Blulite
hi guys. as a follow up to my amp problem the other day i have discovered i am recieviin a high pitched feedback through the speakers when i connect the power cable to my laptop. ive played around with the sound options but nothing is working other than unplugging the power cable.
any ideas??
any ideas??
Posted Tue 12 Apr 11 @ 7:04 am
John Doe 1x67s
Very common problem known as ground loop. Meaning that your computer has a so called grounded power connector which you need to isolate by adding a ground insulator between the power socket and connector or if your computer's power cord is interchangable, change it to non-grounded one. For example, Mac's have power supplies with interchangable power connectors, so you can choose between grounded and non-grounded.
Posted Tue 12 Apr 11 @ 7:25 am
JoeyKJ
Posted Tue 12 Apr 11 @ 7:51 am
Dazmax
Hmmm
Hi pitched sound. Hi pitched noise tends to be an instability problem (The amp becomes an ocillator at a specific frequency) rather than good old mains hum This shows up as a 50Hz or 100Hz noise on the output of the amp.Both can be caused by earth/ground loops though. What connector is on the input to your power amp. You mentioned before that it is an H/H but you didn't mention the model. H/H amps used to have frequent problems with an internal part of the circuit that forms a suppression Network. Sounds complicated but it is just a capacitor and an inductor that is conected in series between the output of the power amp and the speaker jack (This circuit is used to stop the power amp ocillating and improves its stability). if the amp is as vintage as I suspect then this could well have failed. If you still have problems after the following fixes then get this checked. Its usualy only a 20P capacitor that needs changed.
As has been suggested take a look at a replacement laptop power supply. look for one which is double insulated. The hum X device is not currently BS standard safety rated for use in the UK but don't worry there are lots of other things that can help.
For example. some older stereo power amps can have stability problems when both the inputs have their screen wires are connected to ground. Try lifting or as a temp mesure placing some insulating tape around the screen conection (Larger metal portion on a 1/4" jack plug) on one of the jacks at the amp end.
There are some other mods you can make to a standard stereo mini jack to twin mono1/4" jack cable but we will save that for later.
Worst case look at buying a stereo isolating transformer to de couple the ground line between your laptop and the amp.
Daz
Hi pitched sound. Hi pitched noise tends to be an instability problem (The amp becomes an ocillator at a specific frequency) rather than good old mains hum This shows up as a 50Hz or 100Hz noise on the output of the amp.Both can be caused by earth/ground loops though. What connector is on the input to your power amp. You mentioned before that it is an H/H but you didn't mention the model. H/H amps used to have frequent problems with an internal part of the circuit that forms a suppression Network. Sounds complicated but it is just a capacitor and an inductor that is conected in series between the output of the power amp and the speaker jack (This circuit is used to stop the power amp ocillating and improves its stability). if the amp is as vintage as I suspect then this could well have failed. If you still have problems after the following fixes then get this checked. Its usualy only a 20P capacitor that needs changed.
As has been suggested take a look at a replacement laptop power supply. look for one which is double insulated. The hum X device is not currently BS standard safety rated for use in the UK but don't worry there are lots of other things that can help.
For example. some older stereo power amps can have stability problems when both the inputs have their screen wires are connected to ground. Try lifting or as a temp mesure placing some insulating tape around the screen conection (Larger metal portion on a 1/4" jack plug) on one of the jacks at the amp end.
There are some other mods you can make to a standard stereo mini jack to twin mono1/4" jack cable but we will save that for later.
Worst case look at buying a stereo isolating transformer to de couple the ground line between your laptop and the amp.
Daz
Posted Tue 12 Apr 11 @ 3:22 pm
Techno_Tom_57
I overcame this problem along time ago, I also checked with an electrician before doing the following;
Take the plug end of the laptop power cable, Cut of the plug completely (usually a black moulded plug). Put on a new plug and DO NOT wire the earth in the plug. THIS WILL STOP ANY HUM / NOISE when you have your laptop plugged in.
Basically you do not need the earth wired as you are going from 240V MAINS <> down thru the transformer to usually 19Volts then to your laptop which although is LIVE its not massive voltage and doesn't need to be earthed.
You will have no buzz, no noise, nothing and you can charge from the mains while doing a gig. This burst my head for about 6 months and I spoke with an electrician as I was not sure about doing it.
TRUST ME it works and never looked back.
Cheers
Techno
Take the plug end of the laptop power cable, Cut of the plug completely (usually a black moulded plug). Put on a new plug and DO NOT wire the earth in the plug. THIS WILL STOP ANY HUM / NOISE when you have your laptop plugged in.
Basically you do not need the earth wired as you are going from 240V MAINS <> down thru the transformer to usually 19Volts then to your laptop which although is LIVE its not massive voltage and doesn't need to be earthed.
