Unexpected outcome of disconnecting grounding wire
December 8, 2011 11:15 AM   Subscribe

Sound system hum/buzz quieted by removing grounding wire from turntable?

Trying to diagnose some system noise last night, I unscrewed the connection on my receiver from the grounding wire to my turntable. Remarkably, this killed the hum/buzz, but I have no idea why. It seems weird just to leave the ground wire hanging there, but I definitely prefer the new quiet.

Does anyone know if A) this is indicative of some more serious problem I need to address or B) if there is any danger in having the ground wire unattached?

TT is a Pro-Ject 1.3, receiver is a 70s Telefunken sorta like this one. The only other component on the circuit (and on the receiver) is an Airport Express (which appears to contribute no interference).
posted by activitystory to Technology (8 answers total)
Best answer: Is your turntable plugged into the powered outlet on the back of your receiver or directly into the wall/a power strip? It sounds to me like the latter and the receiver is acting as a ground but not as the power source.
posted by mikeh at 11:32 AM on December 8, 2011

Best answer: Ground loop.
posted by TomMelee at 11:41 AM on December 8, 2011

Best answer: You had a ground loop. Removing the grounding wire took this device out of that loop, but I suspect that it still exists for the rest of the house. I have no idea what implications this has for your questions A and B.
posted by JJtheJetPlane at 11:41 AM on December 8, 2011

Best answer: Yeah, you had a ground loop which you've now isolated by basically having the turntable "float". If you were to amplify its quiescent output enough, you'd probably still hear some hum (because it's acting as an antenna), but it's doubtless a lot better than when it was part of a loop.

My personal feeling on all things sound related, absent any safety concerns (like getting zapped when you touch things), is if it sounds good, it is good. If the results you get are now OK, don't mess around with it just for the sake of messing around with it.

However, the "right" solution is to resolve the ground loop by tying together all your equipment to a single common ground using low-resistance wires in a "star" configuration -- each device has a ground line running to a single point; items are not tied to each other and thence to ground. 16 ga THHN wiring is ideal, IMO, for this purpose. But I wouldn't do it unless you need it.
posted by Kadin2048 at 11:47 AM on December 8, 2011

So there's another question here that I hoped a more savvy poster could touch on---and that is the SOURCE of the ground fault.

99% it's inside the device, voltage interference hopping to make the potential difference. I tend to get these things backwards, but I *think* you have less potential to pick up a little zap from the knobs but a greater chance of overall fault because you've removed any option of ground, but I may have that backwards. There's a common thing that happens where people do something like touch their stove and their sink simultaneously and get a little zap, and I can never remember which side of the fault that is. Hopefully smarter people than me will answer that for you.

HOWEVER....there is some possibility that your *house* has a ground fault, which has a LOT of potential to be BAD. I had a friend who had a buzz in his audiophile-grade system and spent HOURS trying to track it down, only to learn that he'd picked up some sort of a fault in his overall wiring.

I think you're fine...and I'm neither an electrician or an electrical engineer---but it's worth asking to make sure I'm not a total idiot.
posted by TomMelee at 1:33 PM on December 8, 2011

I think you are getting a ground loop between the turntable and the amp. Potential is flowing between the negative of the signal wires and the ground wire.

I don't know anything about that turntable, but it looks like it uses an external transformer. Look and see if there is a connection between the negative of that transformer and the ground of the signal wires or the ground.
posted by gjc at 5:28 PM on December 8, 2011

We are getting confused here. The audio hum problem is a ground loop, as mentioned above, involving the connections between audio components. This is different from a ground fault, when house wiring, or a device connected to it, shorts and causes current to flow in an unplanned manner (e.g., shocking the user).

To simplify, I would first completely disconnect the Airport Express. Then you just have the receiver and turntable to test. Definitely plug the TT power cord into the receiver, if it has a power outlet, or at least plug them both into the same outlet. If the power plugs are not polarized, try unplugging one, turning it 180°, and plugging it back in, to see if that makes a difference. With the ground wire attached. In all combinations. Basically, you are looking for the combination where the ground wire is connected (as it should be) and the hum disappears. Only then reconnect the Airport and see what effect it has.

And if all this testing fails, just leave the ground wire disconnected and enjoy your vinyl!
posted by exphysicist345 at 6:42 PM on December 8, 2011

Oops, both of them are right. Ignore me.
posted by TomMelee at 8:54 AM on December 9, 2011

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