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-   -   headphone socket (http://www.physicsforums.com/showthread.php?t=17974)

username Apr5-04 08:15 PM

headphone socket
 
I have a TV which I want to attach a headphone socket.I am guessing that I need the signal going into the speaker but need to match the speakers impedance (capacitive inductance?) with the headphones maybe I should put somesort of a coil not a resister in series with the phones.Is this a simple thing to do considering I have very limited electronics knowledge and no standard equipment.

BoulderHead May23-04 08:26 PM

I don't know the circuitry feeding this speaker, or the impedance of the speaker for that matter. With your limited knowledge of electronics you might end up getting yourself into trouble, but if you just have to do this I'd recommend using an isolation transformer to buffer the headphones from potential line-level voltages/currents. The speaker itself may be marked as to its impedance level which could be a nice way of picking up further clues.

Good luck and be safe!

Cliff_J May23-04 10:00 PM

First off, be very careful inside of the TV. The CRT guns run at like 10,000 volts! The capacitors in the power supply could still be charged at mains voltages. Just stick to the speaker wires and avoid the rest!

A 470ohm resistor on both leads from the speaker to the headphone jack should offer a decent compromise to reduce the level appropriately (current shouldn't be a problem) and yet be loud enough. I assume you're going to wire a switch on the speaker leads to shut off the speaker? While there, a 5,000 ohm logarhimic potentiometer in front of one of the 470 ohms resistors makes sense too so you can adjust the level. And maybe swapping out the 470 for a 100ohm too if you want it louder. Typically a TV should be something like only 2-3 watts of power and an 8 ohm speaker.

Cliff

megashawn May24-04 05:27 PM

Ok, here is a thought that will keep you from making fried username.

Does your television have any RCA ports on it? You know, the lil round things with a hole in the center, generally come in three's, a red (sound) a white (sound) and a yellow (video).


Ok, if so, here's what ya do.

Get one or two (however many ports for sound your tv has) RCA cable, perhaps off an old playstation adapter, and bare the wires.

These wires are actually 2 wires. The outer wire is stranded together, wrapped around another wire. Make sure the 2 wires do not contact when finished.

Once you've got the wires bared, get your hands on something like this:
http://www.pricegrabber.com/search_g...de=googlegfel/

What you want is the female end. Slice that thing in two, keeping the female half. Bare the wires on it.

The wire for the headphone plug will likely be black, with one wire having a white stripe. It doesn't really matter which wire you hook to what, as long as they are isolated from each other when your done.

Seperate the two wires, attach one to the outer stranded wire or the rca plugs, and the other to the inner wire of the rca's.

Tape it up, use wire nuts or even solder, just make sure the do not contact with each other. Plug the RCA's into your television (or cable box or VCR) and plug your headphones into the female port.

Boom, you should have sound. Now, you'd probably want some of those headphones with there own volume control, for this is just a signal your tapping into, and isn't very powerfull. It may be enough to power some small earbuds, but I don't know about larger headphones.

You should be able to get all materials, and quite possibly some advice from your local radio shack. I know they atleast will have the rca and headphone adapters you will need.

Integral May24-04 06:59 PM

If you have RCA connections you do not need to do any wiring, simply get an RCA -> 1/8" stereo jack. If your RCA is line out you will not have volumn control it this case it is handy to plug in a set of self powered computer speakers with a headphone jack. If it is an out for external speakers you will be able to control the volumn with your remote.

megashawn May24-04 08:42 PM

oh, they actually make the rca to headphone adapters? I've never been able to find them, always had to make my own. Well, never a RCA to female headphone adapter, I've got several rca's to male though.

I don't know about the rca output being controlled by a remote though. Its just like a car stereo, and the rca output that is used as a signal for the external amplifier is a low, non changing signal. If you hook a speaker to it, it will play, but very low and doesn't increase or decrease with the volume.

Maybe tvs are different.

Cliff_J May24-04 10:36 PM

Quote:

Quote by megashawn
I don't know about the rca output being controlled by a remote though. Its just like a car stereo, and the rca output that is used as a signal for the external amplifier is a low, non changing signal. If you hook a speaker to it, it will play, but very low and doesn't increase or decrease with the volume.

Maybe tvs are different.

A car stereo is the opposite - it is setup with the voltage over the RCA controlled by the volume on the source unit and the rest of the system is static. Only exceptions are few select people that put their volume control further down the signal chain, but these are few and far between.

Some TVs like Sony's will allow you to select if the RCA output is fixed or variable to match the volume setting on the television. Most outputs are variable and its usually only on the mid-level and higher level units.

Cliff


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