Greetings. I've been having this issue with my new Phonic Helix 18 mixer and my Gateway MX7515 laptop. Whenever I route the firewire audio to the main output I get digital noise. Removing the PSU from the laptop eliminates the noise. I'm thinking that a Cleanbox between my mixer and monitors might be my solution. However, I'm a little wary of using it with my monitors, as they have balanced inputs and the Cleanbox has unbalanced outputs. Would using the cleanbox in this manner harm my monitors at all?

-Dave

No, it wouldn't, although personally I'd make up some pseudo-balanced cables and connect them between the Firewire interface and the mixer, assuming it also has balanced inputs.

You just buy twin-core screened (mic) cable instead of single-core screened, and then solder an unbalanced TS plug on one end (the interface end) and a balanced TRS jack one to the other (the mixer end). The 'tip' connections are made as normal using one cable core, while the 'sleeve' of the unbalanced end is connected to the 'ring' connection at the balanced end using the other cable core, and the 'sleeve' of the balanced end is either left unconnected, or preferably connected via a series eighth-Watt metal-oxide resistor of between 50 ohms and 500 ohms (I normally use 100 ohms) to the 'sleeve' connector at the unbalanced end. Such an approach will completely cure most soundcard ground-loop problems, and if you're going to solder up your own leads anyway it will only cost you a few pence more.


Martin

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YewTreeMagic

In my case the firewire interface and the mixer are one and the same, So the only place I can use the cleanbox is between my mixer and the monitors. I think I'll try making some pseudo balanced cables before shelling out the cash for a cleanbox though.

Are there any sites where I can get twin-core cable?

- Dave

Edited by Radical Ans (10/07/06 03:56 PM)

Hello
I am new on here and have just read through as much info as my brain can take on this subject...

It looks like my specific problem, from what i can tell here, can be solved by buying a Cleanbox II, but i just wanted to check that this is the case before purchasing one.

I have a 2 year old Carillon laptop, and the digital noise when plugged in to the mains is very loud, grinding, and unpleasant. I use a dual-valve TL Audio pre-amp + mics to record acoustic instruments, which then goes in to a Edirol UA-20 and into the laptop.

The problem is that the noise in question is coming in on the input channels, and hence gets recorded along with the instrument whenever the mains is plugged into the computer. Unplugging the mains stops the noise straight away but the battery life is rubbish so this is no solution. I bought two "Milennium" DIBoxes with ground lift, and plugged them in between pre-amp and interface - and now the signal is A) pretty much inaudible and B) very high frequencies only, and C) still noisy. (which is not what i was after.) I wondered if this was the right place to put them, but then realised that there is nowhere else they could go in such a simple set-up.

Will a cleanbox II placed between preamp and interface solve this problem?

thanks very much for any help and sorry if somewhere in this thread the answer already lies..
Jon

Hi Braci,

Well my name's not Martin and I don't live anywhere near Cambridge, but why don't you start a new thread?

ryan

Hullo people,
I have a slightly different problem to most people here although the symptoms are similar.

I PM'ed Martin and he was kind enough to reply giving cause to my problem.

Here is my original message:

Quote:

---

Hello.

Sorry to bother you however I saw on the SoS forums that you seem to know a thing or two about ground loops which is a problem I'm having with my laptop.

The symptoms are: when using the ac adapter, there is hum with headphones plugged straight into the headphone socket on the onboard soundcard. If I touch the metal of the back of the laptop then the hum is reduced somewhat, it's not much fun using the laptop one handed I must say.

When removing the ac adapter and going it on the batteries, there is no hum.

You seem to be recommending a DI box, in most cases you state it should go between the mixer and the speakers/amp/monitors. I would just like to continue using my headphones as this is a mobile rig, so would this mean that I need to plug the DI box between my headphones and the headphone input on the laptop and that should solve things?

If so, what should I be looking for in a DI box?

Thanks for taking the trouble to read this.
Will appreciate any help or info you can divulge.

Regards
-myles

---

and here is Martin's useful reply:

Quote:

---

Hi there!

I suspect in your case that the problem isn't a ground loop, but the opposite - the lack of any ground at all!

I suspect your laptop mains power supply unit has an oval mains cable (not a 3-wire round one with the earth connected), and when you're plugged into the mains the laptop's metalwork 'floats; with respect to ground, which is why touching it reducing the hum level. If you stroke the metalwork with your fingers does it feel 'tingly'? (this would confirm the lack of an earth).

