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Laptop Hum

#1 User is offline   Nutcracker 

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Posted 09 June 2009 - 11:14 AM

Hi

Posting this for a mate....and I quote

Quote

"Recently had a system hum which Ive attributed to stupidly putting one of my amps on a different electric phase (youd think my alleged electrician colleague might have said something). Ive now spent the last two days studying ground earth loops and means of isolating them, not just for the system but because I dj using a laptop and the transformer can cause a hum.

I dont fancy a big DI box with a ground lift and the cheap phono GLI's whilst effective are probably going to colour my sound! To safeguard me against future problems I reckon the passive ART DTI module looks ok. One unit between the mixer and the digital crossover by XLR lead and four units (due to me using all four channels of an audio 8 dj) between my laptop and mixer by phono leads.

Anyone with any advice please chip in, especially if theres a more compact all in one device with 4 stereo connections to connect my audio 8 dj to the mixer (we use either an A&H Xone 42 or 92 at traffic)."


Your thoughts chaps?

Col

#2 User is offline   RoyS 

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Posted 09 June 2009 - 11:32 AM

I too DJ using laptops and have similar issues with power supplies causing hum. For each PC I use a 2 channel DI (http://www.bluearan....semode=category) The result is minimal colouration and no hum...

Cheers.

Roy

#3 User is offline   paulears 

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Posted 09 June 2009 - 11:52 AM

Laptop PSU noise is a constant problem. DIs don't have to be big - in fact, they are all rather similar in size.

It's a shame that a nice multi output device like yours is marred by a noisy PSU - The BEHRINGER - DI800 - ULTRA-DI PRO DI800 - might do as a multi-DI box. Could be cheaper to see if you can borrow an isolating transformer and try that on the laptop psu, then use your 8 out box without DI, if the transformer cures it?

#4 User is offline   LX-Dave 

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Posted 09 June 2009 - 12:48 PM

Not particularly answering your question, but I thought I'd add it anyway;

Some brands of laptop have different degrees of this problem, and some seem not to have it at all, HP's seem to be awful, whereas Dell and Apple laptops have very little problem at all (is it the laptop make or just the PSU?).

Also (don't quote me on it) isn't it something to do with putting ferrite beads on the power and/or audio cables?

Dave

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#5 User is offline   boswell 

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Posted 09 June 2009 - 01:39 PM

Brands don't come into it, it's the type of PSU and inverter used for the screen backlight. The types of PSU used by a brand vary across the range and also can vary within a product run. It's due to the quality of the switchmode PSU they use also it depends on if the earth is carried through to the laptop dc rail.
A DI will sort the earth loop out but it may not filter out the PSU noise superimposed on the signal or the inverter hash.
I had a HP laptop that I used a DI box with but I got noise if I turned the screen brightness up to abt 50% (even when running on Batteries) Its now been sold on!!
It all down to price, if a brand get offered cheaper PSUs or inverters that do the job and are reliable, they will use them, they are not bothered about the very small % of buyers who complain about the system noise. If they used a better unit that cost more, then they would be at a price disadvantage to other brands.

This post has been edited by boswell: 09 June 2009 - 03:07 PM


#6 User is offline   timtheenchanteruk 

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Posted 09 June 2009 - 01:43 PM

I have found the worst offenders in general to be the 3 pin IEC lead type, the older psus with a figure 8 connector don`t cause any problems, I have put it down to the earth just getting the filtered out rubbish shoved back down it.

#7 User is offline   RoyS 

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Posted 09 June 2009 - 01:45 PM

In the past I have had two identical Dell Latitudes with near sequential serial numbers, one hummed, the other didn't...
And IMO Mac's are just as bad as Wx based PC's for humming.

#8 User is offline   benhyman 

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Posted 09 June 2009 - 04:14 PM

Run the laptop connected to the charger, but without the battery. Will solve instantly if you don't have a DI lying around.
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#9 User is offline   osal 

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Posted 09 June 2009 - 04:23 PM

http://www.maplin.co...?ModuleNo=33172

I had that prob use this and solves it instantly

#10 User is offline   Starstruck 

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Posted 09 June 2009 - 04:43 PM

View Postosal, on 9 Jun 2009, 5:23 PM, said:

http://www.maplin.co...?ModuleNo=33172

I had that prob use this and solves it instantly



CPC do a similar one for around 4 each (part number AV12774 - 4.27 ea) . Ive got 6 of them on 3 seperate DJ rigs and they work perfectly.

As for colouring the sound, lets be real, at the volume levels they will be used at no ones going to notice. Also your average clubber couldn't tell you a good sound from a bad ! Not that Im saying they make the sound bad at all . I think you would stuggle to notice the difference in this application.

Kev
www.giantwii.co.uk , www.starstruck-events.co.uk

#11 User is offline   Jivemaster 

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Posted 09 June 2009 - 05:02 PM

Laptops hum fact! They hum sometimes, but only when clean sound is critical!

Either send the sound out through the USBII to a decent external soundcard or send the audio out of the headphone socket and isolate it with GLI from Maplin as linked above, transformers from Maplin and CPC etc http://www.maplin.co...?ModuleNo=46782 or use a pair of DI boxes.

Using an external soundcard allows you to bring two sepaarate audio lines out at one time, so one for playout and one to cue the next track.

Detailed use of laptops esp wrt hum and soundcards will be found on DJ based fora of which mobiledjforums.com is a competent group of DJs likely to help (there may be others too).

#12 User is offline   Starstruck 

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Posted 09 June 2009 - 05:07 PM

View PostJivemaster, on 9 Jun 2009, 6:02 PM, said:

Either send the sound out through the USBII to a decent external soundcard


Even then you still sometimes get the hum !!

I use the internal soundcard and an exteral card on all three of my rigs (hence 6 ground loop isolators) .

The internal card is used for cueing (lower quality) and the external one is output to the crowd (better quality).

Kev :-)
www.giantwii.co.uk , www.starstruck-events.co.uk

#13 User is offline   Andrew C 

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Posted 09 June 2009 - 05:56 PM

Plugging my laptop into a Makie TT dsk for control ONLY, NO AUDIO causes the bggr to hum!

I'm curious about the "running without battery" suggestion above; I'll try it, but I'm not optimistic ^_^

BTW; We've done this before in one form or another. Lots of info in the search box above right. Remember to search the BR, not Google.

This post has been edited by Andrew C: 09 June 2009 - 05:57 PM

Andrew

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#14 User is offline   LXbydesign 

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Posted 09 June 2009 - 05:58 PM

I use a Mac running Serato for dj ing - and ive never had any problems in any venue with humming. However, I do make a point of trying to plug it into the same circuit as the mixer / CDJ's are on.....
Making Light Work....

#15 User is offline   KevinE 

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Posted 09 June 2009 - 05:59 PM

The fact that different bits of the system are on different phases shouldnt really come into it, it doesnt have much to do with hum loops.

Quote

Run the laptop connected to the charger, but without the battery
This sometimes works but only where the hum is due to the power supply switching noise, the smpsu is often noisier when charging a flat battery so makes the audio noisier. The PSU can also generate more noise when it's off load, on load, the laptop is thinking hard, the screen is bright, dim, the fan's on, off, the disc drive is asleep, the screensaver's on, the refresh mode is changed.....you can't generalize.

And it isnt always due to an earth loop, it's sometimes due to bad rfi performance and this is hard to eliminate.

This post has been edited by KevinE: 09 June 2009 - 06:04 PM

Kevin Edwards

K. Edwards Electronics Engineers
Staffordshire Moorlands

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