Old 05-02-2011, 07:01 AM   #1
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Default Fix for a noisy laptop power supply

Thought I'd share this little fix I found in case anyone here hasn't seen it before, and suffers from the dreaded ground loop interference problem associated with laptop power supply units (PSUs).

This is quite common over here in the UK, where we have a three pin power supply incorporating an earth cable (which turns out to be the villain of the piece).

The typical scenario is that everything's fine until you need to take a signal out form your laptop audio interface and into your external amp/speakers for better listening and/or mixing.

The resulting nastiness through the speakers can include humming/pulsing/popping sounds and scratchy/crackly noises associated with on-screen mouse movements.

Suggestions on the interweb for fixing this range from using electronic hum-killing gadgetry to ripping the earth pin out from the PSU's plug with a pair of pliers!

This was the best solution I found that was, a) Fairly cheap and, b) Fairly safe.

Here's a pic of the set-up:



From left to right -
Power outlet; shaver adaptor; continental power adaptor; laptop PSU plug.

Going from 3-pin to 2-pin and then back to 3-pin again breaks the ground (earth) connection, which completely removes the source of the problem.

Although of course the earth cable is there (in the UK) for additional safety, folks on the continent seem to manage OK without it. [I've since learned that this is not the case. Thanks to Oerk for the correction in post #2]

p.s. Thanks to BimmaBlog for this: http://bit.ly/l6jERf


UPDATE:

Apart from the lack of earthing issue already mentioned, I have also noticed another problem with this method.

The shaver adaptor carries an extra-safe 1 Amp fuse (obviously for use in a potentially wet environment), while the PSU plug carries a 13 Amp fuse.

The shaver adaptor fuse carriage is physically too small to take a 13 Amp fuse (again, presumably for safety reasons), so the only way around this is to either tie the fuse carriage across with 13Amp fuse wire, or bridge it completely with a short leingth of screw or nail and thus rely on the fuse in the PSU plug.

Hmm. What started off originally as a quick and clean solution has unfortunately turned into a bit of a botch job, so perhaps on reflection, the electronic hum-killing gadgetry is probably the best way to go after all.

Ah, well. We live and learn.

Be safe!
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Old 05-02-2011, 07:21 AM   #2
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Quote:
folks on the continent seem to manage OK without it
This is not true.

The continental (Schuko) plug has two clips for earth connection on the side, not with a prong. You just aren't connecting them with your shaver adapter.

Since laptops don't have a metal casing you should be fine, but don't take my word for it. I'm not an electrical engineer.

See here: https://secure.wikimedia.org/wikiped...20050207152227
(earth is on the left and right)
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Old 05-02-2011, 07:44 AM   #3
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Quote:
Originally Posted by oerk View Post
This is not true.

The continental (Schuko) plug has two clips for earth connection on the side, not with a prong. You just aren't connecting them with your shaver adapter.

Since laptops don't have a metal casing you should be fine, but don't take my word for it. I'm not an electrical engineer.

See here: https://secure.wikimedia.org/wikiped...20050207152227
(earth is on the left and right)
Thanks for that, Oerk.

I stand corrected.

(Original post has been updated.)
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Old 05-02-2011, 08:45 AM   #4
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So, speaking of electronic hum-killing gadgetry, does anyone here use one of these?

Behringer HD400 "Hum Destroyer"



Link: http://www.behringer.com/EN/Products/HD400.aspx

Does it work?
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Old 05-02-2011, 09:00 AM   #5
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OK.

Just found this.

Quote:
Originally Posted by nofish View Post
Seems like a ground loop to me. I also had this issue with my laptop - horrible buzz.

What you can do:

- Try not to get the power all from one source. If it's possible, try to use different power circuits.

- This didn't help for me since the room I'm in has only one power circuit so I bought this:
http://www.behringer.com/EN/Products/HD400.aspx

All buzzing gone.

