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#11 |
diyAudio Member
Join Date: Feb 2003
Location: Arkansas
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after reading that pdf a couple of times, I have another question!
it says with bridged output that the +ve and -ve supply equal voltage, opposite in phase, thus quadrupling the output power to the speaker load. So... If I leave the -ve wires dangling, won't this reduce the power to my headphones? Plus, you suggested dropping it even more with resisters in series with the +ve wires. Is this because headphones can't handle the same amount of power as two car speakers? Can I calculate the appropriate resistance I need to place inline using the output power of the car stereo versus the input rating of my headphones? ![]() |
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#12 |
Did it Himself
diyAudio Member
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You are correct that doubling the voltage allows the power to quadruple and also (in a way) that the power available to your headphones will be reduced if you only use one side. However, as your headphones share a common connection you have no option other than to leave the -ve amp wire unconnected. Also, there is already more than many times enough voltage swing from just one side, so it's not an issue.
You could calculate the required resistance, but it also depends on how efficient your headphones are. It's much easier just to try a few different values ![]() |
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#13 |
diyAudio Member
Join Date: Feb 2003
Location: Arkansas
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#14 |
Did it Himself
diyAudio Member
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Looks good to me. You will want to connect the battery to the stereo as well though
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#15 |
diyAudio Member
Join Date: Feb 2003
Location: Arkansas
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Just got off the phone with an authorized delco car radio repair guy. He said to wire the speaker commons together and mount that to the headphone common on the jack, then mount the left and right positive wires to the left and right on the jack. Period. Any other way would screw it up.
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#16 |
diyAudio Member
Join Date: Feb 2003
Location: Arkansas
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I went back and read that pdf about bridged amps. It stated never connect two negative terminals or it would short it out. Goodness. Mr. Authorized Delco's instructions sound contrary to that paper.
Which way is up? |
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#17 |
Did it Himself
diyAudio Member
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Indeed, you are correct
![]() If you have an AC voltmeter, set it to read upto about 10 volts and play some music through the stereo. If the -ve speaker connection voltage changes a lot with respect to the 0V battery connection then it's a bridged output. If it never goes above 0.5V then you should be safe to connect them together and use that as the screen/ground connection for the jack. Also, one other thought if the stereo uses a bridged output - it's probably quite likely that you will need to add a capacitor in series with the headphones as there will be DC present on the output which will need to be blocked from your headphones. I need to know the impedance of the headphones to work the value out. If a bridged output isn't used then that would be the best solution giving the easiest method of connection. |
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#18 |
diyAudio Member
Join Date: Feb 2003
Location: Arkansas
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The radio is definitely bridged output. Mr. Delco said it was. And he said it put out 12 watts per channel.
But rather than trying to make the speaker wires fit the headphones, why not make the headphones fit the speaker wires? In other words, can't I simply rewire the headphones so that each ear has it's own pair of wires? Then I could route the radio's left and right wires to their respective RCA jacks, just like it was meant to work. |
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#19 |
diyAudio Member
Join Date: Jun 2003
Location: Connecticut
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Yes you can do that if you want to mess with the headphone wiring.
My preference would be to wire a standard stereo phone jack with the series resistors and hook them to one speaker wire for each channel and ground. It'll be more than loud enough, and you can use any pair of headphones you want.
__________________
dave |
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#20 |
Did it Himself
diyAudio Member
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Well, if Mr Delco said it was a bridged output and still said that you could short the -ve wires together, get him to try it and then explain the smoke that comes out of your stereo
![]() Yes, you could rewire the headphones, but as I wrote earlier, there will be way more than enough volume even just using one side of the amp. It's up to you. All the headphones I've ever come across would be quite hard to modify for isolated operation; the wire and it's inner insulation is very thin, contacts are small and fragile. I agree with maylar's comments. |
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