Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Sorting out Ground Loop problem with Modded Oppo

First see if it works. Then we can do a poll or something

I'd rather see the amp grounded than the Oppo.

That's why I asked earlier if anyone knows if an Oppo is normally shiped with a grounded cord.

The stock Oppo comes with a two pin PSU socket.

Mark,
my recommendation is to connect the chassis of the Oppo with one or more chassis of the other components. This will ensure that you are in no danger from an electrical shock. It should also be easy to try and test the effect. As I said before: this serves as the "easy" route for the current to flow from one ground level to the other. Please take a look at the links that I posted before, because I couldn't explain it any better and the topic is extensively covered.

Yes, you could also try to use a plug with only 2 contacts for the Oppo. Since you don't have a cable without ground you can try this:
- put adhesive tape across that part of the plug (it will work as an insulation)
- use an international plug adapter that either doesn't have a ground contact or where you can retract it or disable it in another way
- take an extension cord but remove/disconnect the cable that goes to the ground contact from the socket part of the cord

I wouldn't recommend this as a permanent solution, but you would be able to see if there's any effect.

Good luck,
Thomas

"Does that mean then because it is connected to the power amplifier, the Oppo would be grounded that way? I'm just checking that this wouldn't potentially eave the Oppo 'live' in certain cirumstances so that I (or the family) wouldn't get a nasty shock."

For a device that comes factory with a safety ground defeating the safety ground can introduce a failure mode where the chassis could be live. 3 prong devices typically ground the chassis through the safety ground. This is so if there is some sort of internal failure that causes the hot to hit the chassis the hot will be grounded out and your 15 or 20amp fuse will do its job and blow turning off the power and taking the power off the chassis

If you defeat the safety ground what happens if you have the same failure? Your chassis may still be grounded (through your interconnects or whatever) but are those interconnects going to be able to handle 15 or 20amps through them long enough to blow your main fuse or trip your circuit breaker? (HINT: Your safety ground is 12 to 16 gauge... what gauge is the ground in your interconnects?)

If your interconnects can't handle that 15 or 20 amps long enough to blow your fuse those interconnects are going to burn up (fire?) and your device will be sitting their live with 15 or 20 amps on the chassis waiting for you to complete the circuit to ground.

Shawn

"I don't believe any audio devices hard wire Neutral to audio ground because it's too easy to defeat the keying and make chasis hot."

It can happen. That is why we went to polarized plugs in the first place. Audio ground/neutral doesn't have to be to be tied to the chassis.

Shawn

People seem to think grounding the chassis together solves the problem (it might reduce it some). Where that basically is the problem. The chassis are already grounded to each other through the audio cables. And that is why optical sometimes fixes it because you BREAK the ground.

The easiest thing to do, is do what Oppo intended which is not ground it.

I believe Gary added a grounded cord and socket with the new power supply, thinking more is always better.

I must have a dozen IEC power cords sitting draws. It's a requirement to being an audio nut. You must too. Just take one and snip the ground pin off. The original power cable as VK verified had no ground !!!

Basically you want a single point to earth ground for the entire system. The Oppo and probably the amp. Amps have a lot of current and high voltage so they are often grounded. DVD's/CD are light duty so they usually double insulate just the power supply and not ground the chassis and let the ground (Audio Ground come from the amp through the audio cables).

Think of it as like a tree spanning out from the trunk. Right now you have two paths earth (two tree trunks and one tree). And they are fighting over which which way to sway in the wind. The suggestion by NutFlush is basically saying lets make the branches between the two trees bigger so they are forced to sway in the same direction. The other solution is to pull up one trunk and let it freely sway in the wind again.

Sorry lads. Gary modified it and it doesn't work as it should. I think he should fix it, or take it back and provide a refund.

George

PS: Shaun has kindly elaborated on what I mentioned earlier. Do not mess around with earthing for mains level power supplies. It's potentially dangerous.

Neutral is never, ever intentionally tied directly to ground. In fact, if you plug it into a ground faulted circuit it will trip as fault.

I don't think it's that risky to lift a ground on a superfluous ground that was added !!

Even though I'm personally not a fan of mucking with power supplies, a ground loop, like this, can happen with some legitimate sources. So you can't completely fault Gary for doing what was specified and could be (I'm not saying is) legitimately built. Legitimately built devices can cause these types of issues. I just don't think it was needed and worth the headaches it might cause.

I think the only thing Gary *could do* is offer to put it back to factory. And for a fee. But I think it's pretty low risk to lift the ground that the Oppo normally never had. To avoid that route. If anything, it will confirm the source of the problem. And Mark can decide what to do. Having a third party modify the power supply in the first place has risk too, but Mark didn't hesitate on that

I respect your caution because I don't know first hand what the mod exactly did.

But just adding a ground wire from chassis to earth can cause a ground loop. So I say take that part back out (closer to factory).

"Neutral is never, ever intentionally tied directly to ground."

Which ground? Audio ground does not always equal chassis ground.

Do a search for some of the problems some people run into when they use balanced power for only some of their components in an audio system. They see things like sparks when swapping interconnects. Three guesses why....

Shawn

If Gary tied (house) Neutral to chassis ground (which is usually Audio Ground) that is dead wrong. If that's common with these "balanced power supplies" then I'd stay away from them. I don't think there is any evidence of that though.

I'm not familiar if a "balanced power supply" can cause a ground loop hum in of itself if correctly installed. Or if running mixed balanced and non balanced can. To be honest I forgot Gary's power supply mod was a balanced power supply. Like I said don't fix something that ain't broke. But buyer asked Gary to "fix it". So he did. Can't fault Gary for that.

But I suspect it's just the added chassis ground that is causing the ground loop. At least I hope so for everyones sake.

I agree chassis ground is not always audio ground but is most of the time.

I agree with you (I think) that if sparks are flying it's because someone did tie (house) neutral to chassis (audio) ground which is extremely dangerous, and dead wrong. Because it's way to easy to swap hot and neutral (by accident or on purpose). Like I said a ground fault circuit (which I firmly believe should be on ALL circuits) verifies house ground is never tied to house neutral. Only place that happens is in house main circuit panel. It's also why I strongly disagreed with the suggestion of rotating 180 degrees (just in case, lot more risky than lifting a ground that was added). Flipping 180 rarely fixes a ground loop anyway. But I admit it ocassionally does.

Grounding chassis to earth or not is seperate in my mind of neutral being tied to chassis.

George, the digital edition Oppo came with the PS mod so other HH's (as well as others in Aust as there was a DTV powerbuy too) must also have this same PS mod in their systems. It wasn't "asked" for in that sense, but I know what you are saying.

My next step is to speak with my amp manufacturer for their thoughts. For my own safety and that of my family, I am not comfortable with playing with grounding and I don't understand all the PS issues to hand here.

If need be, I'll get someone to look at the Oppo PS to advise me.

If the Oppo isn't safe or otherwise compliant, or something is wrong with its PS, then its time to look to Gary for a fix at his cost as Mr Meridian suggests - but i'm jumping ahead a bit and hope it can be swiftly resolved.

Thanks again for everyone's help - though I get the impression you are enjoying pondering all of this anyway