You will have no buzz, no noise, nothing and you can charge from the mains while doing a gig. This burst my head for about 6 months and I spoke with an electrician as I was not sure about doing it.
TRUST ME it works and never looked back.
Cheers
Techno
Posted Tue 12 Apr 11 @ 5:09 pm
sah602
Been using this for over 4 years now with two different laptops! works great and cheap also!
http://www.amazon.com/GE-Polarized-To-Grounding-Adapter/dp/B00006IBFB
http://www.amazon.com/GE-Polarized-To-Grounding-Adapter/dp/B00006IBFB
Posted Tue 12 Apr 11 @ 5:54 pm
JoeyKJ
What you've done is very dangerous, and not reccomended, use a isolator or a groud loop device for your own protection and other, doin't play Russion Roulette with your life....
Good Luck,
Joey....
Good Luck,
Joey....
Posted Tue 12 Apr 11 @ 6:00 pm
Dazmax
Sorry but this is in no way safe.
Earth/Ground connections are there for a reason. Your electrician should be SHOT for recomending this. There are replacement power supplies available that are double insulated and do not require Earth/Ground connections. Buy one of these. Do not go around modifying one that does.
Power supplies that have an Earth/Ground connection do so because they DO NOT PROVIDE FULL TRANSFORMER ISOLATION (usualy this is because of non isolated feedback circuitry in the sensing line of the PSU. Double insulated units have this line Opticaly Isolated.) and do not meet the requiements needed to provide full double insulation.
Almost all laptop PSU's are Switched mode types and not simple step down transformers. They take your 120-240V ac supply and rectify this to give a 3-350V DC supply. This is then "chopped up" to provide a high frequency regulated AC voltage. This is fed through a small transformer before being rectified again to provide your 19V dc.
Is it realy worth risking your, or someone elses life for the price of a replacement power supply????????
Daz
Earth/Ground connections are there for a reason. Your electrician should be SHOT for recomending this. There are replacement power supplies available that are double insulated and do not require Earth/Ground connections. Buy one of these. Do not go around modifying one that does.
Power supplies that have an Earth/Ground connection do so because they DO NOT PROVIDE FULL TRANSFORMER ISOLATION (usualy this is because of non isolated feedback circuitry in the sensing line of the PSU. Double insulated units have this line Opticaly Isolated.) and do not meet the requiements needed to provide full double insulation.
Almost all laptop PSU's are Switched mode types and not simple step down transformers. They take your 120-240V ac supply and rectify this to give a 3-350V DC supply. This is then "chopped up" to provide a high frequency regulated AC voltage. This is fed through a small transformer before being rectified again to provide your 19V dc.
Is it realy worth risking your, or someone elses life for the price of a replacement power supply????????
Daz
Posted Wed 13 Apr 11 @ 12:34 am
Dazmax
Hi all
One other perhaps less important issue here is that many PSU's with an Earth/Ground requirement use the Earth/Ground terminal as part of the mains input surge suppression circuit. This circuit is designed to route mains born surges and spikes harmlessly to ground. lifting this conection can defeat this circuit's function and leave the PSU/laptop vulnerable to damage.
Daz
One other perhaps less important issue here is that many PSU's with an Earth/Ground requirement use the Earth/Ground terminal as part of the mains input surge suppression circuit. This circuit is designed to route mains born surges and spikes harmlessly to ground. lifting this conection can defeat this circuit's function and leave the PSU/laptop vulnerable to damage.
Daz
Posted Wed 13 Apr 11 @ 4:43 am
Techno_Tom_57
Well if that's the case explain why when you buy a 42" TV that they are wired with just Brown (Live) and Blue (Neutral) and most modern TV's are not earthed ?
You are also going from mains 240V (3 Pin) down to a transformer and carrying no more than 20V into a laptop.
If anything were to blow this would take out the fuse in the plug, Also this would get caught via the surge protector the whole thing is plugged into.
The hum is when all this is connected and pushed thru the AMP and it amplifies the earth this is where the NOISE comes from.
I can assure you I have checked this out and been running like this for at least 2yrs and not had any problems HUM, TRIP, BLOW or otherwise I wouldn't put myself at risk and wouldn't pass on this information if it were dangerous.
At the end of the day it is up to you if you do it or not, I am only passing on what worked for me. Regards the old car stereo Loop Isolator's I have tried these and they only reduced the HUM but when you are driving big power thru a system they didn't totally cure the problem, But as I said it is entirely up to you if do this!!
Cheers
Techno
You are also going from mains 240V (3 Pin) down to a transformer and carrying no more than 20V into a laptop.
If anything were to blow this would take out the fuse in the plug, Also this would get caught via the surge protector the whole thing is plugged into.
The hum is when all this is connected and pushed thru the AMP and it amplifies the earth this is where the NOISE comes from.
