 29 Old 10-23-2014, 07:12 PM - Thread Starter
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Update: outlet tester came in today, showed outlets are good. Going to do the lead thing tomorrow - didn't get it in before the Broncos-Chargers game today.

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Originally Posted by DS-21 View Post
The cheater plug worked like a charm on the mains amp. Deep black noise floor with all sources connected to the AVR.
Well, sort of. Some hum did come back over time. Then I power-cycled the amp and it went away. Came back the next day, though.

Regardless, a cheater plug is not (to me, at least) a permanent solution, just a diagnostic tool.

Quote:
Originally Posted by zheka View Post
if everything else fails try this toy:

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

it is the only thing that worked for my studio set up helping with both ground loop and motherboard RFI issues.
But that's only rated for 6A. My amps can pull a lot more than that. The ATI AT2007 is rated 200Wx7 all channels driven, and the ElectroVoice CPS8.5 is rated at 1kWx4 in the configuration I'm using it.

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Originally Posted by m. zillch View Post
Did you sever the actual incoming RF feed to the cable box? That outer shield is quite often the alternate ground potential which causes the overall system's ground loop.
Yes, but the loop happens when nothing's plugged in except for the AVR and my mains amp with an unbalanced connection, or an AVR to a miniDSP with an unbalanced line and miniDSP to my sub amp with a balanced snake. The cable was where I looked first, but alas that wasn't it.

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post #16 of 29 Old 10-23-2014, 08:34 PM
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Are you using a star grounding topology for the entire setup ? Meaning every single thing, even the distant TV, plugs to the same power strip. If you do this and also disconnect the cable company RF feed I'll bet you the problem will be gone.

In A/V reproduction accuracy, there IS no concept of "accounting for personal taste/preference". As art consumers we don't "pick" the level of bass, nor the tint/brightness of a scene's sky, any more than we pick the ending of a novel or Mona Lisa's type of smile. "High fidelity" means "high truthfulness", faithful to the original artist's intent: an unmodified, neutral, accurate copy of the original master, ideally being exact and with no discernable alterations, aka "transparency".
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post #17 of 29 Old 10-23-2014, 09:35 PM - Thread Starter
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Originally Posted by m. zillch View Post
Are you using a star grounding topology for the entire setup ?
Of course not. The subwoofer amp is on a separate dedicated 20A circuit in the basement, for starters. So in my setup that is simply impossible.

However, that also doesn't seem to matter. With nothing else plugged in (that means everything including the cable box physically unplugged from the wall and the AVR, and the coax unplugged at the splitter between cable modem and TV box) I get hum when I hook either of my AVRs(Anthem MRX300 or Sherwood R972) up to an amplifier plugged into the same outlet. That happens on the living room circuit. It also happens when I run an extension cord up from the 20A circuit in the basement.

But after a new discovery today I'm thinking it might be a deeper electrical problem. I noticed today that my cable drops out when the ATI AT2007 turns on. Now, ever since the wires were run I've also had cable drop-outs when the HVAC fans comes to life, but I had pinned that as a cable routing issue (coax is routed above the furnace; didn't have the issue when I used one that wasn't routed over the furnace).

Surprisingly to me at least, I monitored the outlet and did not register a voltage drop as the amp's relays kicked on.

