Mains Hum/interfearence? Laptop

[Phil]

Hey guys, Im hoping you have all came across this before as I have with 4/5 laptops and about 3 PC's. Macs are fine though.

Im getting interfearence as soon as I plug the power adapter into the laptop but not when transformer is switched on and disconncted from laptop.

At first I thought cheap soundcard. I ruled that out when I used a M Audio Project Mix Controller/soundcard that is round £8/900 new.

Then I thought power supply. I have had the same problem with tiny ones and the big ones (that id expect to be well shielded).

Its like a digital interfearence type noise, all glitchy not hiss.

Havent had problem on iMac but Mac's are the boyos and should be perfect for the price! lol

Any suggestions to try and eliminate this?
Its the last thing I want coming through the PA at a gig!

[Rick Sarson]

I have had the same thing. It seems to be a random occurence. I have not found out a good reason yet. Other sound guys I know have had the same problem. Sometimes unplugging the mains adaptor and running on batteries for ten minutes and then reconnecting is enough to get rid of it. Very odd!

[gingerbiscuit69]

yeah, its a combination of cheap PSU's and cheap soundcards often.

Macs (as they bum themselves for making media pc's, charging twice the price for the privalidge) just use higher quality components and design in the PSU and soundcards, and properly earth the internals.

theres a few ways to sort this,

1). buy something good in the first place, not common knowledge but ACER make all the mac hardware, so buying an acer pc or laptop will give u the same quality as a mac (in my case i build my pc from scratch out of mainly acer components, and also silent fans).

2). make sure the internals are all properly earthed where they should be (not really a laptop fix), ive earthed all internal metal to the chassis and made sure the case is hardwired to the earth of the PSU. dont attempt this unless you know what you are doing as you could short the components!

3). update the motherboards firmware if possible, often fixes all mannor of errors (ever had your mouse randomly gitter, or slowly scroll across the screen!?).

4). use a real soundcard with balanced outs, or a DI box when linking to a pc, gives you an earth lift option which will often kill the hum.

good luck, Pat

[Phil]

Used an acer and that was the same lol.

Use my shuttle PC I built up from the barebones with all good stuff and still no luck lol.

I might possibly see if I could use the optical out on laptop. Dont know if converters are pricey though.

Well only £1.5K to go till I get the Mac Pro lol

[gingerbiscuit69]

not saying all acers wont do this, just the higher quality stuff.

thing is, computer components are being churned out for pennies nowadays, and the 'big flashy' bits maybe well rated such as processor power and RAM, HDD etc, but in order to make these saving, something else must be made bad. unless you are prepared to fork out for decent kit, then expect laptops which screens go white from cheap ribbon cables, laptops which overheat when in normal use, noisey fans, and strange electrical ground loops.


my current PC was £1600 to build with the best quality matched components i could get, everything is internally earthed, theres ONE FAN, which makes just over 18db noise at its fastest, many many heatsinks, yet the processor only runs 3-5degrees over room temp.

wouldnt expect skytech to produce total audio transparency (ie: no hiss), so why expect it from budget computers?

[soundmanjim]

all laptop and desktop PC's use switch mode power supplies which are MURDER on audio. The new QSC amps have switch mode power supplies but they dont get buzz or hum; an idea would be to earth any exposed metal parts at back of said pc to ground or to the next bit of kit; may sort the problem - more modern stuff is better but a lot of pc's werent designed to be used with soundsystems.

My laptop is fine on any soundsystem, although it has just struck me that if your laptop dies very quickly on the battery it may be that its power pack is on the way out and the psu is having to work twice as hard to deliver current to the thing and charge the pack.

just my few pennies worth!

[Mark]

I use a Behringer hum destroyer (excuse the cheesey name) to get rid of mains noise on audio signals, all the basics is, is 2 transformers cancelling out the earth loop, the only thing is doesn't get rid of is the sound of the Hard drive ticking over, but thats only really audiable if you have alot of gain and its in a pretty silent room. there are lots of companys that make these deviced not just Behringer, it depends on what connections you want in them as most are RCA or quarter inch jacks.

[guymorris]

Just in case anyone is searching for an answer to this long time issue, I either use a dedicated controller with sound card like a Denon DJ controller unit or if I need it simple I was pointed to a Cambridge audio DAC unit that can also upsample. This is excellent kit for getting line level quality audio from your laptop totally noise free into a mixer. It has a USB link from laptop to DAC and then balanced XLR L/R outputs. The naughty way to get round it when using the minijack out is to remove the earth on the input to the power supply (dubious practice IMO) if you need the laptop powered or just run from battery(not ideal with laptops) . Both my Ipad and I phone when using the charger do not encounter the noise problem via minijack it seems to be just limited to laptops.

[ian hasell]

There are quite a lot of safe solutions, the earth on your laptop power supply is not used anyway (this is the problem).
This is the type of thing to look for
web.rbnet.com/~specialtysal/pacsni-1.jpg

Ian

[ian hasell]

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