Hi all - I'm stumped on this one but I'm sure I'm overlooking something rather simple !!


I have my "comeback" gig next Saturday (17th May) and I have just finished tweaking/upgrading my set up. I used to use a desktop PC but have switched to a laptop. I now have the dreaded hum, squeak and pops when the laptop is running on mains power.

Equipment:
Dell Inspiron Laptop running Windows XP SP2 and PCDJ Red 5.2
Gigabit USB Soundcard
Numark CM200 mixer
Mackie SRM 450s

I purchased two ground loop isolaters from Maplins (the ones that are a tenner each) and have installed them on the outputs of the Gigabit soundcard. But it makes absolutely no difference

Do I need an adapter of some sort to place the ground loop isolators between the mixer and the speakers ?

I've just bought a Micro Max stand, it would be rendered useless if I have to switch back to the desk top !

Any ideas ?

Regards

Netrix

Hi,
I couldn't quickly find the other posts about this.

Here are some thoughts, in no particular order...

-One of my laptops had a humming problem, the PSU had an earth input, but I also had an american (ie non-earthed) Cable/PSU for the same model and it cured the problem.... (I'm not advocating cutting the earth cable btw! your laptop PSU may need that wire!!)

-If possible, can you go direct from you soundcard to your amp - ie remove the mixer?

-I doubt you've got long cable runs, but if your audio cable is run along side any mains cables, move it away.

-If your PC sound card turned "up"- ie you've not sending a really low-level signal and amplifying that?

-Use different RCA cables, a broken screen could also do this.

-Does this appear just on the speakers, or is it also the headphone output of the mixer?


Apologies if you've tried a few of these already!

Jason

The ground loop isolators normally get rid of ye-ol'-domestic-laptop-on-mains hum...not the other rice crispy noises that you've mentioned.



Do all[i] the other noises, (the squeaks and the pops) disappear totally when you're running the laptop on batteriy power, and [i]only[/] re-appear when you're running on mains? If those squeals and pops are still there on both battery [i]and mains, there could be something else causing the problematic pops.



One thing to check is on the little on-screen mixer on the laptop screen, try muting (usually a tick box) all the channels which you dont need to make the music come out...especially any Mic channels and any "stereo mix" channels. Also try dropping the remaining (music) channels on the on-screen mixer down to about 75% (if they were higher) and increasing the signal elsewhere, eg: later on in the audio chain...eg: increase the gains on the CM200 mixer channels (usually at the very top of each channel), or the mixers Master Output, or as a last resort, the gains on the Mackies.



Afterthought: Its not the CM200 USB version of the CM200 mixer is it?

Thanks Jason -
I don't have an rca phono to XLR cable at the minute so I can't go from soundcard to amp (in my case amp in the Mackies)
No long cable runs and psu lead is seperate from the audio leads.#
I've change the phono leads to inferior ones - no change
I've not tried the headphones although I think it will be present.




Hi Gary - no it's not the USB version - I bought it recently off of Ebay and it does send a bit of white noise to the Mackies (I have a very old, very cheap 2 channel mixer as backup and the white noise is not present when using this mixer) but I can live with this noise.

The noise I want to eliminate is only when the laptop is running off of the mains. Plugging the mains lead in and out of the laptop results is a low frequency "whine" on the speakers, and with no music playing just opening up different windows produces noise on the speakers. On battery power the noise is not there !

PCDJ is set for an external mixer so I do not have any on screen mixer controls.

Thanks for your help guys - I will check the headphones just to be sure.

Regards

Netrix

Hi Netrix

I use a Dell Inspiron 3800 circa 2000 (pretty bullet-proof old machine!)

When I was using it with a Synergy mixer/amp combo I had to use a ground
loop isolator but when used with current Behringer mixer/ Warrior amps I don't
have the hum. I can only think it's either the sound card or mixer/amp.
The mains adapter is the source of hum normally. Try using a completely
different power source (run a extension lead from another socket somewhere)
& see if it helps or (I know they're expensive) a main conditioner multi-socket
(Maplin do a 6 way for £40).

I don't use a seperate sound card so I can't comment on your Gigabite unit but I'm
sure other DJs here use one. They may be able to help.

Good luck & welcome back...You know you love it!
Newcie Jon

Hi Jon - as advised by another member I tried a second Dell power cube - no difference, but that got me thinking. I have a Numark DMC-1 controller and that is the cause of my noise !!! (it only has a 9 way d type connector but I use a serial to usb converter lead) - remove the lead and no more noise !