Note:

I only need this for a Live setup and for this the sound is fine for me with the HD400. Haven't made extensive tests if there's small sound degredation with this device that could make it useless for studio work. But must online dealers offer a return policy, so you could test it before.

Note 2:
There are also tips floating around the net to cut the ground pin on your computer or use a three to two (ungrounded) power adapter.
I'm not a expert in those things but I've read several times that this is dangerous. So don't do this.
Ah, it seems that many others have travelled this path before me! (As is often the case)

Conclusion:

Cutting out the earth = BAD
Behringer Hum Destroyer = GOOD

Sorted.
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Old 05-03-2011, 03:44 AM   #6
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I had the same problem and fixed it with a Ground Loop Isolator like this http://www.amazon.co.uk/gp/product/B...H34QWFD3RSZCE7

You plug it in somewhere beween the interface and the speakers. You can get them from maplin/ebay etc, not very expensive.
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Old 05-04-2011, 02:27 AM   #7
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Quote:
Originally Posted by AnyOtherCity View Post
I had the same problem and fixed it with a Ground Loop Isolator like this http://www.amazon.co.uk/gp/product/B...H34QWFD3RSZCE7

You plug it in somewhere beween the interface and the speakers. You can get them from maplin/ebay etc, not very expensive.
Thanks, I'll look into that.
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Old 05-06-2011, 03:19 PM   #8
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Originally Posted by AnyOtherCity View Post
I had the same problem and fixed it with a Ground Loop Isolator like this http://www.amazon.co.uk/gp/product/B...H34QWFD3RSZCE7

You plug it in somewhere beween the interface and the speakers. You can get them from maplin/ebay etc, not very expensive.
15 quid from Maplin. It doesn't *quite* eliminate all noise but just about. Certainly enough to get some work done.

Never remove the earth from your PSU. If it wasn't necessary it wouldn't be there.
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Old 05-06-2011, 06:36 PM   #9
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In the US it is possible to buy simple 3-to-2-prong adapters for 50 cents or so at any hardware store. They all come with a little grounding tab that you are supposed to connect to a solid earth ground, but that nobody does, people just use them to plug 3-prong devices into 2-prong outlets.

This is an extremely bad idea as a long-term solution. That 3rd pin is there for a reason that has everything to do with safety. If you don't mind blowing up your laptop there's not a lot of personal danger since there is an intermediate stepdown transformer.

But this is functionally the same as clipping the grounding pin off the plug. Which means any stray voltage or circuit failure within the device will now send full mains power to ground any way it can, usually through a human being touching it. Have you even been shocked or "buzzed" by a guitar or a microphone? That's invariably the result of a an amp or preamp with a ground fault that was somewhere plugged into a circuit without a ground. If you had touched the same device while wet, or sweaty, or standing in a puddle you would have been full-blown electrocuted.

If you are a full-grown adult without a heart condition in the US (where mains power is 120-volt), and if you are in a building wired to modern electrical codes, you will usually survive such electrocution before the circuit-breakers kick in, maybe with some third-degree burns, permanent scarring, and nerve-damage in the extremities. Pets, toddlers, and people with heart murmurs may need immediate CPR but can sometimes be saved with instant medical attention.

If you are in a country with 230-volt mains, or if are in a US building without proper fusing/circuit-breakers, all bets are off. Being a path to ground in that scenario is easily enough to kill even a grown man.

Moreover, ground-lift solutions are illegal in the EU, where laws govern such things. The only reason that it is "legal" to lift safety grounds in the US is because the US does not have laws, per se, to govern such things. The US instead has a National Electrical Code which is not law but instead a sort of licencing rule. In effect, you can do whatever you want in the US, but your insurance will not cover the claim if you were lifting grounds and burn down your house or kill your kids. The US generally offers a more favorable legal environment when it comes to reckless pursuit of Darwin Awards, compared to other developed countries. In American practice, it's a matter of civil law: your lease, mortgage, insurance, etc all require you to follow code, but there is no government agency per se that regulates that such things, just the quasi-governmental NEC as well as UL ("Underwriter's Laboratories", the laboratory specified for testing such stuff).

