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Matheu · Location: Netherlands

I'm having some recording problems with a laptop computer. When recording with the laptop using only the accu, it's ok. Connecting the mains causes some terrible noise to be added. If unplugging the Line-In jack (where I'm recording from), the noise stops (with the mains still connected).

A sample of the noise is here:http://www.euronet.nl/~3_somers/ruis.wav

I previously heared something about "ground loops". I suspect his is one of them? Will a netfilter help? Or would I need something else?

When searching for netfilters I only came across UPS stuff (apart from Linux firewalls). Shuld I be searching for an other keyword :???:

Any words of wisdom apreciated,
Cheers...

SteveG · Location: United Kingdom

It looks and sounds as though the switching hash from the power supply is getting into the soundcard ground connection somehow. Unfortunately, to say exactly how is going to require a lot more detailed information about your system, and the computer power supply, as strictly speaking, this sort of thing shouldn't happen.

There is no way any filter on its own is going to fix this - it qualifies as a fault in its own right when it happens at the level you've got! You either have to post absolutely everything to do with your system (and then expect difficult questions!), or get somebody who knows about computer power supplies and audio grounding to have a look at it. Trouble is, it's not really a simple 'hum' problem at all - in some ways theses are much easier to sort out.

VoodooRadio · Location: USA

Who is HSZone? Are they like Circuit City or Office Max?

Matheu · Location: Netherlands

Wildduck · Posted - Thu Oct 10, 2002 3:47 pm

We've discussed this before. The noise you hear is quite common when connecting a mains powered laptop to other equipment.

My normal cure is to connect the laptop to other audio gear via audio transformers. This usually cures the problem.

Disconnecting what are probably safety ground (earth) connections can be dangerous.

Matheu · Location: Netherlands

SteveG · Location: United Kingdom

If removing the earth (ground) actually removes the problem, then I'd get somebody to look at the power supply, because the ground connection in it cannot be that 'solid'. If it was, then the switcher hash couldn't get into the ground path, as it would be at too low an impedance. And if you have a faulty ground connection in a power supply, you might actually be safer using a separate ground to the PC chassis, as there are all sorts of implications when a fault is present, which seems to be the case at present.

You really don't need a transformer-isolated system, you need a safe system! Incidentally, is the power supply plugged in at the same point that whatever you are feeding it with is plugged in? If it is connected to another socket, and the results vary when you move the (grounded) power supply connector around between different outlets, then I'd get the grounding in your house wiring checked as well.

Wildduck · Posted - Fri Oct 11, 2002 4:49 pm

I'd still go for the audio transformer method to separate the two systems. I don't pretend to understand exactly where the laptop psu noise comes from or how it gets into the programme path, but the fact is that this has cured the problem for me on three systems.

Looking at the two laptops that I commonly connect to mixer outputs (and both of which exhibited this effect) neither of them has an earth connected to the laptop PSU. It may not be a coincidence that both PSU's are labelled as made by 'Delta Electronics'.

I believe that suitable audio transformers used to be available in the UK from Maplin. I'm afraid to say that the ones I use were rescued from obsolete, broken professional audio gear which was intercepted before it went into the skip. I just used old 1:1 balancing output transformers and didn't carry the earths through.

I'll try to find time to wave an oscilloscope probe around the laptops sometime soon. My guess at the moment is that the high RF produced by the laptop supply causes the whole laptop to be a source of RF. Connecting it to a properly earthed system perhaps causes this RF to flow down the audio earth. The unearthed laptop psu probably completes the RF loop via the supply neutral connection.

Matheu · Location: Netherlands

I've got more info about the grounding at the recording site. In the meter-groups-cupbourd* the energy-company* has connected the Neutral chanel to Earth-ground. This is normally done in the transformer-house* but here they made an exeption. The metal dam-plates* around the basement are also connected so there are many square meters to provide good conduction to earth.
* Please forgive my English, these are litiral translations.

Disconnectin earth can't seriously be considered dangerous since the casing is not metal (it's a laptop), and most of the plugs in holland (in livingrooms and bedrooms) are not earthed at all.

I found a audio transformer at the local electronics shop's site for 8,60 Euro, so I'll get one of those next week if it's a "static" one (that dosn't require additional electronics and a power supply), there's not much info on the site http://www.dil.nl/details.asp?artcode=B070.

I'll be double safe. :]

Cheers

SteveG · Location: United Kingdom

Havoc · Posted - Sun Oct 13, 2002 5:30 am

Wildducks remark that this is frequent with line connected laptops is correct as is its analysis. It is related to the psu construction, but there is not much you can do apart from disconnecting the ground or using isolation transformers.

