Chris Davis Messages: 1695 Registered: May 2004 Location: USA
Has No Life
Evan Kirkendall wrote on Mon, 24 October 2005 22:22
I was just looking at the waveforms and they look really weird...
Doesnt seem normal...
Thoughts?
Evan
There are really two different types of noise I have found with laptops/audio. One is the 60Hz fundamental hum / associated 60Hz harmonics.
The other is what some have already coined as "digital hash". I suspect that is the fault of the laptop and not an external ground loop.
In this case I am led to believe that the internal neutral or common ground is "saggy" and not all too stable with the internal electronics. This might be due to poor power supply design, poor internal wiring, or perhaps even the circuitry itself (perhaps some internal compenents have a neutal-switching design).
Another possibility may be inducted noise, but that would not necessarily explain why external soundcards can be susceptible to this noise if grounded but then just fine if the ground is lifted (cheater plug).Like I always say, there's no "I" in "team". There is a "me", though, if you jumble it up.
And humility is an important quality. Especially if you're wrong a lot...Of course, when you're right, self-doubt doesn't help anybody, does it?
-House MD
Lee Patzius Messages: 1829 Registered: April 2004 Location: St. Louis MO
Has No Life
It's a ground loop. Pure and simple. Yes, it's a digital hash, high speed chirpy sound. I've heard similar sounds on my analog police/fire radio type scanner.
And yes, I lifted the grounding prong on my laptop's DC supply. But this only puts a bandaid on the problem, and breaks the grounding loop.
Is it right? NO.
Is it safe? NO.
I know I'm taking a huge risk.
Of course, with a lifted power ground prong, a fault to the grounding conductor from the computer power supply will find a path to my console, down micro small audio shields, and most likely blow the comp's DC supply fuse, or after that, the audio shields will act as a fuse, and catch fire, or smoke, until it opens.
Then, if I touch any metal part on the computer, I'll be hot. But I say... What metal? No matter what... Smoking cables, along with the first problem, a fault to ground, adds fuel to the fire.
The cure to all this, is a pair of isolation transformers, which allows you to break the groundloop.
Chris Davis Messages: 1695 Registered: May 2004 Location: USA
Has No Life
I think it is a ground loop too, but just internal to the devices in question. Excluding your radio example, it seems most people are pointing to the laptop computer / laptop computer power supplies as the culprits and not necessarily the external power lines. That is an important distinction to me because by doing so, you rule out any audio equipment which does happen to be wired up/working properly (which hopefully is all of it)...Like I always say, there's no "I" in "team". There is a "me", though, if you jumble it up.
And humility is an important quality. Especially if you're wrong a lot...Of course, when you're right, self-doubt doesn't help anybody, does it?
-House MD
Michael E. Messages: 379 Registered: May 2004 Location: TN
Has No Life
blah blah blah I still don't believe the ground on a laptop power supply is really going to help anything. It's not that I think grounds are unimportant, just that there is no situation where there is going to be mains voltage shorted to ground inside the power supply unless someone is just doing something dumb. I think the ground is there so these cheapo companies didn't have to go through all the hassles of making a decent power supply, so they just stuck that on there and copped out of a bunch of extra tests. Of course, it's not just the power supply that's the problem - it's the cheapo built in sound card too - just noone noticed it before because there was no secondary ground connection.
If you roll over the cord with your chair, you are a dumbass - tough stuff buddy. If you drop a laptop power supply in the tub - it's probably going to shock the hell out of you for a bit before the breaker trips anyway. For those of you that are really worried about this, you need to go buy one of those inline GFCIs and put it before your laptop (just incase the power supply were to shit itself ). It doesn't care if you have a ground or not. I'd rather be sailing
Lee Patzius Messages: 1829 Registered: April 2004 Location: St. Louis MO
Has No Life
Chris Davis wrote on Tue, 25 October 2005 10:38
I think it is a ground loop too, but just internal to the devices in question.
Hi Chris,
Since breaking the grounding conductor from the 120/240VAC system stops the noise, then that leads me to believe that the DC output of the laptop's supply is tied directly to the grounding conductor, and passing through directly to the the computer's soundcard chassis as well.
