Noise like ground loop But doesn't seem like ground loop. Help!

leon819

New member
Hello guys.

I've been using my laptop to record my voice with an external mic. However, I found that there's a noise on the background when I record and plugged the laptop's power cable at the same time.

I've searched online and it seems that the noise sounds like a ground loop noise. But only a mic (doesn't plug into the outlet) and the power cable (plug into the outlet) are connected to the laptop, so it confuses me that it doesn't seem to be able to create a ground loop.

There's no noise when I unplug the power cable, so I'm sure it's not the microphone problem. So if anyone could help it would be great! Thanks!
 
Have you tried plugging in at someone else's place, i.e., does it happen everywhere, or just some places? That could isolate if it's noise that's in the AC line (only happens in some locations or outlets), or if it's something in the AC/DC conversion, or maybe in the laptop itself (happens everywhere).

If the laptop AC power goes through a battery charger brick on the cable, then trying a different one of those might be a good test, if that's possible. Maybe you know someone with the same make laptop that has the same adapter/charger.
 
The ground loop explanation never works for these problems, and by and large, it's a problem that just relates to bad power supply and computer design. PCs especially in my experience, Dell computers are the worst, the power supplies are firmly the issue and the interference is nothing to do with the multiple grounds introducing circulating currents, but simply providing a path for spreading the interference. Dell have not just DC but power supply ID components so they know if it's the wrong power supply or worse, a non-Dell one. PCs just seem so prone to spreading noise that the events industry try to avoid PCs and use Macs because it's very rare to plug a Mac into a PA system and have any noise at all! PC users have to accept that DI boxes and transformer couplers are just normal for PC users. CPC in the uk sold some inline cable transformers which were very effective at helping the interface of PCs to audio rigs. If disconnecting the power supply causes the problem, then it's at least enabling the problem, even if not directly responsible for it.

https://cpc.farnell.com/pro-signal/psg08233/ground-loop-isolator/dp/AV12774

This is the device many of us bought to help.

If it is very low level one homemade trick you can try is to put a choke on the power cable. The manufacturers use the little ferrite lumps, but you can make a much better one if you have an old broken big loudspeaker. If you dismantle the thing you will discover a very lar circular donut shaped magnet. Wrap the low voltage cable through it at least ten turns, and then tape it tight. The damn thing thing is of course capable of wiping analogue tapes so keep it separated from things that don't like magnets, but it's very capable of stopping higher frequencies piggybacking on the low voltage DC. With a non brand sensitive computer, you can try different PSUs supplying the same voltage. You can buy variable voltage, lab type PSUs rather than the tiny switch mode ones for less than 30 quid. Not very elegant but there are things you can do with substitution and replacement, but we really should not having to be doing this.
 
Duracell 90 Watt Universal Notebook Power Adaptor | Falcon Computers

I found the above supply totally silent on this Lenovo T510 laptop and it comes with a good selection of alternative DC connectors. It is also earth free, bi-pin classll mains.

Yes! I know this thread is NOT about an earth loop but that IS a quality supply and fixes ground loops for other peeps!

OP might have the opposite problem. No earth. When 'floating' with no charger connected there is no AC field around but if the supply is a bit crap but earth free, grounding the electronics, AI case to water pipe, could stop the hum.

Rob, I have little idea of the circuitry involved but I would be wary of charging a laptop battery with a 'lab' DC supply? The electronics inside a laptop charger are very complex and seem to be much more than are needed to just produce 19 volts or so. I would bet there is some fairly sophisticated 'quick charge' then taper charge control in there. Don't want to be alarmist but there have been cases of laptop and phone fires!

Dave.
 
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OP might have the opposite problem. No earth.

I'd bet on that. Had a similar sounding issue many years ago with a dell laptop when no mains earthed devices were in the setup.
The laptop charger, as is often the case, was two pin - live+neutral.

Connecting to mains powered (and earthed) monitors, preamp...whatever 'cured' it.

I concluded that the entire setup could benefit from a path to mains earth and made an rca (shield) to mains plug (earth pin) cable and plugged that into an unused output on my interface.
Goes without saying...Not every country has mains earth and not every home recordist should be wiring plugs! Be safe!!
 
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