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Amps/Voltage 3.5mm jack

post #1 of 4
Thread Starter 
Just as the title states. I have been modifying old stereo speakers into computer/iPod speakers and just wondering the amperage and voltage that normally comes out of a computer jack.

I've been considering building a couple of speakers out of car component speakers into a T-line box just because I've been bored. And hopefully if the wattage can get high enough I won't have to buy a stereo receiver.

The most I've found is that iPod's generally put out from 2.4v - 2.9v.

I would actually measure it but I don't have a oscilloscope or any other way of easily measuring it
post #2 of 4
Probably the best you can do is assume it's a Line level out or find the spec's for your particular codec, the majority of onboards/soundcards support both headphone and line-level from the same out though with either jack sensing to detect the different resistance or an amp that can drive both so it could be anything. The current will depend on the input resistance of whatever you connect.
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post #3 of 4
They're typically in the range of 1-2 volt peak-to-peak. Never more than 5. But that's with no load. Add a load, and it'll fall. Quickly.

There's no "amperage" on the output of anything, though many things have a current rating. Computer outputs don't have a current rating because they can safely drive a dead short.

Instead, they have an output impedance. This various greatly between devices, and is really the only difference between a line out and a headphone out, if there is one. Headphone outs should have lower output impedance. Basically, its a measurement of how the output voltage sags with load.

Don't expect more than .1W or so out of a headphone jack. It may be enough to get very small speakers to be audible, but no more than that.

You don't really need a scope to measure the output of a port, anyway. Use Audacity or something to make a sine wave file then use your everyday DMM in AC voltage to measure it - that'll get you close, as long as you don't drive the output into clipping! That'll get you the RMS value.

I have an oscilloscope and I guess I could measure the output of the various mp3 players and computer outputs that I have. Would people be interested? If I can find a suitable pot, I could even do it into various loads. I think I may, out of curiosity, compare my on board Realtek to my X-fi just for fun.
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post #4 of 4
Thread Starter 
I think it would just be cool to know some of the odd stuff like that.

I have already decided that i'm going to get a receiver, just because I have changed my plans to build some larger towers.

Right now I just soldered some Sony radio speakers (8Ohm not sure if that's each or paired didn't measure) to a already wired up jack that I cut off from a pair of crappy headphones.

After I hooked them up to my computer they got pretty loud. But you can hear it clip if I turn it up past 5/6ths.
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