We chased a similar problem at the office with a laptop and a modem. Very good when using batteries, but really bad when powered. The problem is capacitive coupling in the laptop line psu. The ferrite will not do much for that. Line chokes need to be enormous (think 10H). Even isolation transformers in the mains did not cure it (we did not had one wih an internal electrostatic screen at hand).

There is not that much danger removing the ground as the laptop is connected by the other equipment to the ground (otherwise there would be no loop). Best thing you can do is get a special extention lead for your laptop where you disconnect the ground and use that for recording, but not otherwise. Use rubber gloves Smile

You can always give an esoteric to that.

Ideal solution: external ADDA and fiber to the laptop.

SteveG · Location: United Kingdom

Havoc is fundamentally correct, but it is still a PSU problem, and really, it's not good. We have fixed a similar problem in the past by rewiring the power supply with a solid earth bond through to the laptop chassis, something which a lot of laptop PSUs seem to **** up a treat - it never seems to enter into the designers' minds that this could ever be a problem! There isn't any need to have hash induced capacitively into the ground connection, even if it is shared with the laptop supply neutral - it really is very bad engineering design.

Wildduck · Posted - Sun Oct 13, 2002 9:24 am

I think the basic problem here is that, as Steve says, the designers of laptops just never think about audio. So most laptops have no line-in socket, no hardware volume control and all the other similar drop-offs. Similarly radiation from the PSU isn't a concern at the design stage. Weight and size of the PSU will be.

I've just waved a medium-wave radio round near this laptop that I'm on now. On battery there's just the normal computery sort of signal pick-up across the band. On mains there's a stonking great radiated signal that can be tuned in on the radio. The same signal radiates from the psu itself and from its 2-wire mains lead.

I still think the cheapest approach is to put audio transformers between the laptop and other gear, but I'd be very ready to be convinced that another method would be better. The trouble is that I've tried other ways such as solid earthing of the laptop etc., and they haven't worked. Similarly, finding a supplier of (for example) a good 19volt 2.5amp psu might be even more difficult than finding decent audio transformers.

Matheu: You were right to say there's not much information on the transformer web site that you were looking at. >:K
I'm actually a bit wary of leading you down this path without knowing exactly what it is that you are trying to connect to. If a test with one transformer works, you'll need another for the other leg of the stereo, and there's all the problem of connectors, boxing it up and so on. Did someone in the past suggest some cheap transformer-based DI boxes as a possibility for this?

I'm afraid that this is a common problem and that there is no easy answer.

Andrew Rose · Location: United Kingdom

drmengler · Posted - Sun Oct 13, 2002 11:26 am

I've just entered the world of laptop audio myself. I have a desktop system using a Yamaha SW1000XG and a Terratec DMX6Fire. These are both connected to a Peavey RQ200 mini console, the output of which goes to a Samson Servo-170 power amplifier. I've never had any noise problems with this. I don't pretend to understand noise problems though...

I've just set up my laptop system - it's a Dell Inspiron 8200 with an emi 2|6 USB audio box. Today, for the first time, I plugged the output of the 2|6 into the Peavey. It sounded great - before I plugged the laptop into the mains. Then I got major noise.

For anyone who would be kind enough to think about what's wrong with my setup:

I stripped it down to the bare minimum. Normally I have my desktop, monitor, keyboard DC adaptor, Peavey, Samson, lamp, etc, etc, plugged into an 8-way beneath my desk. I unplugged everything apart from the laptop PSU and the Samson from the 8-way, and plugged the outputs from the emi 2|6 straight into the Samson (removing the Peavey from the picture). I still got major noise.

I took the laptop, psu, and emi 2|6 downstairs and hooked them up to a cheap and nasty powered PC desktop speaker system, making sure the laptop PSU and the powered PC desktop system were using the same socket (with an adaptor). No noise at all.

Another bit of info - the 8-way has a big light on it that's lit up, saying "EARTHED". And, on the plug-end of my laptop PSU there's a notice saying "WARNING: be sure to insert the grounding pin of the power cord plug into the grounding socket of the electrical outlet".

Does this imply the laptop is properly grounded - in turn, does that imply the Samson power amp is at fault?

I'd really appreciate it if you could spare a few minutes to think about this one for me. I have my first laptop dj'ing gig next Saturday and I won't be happy until I know that I'm not the source of any noise problems at the gig!

Thanks,

Matthew

SteveG · Location: United Kingdom

drmengler, (what on earth sort of handle is that?)

I think that we've all agreed on what the source of these noises is, the only real question being the best way to fix it! Trying to fix grounding problems using this forum, or email, is like trying to wallpaper a room through the keyhole in the door!

