Electrician's advice wanted: safely lifting ground

"Consequently, if your house is properly wired the grounding plug has virtually no benefit."

I would be very careful with statements like that. Imagine hot wire inside of the box getting loose and touching ungrounded chassis. In order to get rid of grounding plug device has to be designed (and tested) differently. Your statement suggests that one, being sure house is wired properly, can safely use cheater plug.

I was born in the 1950's (in the US) and I have many exciting memories of plugging in those loose cords for waffle irons, etc and seeing the insulation blow off the cord in blazing red glory. Those were the days! Space heaters that would set the newspaper on fire. Life used to be exciting.

Speaking of the US and probably for the rest of the world, electrical devices have gotten very wimpy. My main complaint is that 12 volts will not kill anyone so most computer stuff has a transformer brick so the manufacturer can kind of do what he wants to mess things up.

But, there are also now "polarizing" plugs and "grounding" plugs. There were not many vacuum cleaners with ground plugs made in the 1970's. And they consume lots of juice.

The big danger is that there are certain devices like hot plates that are definitely polarized so that they can look like they are off but are still electrified. These are a very big shock hazard and polarizing plugs are necessary.

What has led the massive use of grounding plugs in the past two decades is that there may be a chance that the house has been wired incorrectly and that the polarizing plug will not have the correct hot, neutral configuration.

Consequently, if your house is properly wired the grounding plug has virtually no benefit.

But that being said, I play Devil's Advocate but follow the rules in the end.

For US and Canada the Ebtech HumX is a way to isolate the ground and still follow electrical code.

The trick is that these ground lines can get in all sorts of ways. Through coaxial cable for television (these require grounding at the house drop) and unbalanced interconnect lines.

I do have a question and that is whether RJ-45 (ethernet cable) introduces a ground loop? That is becoming a new possible threat as are HDMI and DVI cables.

sorry, Jea48. I am not familiar with the specifics of the transformer. But I believe the answer to your question is yes. One amp had signal ground connected to the chassis and one did not.

Coincidentally, I believe that it was work on a pair of new monoblocks that my electronics guy has been doing which gave such a quick solution. He had been struggling with just such ground loop before finding the answer. ;-)

I think it was probably comments from some of those guys using cheater plugs that prompted my starting this thread.

Jea48, our forefathers did not have this fun as their ac was ungrounded. With their stuff in wood boxes, I guess they were safe.

Yes, it is two paths to ground when one amp has a connection from input to chassis ground and one does not. Because chassis ground is relative to the transformer ground on each amp, and the transformers don't tap at the exact same voltage, so there is a potential created between the two amps. The slight ground current is running from one amp to the other via the input cables. Two paths to ground.

Dan_ed,

Then what you are saying amp A had the signal ground connected to the chassis ground, amp B did not. Correct?

Because chassis ground is relative to the transformer ground on each amp, and the transformers don't tap at the exact same voltage, so there is a potential created between the two amps.

the transformers don't tap at the exact same voltage, so there is a potential created between the two amps.

Primary or secondary windings? Can you be more specific....

Over the years I have read threads where guys with mono amps tried everything to rid them selves of a ground loop hum. Only in the end forced to use ground cheaters.

Yes, both sets of jacks are isolated from the chassis. However, one amp had it's inputs tied to chassis ground so in effect one set of inputs was connected to chassis and one was not.

Either amp, used by itself, is completely quiet.

Yes, it is two paths to ground when one amp has a connection from input to chassis ground and one does not. Because chassis ground is relative to the transformer ground on each amp, and the transformers don't tap at the exact same voltage, so there is a potential created between the two amps. The slight ground current is running from one amp to the other via the input cables. Two paths to ground.

I agree, amp A was creating the potential through that input chassis ground. Lifting the ground on the inputs on amp A did break the loop.

As I said, this does fix the problem safely. I don't mind continuing the discussion in the hope that someone else will find this helpful. Ground loops can be very difficult to solve and I know how much time I spent on this.

This stuff is only fun after you find the solution. :-)

Are the jacks on both amps insulated from the chassis? You mention that Amp A has a ring suggesting that the inputs are in fact isolated. Have you tried only having Amp B on to see if you have hum? Or only Amp A on? I suspect that Amp A is causing your problem as it has two paths to ground. I have never known two components causing the ground loop, but rather two paths to ground causing the problem.

Did I confuse things by not stating that there are no cheater plugs in use? :-) I do have a habit of glossing over fine details.

I'll try to explain, which means I just may botch this up. :-)

The hum was only between the two amps. Everything upstream unplugged. Only the amps were on. Ground loop between the two amps. The cheater plugs proved this.

Now, amp A had a ground connection from both input (-) rings over to chassis ground as well as the (-) wire going back to the power supply. Amp B had no such chassis ground on the inputs. Both amps have chassis ground from the transformer.

The transformers in the power supplies of the two amps don't tap to identical potential. So you get a ground current between the transformer taps on both amps and it hums like crazy because there are two paths to ground through both amps due to the leakage. Remove the connector ground to chassis (which is really the transformer tap) and no more leakage.

