To be serious and to amplify on the above post: Breaking the third prong will indeed break the gound loop. So will using a cheater plug. Either action will also remove the safety ground and void UL, violate electrical code and leave you subject to a major league negligence law suit --and your liability insurance will not cover this so you will be defending yourself with your own money. You will lose that law suit, your business, your home and any monies you have saved as anyone who is harmed by your voiding UL and safety ground will inherit all.

Solving ground loops by remving the safety ground is among the most stupid actions you could take. Almost any other and you could launch a possible defense. Ignorence is not a defense in a court of law. Either place the electrical breakers on the same phase or purchase an isolation transformer made for sub-woofers.

Because you can does not mean you should.

Alan

What do I do in an old house with two prong outlets?

How do I plug in my (non-Monster) power strip? How do I plug in 3 prong electronics?

Let us assume your question is not a jest as there are perhaps a few people that might not know what to do in the situation described above.

1. Change the outlet to one with a third prong.

2. Use a cheater plug as it was intended and connect the ground to the screw on the outlet.

3. Upgrade your service.

4. Use an isloation transformer

5. change the breaker so that it is on the same phase as the audio equipment

6.Use equipment that has gone through UL and passed UL without resorting to a third prong on the power cord for safety ground.

7. Tell the client that he can eliminate his hum problem by breaking safety ground but only when no one else is around and you have jamming gear to ensure your suggestion is not being recorded. Actually, we have done this until we could order a subwoofer isolation transformer from Jensen. The client purchased her own cheater plug and connected it improperly, thus breaking ground, eliminating the hum and of course removing the safety ground. She did understand the risk and mercifully when we retruned one week later with the isolation transformer we found the cheater plug in place but the power cord disconected from the wall.

Alan

re Alan's post:

1. Illegal unless the receptacle box has a method for grounding in it (A GFCI receptacle is permissable).

2. Ineffective unless grounding method is in box, but will allow insertion of the plug.

3. Won't have any effect on individual branch circuits.

4. Won't have any effect on ground-loop issues.

5. Might help reduce hum, but won't help with 3-prong plugs.

6. Now we're cooking with gas! No loops with no ground.

7. An isolation transformer merely eliminated direct connection with circuit wires. All plug-in isolation transformers I've ever seen had a direct grounding connection around the transformer, plug to socket.

An earlier poster was correct to ask if the A/V receiver is plugged into the same circuit as the subwoofer. Sometimes when multiple components are plugged into the same circuit line noise can be introduced to the circuit that's heard as a common 60Hz hum. Try plugging the subwoofer in a different outlet, one that's not sharing the same circuit as the receiver.

Bob,

He mentioned in an earlier post in the thread that plugging all the components into the same power strip, "Solves the problem". The issue is that he needs them on different circuits due to physical layout.

You mentioned that having multiple components plugged into the same circuit, that line noise can be intoduced and heard as 60Hz hum. This doesn't sound correct to me.

First, if the noise is 60Hz, it isn't line noise! The AC power is 60Hz, so this is the primary frequency not noise.

If 60Hz is getting into a component with multiple units plugged into the same circuit, this is usually an indication that the increased current draw on the circuit is causing the 60Hz to be coupled onto an audio lead somewhere. In such a case I would look for parallel runs of cabling and power.

Any piece of Audio Gear must by definition have excellent AC power line conducted noise immunity over the 20Hz to 20KHz range, or their specs will look horrible, since 60Hz is always present on the power cord at 110V AC levels! So any piece of gear exhibiting the issue you talk of is either poorly designed, or in need of service.

bcf, I think he is referrring to 60 Hz as noise, and since this 60 Hz noise is coming from the power (line), caling it line noise. I think you are referring to such things as whining sounds that may be present on the power circuit when AC/DC motors are used, right?


But it could also be from ground loops if more than one component has a three-wire power cord. I have seen such happen during the design of grounded equipment, where plugging two devices into the two halves of a duplex caused massive hum. However, this was a prototype cassette recorder and the ground on the audio input wwent about five inches to the chassis ground, and along those five inches were the preamp grounds. It was NOT a star ground!