A lot of these power supply devices also have "pi-filters" which dumps hash or noise current, except 50/60Hz, right onto the grounding conductor. The pi filter is symmetrical, it works both ways, from source to load or load to source, it dumps noise from both hot and neutral, to ground.
I can't tell you where the noise source is from, but it does seem to be backfeeding and infiltrating through the power supply's DC output section, and dumping onto the grounding conductor. That's seems OK, as long as there is only one path, and no loop. Hence, floating headphones are quiet.
But of course, if the shield of the chassis grounded unbalanced output of your laptop goes into your console directly, you have a grounding loop.
Quote:
Excluding your radio example, it seems most people are pointing to the laptop computer / laptop computer power supplies as the culprits and not necessarily the external power lines. That is an important distinction to me because by doing so, you rule out any audio equipment which does happen to be wired up/working properly (which hopefully is all of it)...
Regardless of the noise source, or pin 1 problem equipment, etc. etc., unless you have transformer isolation, you will have a ground loop. And of course, we all heard what that loop does.Lee Patzius
Lee Patzius Messages: 1829 Registered: April 2004 Location: St. Louis MO
Has No Life
Michael E. wrote on Tue, 25 October 2005 10:55
For those of you that are really worried about this, you need to go buy one of those inline GFCIs and put it before your laptop (just incase the power supply were to shit itself ). It doesn't care if you have a ground or not.
I agree. On the power side of things, in theory, a nice Hubbell GFCI with a 2 Prong cheater adapter is a much better way to go, than just using a cheater adapter by itself.
Disclaimer... I have not tried it (on a laptop connected to the console) but it should protect you if the 2 prong cheater is plugged into either the line or load side.
On the supply side, this is one case where I totally recommend the use of a 2 prong cheater adapter, rather than busting the third prong off the Hubble adapter.
As Michael E already stated, the GFCI does not need a grounding conductor to sense a hot/neutral differential. A hot fault to an audio shield will trip the GFCI at only 4mA or so.
Bennett Prescott Messages: 8377 Registered: August 2004 Location: Central CT
Has No Life
Michael E. wrote on Tue, 25 October 2005 10:55
blah blah blah I still don't believe the ground on a laptop power supply is really going to help anything. It's not that I think grounds are unimportant, just that there is no situation where there is going to be mains voltage shorted to ground inside the power supply unless someone is just doing something dumb.
I don't see why that makes it any less justified. When transformers fail it's because they overheat, melt insulation, and short out, which quite often shorts mains voltage to ground. People do dumb things all the time, you and I included, and frankly I'd rather have an extra layer of protection between myself and wall voltage whenever possible. The grounding system is an extremely well thought out and effective system that has proven its worth for decades.
Obviously you aren't here to be convinced, however. What you do with your equipment is your prerogative.-- Bennett Prescott
Director of North American Sales ADRaudio d.o.o.
Cell: (518) 488-7190
Bennett Prescott Messages: 8377 Registered: August 2004 Location: Central CT
Has No Life
Lee Patzius wrote on Tue, 25 October 2005 12:37
I agree. On the power side of things, in theory, a nice Hubbell GFCI with a 2 Prong cheater adapter is a much better way to go, than just using a cheater adapter by itself.
Yes! This is the correct way to "lift" grounds if you can't transformer isolate the signal path.-- Bennett Prescott
Director of North American Sales ADRaudio d.o.o.
Cell: (518) 488-7190
John Roberts {JR} Messages: 10485 Registered: April 2004 Location: MS
Has No Life 10,000+
Michael E. wrote on Tue, 25 October 2005 09:55
blah blah blah I still don't believe the ground on a laptop power supply is really going to help anything. It's not that I think grounds are unimportant, just that there is no situation where there is going to be mains voltage shorted to ground inside the power supply unless someone is just doing something dumb. I think the ground is there so these cheapo companies didn't have to go through all the hassles of making a decent power supply, so they just stuck that on there and copped out of a bunch of extra tests. Of course, it's not just the power supply that's the problem - it's the cheapo built in sound card too - just noone noticed it before because there was no secondary ground connection.
If you roll over the cord with your chair, you are a dumbass - tough stuff buddy. If you drop a laptop power supply in the tub - it's probably going to shock the hell out of you for a bit before the breaker trips anyway. For those of you that are really worried about this, you need to go buy one of those inline GFCIs and put it before your laptop (just incase the power supply were to shit itself ). It doesn't care if you have a ground or not.
