Chasing 60 hz hum

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?

Al, if something like that is done with intention, it can only be out of ignorance, like the kind that existed (and was excusable) 40 years ago. Nowadays you can't get away with it!

On top of that, it **compromises** the sound rather than improving it. Another way of looking at that is that audio components really don't like to be grounded on account of noise in the AC ground and also because of ground loops. If, OTOH, the ground *floats* at AC ground potential, the noise issue is gone and so is the ground loop issue.

Years ago I was of the opinion that a preamp is the place where the chassis and circuit ground being the same was acceptable (this is the way most pro-audio systems are done, although instead of the preamp we are talking about the mixer), but have come to realize that if some other part of the system has incompetent grounding, then the preamp is unfairly implicated. On top of that, if proper grounding technique is observed, you will notice right away that the noise floor is improved (for example, less hiss in a phono circuit) and of course there will be no need for exotic and possibly dangerous external grounding schemes.

Greetings,
In a lot of cases the 60Hz hum is not necessarily do to equipment miss wiring. It can be caused by a number of different problems.
In some cases it can be the wiring in your house. An example would be that when the Romex cable was installed and was clamped down to the J-Box the Hot, Neut. or Gnd wires could have crossed over each other at the clamp point. If this happens one of the wires could have compromised the insulation of the other wire and is causing a hum.
When I was doing a re-model of my kitchen I pinched the ground wire over the Hot wire (insulation broke on Hot lead), this in turn caused a direct short and the breaker did trip. If the wire just partially compromised the insulation this could cause a bleed through to the other wire.
A 60Hz HUM drives all us music listeners crazy.
To track down these type of problems will take a lot of time if you do the work yourself. To pay someone to do this would cost a lot of money.
I do plan to pull all my J-boxes (light fixtures & outlets) apart someday to see if this is one of the problems with the HUM.
Thanks for the advice about getting rid of the cheater plug and to just disconnect the ground wire.
I'm also purchasing a MIT conditioner for my front end equipment. I will eventually find were the HUM is coming from and fix it, it will just take time and effort.
Respectfully,
Joe Nies

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.

Hi Al . . . 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.

On top of that, it **compromises** the sound rather than improving it. Another way of looking at that is that audio components really don't like to be grounded on account of noise in the AC ground and also because of ground loops. If, OTOH, the ground *floats* at AC ground potential, the noise issue is gone and so is the ground loop issue.

So much of the terminology commonly used with grounding ends up implying that "noise in the AC ground" is somehow external to the audio system, and evilly injected through third-prong grounds. This is exactly the opposite of what's happening - it's the audio gear itself that's producing the noise current. When it flows through a path that's shared with the audio signal, we then hear it. Taking away the draining path away by using a cheater plug simply alters the magnitude and/or path of the offending part of the flow, frequently transferring it from wiring to the operator. That last bit is why it's dangerous.

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,

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".

The "pin 1 problem" refers to the ground pin on an XLR connector, and the idea is that simply flowing AC current between pin 1 of any two (or more) XLR connectors on a piece of audio equipment should NEVER cause any change in the noise floor of any of its outputs . . . and in practice this should include unbalanced connector grounds and AC safety grounds. If I had to guess, I'd say that at least 75% of all consumer and professional audio products suffer from a "pin 1 problem" to a certain degree.

I'd also have to say that from my direct experience, many McIntosh products suffer from "pin 1 problems", including the C39 and MC7150.

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

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.

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..... .
Jim