Tips For Installing A Headphone Jack

I just purchased a new Apex stereo TV/DVD combo with many bells &
whistles EXCEPT a headphone jack. Have any of you readers been able
to successfully install a stereo headphone jack into a stereo TV?
Thanks.

(E-Mail Removed) (Larry G.) wrote in message news:<(E-Mail Removed). com>...
> I just purchased a new Apex stereo TV/DVD combo with many bells &
> whistles EXCEPT a headphone jack. Have any of you readers been able
> to successfully install a stereo headphone jack into a stereo TV?
> Thanks.

Yes, I have. One thing to watch out for is that both of the speakers'
"ground" or "return" lines are common, i.e., electrically the same
point. I forget what the jack is called, but it's got 5 terminals:
The sleeve, obviously, which is the speaker common. Then it has two
contacts which contact tip and ring, but they get their signals from
the other contacts. When you push the plug in, it disconnects the
speakers and goes to the phones.


audio out o-------------------------\/
^
| <<<---- plug
o----------------+
|
|
+---------------------------------> to speaker


When you plug in the plug, it opens the contact. There are two of
these circuits in the jack.

Good Luck!
Rich

The simplest approach is to wire the headphone jack to the speaker outputs through an attenuating circuit. The things to be careful though is that the output amp circuit needs to be properly loaded in order to provide the correct audio response and to protect both the amp circuit and headphones from over-currents. The impedance expected by the amp and that expected by the headphones need to be accounted for to flatten the frequency response and minimize distortion and noise. Finally, it doesn't take much to drive headphones to painful levels:

WARNING
Headphones are rated in dB SPL at 1mW, and this circuit is capable of producing extreme SPLs. The levels obtainable are sufficient to cause almost instantaneous permanent hearing damage! Never operate the player at very high levels, and never switch the amplifier on with signal while wearing your headphones.

Always start with the volume control at minimum, and gradually increase the level until it is comfortable, but not too loud. Because of the very low distortion, it is easy to increase the level too far without noticing. Your ears are precious - safeguard them at all times.

That said, here is an article to calculate exactly what you need:
sound.westhost.com/project100.htm
and I attached it's circuit diagram:

sound.westhost.com/p100-f1.png

Here is a limiting circuit that you can wire between the above resisters
and the jack itself to protect your ears:
wa0itp.com/audiolimiter.pdf