Buzzing From Computer??

[dbuckley]

If you use an external (USB or Firewire) "soundcard" and a (stereo) DI box that has an isolating transformer then you can pretty much guarantee thats the cleanest audio you're gonna get from a computer whilst staying in the analogue domain.

 

You may be able to get away with less, sometimes, depending on what kit you've got and the electrical environment you find yourself in.

 

The more useful audio outputs are balanced but there is not a huge number of them about.

[bruce]

I had one of those cheapie ground loop isolators in my hand today. I also had a few minutes to spare, and a screwdriver, and curiosity got the better of me.

 

The basic unit:

 

 

That part number doesn't seem to be available from CPC any more, but externally it's very similar to AV12774 at £4.27. I wonder if it's the same inside?

 

Interestingly, the box is obviously for something else - the moulding on the back panel has a wiring colour code - as well as left/right +/- there are also labels for +12V and Ground...

 

So we prise the back off. Inside there's a PCB and some metal screening over the active components.

 

 

So what's underneath there?

 

 

[ceecrb1]

If you use an external (USB or Firewire) "soundcard" and a (stereo) DI box that has an isolating transformer then you can pretty much guarantee thats the cleanest audio you're gonna get from a computer whilst staying in the analogue domain.

 

Its how I do it.. and it works every time..

Infact in my "sound toolkit" that I carry to every job I opp.. I have 2 usb sound cards and a collection of Di's just for this setup... with all cables etc etc...

 

It works out "cheaper" in the long run knowing that every job you do your not going to create problems you later have to fix... Anything that makes life easier is a good thing.. isnt it?

[sleah]

2p.

 

Solution 2 - external card.

 

Well I have a couple of semi-pro/prosumer/disco type USB cards (MAYA44 / ESI) and they buzz like hell with an earthed PSU!

Maybe the SB's mentioned just happened to have earth lifted (or opto isolated) outputs? Or maybe the posted had a different source of noise that wasn't the PSU earth issue?

[JonM]

Hi,

 

Today I was using my laptop to play music at an event and it was really buzzing, we diconnected the audio output of the laptop so that it was not connected to the sound desk and the buzz was still there. We worked out it was the earth of the laptop causing the buzz. Is there a device for stopping this?

 

Jon

Edit: Just found this, will it do the job?

http://www.maplin.co.uk/Module.aspx?ModuleNo=219077

[paulears]

Moderation: Jon - er..... NO

 

I assume you have read the topic? I'm very confused. people have explained in great detail what is happening, and even mentioned a couple of products (and given part numbers) for things that fix this kind of issue. Bruce even showed some pictures of the two transformers found inside the box.

 

You've linked to an expensive, and probably ineffective consumer 6 way surge protector - it makes it clear it protects against mains spikes from thermostats, that kind of thing. Go back up a bit and re-read the advice.

 

Your post is just a little 'random' - or a joke? We're not really too sure to be honest.

 

By the way - if you disconnected the audio, and the buzz carried on, then this is just magic?

[JonM]

I assume you have read the topic?

 

I have read the topic and all the solutions I saw related to adding devices to the audio lead, as the buzz continues when the audio is disconnected I am guessing that the interference is being transmitted by the laptop through the earth and then picked up by the sound desk, but that is just a guess and I apologise if that is totally wrong.

 

I don't really know what the problem is but going with my above assumption it seemed a reasonable suggest, again sorry if not.

 

Your post is just a little 'random' - or a joke?

 

You can take it as 'Random' or 'a joke', I don't mind really, 'seriously' would be nice, but as it’s not an option....

 

this is just magic?

 

I see, well that’s an interesting theory as to why it happens.

 

Well, I guess I will just try and fix this one myself.

 

Sorry for wasting your time,

 

Jon

[revbobuk]

Jon - another possibility is to check the physical location of the power brick for the laptop. Some of them do generate significant interference if they are placed too near other equipment. If this is the case, then moving the power brick around will change the character of the noise.