Yes, consumer PS transformers are routinely double insulated. I have even triple insulated one design to avoid having to do a long thermal aging test and get a product to market a few months faster. So these products are designed to high safety standards. That doesn't change the fact that stuff happens.
Dangerous accidents aren't caused by what we don't know but by what we think we do that is wrong. From reading the reports of who gets zipped each year, a large percentage are technicians and experienced workers who should know better.
I hope the lurkers here don't get the impression that it's ever OK to ignore safety grounds. If the ground pin on a PS plug wasn't serving a purpose the manufacturer wouldn't spend the extra $0.01 to put it there.
Good luck to all, some may need it more than others.
Watch your elected representatives. Then next November give them their job review, with your vote.
----
Tune it, or don't play it...
-----
and it's spelled bus.... Thank You and good night
Michael E. Messages: 379 Registered: May 2004 Location: TN
Has No Life
John Roberts {JR} wrote on Tue, 25 October 2005 13:01
I hope the lurkers here don't get the impression that it's ever OK to ignore safety grounds. If the ground pin on a PS plug wasn't serving a purpose the manufacturer wouldn't spend the extra $0.01 to put it there.
What I'm saying is they spent the extra $0.01 to put it there because it saved them the $0.05 cents that it would take to do it a better way.
My $0.02...
I agree that its not ok to ignore a safety ground. I just think that in this case, there isn't much more safety to be had. Just a wolf in sheeps clothing so everyone jumps to save it...
Michael E. Messages: 379 Registered: May 2004 Location: TN
Has No Life
Bennett Prescott wrote on Tue, 25 October 2005 12:41
I don't see why that makes it any less justified. When transformers fail it's because they overheat, melt insulation, and short out, which quite often shorts mains voltage to ground. People do dumb things all the time, you and I included, and frankly I'd rather have an extra layer of protection between myself and wall voltage whenever possible. The grounding system is an extremely well thought out and effective system that has proven its worth for decades.
Obviously you aren't here to be convinced, however. What you do with your equipment is your prerogative.
I hear what you are saying, but you could apply this to any piece of gear with an ungrounded supply for that matter. Verb in your rack, the who-knows-how-many-millions of ungrounded laptop supplys already out there. If you want to be safer than sorry, use a GFCI. Grounds are great - yes - but aren't always going to save you. Remember it's the path of LEAST resistance. It still could get you or Joe Blow. Some stupid person could have forgotten to connect something here or there that you don't know about. There is just as much "chance" other things down the line could be faulty as there is of the psu being faulty.
Bennett Prescott wrote on Tue, 25 October 2005 12:42
Yes! This is the correct way to "lift" grounds if you can't transformer isolate the signal path.
It's not really removing the ground per say as it is replacing one safety method with another that works with less "notice". GFCIs should have routine checks to make sure they are still working too. I'd rather be sailing
John Roberts {JR} Messages: 10485 Registered: April 2004 Location: MS
Has No Life 10,000+
Michael E. wrote on Tue, 25 October 2005 09:55
blah blah blah I still don't believe the ground on a laptop power supply is really going to help anything. It's not that I think grounds are unimportant, just that there is no situation where there is going to be mains voltage shorted to ground inside the power supply unless someone is just doing something dumb. I think the ground is there so these cheapo companies didn't have to go through all the hassles of making a decent power supply, so they just stuck that on there and copped out of a bunch of extra tests. Of course, it's not just the power supply that's the problem - it's the cheapo built in sound card too - just noone noticed it before because there was no secondary ground connection.
If you roll over the cord with your chair, you are a dumbass - tough stuff buddy. If you drop a laptop power supply in the tub - it's probably going to shock the hell out of you for a bit before the breaker trips anyway. For those of you that are really worried about this, you need to go buy one of those inline GFCIs and put it before your laptop (just incase the power supply were to shit itself ). It doesn't care if you have a ground or not.
At the risk of flogging this dead horse beyond recognition there is a useful distinction about proper safety grounds, namely they will bond dangerous voltages to ground no matter where they come from. Who knows which unit in the chain will decide to take a poop but as long as that rouge path is adequately bonded to ground the mains breaker will trip.