That third prong is there for a reason. You used to be able to kill someone and make it look like an accident by tossing a radio or hair-dryer into their bath. But safety codes are always ruining things for clever murderers.

There are a variety of easy ways to solve the problem of ground-induced hum without turning your equipment into a wet-floor electrocution-machine. The common "ground lift" switch on modern guitar amps, for example, does not actually separate the chassis from the safety ground, it simply isolates the loop between pickups and preamps, and exposes you to no more current than what you generate by vibrating a metal string over a magnet. If you don't have that option, then simple "star grounding" (e.g. plugging everything into the same outlet via clever use of power strips) will typically neutralize any ground hum. If it does not, that's a pretty good indicator that throwing that device into a bathtub might be a good way to murder someone.

But disabling the "third prong" is a really bad idea. Almost anything it resolves can be resolved by simply plugging everything into the same power strip, or by plugging into a different outlet.
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Old 05-06-2011, 07:49 PM   #10
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Thanks to everyone for your replies and comments.

I've ordered a ground loop isolator from Amazon which will hopefully arrive any day now. (Thanks for the link, AnyOtherCity. )

In the mean time..

Quote:
Originally Posted by yep View Post
... simple "star grounding" (e.g. plugging everything into the same outlet via clever use of power strips) will typically neutralize any ground hum.
.. I never realised it was just a case of using the same outlet.

So, if I simply plug my laptop power supply and amplifier into the same socket, it's problem solved? (The audio interface is USB powered).

I'll have to wait until Sunday to try this, as I need to shift some furniture around in the lounge before I can get to the amp plug.
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Old 05-07-2011, 12:04 AM   #11
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This is what I use with my laptop....




The whole safety thing is not really an issue with double insulated, switchmode power supplies such as those designed for laptops. There's no metal casing and the mains is isolated via the switchmode transformer.
Honestly, you've got more chance being killed from a lightning strike whilst in an opal mine underground than being electrocuted from an unearthed laptop power supply!!
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Old 05-08-2011, 07:29 AM   #12
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Quote:
Originally Posted by dungbeetle View Post
So, speaking of electronic hum-killing gadgetry, does anyone here use one of these?

Behringer HD400 "Hum Destroyer"

Does it work?
Results of my test on the HD400 can be found here:http://forum.cockos.com/showthread.php?t=57951

Bottom line: I like it.
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Old 05-08-2011, 08:55 PM   #13
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Quote:
Originally Posted by Dannii View Post
...Honestly, you've got more chance being killed from a lightning strike whilst in an opal mine underground than being electrocuted from an unearthed laptop power supply!!
With a laptop power supply this is 100% correct. Worst case, you fry the computer. With a typical guitar amp it is 100% wrong-- the amp will be fine while you get mains voltage running through you.

I am never quite sure what seemingly-knowledgeable people are getting at when they point out that this or that approach to ground-lifting is "safe" or "works for them", especially when it is divorced from any kind of technical background to describe why their particular approach transfers all the risk to their computer instead of to their body... Is it some kind of braggadocio, like my home electrical is better than yours, or like I don't care about frying laptops and keyboards or some such?

I have never understood the mentality that "safety is trivial, just install this thing that will blow up your computer first". Especially when it offers absolutely zero advantage compared to genuine good practice.