If you connect the laptop to a grounded item like a mixing desk or active speakers this would ground the laptop for you, but if you're simply plugging in headphones to the laptop's headphone output then the whole assembly remains unearthed.

Actually, if you have any more questions why not post your query on the existing sticky thread at the top of the PC Music forum entitled 'Click here if your laptop audio contains strange noises', since I suspect your problem would be of interest to many other forum users.

Hope this helps!


Martin

---

He was correct to spot that my adapter is a 2 prong and thus doesn't have any natural earthing. I suspect that using active monitors or a mixer will solve things however this is my mobile rig for my travels on the road.

At most I am using the Laptop, a USB-powered Sound Interface/Keyboard (Line6 KB37), headphones and a guitar.

A mixer isn't needed and lugging monitors around isn't suitable.

Would anyone care to venture some ideas as to what else I can do to 'earth' my set-up?

Cheers!

That's an easy one - just connect a chunky earth wire to a standard mains plug earth pin, and connect the other end in some way to some metalwork on your rig. Any spare port on your laptop could be pressed into service, such as plugging in a suitable plug to a serial or parallel port, as long as it is metal and is connected to the metalwork of the laptop.


Martin

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YewTreeMagic

Hmm I don't really trust myself to wire up something that plugs from a power socket into the serial port and doesn't end up frying my laptop.
I just relocated to the USA and so I'm not too familiar with the different plug and socket types either.

Any professional solutions out there?

It ought to be perfectly safe, but another approach is to buy an item of gear that IS earthed, and plug that into your rig to provide the earth connection. However, in the US you may only have two pins in some mains plugs used for smaller appliances, and no earth - here are the two types:

www.leadsdirect.f9.co.uk/americanplugwiring.htm


Martin

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YewTreeMagic

Thanks Martin!

Could it be as simple as getting a 3-pronged cable for my laptops power brick?

I suppose if I'm in a place that is older than 1965 and doesn't have earthed sockets, I shouldn't really risk plugging in.. :P

No, not quite a s simple as that, since the third prong (earth) wouldn't actually be connected to anything - the PSU needs to be designed for three-wire mains, with the low side of its secondary (output to laptop) transformer connection connected to earth. A 2-wire PSU will be double-insulated i.e. the designers are doing their level best to keep the secondary side completely isolated from any mains connection.

Ironically I've just had someone email me who's replaced a 3-wire PSU for a very similarly rated 2-wire on his Sony Vaio, to cure an earth loop. Now if yours also requires 19.5-volts at 1.3 amps you could perhaps buy his 3-wire model.

So there's another suggestion for you - find a replacement 3-wire PSU with earth connection, or perhaps someone here would happily swap with you in return for your 2-wire model to cure their ground loop problems. As long as the voltage and current capability are fairly close and the output plug is the same this should work well.


Martin

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YewTreeMagic

Hmm, mine is 19.5v at 4.62 amps, I will probably ask Dell if they can provide a 3 prong PSU.

Bit worrying though that many people have ground loop issues, so I will probably replace my un-earthed noise with 60hz ground hum!

Thank you so much for the advice, it has been tremendously helpful.

Good luck, and may the buzz not be with you


Martin

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YewTreeMagic

Just wanted to say that I was getting nasty digital noise from my Toshiba A120 (3 pin plug).

I just bought a HD400 and I'm using it into an unbalanced amp by losing the cold (mono jack to phono). £15 from Turnkey (pound in the swear box).

http://www.behringer.com/HD400/index.cfm?lang=ENG

Thanks Martin & all..........

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http://soundcloud.com/colossaldj

i have an acer aspire 9500 running out via firewire and yamaha mlan...what i get is not ground loops, but little clicking and sort of faint scratching type noises coming through the speakers whenever i move the mouse (USB) around the screen...does anyone know why this happens and is it fixable?
thanks
dennis

Does it definitley happen when the lappy is running off batterey ?

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http://soundcloud.com/colossaldj

hi wax,
yeah it does
dennis

Okay... here's an interesting one.

HP dv8230ca laptop => M-Audio Firewire Solo => KRK v8 monitors running from the balanced TRS outputs on the FW Solo. Everything is plugged into the power supply on my guitar rack.