In theory, this means as long as all the products in your chain have adequate internal ground bonding (and adequate wiring between) you only need to plug one in with a 3 wire plug. That said I've seen enough questionable designs and practices that in practice I wouldn't make that gamble.
The agency (safety) tests require some tens of amps of current bonding with minimal voltage rise, but one could weasel out of that requirement by not labelling the ground as a ground . With the amount of products that don't even treat pin 1 properly, do you feel lucky?
Watch your elected representatives. Then next November give them their job review, with your vote.
----
Tune it, or don't play it...
-----
and it's spelled bus.... Thank You and good night
Andrew Roberts Messages: 69 Registered: June 2004 Location: Maryland, USA
Should Get Out More
I'm with Michael E. and some others on this one. Yes, safety grounding is something to be honored and always utilized within convention. It is a great system that I'm sure has saved many lives and lots of gear. At the same time, I think that using a lift on the PS of my laptop does not inherently increase the risk of damage or injury (compared to its current state) unless some wayward soul begins to thrash it with a hammer or use it to stir his cocktail.
That being said, I will purchase an in-line GFCI for this set-up as extra insurance with a nod to John Roberts and the the very zealous Mr. Prescott. Bennett, please be advised that stress, anger and anxiety are just as dangerous as 120V AC but it takes a bit longer to kick in.
My thanks to you all and I will think of you as I listen to my noise free system (from the compuetr that is) and glance down at my untripped GFCI unit.
John Roberts {JR} Messages: 10485 Registered: April 2004 Location: MS
Has No Life 10,000+
Andrew Roberts wrote on Tue, 25 October 2005 18:40
I'm with Michael E. and some others on this one. Yes, safety grounding is something to be honored and always utilized within convention. It is a great system that I'm sure has saved many lives and lots of gear. At the same time, I think that using a lift on the PS of my laptop does not inherently increase the risk of damage or injury (compared to its current state) unless some wayward soul begins to thrash it with a hammer or use it to stir his cocktail.
That being said, I will purchase an in-line GFCI for this set-up as extra insurance with a nod to John Roberts and the the very zealous Mr. Prescott. Bennett, please be advised that stress, anger and anxiety are just as dangerous as 120V AC but it takes a bit longer to kick in.
My thanks to you all and I will think of you as I listen to my noise free system (from the compuetr that is) and glance down at my untripped GFCI unit.
Flog flog flog.... OK, there's another relatively inexpensive way to lift a ground and maintain a safely bond to ground if voltage differences are modest. Using back to back diodes (not series but oposing polarity in parallel) between the chassis and power ground will provide isolation for voltages below one or two diode drops, but will conduct for larger fault conditions.
I have done the before on studio gear and it works. It isn't blessed by UL, but I had conversations with them (years ago) and they were receptive, if I'd pay for extensive testing. They did some preliminary work to confirm what I was saying was feasible.
If you're providing a path for tens of amps you can't use tiny signal diodes but you don't have to use diodes rated for the full fault current either. The failure mode for diodes from over current (heating) is to short circuit, which is useful in this case. Of course even a shorted diode will have finite resistance and dissipate watts of power under heavy current flow. To keep the diodes from vaporizing I used PS bridge rectifiers. Remember they only need to survive long enough to trip the mains breaker.
Building the diode trick into a GFI would give you even more protection. Perhaps building the diode trick into a shorty cheater cord might be somewhat safer than the common lift/cheat done under the time duress of live audio emergencies. If the voltage potential is too large to isolate with diodes you probably need to make that right anyhow.
Watch your elected representatives. Then next November give them their job review, with your vote.
----
Tune it, or don't play it...
-----
and it's spelled bus.... Thank You and good night
Jim Bowersox Messages: 1095 Registered: April 2004 Location: Annapolis, MD
Has No Life
So you guys are telling me that this switch should not be used?
The switch next to the power inlet indeed says "AC GROUND LIFT." Nice. The offending rack has 2 Ramsa PSUs, 5 or so PLX amps, some DSP, and some EQ's in it. Nice.
Forum Home
Login
Forum Search
Register
FAQ
). It doesn't care if you have a ground or not. 
. With the amount of products that don't even treat pin 1 properly, do you feel lucky?