Anything that can be solved by plug-in gadgets can be better-solved by star-grounding, which is easy and cheap.
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Old 05-08-2011, 09:13 PM   #14
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I agree with you for the most part Yep. I certainly do NOT condone earth pin removal as a general solution (and this is coming from a background of qualification and experience in electronics and safety). Ground lifting in most cases is EXTREMELY DANGEROUS and in some places, illegal.
As for laptop supplies, it would be an extremely unlikely event that would cause a laptop to be destroyed due to earth lifting the mains supply. In such a fault scenario, if the active pin of the mains supply somehow found it's way to the secondary of the chopper transformer and then into the laptop, it would most likely be fried earth lifted or not.
Given the double insulated nature of these supplies, that scenario would be extremely unlikely. Not impossible, but then again, it isn't impossible to be hit by falling debris from the international space station whilst having a barbecue with friends in your backyard either!!!
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Old 05-08-2011, 09:35 PM   #15
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Quote:
Originally Posted by Dannii View Post
I agree with you for the most part Yep...
I still don't get how any of this amounts to anything other than throwing up a bunch of technical-sounding sand.

Anything with a "third prong" has it for either your safety, or for the safety of the machine, or both. If there is no benefit, it doesn't have one. No sane manufacturer or electrical engineer includes one just for the hell of it.

I'm trying to be polite, but as a manufacturer and design engineer with products both CE and UL-listed, the notion that the ground/earth pin/prong is unimportant is plain wrong. It's cheaper and easier to omit it if there is no reason for it.

In some cases it's there more to protect the equipment than the user, but it's never included for no reason.
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Old 05-08-2011, 09:48 PM   #16
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Originally Posted by yep View Post
I still don't get how any of this amounts to anything other than throwing up a bunch of technical-sounding sand.
Easy buddy. Settle there. Pretty strong statement from someone who I've never met. You're not the only one here with technical knowledge and qualifications.
Quote:
Originally Posted by yep View Post
I
Anything with a "third prong" has it for either your safety, or for the safety of the machine, or both. If there is no benefit, it doesn't have one. No sane manufacturer or electrical engineer includes one just for the hell of it.

I'm trying to be polite, but as a manufacturer and design engineer with products both CE and UL-listed, the notion that the ground/earth pin/prong is unimportant is plain wrong. It's cheaper and easier to omit it if there is no reason for it.

In some cases it's there more to protect the equipment than the user, but it's never included for no reason.
I guess we're going to have to agree to disagree here. FWIW, there are numerous things in the whole CE implementation debacle that I disagree with. Bureaucracy has killed the small scalle/custom design market here in Australia and it is a sore point with many of us.

I've designed, built and sold many things over the last 25 years so I think I can say I understand the risks in removing the earth pin from my laptop supply and I'm happy to take that risk.
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Old 05-08-2011, 10:21 PM   #17
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What happens if you lift all *but one* of the grounds, so everything earths itself through that single connection, breaking the ground loop? I'm under the impression that that's a good way to do it.
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Old 05-08-2011, 10:52 PM   #18
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Quote:
Originally Posted by Analogy View Post
What happens if you lift all *but one* of the grounds, so everything earths itself through that single connection, breaking the ground loop? I'm under the impression that that's a good way to do it.
That's risky and dangerous (an in some countries illegal) for the most part. Star earth configuration, as Yep has already mentioned, is the way to go. Combined with earth lift switches on audio gear, or lifting the earth on one end of some of the audio cables, that will solve most earth loop problems.

