Laptop Ground Noise... Solutions?

C

cherrycobb

New member
Hello,

I get the feeling this may be a regular topic so I'll keep it quick... I am using a Dell Inspiron 1545, EMU 0202 USB with a pair of active monitors. After I finally got everything connected I had not anticipated the ridiculous level of noise created by Dell's power supply. There is no noise when running on battery alone, this is fine for a time but a bit stop/start due to limited battery life...

Aside from getting a better soundcard or new computer, is there any way at all to counteract this devastating noise!?

PS - I am not prepared to remove the earth pin from the power supply as I value my life!

Thanks in advance!
 
Is the noise the typical hum (60 cycles in the USA) that is associated with a ground loop? This is a very common fault when trying to hook laptops up to PA system for live events.

If so, audio isolating transformers should sort things out for you. Jensen make some excellent ones but Googling will probably find you a range.

For the future, an interface with balanced outputs MAY sort out the issue too but that's not guaranteed...you might still need the isolating transformers.

(And happy to hear you won't cut off the mains ground--that's a very bad idea recommended all too often by people who don't know what they're doing.)
 
Many thanks for the reply, I will look into audio isolating transformers. As far as I can see these seem to have RCA phono in/outs. Because my setup is unbalanced I am using ordinary 1/4" jack cables, would the transformer need to be hooked up between the sound card and my speakers...? and if so would I need/be able to use adapters for the jack cables...?

Thanks again! This seems like a real solution if I can get my head around it...
 
You should be able to find them with whatever connector you need. Sorry, can't help in the US market but I know I could find all sorts of varieties in the UK.

Yes, the isolator goes between your E-MU output and the input to your active speakers.
 
It just so happens that I am in the UK... I don't suppose I could be cheeky and hijack your expertise for a third time...?! Are there any particular brands or shops you could recommend?
 
Well, having said I knew where to get all sorts of isolators, I went to my usual supplier and can only find phono and XLR. However, since you're unbalanced anyhow, I guess you could get one of THESE and four suitable phono to TS adaptors. Or, if you're handy with a soldering iron, just lop off the phonos and install some TS jacks.

FYI, CPC (the place I linked to) tends to be cheapest for this sort of specialist accessory even if their online catalogue is a pig to search.

However, other places to try would be Canford Audio or RS Components. Or you could try the dreaded Maplins!

Bob
 
I have answered this question a 100 times now, you need one of these between the usb device and the active monitors, and also between the usb device and mixer if you are using one.

Alan
 
Good one witzendoz. That's the same sort of isolating transformer I was suggesting but with the proper connectors.

HERE'S a UK supplier. It's a bit more expensive than the one I found but, by the time you factor in the adaptors, there's not that much in it.

Bob
 
Isolation transformers are generally a bad idea, IMO. There's nonzero loss every time you go through a transformer, and depending on how cheaply made the transformer is, that loss can be substantial. There are various other isolation technologies that would be better, including various single-chip solutions, but knowing that this was made by Behringer, odds are they did it the cheap, half-assed way (transformers).

You're generally better off fixing the real problem. Ground hum is almost invariably caused by connecting together multiple devices, some of which have a noisy, floating ground, some of which have a solid, non-floating ground. When you plug in a cable between the two devices, the device with the working analog ground becomes a noise sink for the ungrounded device, and all that ground noise on that ungrounded device flows through the shield of the audio cable into the grounded device, causing induced hum in the audio signal cable as it does so.

There are two ways to fix this. The easiest way (that usually works) is to lift the ground at the ungrounded end of your cables so that they do not form a path for hum and other noise to flow across the cable.

The best way (that always works) is to create a series of pigtails that plug into each device, with a plug on one end and a jack on the other end. Solder a heavy gauge (say 12 AWG) wire to the plug end so that each of these cables is effectively providing a true signal ground right at the device. Hook the ground wires together. Then, if that doesn't completely kill the mains hum, tie that star ground to the ground pin on a mains power plug.
 
A couple of thoughts on dgatwood's suggestions.

First, to avoid ambiguity, his first suggestion is referring to lifting the SIGNAL ground, not the mains ground. A signal ground lift is a pretty standard response--when I do live sound work, I carry some carefully marked audio cables with the ground disconnected for just this eventuality. A lot of DI boxes also feature a ground lift switch for the same reason. This is entirely acceptable as a solution but, just to repeat for the umpteenth time, never, ever lift the mains ground.

On his second suggestion, if you have the skills and resources then this is the way to go to avoid ground loop problems. When I designed TV and radio facilities, a huge amount of effort was spent planning the grounding strategy which would work much as he describes. Basically, all technical (audio and video equipment) would be completely isolated from the normal building ground (or "earth" since I was working in the UK!). Everything would be taken back to a "technical earth bus" and from there either to a dedicated earthing rod or to the "electric company earth" generally in the supply room. (London soil tended to be so dry and sandy that even a huge spike driven into the ground couldn't provide a suitably low-impedance earthing point.)

However, I hesitate to suggest working this way to anyone without the electrical skills and knowledge to do it safely, hence my suggestion of the audio isolating transformers.

And, on transformers, I have to say that while there ARE losses, they're generally not severe enough to rule out their use in all situations. Even given the care we used to take with our grounding/earthing scheme, there would always have to be SOME connections to the "outside world" that could mess things up. (For example, we had clients in our building who wanted connection to our facilities--but we couldn't control what they did.) In these cases, the transformers came out and worked well.

Bob
 
dgatwood said:
Isolation transformers are generally a bad idea, IMO.
Click to expand...