I can assure you I have checked this out and been running like this for at least 2yrs and not had any problems HUM, TRIP, BLOW or otherwise I wouldn't put myself at risk and wouldn't pass on this information if it were dangerous.
At the end of the day it is up to you if you do it or not, I am only passing on what worked for me. Regards the old car stereo Loop Isolator's I have tried these and they only reduced the HUM but when you are driving big power thru a system they didn't totally cure the problem, But as I said it is entirely up to you if do this!!
Cheers
Techno
Posted Wed 13 Apr 11 @ 3:07 pm
Dazmax
Techno
With respect. You have not had a problem because you are lucky enough to not have had a fault condition with your system. I will answer your points in the hope that you understand the reason why this can be a verry dangerous practice.
The 42" tv you refer to will be constructed to a standard called double insulated and is designed to operate with no Earth/Ground required. This standard requires that the manufacturer ensures that no mains derived connection can be made between the mains input and any output or conductive part of the equipment case.
I have already explained why the 240V to 20V idea is giving you a false sense of security. Please read the post.
The smallest value of mains fuse available in the UK is 5Amp. The UK health and safety board regulations state that a voltage of 30Volts ac at a current of 30mA is considered a dangerousl voltage. At 240Volts it can kill you long before the fuse even gets warm. The fuse will only fail if a short circuit condition occurs or a path to ground with a low enough resistance allows a current flow that is higher than the rating of the fuse. Without an earth conection that path could be your body and you would be dead long before the fuse.
Your description of what causes earth loop generated hum is simplystic and wrong. Hum generated by earth loops is caused by two grounded audio devices being conected together via their signal cable. A loop forms between the mains supply cables and is completed by the grounded signal cable connecting the two units together. This allows small mains frequency currents to flow in a loop and be amplified to appear at the speakers. The correct place to break this loop is in the low voltage screen linking the two pieces of audio equipment together. The fact that an earth loop is formed when using a grounded laptop power supply is in itself a demonstration of the power supplies non isolation. If you want to isolate the signal lines on two pieces of audio equipment the correct way to do this is by lifting the screen connection (at one end only) on a balanced line cable or by using a transformer/isolator with a non balanced system.
These are the ONLY SAFE METHODS that should be used to deal with this situation.
Daz
With respect. You have not had a problem because you are lucky enough to not have had a fault condition with your system. I will answer your points in the hope that you understand the reason why this can be a verry dangerous practice.
The 42" tv you refer to will be constructed to a standard called double insulated and is designed to operate with no Earth/Ground required. This standard requires that the manufacturer ensures that no mains derived connection can be made between the mains input and any output or conductive part of the equipment case.
I have already explained why the 240V to 20V idea is giving you a false sense of security. Please read the post.
The smallest value of mains fuse available in the UK is 5Amp. The UK health and safety board regulations state that a voltage of 30Volts ac at a current of 30mA is considered a dangerousl voltage. At 240Volts it can kill you long before the fuse even gets warm. The fuse will only fail if a short circuit condition occurs or a path to ground with a low enough resistance allows a current flow that is higher than the rating of the fuse. Without an earth conection that path could be your body and you would be dead long before the fuse.
Your description of what causes earth loop generated hum is simplystic and wrong. Hum generated by earth loops is caused by two grounded audio devices being conected together via their signal cable. A loop forms between the mains supply cables and is completed by the grounded signal cable connecting the two units together. This allows small mains frequency currents to flow in a loop and be amplified to appear at the speakers. The correct place to break this loop is in the low voltage screen linking the two pieces of audio equipment together. The fact that an earth loop is formed when using a grounded laptop power supply is in itself a demonstration of the power supplies non isolation. If you want to isolate the signal lines on two pieces of audio equipment the correct way to do this is by lifting the screen connection (at one end only) on a balanced line cable or by using a transformer/isolator with a non balanced system.
These are the ONLY SAFE METHODS that should be used to deal with this situation.
Daz
Posted Wed 13 Apr 11 @ 5:40 pm
Blulite
hi guys, ive fixed it, i chopped the plug, rewired without the ground and am using a circuit breaker with it. so if something does go wrong the circuit breaker will trip cutting all power to the laptop without risk to the electrical system.
no way was i forking out £70 for a plug to lift the ground. i not sure if this is a permanent solutin as of yet but i am looking for an ungrounded power cable for my acer if anyone knows where to get one
@daz, the lowest fuse you can get in the uk is 3amp, not 5...just thought id point that out lol thanks for all your help guys and thanke tor the detailed posts daz, a great help as usual.
no way was i forking out £70 for a plug to lift the ground. i not sure if this is a permanent solutin as of yet but i am looking for an ungrounded power cable for my acer if anyone knows where to get one
@daz, the lowest fuse you can get in the uk is 3amp, not 5...just thought id point that out lol thanks for all your help guys and thanke tor the detailed posts daz, a great help as usual.