Laptop PSU's on the other hand are notoriously poorly designed as far as noise is concerned. Many times, they will cause buzzes, humming, pops, crackles and other noise even if the laptop and the monitor speakers are the only things connected and are connected to the same power strip. In such a case, where the earth pin is often included simply to satisfy the bureaucrats with little, if anything to do with safety, removing that connection is the simplest and least intrusive (as far as audio quality is concerned) method.
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Old 05-09-2011, 02:40 AM   #19
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Quote:
Originally Posted by Dannii View Post
Star earth configuration, as Yep has already mentioned, is the way to go.
What does this mean in practice? I looked it up and saw some references for working with component level electronics, but say you have a laptop and a sound board etc that all want to plug in... Does this mean keeping everything on the same power strip/power outlet/circuit?
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Old 05-09-2011, 04:02 AM   #20
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Quote:
Originally Posted by Analogy View Post
What does this mean in practice? I looked it up and saw some references for working with component level electronics, but say you have a laptop and a sound board etc that all want to plug in... Does this mean keeping everything on the same power strip/power outlet/circuit?
Basically, you are aiming to power all devices in your studio from one common, central point.
The idea is to avoid any potential difference along your mains wiring as much as possible. In the first diagram, the load on the mains wiring between the mains outlet and the first power strip carries the current requirements of everything on the circuit, the wiring between the first and second power strip carries the current requirements of the loads on the second and third power strips and the wiring between the second and third power strips carries the current requirements of the loads on the last power strip only.
This, combined with the fact that the total resistance of the cable to the last power strip is greater than the resistance to the first and second power strips consecutively, creates a voltage drop along the circuit leading to potential differences across the wiring and induced differential currents. When the audio earths (which are often also connected to the mains earth) between the various units are connected together, this produces a closed earth circuit known as an earth loop. If there's any induced current in the mains earth wiring, this finds it's way into the audio i/o via the common earths.
By wiring everything to a common point, this can be minimised and the earth loop currents significantly reduced.
Also, earth loops can be eliminated by breaking the loop via disconnection of the earth at one end of the audio cables. This is effectively what hum destroyers and ground lift switches on D.I. boxes and amps do.

I did a Google search and couldn't find the diagram I was looking for so I'm going to attempt an ascii version here!!!

Non star earth configuration
Code:
Mains------power strip-----------power strip---------power strip
             |    |               |       |                |
             |    |               |       |                |
           DAW   Synth          Audio   Amplifier       FX rack
                              Interface
Star earth configuration
Code:
                                Mains
                                  |
                                  |
                          Synth   |  FX rack   
                             \    |    /
                              \   |   /
                             power strip
                              /   |   \
                             /    |    \
                           DAW   Amp   Audio
                                      Interface

Last edited by ReaDave; 05-09-2011 at 04:09 AM.
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Old 05-09-2011, 07:35 AM   #21
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Quote:
Originally Posted by yep View Post
I still don't get how any of this amounts to anything other than throwing up a bunch of technical-sounding sand.

Anything with a "third prong" has it for either your safety, or for the safety of the machine, or both. If there is no benefit, it doesn't have one. No sane manufacturer or electrical engineer includes one just for the hell of it.

I'm trying to be polite, but as a manufacturer and design engineer with products both CE and UL-listed, the notion that the ground/earth pin/prong is unimportant is plain wrong. It's cheaper and easier to omit it if there is no reason for it.

In some cases it's there more to protect the equipment than the user, but it's never included for no reason.
It is often the case that the 'third prong' is not electrically connected to the system, it is there simply to physically open the gates for the other two pins. With so many cheap and effective solutions however there is still no case for removing the earth connection on anything.
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Old 05-09-2011, 01:21 PM   #22
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So basically, maintain a tree topology from mains to devices.

Code:
     amp----power strip----keyboard
                 |
                 |
Mains-------power strip----power strip---more stuff
                 |  |
                 |  |--Only plug power strips into this power strip
                 |
  blah blah-power strip----computer
                 |
             bass amp
Now, I'm wondering, how is this affected when you have too much stuff wanting power for a single breaker to handle, or practical concerns require you to do so (i.e. bass amp on the stage, your sound board in the back of the room are on different circuits, but DI-ing the bass connects the ground of the sound board to the ground of the bass amp)
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Old 05-09-2011, 02:49 PM   #23
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Well, I finally managed to try out both the ground loop isolator and the star grounding method over the weekend.

The isolator definitely improved matters, reducing the noise through the speakers to an acceptably innocuous hiss. Interestingly though, it only seemed to do its job while the amplifier volume was set to around 75% or less. Any higher than that, and it was as if it could no longer take the strain and all the nasty noise came bursting through again.