[JonM]

Thanks, I will check that next time.

 

The buzzing stopped when I disconnected the earth of the charger (Which I didnt want to leave like that) but it could have been a coincidence and I moved the power brick.

 

Jon

[Happy Jack]

Well, I guess I will just try and fix this one myself.

 

Sorry for wasting your time,

:)

 

Without the hallmark of the 50hz fundamental Jon, you might want to also consider DC offset. There are loads of bits online that go into way more detail than I can go into, so I'm not even gonna attempt this myself. I've pulled a few bits to consider, though, although there is already plenty of information in this thread.

 

"Your laptop runs off of DC, most power supplies out there today do a poor job of rectification [converting alternating current (AC) to direct current (DC)] - it is a sacrifice that most consumers will never notice. Consumers want smaller sized power supplies therefore one of the tradeoffs is the potential for more ripple which overlaps the DC output of the power supply. We call this the 30 kHz ripple which most smaller power supplies have inadequate filtering of.

 

This ripple or "noise or hum" is then amplified by the system pulling any analog signal from the laptop. (larger wattage AV receivers, PA systems) You won't find this happens with 99% of headphones or smaller computer speakers - why? - because they aren't strong enough to amplify the 30 kHz ripple.

 

Another note: this bleedover of ripple does not take place through digital connections only through analog connections. Hence you can have this problem through the analog headphone jack but not through the HDMI or Display Port.

 

If the laptop is actually generating sound, what you need to solve the problem is an isolation transformer. Many DIs are also isolation transformers, but not all. A transformer will pass the AC signal that has your music, but is a solid wall to DC, thus, the DC hash doesn't happen.

 

Two words that do not go together with power supplies - clean & cheap..."

 

Perhaps re-read the thread again before you dismiss any advice. It's all here!

[sleah]

Thanks, I will check that next time.

 

The buzzing stopped when I disconnected the earth of the charger (Which I didnt want to leave like that) but it could have been a coincidence and I moved the power brick.

 

Jon

 

Just a shot in the dark..... but you say you disconnected the audio cable, are you certain there is no other possible connection between the laptop and any other equipment, such as a USB device?

Removing the audio connection may not make any difference if there is still a ground connection between the laptop and the audio system.

 

For example I have a USB > DMX dongle, that could 'somewhere' have a common ground between lighting and sound. like I say, a shot in the dark but worth checking.

[DonkiDonki]

Unfortunately since someone decided that the "radiation" pouring out of laptops was frying our brains, the answer was to require an earth connection.

 

The problem, certainly on older laptops is they were not designed to have earth connected and therefore do not screen in anyway for the potential issues associated. (depending upon model it is common to get various "noise" issues from any port connected to chassis earth such as audio & video connectors)

 

Even worse for our industry, most manufacturers (Dell is a particular culprit, but is not alone) still seem oblivious to the issue and continue to churn out machines with the same problem (strangely some models are clean others are not/not sure if someone at design stage is aware of the problem or the clean ones are by sheer chance).

 

If you are in a position where you regularly have to interface random laptops to audio/projection systems then the safest route is to have quality earth loop isolators at hand. Among the best I've used to date have been from Interspace (audio) and Kramer (composite/vga/rgb) but there are plenty of other suppliers.

 

 

Basic symptoms (curable short-term by disconnecting psu) audio - buzzing, video; faint rolling lines usually moving up and down the screen (more common on composite video but any analog signal can be affected).

[gafferted]

I have exactly that problem with a Dell laptop and a USB pre external audio interface. Plugging into an un-earthed mains socket cures it fine - if you're not averse to that sort of thing!

[bruce]

It may "cure" it - but in many cases it's a cure that might get you sacked :)

 

An isolating transformer on the audio side will fix it properly.

[paulears]

My Dell studio is appallingly bad when connected direct - but the Lexicon Omega interface I use has a hum free output - no problems at all!