I tried using a seperate ring main for the DMC-1 but as soon as I attach the USB lead I get the whine.

I suppose I'll need a new power cube for the DMC-1 - but it's have to be a generic one as they've been obsolete for ages (or I could upgrade to a DAC 2:))

Thanks for all your help guys - Can I be pretty certain that the power cube is causing the noise or could it be the DMC-1 itself ?

Questions questions question !!

NEtrix

Just a quick addition about the on-screen mixer.



I just meant the little tiddly "Windows" mixer.... rather than any mixer that the "DJ" application that you're using may offer in addition. If you've got a little speaker icon in the task-tray down by the clock in the bottom right hand corner of Windows Desktop, a single click on it should bring up a single "Volume" control, and a double click should bring up a wider, 4 or 5 (or more) channel mixer.



If it appears, see if any of those sliders can be dragged down to reduce unwanted noise.

It is 99.9% the mains for the laptop you need an earth lift for it

Nik

Hi Nik - not sure what an earth lift is ?

As per my previous post - the noise stops if I either remove the DMC-1 from the laptop unplug the DMC-1 from the mains. (when removing the DMC-1 USB lead there is a definite whine on the speakers).

I don't think the laptop power cube is to blame. Even if I do not use the ground loop isolators and leave the laptop powered by the mains it is noise free as long as the DMC-1 is disconnected !

Netrix

Gents, do you think bonding a suitable earth connection to the DMC-1 controller would help ?

I am at work at present but it occurred to me that the PSU for the DMC-1 would not have an earth connection and when the USB lead from it touches the chasis of the laptop the potential difference could be causing my "whines" ?

This is a complete stab in the dark but somewhere in the back of my mind I think I recall seeing an earth bonding point on the DMC-1 when I was installing it into the flight case.

Also, can anyone elaborate on the earth lift that Nik mentioned ? the only response I got from work colleagues was a shovel !!!! - Comedians, the lot of 'em !!

Regards

Netrix

You could try earth bonding the DMC. There is probably one on the back of the mixer too where you would normally connect the earth wires from a pair of record decks, so you could try running a wire between the two.

Some pieces of kit have a switch which breaks the earth connection in the line level cables. Often found on amps, graphic equalizers, active crossovers etc. If anywhere, it would be on the Mackie Speakers but I don't know if they have one.

I've also never found that using a ground lift switch makes much difference.

i had a similar problem with a brand spanking new laptop. turned out to be the mains lead to the laptop. hsd it changed and no more probs.

also, have you tried it without the battery in the laptop? just the mains.

I will try removing the laptop battery tonight when I get in - I thought the battery provided some sort of smoothing on the mains, but I'll try anything to get rid of this noise !!

Thanks for the suggestion.

Netrix

Good news !! sort of -

Earthing the case of the DMC-1 made no difference but insulating the DMC-1 from the mixer has made a huge difference !!

I noticed I still had the whine with the inputs to the mixer removed so I took the DMC-1 out of the rack [still plugged into the mains and with the usb lead attached] and bingo ! no more noise [not exactly true - I get a faint whine when I close PCDJ or open up a program like Excel but it is nowhere near as noticeable as before]

I've used some insulating tape on the underside of the DMC-1 to stop it touching the mixer or the rails of the flight case and all is good :-)

The ground loop isolaters make no difference to the system so I'm going to leave them out as I've heard on other forums that they may impair the bass frequencies.

I would still like to get to the bottom of this and understand why the noise is there but I'm a lot happier tonight that I was at the weekend. Full steam ahead for Saturday's party !!

Thanks again for everyone's help thus far.

Netrix

If it's whine rather than hum then it's probably been picking up digital noise from the DMC circuits, if this has a floating case then it may be that the processor noise has been picked up as indirect radiation via the DMC leads. (acting as a conduit or broadcast aerial!) Insulating the case of this means the noise itself becomes floating rather than earth-referenced (unbalanced)...its like pulling the earth rod out of a radio transmitter, the aerial loses most of its power.

all you need is a 8.99 loop isolater from maplins.. plug the rca jacks into the output from the laptop... and the other end into the mixer.... Problem solved! I had exactly the same noise, its just data and mains hum that can be filtered very cheaply and easily with this little baby

Sounds feasible - I do still get very faint whines as I open new windows or applications and they get slightly stronger if I reboot the laptop whilst everything is still connected.