The thing that surprised me about this, was that it wasn't a gradual increase in noise when it eventually gave up the ghost. Tweak the dial to just over 75% and POW!, the floodgates opened and all the noise broke through. Turn the volume back down again and all is good. Strange.

With regard to star grounding, unfortunately it didn't seem to make much difference for me. I suspect that either I'm doing it wrong or there's just too much electrical equipment plugged into the lounge ring main, wreaking havoc.
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Old 05-10-2011, 03:14 AM   #24
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Quote:
Originally Posted by Analogy View Post
So basically, maintain a tree topology from mains to devices.

Code:
     amp----power strip----keyboard
                 |
                 |
Mains-------power strip----power strip---more stuff
                 |  |
                 |  |--Only plug power strips into this power strip
                 |
  blah blah-power strip----computer
                 |
             bass amp
Now, I'm wondering, how is this affected when you have too much stuff wanting power for a single breaker to handle, or practical concerns require you to do so (i.e. bass amp on the stage, your sound board in the back of the room are on different circuits, but DI-ing the bass connects the ground of the sound board to the ground of the bass amp)
The configuration you illustrate above still has traps for earth loops. Multiple power strips with different cable lengths are a recipe for this. The idea with star earth configuration is to have everything running from one central point.
A true star earth system is a hard wired configuration of power outlets wired by a qualified electrician but this isn't a practical consideration for everyone. My illustration above is an approximation of the configuration an electrician would use in a permanent installation but using stuff we have readily available to us.

To calculate whether or not you are loading one point too much, all you need to do is add up the total power consumption of everything connected and make sure it doesn't exceed the maximum rating of one mains outlet (most power strips have a circuit breaker anyway). In Australia, the total capacity of one domestic mains outlet is 2400 watts into a resistive load or, 240 volts at 10 amps.
I have my entire studio (DAW, UPS, hardware synths & analog sequencers, 8 channel power amp, V-Drums, HD projector, Hammond organ & Leslie, Mackie Onyx 1640, hardware FX rack, headphone distro amp, motorized control surfaces, Digi002r, CMLabs SixtyFour digital router) all running from one outlet via a power distribution setup approximating star earth as much as possible and the total load is still under the maximum rating of one outlet.
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Old 05-10-2011, 03:18 AM   #25
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Quote:
Originally Posted by dungbeetle View Post
Well, I finally managed to try out both the ground loop isolator and the star grounding method over the weekend.

The isolator definitely improved matters, reducing the noise through the speakers to an acceptably innocuous hiss. Interestingly though, it only seemed to do its job while the amplifier volume was set to around 75% or less. Any higher than that, and it was as if it could no longer take the strain and all the nasty noise came bursting through again.

The thing that surprised me about this, was that it wasn't a gradual increase in noise when it eventually gave up the ghost. Tweak the dial to just over 75% and POW!, the floodgates opened and all the noise broke through. Turn the volume back down again and all is good. Strange.

With regard to star grounding, unfortunately it didn't seem to make much difference for me. I suspect that either I'm doing it wrong or there's just too much electrical equipment plugged into the lounge ring main, wreaking havoc.
A star earth setup won't solve the problem of noisy laptop power supplies in most cases. The problem here isn't a potential difference in the mains wiring due to wiring resistance, it is noise induced by the laptop and it's PSU finding it's way into your monitors via the ground connection. Somewhere along the path, you have to isolate the mains earth from the audio earth and break the loop between the laptop and the monitors. The only thing I have found that does this reliably is to remove the mains earth connection from the PSU.
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Old 05-10-2011, 04:21 AM   #26
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Well, I finally managed to try out both the ground loop isolator and the star grounding method over the weekend.

The isolator definitely improved matters, reducing the noise through the speakers to an acceptably innocuous hiss. Interestingly though, it only seemed to do its job while the amplifier volume was set to around 75% or less. Any higher than that, and it was as if it could no longer take the strain and all the nasty noise came bursting through again.

