Ground loop is eating my lunch (again)

[Boomzilla]

Personae Dramatis:

AR tube power amp (grounded IEC plug) connected to Oppo BDP-105.

But the Oppo is also connected to:

Emotiva PT-100 preamp (via grounded coaxial digital cable)

and the Emotiva is connected to a Crown PSA-2 power amp (grounded IEC plug).

Both the AR tube amp and the Crown PSA-2 (the only two grounded items in the system, since I cut the grounding plug off the Oppo in hopes of avoiding the loop) are plugged into the same Emotiva power strip.

If I lift the ground between the Oppo and the PT-100 (by using an optical TOSLINK cable instead of the electrically-grounded coax), then the hum goes away.

Simple solution: Unplug the AR power amp when using the Crown & vice versa.

Any other way to get 'er done without the irritation of continuously plugging & unplugging the equipment?

Thanks - Boom

[DYohn]

What are you trying to do? Create separate analog and digital systems?

[garbulky]

Try different power cables? One of them may have gone bad.

[bluemeanies]

Ground loops are like CANCER. most times they are hard to fine without doing the BIG JOB of dissection.
I had a ground loop years ago and played around with this and that for hours on end and the final solution was to take the entire system apart. Starting as if you were putting together your first 2channel or HT system.
I first started with the processor and amplifier (Outlaw 990 &7700)
Short story is I eliminated the ground loop.
Patience and mine is short but I was successful.
Again if it were me no matter how involved your system I would " take everything apart", and also clean everything making sure ALL CONNECTIONS are TIGHT!

[Casey Leedom]

And what's the down side of using Optical TOSLINK S/PDIF instead of the Grounded Coaxial S/PDIF?

Casey

[Boomzilla]

OK - To answer the multiple questions as efficiently as possible, allow me to lump the answers into this one quick reply -

What I'm trying to do is to have a single stereo that gives me the choice between a tube power-amplifier and a solid-state power amplifier. Optimizing the system for both takes different components (and not just the amplifiers).

The tube amps (currently three in the house) all have input impedances of 300K ohms. The Oppo drives these directly and sounds good doing it.

The solid state amp (currently only the Crown PSA-2) has a much lower input impedance (10K ohms?) and the Oppo sounds very anemic (particularly in the bass) when driving it directly. So for the Crown, I need the Emotiva PT-100 preamplifier (which sounds lovely with the Crown, but not so much with the tube amps - go figure).

The reason I don't want to use the TOSLINK on the PT-100 is because (to my ears), the coax sounds so much better.

Further adventures in grounding:

Removed the ground plug from the Oppo - no difference - Crown still hums

Reversed the AC plug on the Oppo - no difference - Crown still hums

Unpluggd the tube amp - no difference - Crown still hums

Unplugged the preamp from the Crown - dead quiet

Electrically disconnected the Oppo from the PT-100 via use of TOSLINK - dead quiet

Oppo via unbalanced RCA to the tube amp - Tube amp hums

Oppo via balanced XLR to the tube amp - Some hum, but far far less

Used a "hum eliminator" box (stereo RCAs in & out) between the PT-100 and the Crown - dead quiet (but didn't sound as good)

So far, the ONLY two solutions that seem to keep the Crown happy are the two that sound the worst - optical connection & "pro" grade hum eliminator.

Ideas?

Thanks - Boomzilla

[Casey Leedom]

Feb 2, 2017 17:05:19 GMT -5 Boomzilla said:

... The reason I don't want to use the TOSLINK on the PT-100 is because (to my ears), the coax sounds so much better. ...

Okay, I'll bite: aren't these both just delivering digital data via S/PDIF? If one sounds better/worse than another what would that mean? A non-asynchronous input on the PT-100 Optical versus the Coaxial? Or maybe the grounding between the Oppo and the PT-100, while it is introducing a Ground Loop Hum, is also somehow "fixing" elements of the Analogue sections in the PT-100??? Or maybe the Ground Loop Hum is somehow subjectively making it sound better?

Casey

[qdtjni]

Is your Oppo connected to a TV?
If so is the TV connected to some cable box?

[Boomzilla]

Hi gents - good questions all...

First, yes - the Oppo is not only connected to the television via HDMI, but that same Samsung HDMI junction box is also connected to the local Cox Cable box & then on to the local coax network. The Oppo is also connected via Ethernet to the music server that is also connected (by Ethernet) to the switch that is connected to the Cox Cable internet modem in the computer room.

So supposedly grounded connections abound, and many are (probably) not at the same ground potential.

Also, in theory, there should be absolutely no difference between a bit-perfect digital stream regardless of how it's delivered. TOSLINK, SP-DIF, or even USB should sound identical. But they don't. The why is beyond me, but I can tell you for sure that my preference (between those three) is for the RCA digital connection, and by no small margin.

So where do I go from here?

[Loop 7]

Well, for some ridiculously frustrating reason, a ground loop has reared it's ugly head here as well. I changed nothing so I'm WTF.

[qdtjni]

Ethernet is designed with galvanic insulation.
However, depending on what of ethernet cables you have and what equipment that is connected together,
ground loops can occur.

Cable TV connections are infamous for causing ground loops, at least here in Europe.

Just disconnect Ethernet from Oppo first.
If the ground loop is still there, then the TV, etc.
Note that you may have to try different orders to since it may be a combination of things.

[KeithL]

Check the ground lead from the cable junction box (the big heavy wire that leads to physical ground from the cable splitter or junction box).
Just disconnect the HDMI cable coming from your cable box - if the hum stops when you do that then go look at the ground wire.....