Perhaps if such an item exhibited noise, either at 60 Hz or across the audio spectrum, it is poorly designed or in need of service, but once you interconnect items you cannot make such a blanket statement. This is a case where guilt is mostly by association!

I'm in a state that uses almost exclusively BX which is by definition conduit and a machanical ground. I certainly do not have you experience getting shocked but my experience in NY ( the home I am in was built in 1953, had not 3 prong outlets but was wired with BX cable ) is that older homes were wired with pipe or bx cable and thus an electrical gournd exists in fact due to the machanical coupling of the pipe to the service panel --- whcih should be earth grounded.

See Above.

True but in most homes, save those we work in, there is usually one or two panels in a machanical room. Hence placing a breaker on the same phase is usually possible with a little work and a trough. Often the issue is space to move the breaker. Upgrading the service can provide the needed room. In and of itself it will do nothing.

Huh? An isolation transformer would be for the low voltage circuit not the mains. In the case of the latter you are correct, but in terms of the former you are entirely incorrect.

.


But his problem is due to the safety ground hence placing both circuits on the same phase will result in those circuits having the same ground potential and in all probibility reduce or eliminate the ground loop.


Then you need to spend less time in the supply house and more time in the low voltage business. There are isolation transformers used in high voltage and low voltage and they are different and provide different solutions to different problems. Do not confuse those used in high voltage with those in low voltage systems. About once per month this subject comes up here, AVS or Integrationpros and someone provides the address of Jensen Transformers. You might wish to a) peruse what is for sale and b) purchase their isolation transformer kit and use it. Not only is your information wrong here but it is dreadfully wrong. An isolation transformer works by stoping the stray voltage at the transformers air gap while permitting the signal to pass magneticly over the air gap.


Alan

1. If BX or other metallic cabling is used, then a method for grounding exists. The idea is to not mislead users by thinking that a grounding receptacle automatically indicates a ground.

4 & 7. You're right. When I saw "isolation transformer", I thought 'power isolation transformer', and not what is often called a "ground breaker" usually used on cable feeds and other signal cables.

I've seen them for car-stereo systems for ground loop problems, too. Power isolation transformers do not interrupt the grounding path for safety reasons. They do isolate the hot and neutral paths.

I don't know if I'd call this dreadful.

Sub-woofer ground loops like this happen because the two circuits in use do not have the same potential on their grounds, and because the signal and power grounds are tied together. The interconnect's shield is carrying current, and this is superimposed on the signal conductor.

The two devices' power supplies already provide hot and neutral isolation, which is why I mentioned that a(n additional) isolation transformer (again, I thought 'power') wouldn't help. Of course, breaking the afore-mention shield pathway will stop the afore-mentioned (dreadful!) current.

Larry, you must also remember that while you and Alann are both bright guys, he cannot possibly be wrong. I believe it is in his contract. Alan, you are a great contributor, just lighten up.

Seriously, treat this like a PJ or plasma with a ground loop, and create the power inlet to dedicated outlet solution that extends rack power out to an additional location, this has been discussed thouroughly in this forum and works well for PJs and Plasmas.

Also, since you are abandoning Earthquake and seeking a new vendor, consider Triad.
I use the rackmount amps and plug them into the same line conditioner as the other receivers/amps power. All I have to run to the sub location is 14/2 speaker wire.

Another benefit is that the speaker wire connection is tucked under the very bottom of the back side, and all sides are finished.
There isn't an "ugly" side with heatsink plates, cables, connectors and dials for people to screw up.
You can choose something like 25 different veneers in addition to painted black or painted white, or you can send out a custom stained or painted block to get the sub custom matched to the existing furniture. ASID designers, and the type of clients that hire them, love this line.

Sad but true. Such a burden to carry, too.

Actually what is "dreadful" is that Larry confused high voltage isolation transformers with those used in low voltage which are not just for CATV signals but for all sorts of video and audio signals and are the preferred method of removing these problems. I understood his misaprehension but Larry's advice is so often taken on face value that it could only have led to more confusion and more of these theads. This subject comes up so often that confusing the two will only cause it to come up again and again. It is not that Larry will not know how to deal with the problem but others who lack his knowledge will assume that isolation transformers do not solve ground loops. This thread has gone on and on when all that needed to be said was Jensen Transformers and model Sub RR.

