Dear all.

I am using a DELL Inspiron 6000 (yeah, rather old... bur works) as a VST host for some Soft Synths.

When I connect the headphone plug to the unbalanced in of my Mixer, I hear a short buzz (~half a second long) every 4 or 5 seconds. I lowered the channel volume and is still there... the only way to avoid it is by either unplugging the PC from the mixer or running on batteries.

Is there any nice tech solution for this other than running on batteries (i.e. using DI boxes) or a tweak in the machine BIOS or configuration (I am running Win XP SP3).

Thanks for your help!!

Best regards from Argentina.

You have a ground-loop.

You either need to use a stereo DI box (or two DI's of course!) with the outputs feeding into mixer mic inputs or an isolation transformer such as the ART DTI with the outputs feeding into line inputs on the mixer.

HTH. Mike

Yup, hum/earth/ground loop.

Since you are coming out of the lo-fi headphone circuit of the laptop no point in buying better than this.
http://www.maplin.co.uk/ground-loop-isolator-33172

If the guys at your store are as good as those at Northampton they will advise on adaptors, take the mixer.
You might also strt to consider an Audio Interface?

Dave.

I picked up an EBTech hum eliminator for exactly this problem. It does the job, though I don't understand why there are things retailing for £100+ on Amazon...

http://www.amazon.co.uk/gp/product/B00101WA4C/ref=pd_lpo_k2_dp_sr_2?pf_rd_ p=103612307&pf_rd_s=lpo-top-stripe&pf_rd_t=201&pf_rd_i=B0002E4YH4&pf_rd_m= A3P5ROKL5A1OLE&pf_rd_r=16KBYF4KYR0BKPNYQKEB

...and other gadgets which seem to do a similar job for £3.50.

http://www.amazon.co.uk/gp/offer-listing/B000NVWB9O/ref=sr_1_1_olp?ie=UTF8 &qid=1337980109&sr=8-1&condition=new

Quote ef37a:

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Yup, hum/earth/ground loop.

Since you are coming out of the lo-fi headphone circuit of the laptop no point in buying better than this.
http://www.maplin.co.uk/ground-loop-isolator-33172

If the guys at your store are as good as those at Northampton they will advise on adaptors, take the mixer.

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Of course, there are no Maplin stores in Argentina, Dave, but maybe the O/P could get something similar. Not sure I go along with your view of 'lo-fi headphone circuit' on a laptop. In my experience the headphone outputs give a decent quality signal in many cases. The input side of things is usually a completely different story though!

Heh! Did not spot the South American connection Mike!

Headphones out on any computer must be driven from the $1 soundcards which are pretty universally considered poo so even if the H/P amp was a Lavry it will not deliver great sound. Cans outs are however low Z, usually 100R or less and that is good news when driving transformers.

That Maplin isolator can actually be found on the Bay and at 1/3 the price and I guess in any country.

Dave.

I noticed this the other day:

http://www.ebay.com/itm/Skytronic-Ground-Loop-Isolator-Laptop-PC-Hum-Elimi nator-/170602063703?pt=UK_Sound_Vision_Other&hash=item27b8ace757

It looks very similar to the two I bought from Maplin.

I'm told that, while a decent line level signal is required, too big a signal will bring out the worst in cheap transformers. I'm not an electronicist myself (didn't have the Latin) so can't say with any authority but would like to hear any informed opinions on the subject.

To the OP:

While all this is valuable advice the sound you describe is not the ground loop hum I experienced. It does however sound very similar to a sound I was plagued with for a few years until I was finally driven to do a systematic search. I found that turning off the wireless system on the laptop solved the problem.

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Ohm's Law states, "Your PA isn't as powerful as you think it is".

That is indeed the very chap Shuffs!

Yes, transformers produce distortion proportional to level and this gets worse the lower the frequency but a laptop headphone output is unlikely to supply enough signal level to bother even these cheapies, especially feedng a 10k or so mixer input when the actual POWER delivered is minute.

Wireless systems should always be turned off on any music computer together with the various other "tweaks and optimizations" one important one of which is stopping Windows sounds.

Run dpclat as well.

Dave.

Thanks chaps!. I'll see what kind of cheap DIs I can find down here. In any case they will be far cheaper than the cheapest audio interface for sure!

Nevertheless, I am not sure if it is a ground loop, since GLs are usually "always on" and this one sound like driven by a "sqare wave LFO!!", but DIs look the proper way to go. I remember that Radial have something for this application (I mean, audio from the Notebook Headphone jack..). Maybe expensive but being a mainstream brand, it is probably distributed down here.

Whith this same PC and using an M-Audio interface some years ago, this issue was unbearable since the mains cabling in the rehearsal room we were using was far from OK... so I better run on the el-cheapo side.

Best and thanks a lot!

Quote SMV_Argentina:

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Nevertheless, I am not sure if it is a ground loop, since GLs are usually "always on" and this one sound like driven by a "sqare wave LFO!!"

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Once created, a ground loop is always present since the physical wiring that creates the ground loop remains in existence.

However, the currents that flow around the loop are not necesarily constant, and they do not necessarily always cause audible problems. The latter depends on the amplitude and frequency conponents of the ground current and ther design of the internal circuitry.

In your case, it sounds like the laptop circuitry is dumping a noise currents into the ground path at regular intervals for whatever reason*, and hence you are hearing bursts of noise rather than a continuous hum or whine. But since the problem goes away when you break the ground loop (either by diconnecting the mains charger or the audio output screen), it most definitely is a ground loop problem.

Ground isolating transformers in the audio connections is the most appropriate and cost-effective solution -- and it provides a balanced connection on to the mixer for free, which might be handy!

* It could be, for example, due to the way the charger sends pulses of power to reharge the battery, or perhaps some regular polling action of the operating system, maybe to check wifi connections or something like that.

hugh

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Technical Editor, Sound On Sound

Thanks Hugh.

Just checked with my local (nearest, I mean) music shop and they carry the Behringer DI-20 box that hopefully will do. I will cost me less than 100 US Dollars (yes, things here are more than double the cost in dollar terms...), and will give me 2 channels in case I want to go all stereo with my laptop... I also have 2 Mic inputs in the little mixer I use to feed FOH (and my personal monitoring gear), so I think I'll go for it.

Best regards and Thanks, thanks, thanks.

Quote SMV_Argentina:

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Thanks Hugh.

Just checked with my local (nearest, I mean) music shop and they carry the Behringer DI-20 box that hopefully will do. I will cost me less than 100 US Dollars (yes, things here are more than double the cost in dollar terms...), and will give me 2 channels in case I want to go all stereo with my laptop... I also have 2 Mic inputs in the little mixer I use to feed FOH (and my personal monitoring gear), so I think I'll go for it.

Best regards and Thanks, thanks, thanks.

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Consider thinking again, those Behringer boxes are noisey, harsh sounding and unreliable. I have one on my shelf, not in my gig box.

The small transformer described earlier is cheaper, better sounding and has no active parts to go wrong.

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Ohm's Law states, "Your PA isn't as powerful as you think it is".

I actually doubt it is a ground loop. My Dell 6400 generally makes noises when charging and reduces to very little once charged. Its far more likely to be RF interference from a noisy switchmode supply which is a lot harder to get rid of.

Quote Falconhell:

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I actually doubt it is a ground loop. My Dell 6400 generally makes noises when charging and reduces to very little once charged. Its far more likely to be RF interference from a noisy switchmode supply which is a lot harder to get rid of.

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Tis an earth loop.
See Hugh's last post.

Dave.