Chasing 60 hz hum

Guess I stimulated some good discussion here. Thanks to all for chipping in.

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

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

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

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.

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

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.

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

I've never been able to figure out how to navigate through long threads at AA in an efficient non-confusing manner :-),
11-09-11: Almarg

LOL..... That's why it's called the Asylum....

Try this, it might be a little easier....

http://www.audioasylum.com/cgi/t.mpl?f=amp&m=156311
.

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

Al,

Here is an interesting post that ran over on AA.
Note the responses of the equipment manufactures.

Plain and simple good sounding equipment can be built without the need of an equipment ground if the manufacture would only spend a few extra bucks and use double insulated wire for his AC power.

Floating ground... Does it cause damage?
.
Jim

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

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.

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, as other than using ground cheaters, or breaking ground pins off of the AC cords (neither of which is recommended) there will be nothing else that is effective.

Resist the temptation to install an external ground outside the house or other such nonsense- you don't need it! That will simply add to the ground loop problem, which can really only be solved by having the equipment itself wired correctly.

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.

Does the 7150 have a two-prong cable? If it has a non- polarized plug, take a voltage reading from the chassis to the screw that holds the wall-outlet cover in place. Reverse the plug and take a reading again. The plug orientation with the lower voltage reading should be the quieter of the two.
2) The filter capacitors in these components power supplies are supposed to filter out 60 cycle hum after the line voltage has been rectified."Leaky" or worn out caps will not filter the ripple, leading to increased hum. In older equipment replacing the caps might be worth looking into.

Greetings,
I lot of people will say not to use a cheater plug, but it works. A lot of dealers use cheater plugs also due to AC hum.
Having an AC hum happens in a lot of systems.
I would suggest using the cheater plugs and maybe going with a Very Good power strip or possibly a PS Audio Ultimate Outlet, I have seen them listed here. I have used them for years in my system except on power amps. I did use them for awhile on my amps when I went with the cheater plugs with no ill effects.
After talking to my dealer I now just use the cheater plugs right into the outlet.
I had the same type of problem with AC hum, 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. I'm on a well system at my house and my well goes down 250ft. Could not ask for a better ground. Cleaned it up a lot but not totally, so I'm also using cheater plugs.
Getting rid of the hum using the cheater plugs made my amps sound Great. After talking to my audio dealer he suggested to get rid of the Hospital grade outlets that I have and go with the MIT outlets. Should get them soon. His opinion was Hospital grade outlets are not meant for audio, and I should get a nice improvement with a audio grade outlet.
If budget allows maybe a PS Audio re-generator or some other brand of power conditioner. I have read some very positive reviews of the MIT Stabilizer and the Audience ARP2-T.
I'm also purchasing a MIT Stabilizer for my front end equipment.
Hope my opinion might help you.
Joe Nies