Interference from laptop USB using USB sound card

PostmanPot

Hi all

Well got the Rokit 6s (drool!) and Audiophile USB this morning.

Problem now is that there is interference coming from the boy's laptop's USB connectors (Toshiba tablet). ☹ If I listen closely, the interference, which comes from the left speaker, seems to be in "harmony" with what I think is the CPU making noises.

The laptop is still under warranty, unfortunately bought in Australia though (will look into possible international warranty). So I suppose it could go back for a motherboard swap-out, or perhaps it will always be that a tablet laptop's motherboard is lacking. The other option I am thinking of is to convince the father to buy a desktop PC with a decent motherboard and 19/22" monitor, which will definitely be better suited for producing music.

What do you guys think?

Heath

i highly doudt the machine is causing the interference , also if it was the machine both speakers would have it . sounds to me more like a grounding problem , also check the common sources of interference , powersupplys , tv's , cellphones , wireless keyboards and mice . try moving the speaker to another position .

PostmanPot

Grounding as in solid surface? Yip, solid. PSUs and sources of interference are well away.

Thing is, I can hear the CPU or something else in the laptop making the same interference sound "in harmony" with the interference sound coming from the speakers. Why would this be?

Will try moving the speaker.

PostmanPot

Also, the interference is amplified when the laptop's PSU is connected.

The interference stops when USB is unplugged.

Heath

then theres a grounding problem on the laptops PSU , it may not be connected to ground

Renesongs

Remove the the earth from the plug of PSU because the PSU is sending the hum to the speakers via the earth line - I had the same problem first time I used a laptop for recording

PostmanPot

Thanks so much for the help thus far Tailon and Renesongs.

Just to be crystal clear, we're talking about the laptop's PSU, correct? Did you have the same problem in that it was only one of the speakers getting interference?

I don't want to go and stuff up the laptop's PSU... ?

PostmanPot

Also, I'm pretty sure the laptop's PSU only had a two-prong connector?

Heath

nah you wont mess up the laptops psu , they all double insulated anyway

PostmanPot

Going to try this. Laptop's plug is three-prong. 8)

AlanRatcliffe

Same happens on my laptop. It all has to do with the horrible switch-mode power supplies they use for laptops. Disconnecting he earth on the power is one way to go - the laptop will still be earthed via earth on the interface and monitors.

One big word of caution: when the laptop is not plugged into the interface and speakers, it will not be earthed. In normal circumstances, this isn't a problem, but in the (admittedly rare) event of a serious short in the power supply sending mains to the laptop, the user is at risk of "potentially lethal voltages".

Having said that (largely to cover my and other members legal butts), this is extremely unlikely to happen and I use my laptop this way - even without the speakers plugged in. The only problem I find is the metal jacks on the front of the laptop tingle on my stomach with low voltage when I use it in bed (ahem ?).

The proper and safest method to fix this problem is to use a stereo DI box between the interface and speakers, which safely lifts the earth between the two.

Renesongs

I find is the metal jacks on the front of the laptop tingle on my stomach with low voltage when I use it in bed (ahem Smiley).

Buy a bed tray from your local chemist cost: about R200 you will be surprised at how useful they are. I probably will have to buy at least one more to avoid divorce proceedings.

PostmanPot

Many thanks Alan, great to know.

Would one of these suffice? http://www.muz.co.za/index.php?main_page=product_info&products_id=1552

Is there a universal input that will accept the laptop PSU cord connector?

AlanRatcliffe

Buy a bed tray from your local chemist cost: about R200 you will be surprised at how useful they are.

I went a different way and have a second power lead for the PSU that has an earth connection. ? I just swap them out as needed. I just forget to take it to town with me sometimes (the only time I use the laptop without speakers).

Would one of these suffice?

No - that's more to use on the inputs and is only mono. I haven't looked at these things for a while, but I think Behringer have the Ultra DI-120 which is two channel, (but active, so needs a battery).

I almost mentioned a safe way to lift the earth by using a balanced cable, but then I remembered the Audiophile is unbalanced outputs only.

I actually think the power cord with lifted earth is the best way to go, just using a different one with an earth when the laptop is not connected to the speakers.

Neps

Alan stop reading my mind!! I was just about to post about DI's..

Postman the DI's will be the safest route.. Anything where you disconnect the earth or bypass an earth is dangerous for your health!!

AlanRatcliffe

Thanks Neps! Can you recommend anything specific? I'm a bit out of touch with current models.

Neps

budget concious, I'd just say Berringer (did i say that out loud?!)

But seriously, the berringer DI's are CHEAP and work like a bomb. But get active ones that work on batteries and have ground lift switches. sounds funny but some dont come with a ground lift switch.

Because a DI normaly need Phantom, batteries are a must, cause on your out put buss, you wont get phantom! otherwise some passive models can also work, but I'll rather go for an active version.

On berringers website there are quite a few options. Someone earlier mentioned the stereo version, cant remember the model, but I'd go for that.

AlanRatcliffe

did i say that out loud

LOL! I'm the same about Behringer, but ultimately some of their stuff is good. Where would we be without Behri HP amps and patch bays?

Because a DI normaly need Phantom, batteries are a must, cause on your out put buss, you wont get phantom!

Yeah, I'd thought of that, so specified batteries. I would say go passive, but no-one I know of makes a stereo model (except maybe Radial and they're way too expensive).

PostmanPot

Hi guys

Well I'm back from setting everything up again. No more interference, possibly because of the latest drivers I downloaded? Or maybe it's because I swapped the speakers around. Lol, don't know. Anyway, the Rokit 6s sound awesome.

Only thing now is that there is sometimes a bit of lag/distortion when some Windows sounds play (i.e. removing flash drive) and when changing MP3s. Any ideas?

The kid is damn happy though, and so am I. 8)

AlanRatcliffe

Ah. Windows sounds are at 16 bit 44.1KHz, so the soundcard has to change sampling rates and bitdepth on the fly if you have it set to higher rates and depth. Usually you should disable the Windows sounds to avoid this.

In fact, download this document: http://ratcliffe.co.za/sundry/W2k_XP_Optimize.pdf and go through as many of the steps as possible aside from the install stage stuff and you should have a computer that is much more stable when used for audio.