The thing that surprised me about this, was that it wasn't a gradual increase in noise when it eventually gave up the ghost. Tweak the dial to just over 75% and POW!, the floodgates opened and all the noise broke through. Turn the volume back down again and all is good. Strange.

With regard to star grounding, unfortunately it didn't seem to make much difference for me. I suspect that either I'm doing it wrong or there's just too much electrical equipment plugged into the lounge ring main, wreaking havoc.
If the isolator is connected to the input of the amp then the volume the amp is set at should make no appreciable difference to the isolator.

If you set up the system with amp at high level and run the laptop on battery what is the result?
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Old 05-10-2011, 05:36 AM   #27
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... The only thing I have found that does this reliably is to remove the mains earth connection from the PSU.
Indeed.

The only thing that completely solves the problem for me is the setup pictured in my original post (i.e. using the shaver and continental adaptors).

Having said that, for anyone who'd rather not to do away with the earth connection, the isolator is a good compromise. At normal listening levels the remaining hiss is fairly unobtrusive and obviously never finds it's way onto the actual audio track(s) anyway.
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Old 05-10-2011, 05:49 AM   #28
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If the isolator is connected to the input of the amp then the volume the amp is set at should make no appreciable difference to the isolator.
Yeah, I agree. This came as a complete surprise to me, but it does happen.

You could maybe understand it if the isolator were placed between the amp outs and the speakers, so that higher output levels might conceivably push it beyond its limits, but no. It sits between the audio interface and the amp inputs. Weird.

I think I might try tinkering with the line out levels from the audio interface to see if that affects how the isolator/amp combination responds.

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If you set up the system with amp at high level and run the laptop on battery what is the result?
Hmm, I don't know. I'll give that a go this evening if I get a chance and see what happens.
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Old 05-11-2011, 11:36 AM   #29
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My experience was always that running my laptop on battery eliminated the noise. However, being a crappy windows laptop the battery life is only about 1.5 hours so I now just live with the compromise of ground loop isolator and very slight hum.
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Old 11-08-2012, 03:05 AM   #30
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Default Simply fix for power supply problems

I have had this problem recently and have come across a safe easy solution.

I run on a samsung s3510 laptop and have noises thro my yamaha powered monitors when using an m audio interface.

The noises aren't there using the pc onboard soundcard and it also dissapears when you remove the laptop power supply and run on the battery only.

The answer is this.......

I decided to try ordering a new powersupply ( as I thought mine must be faulty) whilst waiting to recieve it I got bored and thought I'd see if the Mrs power supply would work.

I chopped the end off hers whilst she was at work ( lol) and soldered my connector on.

Hey Presto silence..........................


Unfortunatley my new supply turned up next day and did did the same as the old one ......


If you want a silent power supply Order the following:


Original Hp laptop power supply from Amazon arround £20( pc world will charge you £40 -£60 plus tutut)

The Hp part no is: 608425-003
Or replacement part no: 609939-01

It is for a Hp G62 laptop

NB: in the wiring on this PS there is a small green cable its something Hp use for smart charging. My laptop doesn't need it so I just put white to white and black to black and trimmed the green one off.

Hope this helps

Cheers!
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Old 11-08-2012, 06:44 AM   #31
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If you want a silent power supply Order the following:


Original Hp laptop power supply from Amazon arround £20( pc world will charge you £40 -£60 plus tutut)
And so you assume any power supply will work with any laptop? This is WRONG and a dangerous thing to spread.

You have to at least get the voltage right and make sure the power supply can deliver the necessary amount of power (i.e. if the old power supply delivered 19V and 2.3A, you have to get one with 19V and AT LEAST 2.3A). Furthermore, it has to have the right plug, which differs from manufacturer to manufacturer (yeah, I know, you happened to have the right plug and managed to solder it on - not a solution for everybody). And thirdly, some manufacturers employ additional functionality, which you already admitted to with the green HP cable. Best case, say goodbye to better charging, worst case, say goodbye to your laptop.