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Last edited by DS-21; 10-23-2014 at 09:38 PM.
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post #18 of 29 Old 10-23-2014, 10:31 PM
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Quote:
Originally Posted by DS-21 View Post
With nothing else plugged in (that means everything including the cable box physically unplugged from the wall and the AVR, and the coax unplugged at the splitter between cable modem and TV box) I get hum when I hook either of my AVRs(Anthem MRX300 or Sherwood R972) up to an amplifier plugged into the same outlet. That happens on the living room circuit. It also happens when I run an extension cord up from the 20A circuit in the basement.
Sorry, but you are doomed. If using either receiver A or B plus just one power amp, both plugged to the same power strip [or for that matter AC outlet since we are now down to two devices], with nothing else plugged to the power strip, you still get hum which doesn't exist when listening to the power amp alone feeding the speakers without any input to it at all, THERES NOTHING YOU CAN DO. You will have to use some combination of the bandaid approaches such as cheater plugs, Hum-X, a cable feed transformer marketed as "cable surge protectors" such as "Xantech - 634-00 - Ground breaker", Radio Shack or Jensen RCA transformers on the RCA connections, and/or breaking wired audio connections by converting to optical Toslink communication, or 2.4 GHZ communication such as "Dayton Audio Sub-Link XR 2.4 GHz Wireless Audio Transmitter Receiver System for Subwoofers".


As for XLR connections, as Rane points out, many companies configure them the wrong way, so they aren't guaranteed to kill ground loops like people think.


Good luck. I'm out.

In A/V reproduction accuracy, there IS no concept of "accounting for personal taste/preference". As art consumers we don't "pick" the level of bass, nor the tint/brightness of a scene's sky, any more than we pick the ending of a novel or Mona Lisa's type of smile. "High fidelity" means "high truthfulness", faithful to the original artist's intent: an unmodified, neutral, accurate copy of the original master, ideally being exact and with no discernable alterations, aka "transparency".
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post #19 of 29 Old 10-23-2014, 10:44 PM
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Are both AVRs 2-wire power?

I'll be back later...


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post #20 of 29 Old 10-24-2014, 04:12 AM
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Quote:
Originally Posted by m. zillch View Post
Sorry, but you are doomed. If using either receiver A or B plus just one power amp, both plugged to the same power strip [or for that matter AC outlet since we are now down to two devices], with nothing else plugged to the power strip, you still get hum which doesn't exist when listening to the power amp alone feeding the speakers without any input to it at all, THERES NOTHING YOU CAN DO.

Actually there is something he can do if one of the two items in the system has a three prong (grounded) power cable. If the AVR and amp both have two prong plugs on the power cables then yes, isn't much that can be done to solve this.

DS-21: do either of the components (AVR or amp) have a three prong power cable?

Packing a lot of sound into a small room.
268 square feet/2144 cubic feet
7.2 surround sound.
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post #21 of 29 Old 10-24-2014, 10:36 AM
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Quote:
Originally Posted by DS-21 View Post
Surprisingly to me at least, I monitored the outlet and did not register a voltage drop as the amp's relays kicked on.
AC voltmeters that aren't of the true RMS type work by full-wave rectifying the AC signal (same as taking the absolute value), then determining and scaling the time average (DC value) of the rectified signal. The time average is performed by a low-pass filter with a very long time constant, so if there's a dropout that's just a fraction of a cycle or so in duration, the AC voltmeter won't pick it up. It takes special circuits to detect short dropouts.

Last edited by andyc56; 10-26-2014 at 06:19 AM. Reason: Removed stuff that was due to not reading the original post carefully!
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post #22 of 29 Old 10-24-2014, 12:31 PM
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post 3

"Both AVR's have 2-prong IEC sockets. Both amps have 3-prong IEC sockets."

Oh, that made my later question dumb, maybe he editted it.

Ok, I will draw up my analysis later.

I'll be back later...


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post #23 of 29 Old 10-25-2014, 05:26 PM - Thread Starter
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You can see when a post was edited by looking at the bottom. But it's a long thread so easy to miss details.

Did some more playing around today. Discovered I really have four problems, not one.