When the laptop is plugged in, there's the usual laptop power supply noises. Unplugged, it's silent running. Normal, though not desirable, behaviour.

However, while the laptop is plugged in, if I unplug the KRKs from the FW Solo and plug in my Audiotechnica headphones, no noise. I plug one monitor into the FW Solo headphone jack - noise. AT Headphones in the same jack - no noise.

I tried unplugging the monitors from the FW Solo, to see if they were picking up the noise as RF interference "on air", possibly with the cable acting as an antenna, as opposed to "on the wire." They were silent, so the noise appears to actually be on the wire.

The volume level of the noise appears to be fixed-- the output volume on the FW Solo does not affect it. I can zero or dime the output level on the FW Solo and the noise coming from the monitors is at the same level. This would seem to indicate to me that the noise is only becoming a problem *after* the Solo's D/A conversion, but I'm not an expert on how either ASIO drivers or Firewire work so I can't really speculate on how that would be happening.

So my thought is, what are the headphones doing to cancel the noise, and how can I make my monitors do that? I'm wondering if all I need to do is ensure that I have properly balanced/shielded cables between the FW Solo and the monitors?

Welcome to the SOS Forums CoG!

Actually this sounds like a classic ground loop problem, except that it shouldn't be happening because of the TRS-wired cables between your Solo and active speakers, which should break the loop.

When the headphones are plugged in you have no ground loop, so the noise is gone, but as soon as you plug in one cable from your active monitors to the same headphone output you get the noise - the ground loop is back.

Connecting the cable screen at each end guarantees the best possible rejection of RF interference, but you can probably solve your current problem by disconnecting it at one end of both cables (the best end is the receiving end i.e. the ends that you plug into the active monitors - if you disconnect the FW Solo 'transmitting' end of the screen it can act as an aerial picking up RF interference).

Good luck, and let us know whether or not this solves the problem!


Martin

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YewTreeMagic

Martin, thanks a million!

Errrrm... that said, how would one go about disconnecting the cable screen...?

If it works I promise to write up an a-z, including pics.

Actually, on that note-- it's clearly the "laptop DC power supply" noise, I can hear myself moving the mouse around, closing windows, etc. and it stops when the laptop is running on battery. Is this still consistent with a ground loop? Forgive my ignorance...

Yes, these are exactly the noises you'll get with a ground loop. Sometimes you'll hear each and every hard drive access as well as a scratching sound.


Martin

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YewTreeMagic

Martin--

I'm afraid there may be a slight north-america-versus-UK technical vocabulary issue here; are you suggesting disconnecting the ground in the TRS or XLR cable that I have going to the monitor, on the speaker side?

Related, I tried a high-quality XLR connector instead of the lower-quality TRS I was using and while the problem is still present, the volume of the ground loop noise is considerably lower. Does this make sense?

Quote CoG:

---

I'm afraid there may be a slight north-america-versus-UK technical vocabulary issue here; are you suggesting disconnecting the ground in the TRS or XLR cable that I have going to the monitor, on the speaker side?

---

Yes.

Quote CoG:

---

Related, I tried a high-quality XLR connector instead of the lower-quality TRS I was using and while the problem is still present, the volume of the ground loop noise is considerably lower. Does this make sense?

---

Anything can happen with ground loops - they can be rather unpredictable things, with noise levels changing significantly as you alter the path the loop slightly, or change the impedance to ground at some point (for instance, if you shine up the earth pins of your mains plugs with wire wool this may also change the noise levels, although this may not apply quite the same with US mains wiring).


Martin

--------------------
YewTreeMagic

Hi,

I have been watching this thread for a while now and are experiencing firewire ground loop problems with my MOTU Traveler when connected to my laptop via a 4 to 6 pin cable. When using microphones I never have a problem, but when I start connecting to other equipment the problems occur (sometimes even when using balanced cables). The hum can be stopped by running on batteries or connecting using DI boxes .

The laptop power supply is the earthed type.

When I want to connect to a desk I find that I need alot of DI boxes or isolation transformers. That clearly isn't practical so I am looking for a simpler solution.

My questions are:
1) Is there a way of isolating the earth loop at the firewire connection? I have considered lifting the firewire ground connection, but read somewhere that the ground to signal pair connection is used for signalling. I have found references to firewire/1394 isolators, but are unsure if they isolate the ground or only the DC supply (which the 4 pin connector does anyway).
2) Has anyone experienced problems lifting the laptop power supply earth? As the power pack is double insulated and the output is low voltage DC I can't imagine it being a safety issue.