Almost every live sound installation has Isolation transformers between the FOH and Monitor consoles, almost every broadcast rig has isolation transformers between in house equipment and the broadcast van, almost every live album was recorded through isolation transformers between the FOH PA and the recording rig.

Were are only talking about 1 set of transformers in a home studio situation. The computer ground loop problem is not solved with the usual ground loop solutions. You cannot lift the ground in a USB or firewire cable, this is where the ground loop is present in the computer problem. The ground voltage in the USB / firewire cable is what is causing the digital noise. If there is a hum, that's a different issue.

I can also tell you there is no hearable loss of sound quality through the Behringer hum eliminator, and even if there was, the quality has just gone up by eliminating the noise. Maybe the same people that spend $1000 on speaker cables or buy Gold plated connectors may think there is a problem.

If you don't like Behringer, there are many other brands of isolation transformers, ART, Jensen, DBX, Radial, ARX, etc etc.

Alan.
 
witzendoz said:
Were are only talking about 1 set of transformers in a home studio situation. The computer ground loop problem is not solved with the usual ground loop solutions. You cannot lift the ground in a USB or firewire cable, this is where the ground loop is present in the computer problem. The ground voltage in the USB / firewire cable is what is causing the digital noise. If there is a hum, that's a different issue.
Click to expand...

Yes, but usually the only reason it leaks into the signal is because it is flowing from the shared digital/analog ground on your interface through some audio cable to a viable analog ground somewhere. So a ground lift on the signal at the audio interface end should still usually fix the problem unless the interface was designed wrong, and grounding the analog ground on the interface will invariably fix the problem. Been there, done that to work around a really noisy PowerMac G5 PSU and a poorly designed PCI card.
 
My use for the Behringer is for the home stereo system upstairs that is fed by the interface>headphone amp. It is on a different circuit and lifting the ground on the interface didn't do it.
 
witzendoz said:
I have answered this question a 100 times now, you need one of these between the usb device and the active monitors, and also between the usb device and mixer if you are using one.

Alan
Click to expand...

I'm having what appears to be the same issue between a 27" i5 iMac and my mixer. When I plug phones directly into the iMac, the signal is squeaky clean. When I take the headphone out and plug it into the mixer, there is weird static noise coming through the monitors and phones. I'm very glad to have found this post! Can someone confirm for me that:

a) the unit linked above is likely to fix the problem, since my mixer wants balanced ins, and;
b) i'll also need to order a set of balanced cables for the output from the Behri unit to the mixer to make this work. I have a set, but they're about 15 feet long, and I only need a foot or so.

If the answer is yes, I'll order immediately, and will be very glad to have found the answer so easily. Through the monitors at low volumes, it's not so noticeable, but through the phones it's totally unacceptable.
 
Chris F said:
I'm having what appears to be the same issue between a 27" i5 iMac and my mixer. When I plug phones directly into the iMac, the signal is squeaky clean. When I take the headphone out and plug it into the mixer, there is weird static noise coming through the monitors and phones. I'm very glad to have found this post! Can someone confirm for me that:

a) the unit linked above is likely to fix the problem, since my mixer wants balanced ins, and;
b) i'll also need to order a set of balanced cables for the output from the Behri unit to the mixer to make this work. I have a set, but they're about 15 feet long, and I only need a foot or so.

If the answer is yes, I'll order immediately, and will be very glad to have found the answer so easily. Through the monitors at low volumes, it's not so noticeable, but through the phones it's totally unacceptable.
Click to expand...

A quick check is to run the imac on battery and disconnect the power lead, if the noise goes away or reduces, the answer is yes the behri will fix the problem.

The behri is balanced tip, ring, sleeve jack plugs, it will also convert unbalanced to balanced and balanced to unbalanced.

Alan.
 
witzendoz said:
A quick check is to run the imac on battery and disconnect the power lead, if the noise goes away or reduces, the answer is yes the behri will fix the problem.

The behri is balanced tip, ring, sleeve jack plugs, it will also convert unbalanced to balanced and balanced to unbalanced.

Alan.
Click to expand...

The iMac is a desktop, so I can't do that, but everything else seems to fit. If this is the problem, I'll be sending what ends up as two unbalanced 1/4" out from the headphone out on the computer into the hum destroyer, and would then run two balanced 1/4" cables from the outs on the Behri unit to the balanced ins on the mixer. The Behri unit would convert the unbalanced to balanced, thus killing the hum. Does that sound right? (thanks for the quick reply, BTW)
 
Chris F said:
The iMac is a desktop, so I can't do that, but everything else seems to fit. If this is the problem, I'll be sending what ends up as two unbalanced 1/4" out from the headphone out on the computer into the hum destroyer, and would then run two balanced 1/4" cables from the outs on the Behri unit to the balanced ins on the mixer. The Behri unit would convert the unbalanced to balanced, thus killing the hum. Does that sound right? (thanks for the quick reply, BTW)
Click to expand...

It's not balancing unbalanced inputs that fixes the problem, the behri has small transformers inside that lifts the signal and shield connections and breaks the earth loop.

Really you will not get top quality from the built in headphone jacks, you should buy a proper USB or Firewire interface, but even with a good interface the noise problem could still persist.

Alan.
 
Thanks - I'm not recording this way, just trying to kill the noise when I have stuff on iTunes that i want to listen to through the system (which is fairly often since my music room doubles as my office). I'm in the middle of reconfiguring my recording setup from MOTU to Logic, and will be replacing one interface with another. I'll try the unit you suggested for the hum. Unbalanced cables in, balanced out.
 
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