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AnthoMac
9th April 2006, 02:52 PM
I sometimes listen to audio through a 3.5mm audio cable connected to another two way adaptor (connecting the pc) that connects to my audio speakers (Altec Lansing 251's) and I can usually hear an irritating buzz sound suggesting noise. What's strange is when the Powerbook is not connected to the mains (ie running off battery), it is gone. Havent tried connecting it directly, but another set of speakers find no problems.

Is there a solution or a better alternative to connect 2 audio sources (powerbook and PC soundcard) through standard 3.5mm to speakers or is it the Powerbook problem whist plugged in?

Latest Powerbook 1.67ghz with OS X 10.4.6

forgie
9th April 2006, 04:41 PM
It's an earth loop. The problem arises when an analog system has a 'loop' of earth signal - you have an earth signal going from your PB power adaptor, into your PB, into your speakers via the audio lead, into the power point via the Altec Lansing's power lead, and back into your PB power supply.

There's a few different ways to fix the problem. The first (and usually easiest) is to 'break' the loop. This can most easily be achieved by using digital audio connections. A SPDIF connection will do the trick nicely.

If your PB has a removeable 3-prong AC lead on it, and it came with a 2-prong AC adaptor thingy, then use the 2-prong adaptor instead. This'll solve your problems.

eroda
9th April 2006, 05:02 PM
go the digital out no more noise, i love it, although i dont think your speakers have digital pluggy things (forget name)

AnthoMac
9th April 2006, 06:01 PM
Yes this electrical loop phenomenon is the problem. Even with the speakers connected to the iPod headphone jack>Powerbook via usb>mains it continues to provide the noise. I have however noticed that on some occasions (such as now) there is no noise. That is when I switched off the mains for the powerbook then switched back on again. Strange.

I'd go with the 2-prong adaptor approach, except the powerbrick would require an extension cord.

My speakers are analog and unfortunately only provide 3.5mm audio plugs -i'd love the digital option but then i would have to get a sound receiver (or new sets of speakers).