Chasing 60 hz hum

11-09-11: Broimp
Will study all these suggestions. Many thanks! I was getting the hum (just realized) with TV input selected only and will look at maybe a missing ground where the coax comes into the house.

Ground loop issues involving connections between cable tv and audio systems are common. A good solution is often a ground isolator such as this one.

1-09-11: Stringreen
Joenies....glad you got rid of the hum, but cheaters degrade the sound of your system....instead... remove the plug from the wall and make the necessary wire changes behind the wall.

Besides being a code violation, intentionally miswiring a wall outlet compounds the risks that would result from using a cheater due to the fact that the miswiring may be forgotten in the future. If a component is acquired in the future that is old and/or in questionable condition, and it is plugged into that outlet, the fire and shock protections that properly wired 3-prong outlets are intended to provide may be necessary but not present.

11-08-11: Joenies
I totally disconnected the ground wires that comes from my breaker box and installed a real Isolated ground to my outlets. I ran a dedicated ground from the outlets to a water pipe in my house.

Hopefully a very low resistance path exists between the water pipe ground and the ground at your electrical service entrance. Otherwise fire, shock, and lightning hazards may exist. Those risks are presumably small but cannot be said to be zero. See section 1.2 of this paper, especially the part of that section on page 8.

11-09-11: Atmasphere
If you have to use cheaters to get rid of hum, then the problem is that the equipment itself is incorrectly wired. The problem is that the chassis ground and the circuit ground are the same thing, which means the equipment is wired with a ground loop. IMO, you should send the equipment back to Mac and have them fix it,

Ralph, isn't that very commonly done intentionally, notwithstanding the fact that it creates the ground loop issue you are describing? And if so, wouldn't a fix (a)be likely to be hard to implement, and (b)be likely to degrade the integrity of the internal grounding scheme that was intended in the design, thereby affecting sonics?

Regards,
-- Al

Thanks, Jim.

I've never been able to figure out how to navigate through long threads at AA in an efficient non-confusing manner :-), and in trying to do so in the thread you linked to I just encountered a lot of disagreement and arguing.

In any event, my point is that while good sounding equipment can certainly be designed and built without making circuit ground and safety ground common, the fact is that many designs do have them in common. And I would expect that modifying an EXISTING design to isolate the two grounds from each other might not be simple to do, and may have adverse sonic effects.

Best regards,
-- Al

Thanks again, Jim. I read through the entire thread, which unfortunately fails to reach consensus, due as I see it to personality conflicts getting in the way of what could have been very constructive exchanges. Which is particularly unfortunate considering the impressive backgrounds of several of the participants.

In the end, I'm left with the feeling that simply double-insulating the ac wiring and isolating safety ground from chassis could very well be a solution that can be directly applied to most if not all designs without sonic penalty, but the thread would seem to leave at least a little bit of doubt about that.

Best regards,
-- Al

11-10-11: Kirkus
Actually I've experienced at least as many grounding-related problems with "double-insulated" equipment as those with safety grounds. This is because they still have leakage reactances in their power transformers, and thus AC-related currents will still flow between their chassis -- this will now be flowing wholly through the interconnect shields. And for unbalanced interconnects, the shield resistance then becomes the primary dictator of the attainable hum level.

Thanks, Kirk. Yes, that of course makes sense; thanks for pointing it out.

I wholly agree that most hum problems in audio equipment are caused by poor grounding choices inside the gear. The classic expose of this is an AES paper by Neil Muncy from the early 1990s, where he coins the term "the Pin 1 problem".

Your mention of Neil Muncy and the "pin 1 problem" brings to mind this excellent Rane paper on these issues, which was called to my attention a while back by member C1Ferrari (Sam). It too emphasizes that the grounding scheme in most equipment is poorly conceived. The paper's summary is worth highlighting:

If you are unable to do things correctly (i.e. use fully balanced wiring with shields tied to the chassis at the point of entry, or transformer isolate all unbalanced signals from balanced signals) then there is no guarantee that a hum free interconnect can be achieved, nor is there a definite scheme that will assure noise free operation in all configurations.

Best regards,
-- Al

And in how many cases can the problem be blamed on the manufacture of equipment for not checking for the proper AC orientation of the primary winding of the transformer.....

Good question. I don't know the answer, of course, but it wouldn't surprise me if it is 50% :-)

Best regards,
-- Al