Tbg,

IT is not the chassis ground! Chassis ground is intact, still there, grounding away, at the AC input. The inputs to both amps are grounded back to the preamp.

The lift is to the input connections ONLY, and they are tied to the power supply ground. Everything is grounded! Why doesn't it hum anymore?

One amp had an ADDITIONAL ground from the inputs to the chassis, one did not, simply due to different type of connectors.

Take a look at Rogue, Bryston, any other manufacturer that provides a ground lift. This is what they do also.

Dan ed, your solutions is good only for components in which the input and output jacks are isolated from the chassis. I have seen few where there is such isolation.

Lifting the chassis ground is dangerous if there is a hot wire in contact with the chassis and you are grounded and can complete the circuit, such as being barefooted or touching the defective chassis and another grounded one.

My line stage only operates at it max if all other components have no ac ground but it does. Would Underwriters Labs take exception to this and deny certification to a manufacturer doing this? Yes. Would you city electric department? No. Do I feel unsafe? No.

is why are you using equipment that is so poorly designed that you have to lift the ground to avoid hum?

Thanks for your opinion, but did you read my last two posts?

The only ground lifted is the chassis ground to the INPUT connectors. The chassis is still grounded at the power input to the amps. There is no safety issue with my solution.

Folks. I did contact the person who built/mod'd my amps and it was he who provided the solution based on my experiments to track it down. Once I opened both amps, the problem was clear. One amp was using wbt input connectors and had a connection between the ground rings and chassis ground. The other amp did not have such a ground connection. The are not mono-block amps, just two stereo amps bought from different people who chose different options as far as the input connectors are concerned. Things are still grounded through the power cords.

The cause is that the center taps on the transformers are not identical and you get a ground loop current between the amps when their inputs are connected together. Simple once I saw that one amp did one thing with input ground and the other didn't.

Not completely sure where I got the idea I originally posted about. Probably from reading forum posts. ;-) :-)

The danger from electric shock depends on several factors including but not limited to the persons own electrophysiology, the impedance of the person at the time, and the current path through the body. None of these depend on the potential. For example, an arm to arm path will result in more current flowing through the heart than most other paths and put you at more risk of vfib - not a fun thing. While a GFCI provides protection (in a different manner than a grounded chassis) the question to really ask is why are you using equipment that is so poorly designed that you have to lift the ground to avoid hum? And, no, hum is not unavoidable and "just part of the unique, wild and dangerous life of the audiophile." In short, there is no excuse or valid reason for placing yourself at any additional risk in this regard. Remember, there are those who in bygone days would use pennies rather than fuses in their panel. Just because something works (look ma, the lectrics on and ain't never gonna blow that penny, plus we done saved 14 cents on the fuse) doesn't mean its a good idea (darn ma, the house burnt down, with junior long with it - oh well, them's the breaks). Do not defeat safety grounding, don't smoke, use your seat belt, avoid crack - just common sense.

yeah.. I'm sort of surprised too that the origin of the loop wasn't or isn't being addressed by the Jensen idea or some other like Dayton. Finding the unit causing it I'd think is the better approach, if after all, you want to do things the right way here.

Outsiders do not appreciate the dangers audiophiles routinely embrace . . . all for the love of music . . . Courage!

Wow, what a great thread, I really like (and agree with) Elizabeth's rules for living, and who'd believe someone would actually quote Captain Beefheart. Way to go, Pehare. This thread has really brought out the "inner poet" in you two.

Regarding ground loops, consider trying Jensen input transformers just ahead of your amps. Totally solved my problem going from a single-ended preamp to my balanced only amps. Went from all sorts of noise (almost sold the Clayton's) to dead-nuts quiet. Go to their website and give them a call - very helpful folks and the stuff is not that expensive. BTW, since you have "multiple amps" be aware that they sell single line models of the transformers that may be logistically easier for you than the twin versions shown on the website. They will make them as you need, rca-rca, xlr-xlr, rca to xlr, and xlr to rca.

yeah, some folks are afraid of tube amps, imagine that. like capt. beefheart said it's "safe as milk" :)

Dan_ed - If device was designed with grounded chassis removing this ground creates danger of high voltage appearing on the metal and killing somebody. Yes, a lot of things would have to go wrong but that's how accidents happen. I'm not sure if GFCI can legally replace ground but at least gives you some protection. Imagine that hot 110V wire got loose and touches case inside while person places hand on the case touching another piece of equipment that is grounded. Current will flow thru the body but won't return to GFCI Neutral. GFCI will "see" different currents coming out and returning and will switch off.

It is not safe. Thanks anyway, I got the answer and a better solution. :-) There is a ground wire that runs between the grd at the input connectors and over to a chassis ground near the ac inlet. I removed that connection and things are every bit as quiet as with the cheater plugs. I'll get a switch to mount on the back and use that as a grd lift. The power supply is still grounded and all is well. Happy feet!

So what's wrong with the cheater plugs? Parasound amps were noted for having to use cheaters to avoid the hum. A GFCI isn't going to change anything. Gound wire and neutral wire are tied together in the panel anyway, technically.