This HP power supply worked in your case, it isn't guaranteed to work in others.

Sorry, not a good idea all around.
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Old 01-22-2014, 10:02 PM   #32
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Default Noisy leads

Manufacturers do go about the whole power supply cords the cheapest way possible regardless of what these other guys are saying. The reason they have three pin leads is because they use standard jug (kettle) chords that every musician carries, (Speaker and desk power leads) and are available anywhere. It has nothing to do with earthing the power supply blah blah blah just because it's there. They have three pin leads because they are the cheapest and most common lead in the world. If you feel the need, get yourself an old power supply and take it apart and see what is connected to the earth pin. The best thing you can do is look yourself and stop taking advice from people who have nothing better to do all day but sit on a computer putting largely unqualified advice on forums!!
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Old 01-23-2014, 07:07 AM   #33
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Here is a thread where we plowed much of the same ground discussed in the current thread, but also dug into the guts of the system in question (not a laptop with external power supply, but a desktop with the same noise issue) to try to better understand the source of the problem.

http://forum.cockos.com/showthread.p...ht=ground+lift

For reasons that are not totally clear to me, plugging the PC into the power outlet through an Ebtech Hum X Voltage Hum Filter (which appears to filter out ANY signal on the ground line)solved the problem. Indeed, the system had even less electrical noise than when a ground lift was used, and it is a totally safe solution.

T
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Old 01-23-2014, 08:34 AM   #34
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If the laptop PSU has a three-pronged connector it is class1, ie an earthed device and needs that earth (ground) connecting.

If it has a two pronged connector and the "double-square" symbol on the case, it is class2, double-insulated, and doesn't need an earth (ground).


Class1 switch-mode PSUs have a nasty habit of putting electrical noise onto their outputs relative to ground potential, which ends up via the negative connector joining to the laptop's ground-plane and audio output connectors, which will create audible noise then if connected to another grounded device (ie monitors, amp, etc). The noise voltage will run to ground through the audio connection's ground and you'll hear it as crap (it really is horrible).

Don't remove the earth connection to the PSU!

It is there to protect you and your computer and other connected equipment if there is a fault in the PSU circuitry. It needs that earth connection to leak the current and trip RCDs/blow fuses.

Ways around the noise? Put a pair of DI boxes on the output (or other signal isolating device -usually containing isolating transformers), or replace your PSU with a class2 (double-insulated) one.

UK users -Maplin do a class2 universal laptop PSU for about £40 that will solve all this.

REPEAT. Don't disconnect the PSU earth connection. It's there for a reason. Yeah I know stuff is reliable now and faults like that never seemed to happen, but they can, and unless the manufacturer went for a more robust class2 design it is possible to hurt people and gear in a fault condition.

There, you've been told now...



>
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Old 01-26-2014, 12:15 PM   #35
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Put a pair of DI boxes on the output (or other signal isolating device -usually containing isolating transformers)..
>
Actually, in the case described in my previous post, DI boxes did not solve the noise problem at all. Indeed, the noise was still present when the internal sound card on the PC was used and there was no separate path to ground from the sound card. The Ebtech Hum X Voltage Hum Filter on the ground line for the PSU did the trick.

T
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Old 01-26-2014, 12:33 PM   #36
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I like to live dangerously!!! I wouldn't use this configuration on a Vox AC30 (or any other tube amp) but it has proven simple and effective for my laptops for the last fifteen years and the danger factor is about the same as dying from being hit by a falling roofing tile inside your home!



Seriously though, if this was going to kill me, it would've happened on one of the many band tours I went on in the 90's. The crazy stuff we did on those tours would make people shudder!! ---Creating three phase outlets from three different GPO's (on different phases) wired to a makeshift distro box with a three phase socket on it and a bunch of extension cords was always fun!!!
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