1) The outlet behind the audio cabinet is no good for audio. That's why I got hum from both AVRs. I was surprised to learn by playing with my panel that the outlet actually isn't on the "living room" circuit. It's on the "dining room" circuit. Same as the dimmer and the thermostat on the other side of that wall. So, I'm definitely calling an electrician to change that. Now, the question is, do I suggest the electrician put the audio equipment on the same 15A circuit as the TV, or on the same 20A circuit as the subwoofer amp (basically right under the living room)?
Other considerations:
-Easy access for both. The 15A outlets are separated by, inter alia, a double doorway, but there is easy basement access. The 20A circuit is right below the living room.
-I also have a UPS there, because my cable modem and router (Apple Time Capsule) are plugged in there.
-I run balanced from miniDSP to sub amp, so I could use disconnect the shield at the miniDSP per the Rane app note. Both miniDSP and amp use Phoenix connectors so I wouldn't even need to open up a cable to do so.
-There would be a lot of amplifier on the circuit. Mains amp is Class AB and rated 200W/8Ω/7ch driven, sub amp is Class D and rated 1kW/4Ω/4ch. That said, I ran both amps and all of my other A/V stuff from the same 15A circuit in my old loft without any breaker-tripping issue. And that living room was considerably larger than my current one, because the living/dining/kitchen was one large space.

2) There's a ground loop between my TV (or my HDbaseT baluns) and the audio gear. That's why I thought there was hum from the basement circuit. If I disconnect either end of the HDbaseT transmitter (either the ethernet or HDMI cords) the hum goes away on that circuit. It also goes away if I put a cheater plug on the TV. My TV is over 5' off the ground, plugs in to an outlet directly behind it, and has a plastic case, So unless someone can give me a good reason not to use a cheater plug there, I'm less bothered by it than I am with a giant metal-cased amp at toddler level.

3) Ground loop on the incoming cable. I'll be getting an isolation transformer for that by Tuesday. Interestingly, with an extension cord running to the TV outlet, when I plugged the cable into my power strip/UPS, the hum got much much worse.

4) Cable-box dropouts are still a thing when the HVAC cranks on, no matter where I plug the system in. I'm wondering if rerouting the coax might fix that. Cable box and AppleTV do not drop out when the amp relays kick on when the system is plugged in downstairs or to the TV outlet, but the HVAC does it regardless. I haven't had a chance to the load test Andy discussed above, but it's next on deck.

So, I'm thinking the second problem I solve with a cheater plug on the TV, and the third I solve with a catv isolation transformer. The first and fourth I solve by engaging the services of a licensed electrician. Sound like a good plan?

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Last edited by DS-21; 10-25-2014 at 07:23 PM. Reason: clarity
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post #24 of 29 Old 10-25-2014, 05:38 PM
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Another little tool in my tool box is a Kill-A-Watt monitor.

4400 is a little more basic than the 4460. 4460 holds a reading if it gets unplugged.

http://www.p3international.com/produ...avers-all.html

I'll be back later...


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post #25 of 29 Old 10-25-2014, 07:18 PM - Thread Starter
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I have one of those. I never thought to use it for diagnostics here. I really just use it to confirm standby power consumption on different things.

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post #26 of 29 Old 10-25-2014, 08:53 PM
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DS-21, from your list of issues in your latest posting...

Regarding numbers 3 and 4 I am assuming you have cable service coming into your house? Once the primary feed line enters the house are their any splitters in use? If your answer to my first question is yes, then call the cable provider and get them to come out and replace the line into your house. If you also answered yes to my second question, then the splitters need to be grounded. Coax splitters always have a ground screw on them and they should be grounded, but rarely are. All of the splitters (if you have multiples) can share a common earth ground, but that ground should be unique for the splitters, and not shared by the electrical service for your home.

Did you get the outlet tester and if so have you checked your outlets to see if they are wired correctly?

Packing a lot of sound into a small room.
268 square feet/2144 cubic feet
7.2 surround sound.
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post #27 of 29 Old 10-26-2014, 07:53 AM - Thread Starter
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Quote:
Originally Posted by They_call_me_Roto View Post
Regarding numbers 3 and 4 I am assuming you have cable service coming into your house?
Yes. (Sigh.)

