Monday, September 27, 2010

The age old Laptop Audio hum/buzz problem - What causes it and how to fix it.

So recently there has been a little buzz (pun? haha)  about laptops, power supplies and audio issues, usually all related. Now this affects a variety of people who don't always comprehend the fundamentals of power and sound, and as i have little experience in the field, I thought id share my knowledge. Note this is article is actual OC from me, Something i don't do very often!

Now  i don't like to crap on too much, in fact i have too much already, so down to business;

The  problem here is we have old tech meets new tech.

The old technology is the double insulated plugs (that's a power plug with only 2 pins) and the new tech are the newer-age Switch-mode Power supplies now coming out with most laptops and netbooks.

The issue is that the switchmode transformer, whilst very efficient power-wise, produces a high-frequency (HF) Wave that cariies ever so slightly down the power cable to your laptop.

It then floats around inside with no where to go, collecting other stray poorly - shielded radio waves that reside in the computer. Now in a desktop we have metal inner frame, which is grounded to the world outside via your power cable and acts a perfect drain or "earth", somewhere for the stray signals to go.

Electricity, like us Aussies, is basicly lazy, So it will always take the easiest path to the ground. 

Now, if you have no earth, like on a laptop with double insulation, But you plug in say a line out that goes to your PA, a Sound desk, Home Hifi,  DJ Decks...some sort of amplifier, well these devices are all grounded, so the stray RF waves float long whatever cable you've plugged into the computer -  The waves hit your sound mixer, deck , hifi or whatever but, as they are unbalanced, the RF noise has usually already been induced into the cable along the way, Once it hits your sound system, it get AMPLIFIED and becomes a BIG problem...

Remember, USB, Headphone and firewire are all unbalanced BUT shielded transmission routes, which makes another great breeding ground for RF problems.

Sometimes, if you have a metal/ aluminium laptop, YOU may be the path it takes to get to the ground.

So, how can i fix it man? Well there a few remedies to try:

-Make sure all your all you equipment is plugged into the same power outlet, 4 way strips / powerboards are fine unless running high powered amplifiers - they'll trip the board.

- Sometime those special power boards with surge filters and hum filters work, sometimes they don't.

- Check you have a  3 pin power plug on your laptop, if you already do:

- Try a DI Box, U can them from most music / Pro audio stores from around $50 upwards.

- Something like a di box but aimed at this exact problem is this thing from Trillium. Its an OZ product but they seem to ship worldwide..I haven't used it , nor can i recommend it ( nor get affiliate sales ect ect) but it looks the part. If it didn't work Id go straight back and choke them with it. But hey, im an angry sort of guy and you probably don't mind parting with the $38.50, so each to their own.

-If you using a USB or FIREWIRE cable, an earth lift cable is known to work, you ll prob need to make one as i cant find one for sale - ill update if i do.

- Another option, Though only ad-hoc is to run the laptop on battery power, this works by removing the problem all together, but creates more in the process.

-Often the cables are the problem all together, if you are using a $2 cable you will get $2 sound. You don't need to spend $260 on one cable but $10-20 should be the minimum spend per cable.
 Other common Earth and Hum problems include:

Equipment on different sockets / phases
This really would be another post if i were to explain why, Lets just says its really important

Missing earth pins
May have been snapped in the past to solve another problem, or the wrong IEC or cloverleaf plug was a 2 pin instead of a 3 pin, or vice versa.

Equipment on same power circuit as a motor or compressor
This really interferes with things.. Do some troubleshooting and try a different phase, room, outlet, venue etc.

Same goes for Fluorescent lighting
Ditto. See above

Broken earth inside cable.
Its like not having one at all. Try some more troubleshooting by swapping your cables around - the process of elimination is painful, but well worthwhile in the long run.

Power transformers
All produce stray RF waves not just inside these, but some that also radiate out of it too. A coiled up cable near or on top of acts a nice antenna for these signals.

Note that all laptop makers do things differently and use use a varying quality of parts, assembly methods and transformers. This info may not apply to every single make and model in the world. Something else of note is that some cheap nasty Chinese adapters will do this, either they do not have an earth pin ( a luxury in china) or have really poor/non existent electrical isolation within the transformer.

Well Ive really tried to be quite comprehensive here,but im sure ive missed something -  if you don't follow something, cant understand some of my jargon, hold different ideas or have something to add, i would love to hear from you below, and don't be shy to drop me a comment below.

MC Checkers

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