I have an 80s Delco AM/FM car stereo that I want to play with for home audio. I want to set it up so I can listen to it with my headphones.
Any suggestions on how to hook up a headphone jack to the speaker wires? It's not just a matter of soldering them to the jack, is it? On another board, someone suggested I would need to match the radio's speaker output with the headphones and that it could be done with a resistor divider, as follows:
Since I'm strictly an amateur with electronics, I'm not sure how to build this. Can someone help (a picture, for example) or is there an 'off-the-shelf' solution?
Regards,
PSF
Any suggestions on how to hook up a headphone jack to the speaker wires? It's not just a matter of soldering them to the jack, is it? On another board, someone suggested I would need to match the radio's speaker output with the headphones and that it could be done with a resistor divider, as follows:
Since I'm strictly an amateur with electronics, I'm not sure how to build this. Can someone help (a picture, for example) or is there an 'off-the-shelf' solution?
Regards,
PSF
The standard way to use headphones from a speaker output is to just put 220 ohm 2-watt resistors in series with the headphones on each channel. Radio Shack used to have an adapter for that but I don't see it on their web site.
Since headphones have a common connection between channels, you will have to hook the common to the radio's ground wire and use only the + speaker wire from each channel.
Since headphones have a common connection between channels, you will have to hook the common to the radio's ground wire and use only the + speaker wire from each channel.
I honestly don't know where the resistor value came from... but that's my recollection of the resistor used in the Radio Shack adapters (I used to sell them back in the 70's). 220 ohms is also typical of what's used inside most amps with a headphone jack (if they don't have a dedicated driver).
You can hook them direct without a resistor, but the volume adjustment will be touchy.
You can hook them direct without a resistor, but the volume adjustment will be touchy.
If your headphones are rated at 300 ohms, then you can hook your speaker output directly to your headphone jack with no resisters and the volume will be about right.
You would probably want to add 8 or 16 ohm resisters from the left & right wire to the ground wire to load the amp down enough to sound clear.
You would probably want to add 8 or 16 ohm resisters from the left & right wire to the ground wire to load the amp down enough to sound clear.
thanks for the info. 8 or 16 ohm resisters to the left and right (-) wires, then to the ground, you say?
so this means the (-) wires for each channel are grounding wires for the speakers? Is there not a place for ground in the headphone jack? Should I also have a ground wire going to the jack?
so this means the (-) wires for each channel are grounding wires for the speakers? Is there not a place for ground in the headphone jack? Should I also have a ground wire going to the jack?
Don't connect the speaker -ve to anything on the jack! Car stereos have what is termed a bridged output where both connections move around with respect to ground as it maximises voltage swing. So if you either connect these -ve wires together or to ground you will fry your stereo.
You probably don't need to load the output with anything, but if you think it sounds harsh then connect a 10 ohm resistor of 10 watts or so across the +ve and -ve speaker wires. Connect the +ve wire to the jack 'signal' connection via a resistor in the range 47 to 220 ohms, this will allow you to turn the amp up to at least a little bit before it blows your ears out. Use the 0V/ground supply star point as the ground/shield for the jack.
You probably don't need to load the output with anything, but if you think it sounds harsh then connect a 10 ohm resistor of 10 watts or so across the +ve and -ve speaker wires. Connect the +ve wire to the jack 'signal' connection via a resistor in the range 47 to 220 ohms, this will allow you to turn the amp up to at least a little bit before it blows your ears out. Use the 0V/ground supply star point as the ground/shield for the jack.
What is "ve"? I'm an amateur when it comes to electronics and I think in terms of (+) and (-). Whenever I connect speakers to the two channels, I connect the (+) to the (+) post and (-) to the (-) post, left and right. That's my simple understanding of it.
So are you saying I can connect both (+) wires to the headphone jack (for left and right), but leave the (-) wires dangling, not connected to ground, not connected to anything? If so, don't I need to ground something? What about the radio itself? Do I need to ground the headphone jack with a separate wire of it's own? And if I do ground something, what do I ground it to? A copper rod outside in the ground? I apologize if I sound dense, but I don't clearly understand.
I know it would be a lot simpler just to buy a ready made stereo, complete with headphone jack, but that's no fun.
So are you saying I can connect both (+) wires to the headphone jack (for left and right), but leave the (-) wires dangling, not connected to ground, not connected to anything? If so, don't I need to ground something? What about the radio itself? Do I need to ground the headphone jack with a separate wire of it's own? And if I do ground something, what do I ground it to? A copper rod outside in the ground? I apologize if I sound dense, but I don't clearly understand.
I know it would be a lot simpler just to buy a ready made stereo, complete with headphone jack, but that's no fun.
An externally hosted image should be here but it was not working when we last tested it.
+ve is simply shorthand for positive, hence -ve is negative!!!
Yes, just leave the speaker -ve wire dangling, insulated of course
As I mentioned before (but maybe not clearly enough), the 0V/ground/screen connection for the jack is taken from the battery/PSU 0V connection.
That's it. No extra earthing or anything required. Just remember to insert some resistors maybe 47 to 220 ohms, one or two watts, in series with the jack connection, unless you want to suffer deafeningly loud levels even at very low volume settings.
Yes, just leave the speaker -ve wire dangling, insulated of course
As I mentioned before (but maybe not clearly enough), the 0V/ground/screen connection for the jack is taken from the battery/PSU 0V connection.
That's it. No extra earthing or anything required. Just remember to insert some resistors maybe 47 to 220 ohms, one or two watts, in series with the jack connection, unless you want to suffer deafeningly loud levels even at very low volume settings.
nice. thanks for clearing it up.
I also searched on the term "bridged output", since you mentioned it. I found this helpful pdf document, which explains it nicely I think. It also has pictures, which I tend to think in.
http://www.tripath.com/downloads/an12.pdf
I also searched on the term "bridged output", since you mentioned it. I found this helpful pdf document, which explains it nicely I think. It also has pictures, which I tend to think in.
http://www.tripath.com/downloads/an12.pdf
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?
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?
An externally hosted image should be here but it was not working when we last tested it.
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 Unless your headphones are really cheap nasty items at normal listening levels you will not run into the power limit. If you omit the resistor you are likely to cause damage to your headphones and you will probably find that because you have to have the volume set so low, even a small adjustment makes a lot of difference.
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
Unless your headphones are really cheap nasty items at normal listening levels you will not run into the power limit. If you omit the resistor you are likely to cause damage to your headphones and you will probably find that because you have to have the volume set so low, even a small adjustment makes a lot of difference.okay, last post on this (maybe) to make sure I got it straight. I sketched up this picture. Is this correct?
An externally hosted image should be here but it was not working when we last tested it.
Indeed, you are correct If the stereo uses a bridged output then shorting those -ve speaker wire will be a very nasty thing to do. However, perhaps Mr Delco knows that the stereo is an old one before the time of high-power output stereos and it does not use a bridged output, hence it's safe to connect those two wires together?
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.
If the stereo uses a bridged output then shorting those -ve speaker wire will be a very nasty thing to do. However, perhaps Mr Delco knows that the stereo is an old one before the time of high-power output stereos and it does not use a bridged output, hence it's safe to connect those two wires together?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.
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.
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.
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.
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.
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.
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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