Quote:
Originally Posted by They_call_me_Roto View Post
Once the primary feed line enters the house are their any splitters in use?
There are two splitters:
One in the basement, which I've thought about removing, as we only have cable coming to one spot. The house has coax cables run for every bedroom and the study, but we have no interest in television in our bedroom, etc. I've disconnected all of the extra coaxes, so the splitter is just feeding one line.
One in the living room, to split between TV and cable modem.

Quote:
Originally Posted by They_call_me_Roto View Post
If your answer to my first question is yes, then call the cable provider and get them to come out and replace the line into your house. If you also answered yes to my second question, then the splitters need to be grounded.
Interesting. The one in the basement is grounded. The one in the living room is not.

Quote:
Originally Posted by They_call_me_Roto View Post
Did you get the outlet tester and if so have you checked your outlets to see if they are wired correctly?
Yes and yes.

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post #28 of 29 Old 10-26-2014, 08:23 AM
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OK I'm guessing that your outlets checked out for being wired correctly based upon your answer.

To address the ground loop hum between the AVR and amp. You said that your amp has a three prong grounded power cable. I would suggest that you plug the amp into an outlet separate from the outlet that the AVR is plugged into. But the outlet for the amp needs to have the ground rewired. All of the neutrals and grounds on your home wiring should all return back to your circuit breaker box. For the outlet that you will plug the amp into, give that outlet it's own unique ground. The outlet will have to be pulled out of the wall box and add a 14 or 12 gauge insulated wire (this wire should have green insulation) and then there are two ways it could be grounded to provide a unique ground path for this outlet. 1) that wire is routed to outside the house and clamped to a 4 foot copper rod that is driven into the ground. This solution is the more expensive option. 2) The new outlet ground wire can be grounded to the cold water piping in the house provided the water supply tubing is galvanized steel or copper. If your house is newer and has PEX tubing, this method will not work. But if you do have metal water tubing buy three ground clamps that look like this:

These can be purchased at Home Depot, Lowes, True Value, ACE, etc... These ground clamps are available in either aluminum, mild steel or brass. I would highly recommend buying brass ones.

I said you should buy three of these and here's why: one will be used to ground the new wire from the amplifier outlet to a cold water tube in your house. MUST be a cold water supply tube, not a hot water tube. Then the other two ground clamps will be used on each side of your water meter, one on the inlet side, and one on the outlet side. With these two ground clamps you connect another length of the ground wire between the two clamps to "jumper" the meter. Basically this provides a guaranteed ground path through the tubing to earth. Without the jumper at the water meter, any voltage in the tube may not get grounded to earth depending on the internals of the water meter.

By doing this, the outlets providing electricity to the AVR and amp have two separate ground paths and that will eliminate the ground loop.

Packing a lot of sound into a small room.
268 square feet/2144 cubic feet
7.2 surround sound.
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post #29 of 29 Old 11-09-2014, 05:44 PM - Thread Starter
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To cap this thread, the problem is completely solved and I'm enjoying the basically nonexistent noise floor one reasonably expects from Anthem and ATI electronics. Here's what it took:

1) The outlet behind the equipment cabinet was unsuitable for this purpose. It was connected to a dimmer and the thermostat. I had a licensed electrician cap the wires and connect the wall to the 20A circuit in the basement. So now everything but the TV is on the same circuit.

2) Isolation transformer on cable. The cable is grounded to the water meter and not to the ground rod. A Comcast person came out, and wrapped the ground wire around the top rod. (The rod is right under the water meter.) I got him to come back and put it where it was because that's unacceptable. I'll buy a proper ground clamp and do it, maybe. The isolation transformer doesn't seem to hurt anything. Also, in retrospect the mains amp (200Wx7 into 8Ω class AB) probably needs a higher-amp circuit more than the sub amp (500Wx8 into 8Ω Class D) does!

3) Cheater plug on TV. The TV is on a different outlet, but the outlet is literally right behind the TV. above the mantel The TV has a plastic frame and is over 5' off the ground at its lowest point. So it's a kludge, but one totally I'm willing to live with.

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