Thanks in advance,

Mike

Welcome to the SOS Forums Mike!

Tricky questions to answer. Officially I'd have to say that using balanced connections should always work (even if you have to disconnect the screen at one end as mentioned above), or with unbalanced connections you'll always have to fit a DI box in line with each and every audio connection.

The problem with lifting the laptop PSU earth is that (however unlikely) it's theoretically possible for a lethal mains voltage to end up on the PSU output in the event of a fault condition. With the earth connected this would immediately blow the mains fuse, but with the earth lifted it's possible for this lethal mains voltage to end up connected to the metalwork of your laptop. However, with a double insulated unit (look for the double box logo) the earth is often not connected anyway, as it doesn't need to be.

Others have pondered the option of stripping back the plastic sheath on a Firewire cable and cutting through the screening at one end of the cable to break the loop, but I dont' know anyone who's tried it, or if there's any possibility of the data stream being comprised.


Martin

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YewTreeMagic

Thanks for the response.

One thing that I haven't tried is lifting the earth at one end on my balanced cables as unfortunately I normally use a multicore with moulded ends. I think I will give it a try.

I too am not comforatble with lifting power earth connections, though in this case I have been seriously considering it. If lifting the balanced cable earths works I won't have to do it.

Thanks again,

Mike

Hi folks,

Managed to eliminate my laptop noises w/o cutting anything, though that would probably have worked too!

Laptop and I/O device are plugged into the power supply on my rack; speakers are plugged into a plain old power bar in a different outlet (though both outlets are on the same breaker, if that matters.) No noise.

If everything is plugged into the same power supply, even if it's a fancy Furman PC, noise.

I would have saved myself a good bit of trouble by trying rational things with different outlets first. So, do.

One thing for guitarists-- if you have hot pickups, you can actually pick up similar laptop noises occasionally. It's just like amp feedback, change the position of your guitar a little and it should go away...

hello all,
i have tried using the di120 from behringer and whilst it removes the hum. cracks and pops from my laptop it introduces and unacceptable (well to me anywway) level of white noise hiss...have you experienced this too, and if so what did you do to defeat it?
thanks
dennis

CoG - you may have accidentally reduced the noise by plugging in multiple devices to different mains outlets, but you haven't cured the ground loop (assuming that is that all your mains outlets are corrected earthed!). WHat you've done is altered its impedance, such that the noise has coincidentally dropped in level.

You may find in future that when you plug something else into your setup that the noises reappear - the only permanent cure is to break the ground loop (although I can see that you're quite happy at the moment )

jodenmi - Welcome to the SOS Forums! I haven't used it myself, but Behringer's Ultra-DI D120 seems to be an active device (containing electronics) rather than a passive DI box using a 1:1 isolating transformer. Active designs ought to have a low background noise level, but make sure the output levels from your audio interface are optimised to suit the D120 input levels to keep it as low as possible.


Martin

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YewTreeMagic

Hi, pardon my ignorance but I'm a computer techie and not an audio whizz. At my church we are recording services to my laptop (Acer Aspire 5101) and I think I'm getting the ground loop problem you describe when on mains - major intrusive buzzing. The feed is tapped into the output signal from our mixer desk that feeds the tape recorder.

Where would I put the DI in this case - in the feed from the mixer to my laptop line-in I assume?

Welcome to the SOS FOrums plusmore!

Yes, that sounds like the most suitable place to stick a DI box, assuming that's the only connection between the laptop and the mixer (if you have the audio output from your laptop connected back to the mixer then you'll probably need to DI this as well).


Martin

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YewTreeMagic

hey there, i read the posts and many more on this site as well as google. Ive read posts about using DI box's but i wouldn't know where it would go in my situation, and also using dummy cables?
If i where to use these techniques where would they be used?
I have a laptop with an Mbox 2 plugged in via the USB port. Then from the Mbox i have two active monitors plugged in to the L and R channels. Any help much appreciated!!! Thankyou...

Welcome to the SOS Forums bequick_x!

Where you place the DI box depends on what two (or more) pieces of gear are causing the problem. Have a read of my step-by-step guide here:

www.soundonsound.com/sos/jul05/articles/qa0705_1.htm

In your case the most likely place is between the Mbox-2 and your active monitors.


