ac or dc ????

evo6tme

New member
Apr 17, 2008
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I'm a bit confussed and hope someone can help . a speaker cable carries ac right ??? then that means my car speakers which has a 12 v dc supply somwere along the aplifier stage its converted to ac ???. To make things more confussing a sound enginner friend of mine said that directionall interconectors are a waste of time becouse ac goes both ways .Now i understand the comment about ac current but as my turntable rca inputs carrry no current atall is it true that its ac runnig through the interconectors ????
 

fatboyslimfast

Well-known member
Jan 10, 2008
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all sound, well nearly all sound, is AC - if it were DC then the speaker cone would only go out, and then back to centre when the signal shut off, whereas in reality it goes both ways.

Therefore, the signal from your turntable is also AC, albeit at tiny levels.

without going into serious physics stuff, the 12v DC in your car is used to amplify the ac signal coming into it - therefore simply making it a bigger AC signal.

The amplifier doesn't use AC as it's supply - in fact no amplifiers do, otherwise every sound would have a nasty 50hz buzz associated with it (along with the fact that transistors need DC to work). All home equipment that runs off the mains, converts the AC into DC either in the mains adaptor, or internally in a power supply circuit.

At this point, you are probably wondering why we use AC at all, well that is down to the fact that AC can be transformed into different voltages (which makes sending it across power lines far easier when transformed to thousands of volts) whereas DC cannot. Which would mean that if our mains supply was DC, everyone would need a power station within a couple of miles of their house...
 

evo6tme

New member
Apr 17, 2008
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Mainlly as i thought, cheers.

so my freinds comment about dirrectional markings on interconectors is correct then, ??

as an afterthought were does the current for the tonearm come from as i know its not magic but it has no power supply
 

chebby

Well-known member
Jun 2, 2008
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evo6tme:
..as an afterthought were does the current for the tonearm come from as i know its not magic but it has no power supply


The current comes from the movement of magnets within coils in your cartridge. (Or coils within magnets). It generates according to the principles of EMF (Faraday I think) like a little electrical generator.
 

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