Thanks Jeff but I already have two of these and they make absolutely no difference whatsoever [they are installed on the phono leads from usb sound card output to mixer input ]
I was wondering if using an adapter to put them on the output of the mixer [xlr to Mackie 450s] would make any difference.

As I said before if I turn the DMC-1 off I have no noise on the system even when the laptop is running on mains power.

My daughter works at a local college that has large AV department - I will try and have a word there to see if they've come across a similar scenario.

If I thought buying a newer DAC 2 controller would solve the issue I would order one but I'm not convinced it would in this case.

Regards

Netrix

daft question maybe... but you sure the surpressors are working ok? Coz the maplin one i use just stops it dead and is brill! Was using 450's as well at the time, and the "data noise" and "hum" was exactly as you describe. As long as you put them anwhere on the "line level" they should filter the noise out before amplification, so worth a try before the mackie and after the mixer... but cant see why the ones you have dont work tbh

Jeff

Cured the noise, just thought I'd post the cure -

The techie guy at my daughter's college gave me one of these to try

http://showtechnic.de/omnitronic/omn_artde...5070&lang=E

Once installed between the mixer "outs" and the Mackie "ins" everything is silent [the button marked GND Eth Lift is the magic button !!]

With this kiddie installed on the mixer "outs" and nothing on the mixer "ins" I got a faint ticking - re installing the Maplin isolators on the mixer inputs has cured that up as well !!

To recap on the setup -
Dell Inspiron 9300 using a Gigaport usb soundcard - two Maplin ground loop isolators in line with the audio path to the Numark CM200 mixer - The LH 070 active DI box in line with the audio path to the SRM 450s [with the ground lift switch thrown] luvvly jubbly !!

again for all your help and suggestions.

Regards

Netrix

So...How much did it cost you in total to cure the unwanted noises on the laptop?

In terms of more grey hair - it's un quantifiable !!!
In pound notes it's not much at the minute because I may be able to permanently borrow the DI box from college

£18.00 for two ground loop eliminators from Maplins - the DI box looks like 90 Euros plus a bit of p&p should I need to purchase one.

If a small 2U rackmount case appears on Ebay I'll look into building another PC, I'm still not entirely comfortable with using a laptop - the old desktop pc I used was bullet proof !

Netrix

Didn't think of the interference being caused by grounding through the flight case. That can happen with any set up where you use a metal framed flight case. I use wooden ones so don't get the problem.

You can get things called "Hunfrees" to isolate rack components when using a rack with metal rails http://www.terralec.co.uk/fixings/humfrees/17302_p.html

Thanks for the link Tony, it's bookmarked. - I'll see how long the insulating tape lasts !!

Netrix

A DI box?

Just noticed..the one you posted appears to run on battery only.

I suggest you find one that is mains powered (it will probably be DC).

You could run into all sorts of problems during discos if it goes flat.

Not sure if it has a bypass circuit but still.

Will save you on 9v battery costs too!

Yes fella ! already thought about that. At the moment I do very few "gigs" so I'll probably get a rechargeable 9v and make sure it's fully charged before each outing. I carry a couple spare of 9Vs for the radio mic.

I don't think it has a bypass option - it had a flat battery when I got the box and it was totally silent

Thanks for the heads up.


Netrix

Hi, Your problem is your charger to the laptop. Try pulling your charger out and if the noise goes go back to Maplins with your receipt for your ground loop isolators - get your money back and buy a new charger (Kingston Charger Universal AC Adaptor. I had the same problem!



Good Luck. ronnie-s-dj.co.uk

Would that be the one thats actually advertised as being for Car Audio hum problems?

Looks like a slightly oversized "D" size battery with the audio in wires on one end and the audio out wires on the other...........solved my problems almost completly, you can only hear a very very faint hum when using very high volumes and no music is playing at the time, once the music is playing you cant hear the hum at all.

Thems the ones - unfortunately they don't clear up all the problems/hums/whines !

If I remove them from my setup I do get a few ticks and hums so they are working to a degree [ticks and hums are only when using mains power]

Using the DI box completely stops the noise

Netrix

The newer Dells use an intelligent charger with 3 terminals rather than the standard 2 pin chargers.

Jim