Posted Thu 14 Apr 11 @ 8:46 am
Dazmax
Hi Blu
Thanks for pointing out about the 3/5 Amp fuse. I realy should re-read my posts as you are of course quite correct.
Moot point anyway as the advice is still valid. Unles there is a low resistance path to ground via the earth connection. The power plug conecting to the laptop can become LIVE under fault conditions and remain so untill something or someone gives it an alternate path to ground. The computer can even remain working with no obvious fault present. Until you touch a metal part of the computer or the power plug.
The main reason for having an Earth connection is to provide a low resistance path to ground. This ensures that should the case or any exposed metal part of an appliance become Live due to a fault condition the current will be routed to ground and blow the fuse instead of continuing to pose a risk of electrocution.
No point in bangin on about it. You have made your choice. It is the wrong choice!
Is the circuit breaker you are using an RCD type or just an over current trip? It may well not protect you for the above reason.
Daz
Thanks for pointing out about the 3/5 Amp fuse. I realy should re-read my posts as you are of course quite correct.
Moot point anyway as the advice is still valid. Unles there is a low resistance path to ground via the earth connection. The power plug conecting to the laptop can become LIVE under fault conditions and remain so untill something or someone gives it an alternate path to ground. The computer can even remain working with no obvious fault present. Until you touch a metal part of the computer or the power plug.
The main reason for having an Earth connection is to provide a low resistance path to ground. This ensures that should the case or any exposed metal part of an appliance become Live due to a fault condition the current will be routed to ground and blow the fuse instead of continuing to pose a risk of electrocution.
No point in bangin on about it. You have made your choice. It is the wrong choice!
Is the circuit breaker you are using an RCD type or just an over current trip? It may well not protect you for the above reason.
Daz
Posted Fri 15 Apr 11 @ 10:34 am
Simon Bailey
One thing to remember when altering any electrical item, is that if altered it will fail it's P.A.T (Portable Appliance Test) and will also render your public liability insurance invalid, if it is found that you altered it and an incident occured.
I cannot comment on other countries, but this holds true for the UK.
I cannot comment on other countries, but this holds true for the UK.
Posted Fri 15 Apr 11 @ 4:35 pm
Tear Em 'Up
Techno_Tom_57 wrote :
I overcame this problem along time ago, I also checked with an electrician before doing the following
Sound like the bloke you spoke with might have his head firmly implanted in his rectum. So much so in fact, that if he had diarrhea for a month he would still not see daylight. Lifting the ground from any electronic device power cable is dangerous!!!!! Have you ever seen anyone killed by electrocution? I have, it is not a pleasurable experience. Those grounding tabs are there for a reason.
This debate has been had several times on these forums. All it takes is one volt crossing your chest when your heart is between beats and you're dead!! Use a "ground loop isolator" like this or a ground lifting device like this. No other method is remotely safe, and it is not recommended by this site.
When it comes to electricity don't cut corners, and don't cut grounding tabs.......
Posted Fri 15 Apr 11 @ 6:01 pm
Blulite
@daz, hi mate, i know its the wrong choice, but its the only choice i have untill i find and purchase an ungrounded or doube shielded acer power supply. the breaker i am using is an rcd type. i use it to test faulty electrical equipment to avoid blowing the ring main. i repair a lot of varied electrical appliences, power tool etc.. the breaker is a precausion from being blown to bits by a power drill or a tumble dryer.
im not 100% certain on its exact abilities but its saved my ass several times in the past.
if anyone can point me to a replacement power supply i will gladly buy one.
im not 100% certain on its exact abilities but its saved my ass several times in the past.
if anyone can point me to a replacement power supply i will gladly buy one.
Posted Sat 16 Apr 11 @ 1:42 pm
Dazmax
Hi Blu
I am actually just starting to work on a design for an isolator to use with laptop sound cards. As soon as I get a chance I will email a parts list so you can knock one up. It will only cost you a few quid to make and will safely solve your problem.
There are isolators around but good ones are quite expensive. I want to make one that is specificly designed for our purposes.
I have a few ideas for different versions of this, to cover for single and balanced line setups but will post more when I have something up and running.
Daz
I am actually just starting to work on a design for an isolator to use with laptop sound cards. As soon as I get a chance I will email a parts list so you can knock one up. It will only cost you a few quid to make and will safely solve your problem.
There are isolators around but good ones are quite expensive. I want to make one that is specificly designed for our purposes.
I have a few ideas for different versions of this, to cover for single and balanced line setups but will post more when I have something up and running.
Daz
Posted Sat 16 Apr 11 @ 3:31 pm