Trying to keep electrical outlets of interconnected audio and video systems on the same phase is sound engineering practice and will mitigate the need for isolation transformers.

I should have been clearer as to what I meant with respect to installing grounded outlets. My brain saw a machanical connection but I failed to make that image clear in what I wrote when obviously this would not necessarily be the case in all instinces and no ground is no ground. I am sure that 2 wire Romex without a ground wire or bx cable ( not MC ) in plastic boxes exist. I have never come across it in old homes. But I do not do half the high voltage work in 10 years what Larry does in a week.

I do make errors and admit them. Ernie has found them as has Impacq to name but two. Follow the Yahoo site and you could fill trucks with the mistakes I make. It just was not the case here.

Alan

I would call anything other than 60Hz, noise on the AC power line.


Putting the preamp ground partway along the path sharing a high current ground is what I call... bad design. Where I work, we find the engineer, and stick his nose in the offending layout. If you find the problem as soon as they do it, and stick their nose in it right away, they remember! (And don't forget to say "BAD ENGINEER, BAD ENGINEER" in a really stern voice.)


What I was trying to say is that, any audio device must have excellent immunity to all audio frequencies that might be conducted down the power cord. If it doesn't, it will sound horrible on a regular basis... because everyones power has a fair amount of audio frequency noise on it. I'd be very surprised if AC line conducted noise was this issue for any situation where hum is being heard.

Ground loops are by far the most common offender, followed by 60Hz coupled from AC power onto cables.

This message was edited by bcf1963 on 03/05/05 14:45 ET.

Alan, no hard feelings here. I accept responsibility for the miscommunication, but I do defend it. I went back through the entire thread and found all the references to signal-level ground-loop-breaking devices:

car stereo transformer-coupled ground lifter
cable TV isolator
hum eliminators
ground loop isolator
RCA analog isolator
coax ground isolators

Notice none has the word 'isolation', and only one of them has the word 'transformer' in it. Even the equipment sites linked to use different terms:

Ground Guard
Cable TV RF Isolator


Therefore, when you said: "Either place the electrical breakers on the same phase or purchase an isolation transformer(Italics mine) made for sub-woofers.", I understandably took that to mean what is typically referred to by the term; a 1:1 power isolation transformer, usually with an electrostatic shield between the primary and secondary.

Plus, enclosed units are usually equipped with a cord and plug and a receptacle, and the grounding conductor is always directly connected between the power cord and the output receptacle. These units do eliminate the DC path between primary and secondary, but not for the grounding conductor.

You are absolutelt correct that RF and AV ground breakers are almost always transformer-coupled devices. However, another simple, free, and effective option is to eliminate connecting (if building cables) or to cut through the shield (if using assembled ones) at one end of the offending interconnecting cable.

This message was edited by Larry Fine on 03/05/05 15:34 ET.

And this is my point,
[Link: remotecentral.com]

I guess this thread never existed nor did any of the 4000 others on the subject of gound loops here, AVS and god knows how many other sites. Pardon my over reaction to what I fear will be still more ignorence of what you call ground breakers I call isolation transformers. Lord knows what confusion would ensure if an attempt at explaining when and wny high voltage isolation transformers ought to be used.

Reading your comments, Larry, caused me to go back and try to figure out if isolation transformer is the incorrect name for what you call a ground breaker. I read through the papers on Jensen's web site and found hardly a mention of isolation transformer but did find ground breaker. I googled isolation transformer and found the results 50/50 between high voltage and low voltage. Perhaps we are both correct and incorrect in applying or misapplying the term. I have always thought the correct technical term was isolation transformer, eg., [Link: blackmagic.com]

Does this site have a serach facility or is it that too many prefer not to use it? Ground loops are common in both interconnected audio and video systems. There are really no short cuts to solving them save hard work, common sense and Jensen transformers or similar product. But I wonder how many more discussions on this topic will there be. I really did try to stay out of it. I shall really have to try harder, especially as I seem to be rubbing some like Mr. Rick the wrong way. I, too, apologize Larry if I came across as too much a prig but I do wish someone would at least attempt to seach for past threads on the topic before posting anew.

Alan