How to REALLY get rid of your Dell's ground loop problem......

Before anyone even thinks about doing anything that I have talked about in this post, read the disclaimer at the end. I take no responsibility for YOUR actions, even if you claim to have followed my advice. If unsure, ask someone who knows.







Hi everyone. I have an Inspiron 8200 which I use (or have been trying to use) with a Tascam US-428 external USB soundcard. As most of you who have tried using a recent dell laptop with external audio equipment will already know, the grounding scheme that modern dell laptops (and their power supplies) use is slightly less then ideal. This is due to resistance between the different 'grounds' which should all ideally be at exactly the same voltage (impossible unless the ground conductor has 0 resistance). All equipment exhibits some resistance in the ground conductors, as this is a requirement by the laws of physics. Ok there's my "it's not ALL dell's fault disclaimer....." well, actually, it is (or appears to be) all Dell's fault. My reasoning is thus:

After a lot of research on earthing techniques and ground-loops on the net, I came across a paragraph (can't remember where) that said that a possible solution is to create a really really low resistance link between the earth points at each end of the noisiest analog connection (there is often only one analog connection)....... sorry that's phrased badly, but basically in my case, the earthing goes like this:


power point --> Laptop --> US-428 --> Amp --> power point


The analog stage connection here is between the US-428 and my Amp, so that's where the ground link has to go. To make the ground link, I bought a length of heavy duty DC power wire (rated at 25A or something like that, you want the lowest resistance possible), and soldered appropriate connectors on each end so that I could screw it onto a ground connection at both my amp and my US-428. At the US-428 I put a solder lug (with a star washer) under an external screw that went straight into the (earthed) chassis. On my amp I connected the earth cable to one of the negative speaker terminals, which I happen to know is earthed directly, because I built the amp myself ;) Please note: DO NOT ASSUME THAT ONE OF THE SPEAKER TERMINALS ON YOUR AMP IS EARTHED! It may not be, and it could spell some messy repairs if it isn't and you try and wire it how I have done. A lot of consumer equipment will have earth connection lugs on the back, sometimes for antenna purposes, or for the exact reason you want it for. A screw terminal or lug or whatever that is directly screw-ed into the chassis is what you're looking for.

(the dell forum didn't like me saying 'screw-ed'..... lol)

Connecting the earth link cable cut the 'whine' to about 2-4% of it's original volume..... as in it's still audible if I turn down the volume completely and put my ear next to the tweeter on my speakers. With any, and I mean ANY audio playing, you shouldn't be able to hear the whine at all. This is assuming you manage to find a good enough earth connection on whatever various pieces of equipment you are trying to connect. The lower the resistance of this connection, the less whine. Gold plugs and thick wire (multistrand DC power cable is best) will help here.

(side note: wiring your system like this means that you will have a ground loop between your audio connectors and your earth link. To get rid of that last inch of whine, try cutting the earths on your signal cables at one end - generally the end that's not your laptop, shouldn't matter too much. A resistor in series with the audio connectors earth could help if you don't want to leave the shielding disconnected completely.)

If you are connecting something external straight to your laptops sound plugs, you can get the earth by putting a 3.5mm plug into one of the audio plugs you aren't using, and solder the earth link cable to the earth inside the plug, leaving everything else disconnected.

So basically: dell laptop + power supply = bad earth voltage (which is common, but it's particularly bad with these laptops, and it only happens on equipment which is earthed, which most other laptops aren't).
Solution: connect a 'perfect earth' across any connections that have an analog audio signal running through them (if said connection is part of a ground loop that is).


Now then. Sorry if this seems like techno garble to you - I haven't had much sleep, but I thought I'd share this with the people at this forum, since I don't really know where else I could put this information.

If you're not sure what you're doing when it comes to earthing, grounds, wiring and soldering and that sort of thing, DON'T MESS AROUND WITH IT. I don't want people to read this and then go and solder a cable between their power point and their laptop in an attempt to destroy a ground loop...... you may end up destroying yourself. I take NO responsibility for people destroying any equipment as a result of misreading this and doing something stupid. Stupid is as stupid does. End disclaimer.

over and out,
forgieboy