I didn't know that connecting a firewire device could produce the ground loop but it obviously can.

Symptoms would include a scratchy staticy noise when moving the cursor, and the noises occurring only when attached to another device while plugged into the power adapter. Here are my thoughts on dealing with the ground loop, if that is the problem:

1. Eliminate the ground either on the computer or on the other device it is connected to, by using a 3 prong to 2 prong adapter. This fix should only be used for diagnosing the problem ... if this eliminates the noise use one of the other solutions for long term.

2. Or isolate the grounds from each other by using a ground isolator or a direct box with ground lifter. Two members have given us positive reports on Radio Shack's $16 Ground Loop Isolator (270-054).

3. Or use non-conducting material to connect the 2 devices; specifically by using optical spdif to transfer the audio signal rather than copper cables.

JIm

Aha I was thinking of buying the Audiophile firewire ... was hoping it might resolve the noisy ground problem but looks like DI will be part of my setup after all ...

Just a word of caution. These ground loop isolators have been known to cut the lows out of your audio signal. I decided to ditch the MAudio and get a more professional audio setup.

Try http://www.digidesign.com/products/digi002/

or the more affordable Mbox

http://www.digidesign.com/products/mbox/

EmDe

Thanks for your comment...

Certainly the Mbox is more nearly in my price range than the other (completely skint at present!).

Interesting to see from the specs that it has a DI input ... from what you are saying it also isolates the output signals from the noisy PC ground (i.e. it "lifts" the ground on the output signals???)

It also looks like I could add a touch of reverb if needed, which would be really useful.

On the other hand though it may be slightly overkill for what I need, and I was wondering if connecting the MAudio outputs through a proper DI box (rather than just using a cheapo ground loop isolator) would essentially do the same thing with regard to earth loop/earth noise.

> cut the lows out of your audio signal
Not sure quite what you mean ... can you amplify (!!!)

Maybe another option would be to find an audio card that has its own power supply ... and hopefully uses the ground from that rather than from the PC ...???

Thanks
Giles

Message Edited by GilesKennedy on 06-21-2005 08:13 AM

Actually ... come to think of it ... why on earth do the Dell laptops have a 3 pin supply from the adaptor/transformer into the laptop given that the supply is 20V DC?

Pin 3 is +20V
1 and 2 are 0V

1 and 2 are "connected" but my digital AVO can't give a stable reading. It oscillates around 400 ohm. Similarly 1 and 2 are "connected" to the earth pin on the mains plug but pin 1 to earth oscillates around 20 ohm and pin 2 to earth around 2 ohm.

Maybe this explains why the ground on the audio signal is all over the place.

Are Dells the only laptops with this problem? All the others I've used/borrowed have had a 2 pole DC power supply.

Is DI the right thing to sort this out?

Giles

>>Not sure quite what you mean ... can you amplify (!!!)

The low frequency (bass) levels have been known to be cut off or "lost" with devices similar to the radio shack isolator.

If the MAudio had it's own ground I am sure we would not have any issues with it being connected to a laptop that does have a ground. Such a headache!

Oh I see what you mean - obvious! Thanks!

> If the MAudio had it's own ground
I thought that using its own DC adaptor would "give it" a ground but maybe not ... I'm a bit of a novice here

Sorry fo rthe incessant queries!!!

Cheers
Giles

Had this reply from M-Audio tech support - may be of interest. 2a clearly applies; they are suggesting running the laptop from a 2-pin supply, with the caveat: "(IMPORTANT: Contact the Laptop’s manufacturer to find out if lifting the ground is supported on this device). "

Giles

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GROUND LOOP TROUBLESHOOTING

All devices in your studio should be connected to the same ground. If this is not the case and one or more of the devices are getting their ground from somewhere else, (e.g. a different power outlet that is running on a different electrical circuit or the device has physically contact to a metal surface such as e.g. a doorframe etc.) and devices with different ground are connected to each other, this type of noise might occur.

There are different ways to fix this type of problem. The easiest and most cost efficient way is what is called a “ground lift” in order to interrupt the “ground loop”. Not all devices work correctly with lifted ground and might overheat and/or create an electric shock hazard. Before lifting the ground on a device, please contact its manufacturer in order to find out if this device will work properly and if it will create an electric shock hazard under these conditions.

Another and perhaps safer way to deal with this is with a ground loop isolator, you can get one of these at an electrical supply store.

Depending on the amount of devices in your studio, it might be hard to find the device that is causing the problem. For this reason we suggest the following approach in order to detect the source of the problem:

1. Disconnect ALL peripheral devices from the computer except for your audio interface and speakers. Printers, network, antenna cable to a TV Tuner card, audio cables etc. should all be physically disconnected from the computer.

2. Check if the noise is still there. If not, skip to step 3 in this guide. If yes, continue with number 2a.

2a. If you are using a Laptop, unplug the power supply and run on battery power. If this resolves the problem, you will have to lift the ground on the laptop’s power supply. (IMPORTANT: Contact the Laptop’s manufacturer to find out if lifting the ground is supported on this device).

2b. If you are using a Desktop computer, while you can hear the noise or have audio playing, turn your Monitor off, and then disconnect it’s power cable. If the noise is gone, you will have to lift the ground on the Monitor. (IMPORTANT: Contact the Monitor’s manufacturer to find out if lifting the ground is supported on this device). If the noise is still there, reconnect your Monitor, turn it back on and go to the next step in this guide.

2c. If your audio interface has a headphone output, disconnect the powered speakers or power amp with speakers from the interface and check if the noise is audible on the headphones. If the noise is gone, you will need to lift the ground on the powered speakers or amplifier (IMPORTANT: Contact the Monitor Speakers / Power Amp’s manufacturer to find out if lifting the ground is supported on this device).

3. If disconnecting all devices resolved the noise issue, start adding one device at a time and check if the noise reoccurs. Then, lift the ground on the device that made the noise problem reoccur. (IMPORTANT: Contact the manufacturer of the device you determined is causing the ground loop to find out if lifting the ground is supported on this device).

GROUND LIFT PROCEDURE:

IMPORTANT: Before you proceed, make sure that you have contacted the manufacturer of the device you intend to lift the ground on. If this is not supported for this device, lifting the ground can cause damages, serious injuries or death!

The best way to lift the ground on a device is to use a 3 prong to 2 prong adapter. These are available at electronic stores such as Radio Shack or Home Depot etc. Simply plug the 3 prong power cable in the adapter and the 2 prong end into the power outlet.

Please let us know if you need further assistance.

Giles,

Ha, that's very funny to think of Dell 'supporting' defeating the ground. In Dell's words it is 'not recommended'.

Jim

Only "not recommended"? The bright yellow label on the cable says WARNING: blah blah ... electrick shock, fire, or damage to your computer

Cheers
Giles