Martin

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YewTreeMagic

i recently got a behringer bcd 2000 mixer,i have a hp pavilion dv2000,i hooked up all together with my decks and there is a latency sound coming from the speakers,i regulated the latentcy from low to high and still the same problem.is it my laptop thats the problem,it meets all the minimum requirements for the bcd2000.i have a gig in 2 weeks and really need to sort it out asap,please help[quote="Martin Walker"]Since so many new posters on this forum seem to be suffering from 'funny background noises' in their laptop audio, here's a direct link to my two FAQs on the subject to hopefully save us pointing newcomers there by hand ;)

The first describes the probable cause of most problems, and suggests a couple of possible solutions (and one to avoid):

<a href="/forum/showflat.php?Cat=&Number=317&page=2&view=collapsed&sb=5&o =&fpart=1#317" target="_blank">www.soundonsound.com/forum/showflat.php?Cat=&Number=317&page=2& amp;view=collapsed&sb=5&o=&fpart=1#317</a>

The second discusses some specific laptop models that seem to cause problems due to a grounded power supply:

<a href="/forum/showflat.php?Cat=&Number=318&page=2&view=collapsed&sb=5&o =&fpart=1#318" target="_blank">www.soundonsound.com/forum/showflat.php?Cat=&Number=318&page=2& amp;view=collapsed&sb=5&o=&fpart=1#318</a>

There are lots of other FAQs as well - the full list can be found by following the link from our main forum page, or by clicking on the other sticky thread next to this one.


Martin [/quote]

Quote dj ob:

---

i recently got a behringer bcd 2000 mixer,i have a hp pavilion dv2000,i hooked up all together with my decks and there is a latency sound coming from the speakers,i regulated the latentcy from low to high and still the same problem.is it my laptop thats the problem,it meets all the minimum requirements for the bcd2000.i have a gig in 2 weeks and really need to sort it out asap,please help

---

Welcome to the SOS Forums dj ob!

I'm afraid you'll have to provide more details on how this gear is connected up, and I'm not sure what you mean by 'regulating the latency from low to high' - are you referring to your audio interface's buffer size?

If you have ground loop problems the only way to track down the cause in your particular setup is to follow the step-by-step advice I linked to above:

www.soundonsound.com/sos/jul05/articles/qa0705_1.htm


Martin

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YewTreeMagic

Hi Guys,

I have the same problem with a Phonic Helixboard 24.
The digital noise i get when the PSU for my Vaio is plugged in is unbearable.
But, the sound comes through headphones when i have no monitors or Mics plugged into the Helixboard, it's always there.
All the posts i've seen refer to DI boxes and Pseudo cables, but if the noise is there when all i have connected are the laptop to helix via firewire i can't see how to remedy this.
Any suggestions?

--------------------
Cheers,
Baj.

Hi Baj!

And welcome to the SOS Forums!

Your problem is a tricky one to solve, since both laptop and mixer will no doubt be earthed via the mains, and connecting the two with a Firewire cable will create the ground loop. Other people have experienced this problem, and there's no obvious solution that doesn't involve safety concerns by removing the mains earth connection of either laptop or mixer (please don't do this - your life is more important than background noises!)

Before you go any further, try to minimise the problem by making this loop as small as possible - make sure both pieces of gear are connected to the same mains wall outlet. If you have a spare, try a different length Firewire cable, which will change the ground loop slightly and might just help. You could also try modifying the Firewire cable to remove its earth connection and break the ground loop, but since every one I've ever seen has had plugs moulded onto each end this isn't easy.

Fundamentally this is a design issue for any gear that's USB or Firewire connected and with mains power of its own. Sorry I don't have any definitive solutions for you, but do report back if any of these suggestions help.


Martin




--------------------
YewTreeMagic

Thanks for the swift response Martin.
I'll try a bit of cable surgery on the firewire lead.
If i find any other ways, i'll be sure to let you know.

--------------------
Cheers,
Baj.

Hi,
I've read this discussion/links and have bought a behringer D120 for my EHCO indigo DJ (PCMIA soundcard) and ASUS Centrino laptop.

At last weeks band practice, through the PA, the ground lift switch did the job, and the ground loop hum went away.
Last night, the switch only reduced the volume of the hum by about 50%, but it was still quite noticible and annoying.

What has changed it one week?
How can you get a partial cure?

Please help thanks
Gav