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#1
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Ground Loop? (Ground Loop Isolators Have No Effect)
I have a laptop in my trunk which I'm using as an MP3 player. Up until
recently I used a cassette adaptor to pipe the sound into my 2000 Passat's factory head unit. I decided to upgrade the sound quality a bit, and bought a PIE VW-AUX (a device which converts the unused CD Changer connector in my trunk into an auxiliary input) adaptor and now have the audio from the laptop running through it to the head unit. Everything works like a charm as long as the laptop is running off its own internal battery. If I select CD1 on the head unit, I can hear nice clean(ish) audio from the laptop. When I have the laptop connected to the power inverter (plugged into the cigarette lighter socket in the trunk), though, I get this really loud buzzing/humming sound coming through the speakers (lound enough to almost drown out the music completely). It doesn't matter whether the laptop is on or not - as long as its plugged into the car battery through the inverter, I get a loud humming sound when the CD changer is selected on the head unit. About 5% of the time, the humming sound might go away for a little while, but always comes back again. I did some research, and it sounds like I have what's called a "ground loop" problem. However, I've tried two different ground loop isolators (one was made by a company called Stingray, and the other was the PIE EIS-ILNO, which is supposed to be both a ground loop isolator and noise filter) and neither one has had any effect. I've tried a different power inverter, but the humming sound is still there. If I'm in the garage and plug the laptop to house AC current the humming is gone (although this isn't a viable solution for the obvious reason ;-) Is this a ground loop problem, and if so why aren't the ground loop isolators making any difference? If not, what is it and how do I fix it? Is it "safe" to leave things in this situation? At the moment, I have the inverter on to charge the laptop battery only when I'm NOT listening to music through it and switch the inverter off when I'm listening to music. However, the radio is on when the laptop is charging so whatever is causing the humming is still coming in through the CD input even though I'm listening to the radio. Is this harmful? Thanks! |
#2
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I think you have accurately identified the problem, but it looks like
the only solution i have is the one you have tried. http://www.epanorama.net/documents/g...oop/index.html here is a good explanination of ground loops and ways to fix according to this site, ground loops could cause damage to the system. according to the site "A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components, or the ground potential between two pieces of equipment is not identical" my personal suggestions: (not based on experience, only on information from the above site.) OBJECTIVE: Eliminate ground loops Ground loops are caused by the resistance between the grounds of two electrical items not equaling zero. So, how do you make the resistance between the two grounds equal zero? Solution. 1 move the grounds closer together(inverter ground closer to wherever the audio ground). Less distance = less resistance. Methods for execution are : Try hardwiring the inverter to your car instead of using the cigarett adapter (remember thicker wire means less resistance, but at some point the effects of larger wire become insignificant. There are charts that give the resistance of a certain gauge wire over a specified distance. the relationships are also not linear.). this may just be a waste of time. you might want to barrow somone else's inverter and test the effects as well. i am not implying that there is anything wrong with the inverter, but different circuitry might have a different effect on the system. |
#3
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#4
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Kevin McMurtrie wrote:
In article .com, wrote: I have a laptop in my trunk which I'm using as an MP3 player. Up until recently I used a cassette adaptor to pipe the sound into my 2000 Passat's factory head unit. I decided to upgrade the sound quality a bit, and bought a PIE VW-AUX (a device which converts the unused CD Changer connector in my trunk into an auxiliary input) adaptor and now have the audio from the laptop running through it to the head unit. Everything works like a charm as long as the laptop is running off its own internal battery. If I select CD1 on the head unit, I can hear nice clean(ish) audio from the laptop. When I have the laptop connected to the power inverter (plugged into the cigarette lighter socket in the trunk), though, I get this really loud buzzing/humming sound coming through the speakers (lound enough to almost drown out the music completely). It doesn't matter whether the laptop is on or not - as long as its plugged into the car battery through the inverter, I get a loud humming sound when the CD changer is selected on the head unit. About 5% of the time, the humming sound might go away for a little while, but always comes back again. [snip] You probably have one of the many piece-of-crap inverters that have a live neutral. An audio ground loop eliminator is meant to block a volt or two of ripple, not a spiky 60V square wave. There are solutions - 1) Find a quality, true sine wave, AC inverter with an isolated output. [snip] I thought I'd post a follow-up with the "final solution". Kevin was correct: the problem was with the power inverters. True sine wave inverters are massively expensive, but there's a cheaper (and totally adequate solution). While doing research, I came across a product made by a company named Vector. They make a line of inverters (MAXX SST) that advertise ("New Noise-Free Technology"). I bought the 225 WATT model (TVEC034) at the local Target for less than $30 and it has almost completely solved my electrical noise problem (if I gun the volume up to the max I can hear a very soft buzzing, but I'd never have the volume anywhere near that high when listening to music). My "only" complaint about the unit is that it's cooling fan is pretty loud (loud enough that I can hear it in the trunk of my Passat sedan when I'm sitting at a stop light), but I can live with that! :-) |
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