They're notorious for coming loose on their own, or from the weather, or when someone else fiddles with the junction box.
They're a ground point for the cable stuff coming into the house and, if they get loose, you'll get hum coming in through ground on the cable.

Feb 2, 2017 17:24:22 GMT -5 Boomzilla said:

Hi gents - good questions all...

First, yes - the Oppo is not only connected to the television via HDMI, but that same Samsung HDMI junction box is also connected to the local Cox Cable box & then on to the local coax network. The Oppo is also connected via Ethernet to the music server that is also connected (by Ethernet) to the switch that is connected to the Cox Cable internet modem in the computer room.

So supposedly grounded connections abound, and many are (probably) not at the same ground potential.

Also, in theory, there should be absolutely no difference between a bit-perfect digital stream regardless of how it's delivered. TOSLINK, SP-DIF, or even USB should sound identical. But they don't. The why is beyond me, but I can tell you for sure that my preference (between those three) is for the RCA digital connection, and by no small margin.

So where do I go from here?

[Boomzilla]

Might it be easier to measure for voltage between the coax shield and the grounding pin of an inside socket?

[Casey Leedom]

And one other issue which hit a bunch of people in the Livermore/San Ramone Tri Valley area here during the drought in the late '80s: the ground became dry enough that the "ground" provided by in-ground metal plumbing pipes wasn't very good. As a result, people started complaining about "funny tasting water" and even "green water" and/or "green stains" on their sinks. Of course using plumbing for a ground is against code and very dangerous, but it also led to the discovery that a bunch of properly installed ground rods weren't doing as good a job as needed. So basically, one shouldn't even trust "ground state truths" till they've been tested ...

Casey

[Axis]

Boom, I hope Ground loop does not eat your lunch anymore. You need to eat your lunch and it is not right for Ground loop to eat your lunch. I am with you Boom. Good luck, and get something to eat.

[garbulky]

Feb 2, 2017 13:06:31 GMT -5 garbulky said:

Try different power cables? One of them may have gone bad.

[Boomzilla]

I changed all power cords today. No difference in the hum.

My gut feeling is that either the HDMI or Ethernet connection to the Oppo is the culprit. I'll find out which tomorrow. Since both of those connections are absolutely necessary for the Oppo to do its job, I'll just have to work around as best I can:

The PT-100 / Crown combo will have to live with TOSLINK connections.

The tube amps will all have to live with XLRs.

If the hum is still bothersome, then the inline hum eliminator will be dissected & any components replaced with better quality ones. The inline hum eliminator, by the way, is 100% effective in doing its stated job...

The house ground rod was replaced within the past five years when a generator was added. The ground is moist enough for the rod to do its job. OTOH, although the rod & ground wires are copper, I think the the clamp isn't. I'll go out & look for galvanic corrosion tomorrow as well.

Thanks for the feedback - Boom

[qdtjni]

For Cable TV induced ground loops, this often helps:

www.amazon.com/Viewsonics-VSIS-EU-Cable-Ground-Isolator/dp/B0017I3K9M

For ethernet based ground loops, just switch cables connected to consumer electronics without ground to CAT5e UTP or CAT6 UTP, which usually are cheaper than cables with screen.

[KeithL]

The clamps have a way of working themselves loose over time. (We've also had quite a few cases where someone had work done on something like a burglar alarm, or their satellite dish, and the technician simply neglected to properly tighten the ground clamp after they were done.)

Feb 3, 2017 1:06:41 GMT -5 Boomzilla said:

I changed all power cords today. No difference in the hum.

My gut feeling is that either the HDMI or Ethernet connection to the Oppo is the culprit. I'll find out which tomorrow. Since both of those connections are absolutely necessary for the Oppo to do its job, I'll just have to work around as best I can:

The PT-100 / Crown combo will have to live with TOSLINK connections.

The tube amps will all have to live with XLRs.

If the hum is still bothersome, then the inline hum eliminator will be dissected & any components replaced with better quality ones. The inline hum eliminator, by the way, is 100% effective in doing its stated job...

The house ground rod was replaced within the past five years when a generator was added. The ground is moist enough for the rod to do its job. OTOH, although the rod & ground wires are copper, I think the the clamp isn't. I'll go out & look for galvanic corrosion tomorrow as well.

Thanks for the feedback - Boom

[KeithL]

In the old days (the 1950's), back when virtually all home plumbing was really copper, and even your main water drop pipe was some sort of metal, your main copper water pipe was considered to the the PERFECT place to connect a ground. (And what little code there was agreed.) That's why you will still find a lot of grounds on older houses connected to it.

It is also customary and necessary to ground the transformer out on the pole - and those grounds can also corrode - or just plain fall off - over time. In most instances, it's just a heavy bare wire stapled to the pole where the transformer is mounted, and it can get damaged or broken inadvertently. It's also important that the ground lead between the pole and your house is secure. If either of those is damaged or missing you can get a situation where the electrical equipment in your house will still run, but the voltage balance between the two 110 VAC legs of your power system will be off, and you'll get all sorts of odd problems (and it can be dangerous).

Feb 2, 2017 21:10:46 GMT -5 Casey Leedom said:

And one other issue which hit a bunch of people in the Livermore/San Ramone Tri Valley area here during the drought in the late '80s: the ground became dry enough that the "ground" provided by in-ground metal plumbing pipes wasn't very good. As a result, people started complaining about "funny tasting water" and even "green water" and/or "green stains" on their sinks. Of course using plumbing for a ground is against code and very dangerous, but it also led to the discovery that a bunch of properly installed ground rods weren't doing as good a job as needed. So basically, one shouldn't even trust "ground state truths" till they've been tested ...

Casey