In general,this sort of noise can be induced anywhere in your system where the earthing lets it. The rules are essentially quite simple, but the practical application of them often isn't, and without actually checking every single detail of your system's earthing configuration, it would be pretty hard to pinpoint exactly what the casue is, since it's almost invariably related to the interconnection of two bits of kit.

We've managed to sort out turntable grounding problems before (sort of), and the amount of detailed discussion has been considerable - a search should reveal the threads - and most of the principles are discussed in them. If I get a chance later, I'll see if I can locate them if some other kind soul hasn't already. (I know that searches are getting to be a bit of a pain!)

Havoc · Posted - Sun Oct 13, 2002 1:42 pm

Well, drmengler's problem is exactly the same as matheu's one. The difference is that when using the pc powered speakers (that use an adaptor as he said) then there is an extra transformer in the loop. If this is a cheap E core one or if they are not grounded at all (or both!), then it can block the ground current because the capacitive coupling between the windings is small or there is no ground connection. Thus no ground loop.

I'll try to find someone at the office who remembers what the solution was if we ever found one.

Wildduck · Posted - Sun Oct 13, 2002 3:13 pm

Of course the most constructive help would be if someone who has a laptop that doesn't exhibit these problems could tell us what make it is.

And, as for Andrew mentioning Wi-Fi, I could join in with my sorry tale, but that's probably best left for another thread as I haven't yet got as far as RF problems with it. Sad

drmengler · Posted - Sun Oct 13, 2002 4:25 pm

drmengler · Posted - Fri Oct 18, 2002 6:50 am

I tried 'disconnecting' the earth - taping over the pin on the plug. This indeed removes the problem, but I don't like the idea of about �2500 of laptop/audio equipment not being grounded properly - I imagine sparks might fly. literally.

So - the laptop is obviously grounded through the PSU. All cables have 3 pins, and there's a big notice saying "make sure this plug is plugged into something that's grounded". And I'm having to tape over a pin of the plug to stop the noise, but also that stops it being grounded correctly.

Is it the case that the ground is somehow 'contaminated' by interference from the laptop, which should be filtered out in the PSU but isn't?

What can I do about this? Get a PSU that doesn't suffer from this problem?

Any ideas? SteveG? Anyone?

Matthew

(sorry - panicking because I have a gig with the laptop tomorrow and I *really* don't want to run off battery)

FullTime Tim · Location: Canada

I have had the same noise problem as Matheu (actually the sound/noise is identical to the ruis.wav he linked to) I've been following this thread all along, but didn't want to jump in until I had a sure solution.

But, because drmengler seems to NEED a solution....It looks like the noise is in fact caused by AC adapter sending noise though the ground(not a techie so maybe not a perfect explaination) I have solved the problem temorarily by using a portable DC power source that we use to run equipment on location. It totally cures the problem. Now, I know no one wants to run out and get somehting like that, but it stands to reason that you could use any kind of Back-UPS power supply/Isolated filter that regulates power/voltage and isolates the power supply. Normally these devices are used to protect equipment, but in this case your protecting the everything else in your studio/setup because the laptop power supply is corrupting the system and there by adding noise.

I plan to test my theroy ASAP, and will post when I have it working.

SteveG · Location: United Kingdom

Wildduck · Posted - Fri Oct 18, 2002 10:47 am

I've now looked again at my 2 Delta Electronics power supplies. Both are in similar casings, both provide 19volts, but at slightly different rated currents. One of them is indeed earthed, with a 3-wire mains lead, the other isn't, just using 2 wires. The second psu has the British double-insulated symbol, the earthed one doesn't. The earth on the first psu is carried through to the laptop power input and hence to the sleeves of the audio jacks. This is what I would expect.

The interesting thing is that I've had noise problems with both of these laptops when connecting them to various studio mixing desks.

I realise that this post will only confuse things more, but hopefully it might add to the build up of knowledge.

Matheu · Location: Netherlands

I got one of those isolation transformers and it works great.

The technician who sold the thing explained it as follows: The grounding of both machinnes are connected via the audio cable, and also via the earthing sleevs of the plug. This loop somehow works as an antenna and can resonate with any present radio signal in it's frequency. This is what causes the noise. When breaking the loop the antenna is disabled. Sounds a bit googledygook to me but anyway both solutions work. Disconnecting earth on one machinne or using the audio transformer.

The audio transformers are usually used for car-hifi where standards are not so high. I was told that it lowers the quality of the signal. I didn't notice anything with mine but disconnecting earth will save you 15 Euro, so that's what I would reccomend anyone with the same problem. The laptop will be earthed anyway thrugh the audio cable.

Cheers

SteveG · Location: United Kingdom