Ground loop/hum with USB headset on a laptop

[ric_cde]

Does anyone have any experience with solving this?

- The AC power supply on a laptop can cause a loud buzzing/humming noise on the microphone or line in (either USB & analogue audio connections). When you unplug the power supply (and run on battery) the noise ceases.

One explanation I found is that is that every component in a laptop shares the same ground (earth), and other appliances on your power circuit cause feedback on the ground which leaks into your microphone/sound card.

Another explanation is that badly shielded microphone/headset cables can contribute to this - but that may only apply to analogue (3.5mm) cables, not USB, according to some threads I've read.

Possible solutions:

- Use a 3 prong to 2 prong power adapter to remove the ground. This is not ideal though - power surges can fry the laptop battery, and touching certain parts of a laptop can cause electrocution.

- Use an 'Inline Surge Suppressor'. I saw this suggested in a thread, but I haven't found any other examples of people using one to fix this problem.

- Apparently USB cables have a ground wire in them - is there some type of USB adapter I can get to disable it? Or some other type of USB adapter which will solve the problem?


- Use a 'Ground Loop Isolator'. However these only seem to be available for analogue audio wires, not USB.
- Sound card is defective: get a new one, or buy an external sound mixer. Again, not ideal and the problem is apparently very common with many types of laptop.
- Some very complicated (to me) rewiring, cutting cables, and adding of electrical parts. (???)

Has anyone fixed this problem on a USB headset, or can comment on the first three solutions? Thanks!

 

[frozenlead]

A ground-lift adapter (3-2 prong) should solve the problem, and not cause shocks to you. Your notebook is not directly connected with the ground you remove on the AC side of the adapter (notice how your notebook's power jack has only 2 poles). Your notebook is run entirely on DC power, and it uses the "negative" lead as the ground. Your notebook shocking you, though, is not something someone can misinterpret.

You should look into getting a large choke or two for your PSU cable. They should help reduce the noise, though not by much.

The fact that removing your PSU immediately removes the noise directly indicates it as the source of the problem. Have you thought about replacing the PSU?

 

[ric_cde]

Hey, thanks for your reply.

The sound seems primarily a buzzing noise, with a fainter humming noise behind it. The buzz/hum does not occur with the headset on a PC I've tried it with. I have not tested it on any other laptops. The problem remains using the laptop in outlets at places other than my home. The interference only affects the microphone input on this USB headset. Hence the buzz/hum isn't audible on my speakers/headphones (mic is muted in my master value) - just for others whom I talk to with VoIP.

I'm convinced it's to do with power adapter, since the issue goes away when the laptop is on its own battery power.

- How effective are toroidal or ferrite chokes? I don't need to solve the problem completely, just reduce the noise somewhat in a relatively cheap ($5-20) way. A new PSU sounds like a good idea, but it's outside the price range I'd be willing to spend to fix this problem. I only use my headset to talk directly to people, not for recording, so a small amount of static isn't too bad. Could I place a ferrite choke one at the bottom of my USB headset cable, and one toroidal on the laptop power cable and notice a difference?

- Is a ground-lift adapter safe with regard to surges/lightning? I've seen some threads were people say they work fine, others state that there is a risk.

Incidentally the buzz/hum all but disappears when I hold a cellphone (during a call) very close to the headset.

 

[frozenlead]

I've never used a toroidal choke (other than one that came pre-installed) to be honest, but I can't imagine winding the cord around the ring is easy, especially with the power connector on it - I would suggest you use ferrite chokes, instead. They're much easier to install, won't cause cable stress, and can be returned easily if you find they don't solve the problem. As to how much they'll solve the problem...I really can't say, it depends a lot on your situation. If the buzz is only picked up by a mic, then the E field shouldn't really be that strong, and the choke should do the job.

I would get two ferrite chokes, and try them in three different configs:
One choke near the PSU on the DC side, and one on the headset
One choke near the power jack for the notebook, and one on the headset
Both chokes on the PSU cable, at both ends of the DC side.

The ground your PSU uses is not really meant to protect against surges and lightning. Excessive current in a circuit is best dealt with by a surge protector; you should always be behind one with a computer. Lifting the ground really isn't reducing your safety a whole lot.

 

[felis]

USB isolator will fix that since it breaks ground loop. Until recently, those devices were fairly expensive. Recently, Analog Devices released USB Isolator IC, ADuM4160, which is much cheaper solution. I made a device based on this IC, this is the description -> http://www.circuitsathome.com/mcu/usb/usb-isolator.