Introduction: Private Listening for Our TV
We have grandchildren at our house daily for on-line schooling. I am retired and there are programs I would like to watch during school hours. But, audio from the TV would make it impossible for the grandchildren to hear their instruction over the computer audio. I decided to buy a little Bluetooth receiver/transmitter. It connects by means of a 1/8 inch stereo plug.
Our TV is a three year old Samsung. It has no Bluetooth capability and no 1/8 inch headphone jack. I added a headphone jack. It works, but could use some improvement. What follows describes what I did and may help someone as a starting point.
The photo shows the back of our TV. I could not remove the whole back, but a metal inset portion that covers more than three-fourths of the back. I was not able to remove the outer plastic frame around the metal portion. If I were to try harder, I would lay the TV face down on a table to support it. Some caution is needed before laying a TV face down on a table. It has happened that the glass on the screen is too heavy and breaks when not in the vertical position.
22 gauge plastic covered stranded copper wire
1/8 inch switching stereo jack
Step 1: A Cautionary Step
I made a quick photo of my cable connections so I can put them back as they were later without rethinking the whole process. Not shown is the line connector to the power board inside the TV. Removing the back from the TV requires removing the AC line. Nothing in flat screen TVs holds a massive charge of electricity like a cathode ray tube TV from years ago does. Once the AC line is removed, the danger of electrical shock is eliminated, even though capacitors on the power board may hold a small charge.
Step 2: Where to Tap the Audio
Newer TVs sometimes use a digital output and a digital-to-analog converter is advised for an audio tap. I am tapping into the wires running from the main board to the speakers. The set in this photo are yellow and yellow-black. The set to the other speaker are red and red-black. I am assuming the yellow-black and the red-black wires are the commons. I will make my taps near the connector at the main board.
See the second photo. I have removed the yellow four-wire connector from its socket at the main board. I stripped the red-black and the yellow-black wires so I can solder to them.
Step 3: A Discovery
The photo shows the yellow speaker connector in its white socket. Notice the four solder points on the white connector. The red-black wire is at the second solder point from the left. The yellow-black wire is at the fourth solder point from the left. I set my electrical meter to the diode test mode because it has a very low current to protect semiconductors and used the meter like a continuity tester. The red-black and the yellow-black wires do not have a direct connection to each other. The meter reading shows they go through something. I want to keep them isolated from each other by means of two capacitors. Those capacitors will allow audio signals to pass, but will block DC current so nothing is damaged in the amplifier section. I am describing what I did. I am not necessarily recommending that you try this with your TV.
Step 4: My Circuit
The photo shows the circuit I used. The two commons need to go to the same common terminal on the headphone jack. See the second image for a drawing of the circuit path. You may need to tap on the photo to see it full frame.
Capacitance values for audio coupler circuits by capacitor vary quite a bit from .13 microfarad up to more than 200 microfarads. I arbitrarily chose a 1 microfarad mylar film capacitor. Plastic film capacitors are supposed to possess better qualities for audio, particularly less distortion. I added a 1,000 Ohm resistor to reduce volume. Afterward, I would say I could have easily doubled or tripled that. In the first photo the black wire from the resistor goes to the common or ground terminal on the headphone jack.
Step 5: More Connections and Insulation
I insulated bare conductors with cloth electrical tape. I chose it because plastic electrical tape sometimes becomes gummy and either moves from where it was placed or unravels. Cloth tape tends to become more stuck to itself with the passage of time.
See the text box in the photo. I needed to cut the yellow and the red wires to run connections to the headphone jack. See the next step for the wiring diagram on the switching headphone jack. It is a switching jack because the circuit is routed through earbuds when plugged into the jack, but goes to the built-in speakers when the jack is removed. The connection highlighted by the text box is insulated with some heat shrink tubing. It is easy and it stays in place very well once sufficiently shrunk.
Step 6: Headphone Jack Circuitry
The package in the first photo gives no clue about how to make connections to the jack. There are five terminal points. Once the package is opened one can see the internal parts through a clear plastic cover. See the second photo. Still I needed to check with a continuity tester. “Source” is the wire from one channel of the stereo amplifier. See the drawing in the first photo.
I cut the solid yellow wire. The side coming from the amplifier connects to the Source terminal on the headphone jack. The yellow wire going to the speaker connects to the terminal marked To spkr. I also cut the solid red wire. The amplifier side goes to the other Source terminal. The speaker side goes to the To spkr terminal on the headphone jack.
Step 7: Mounting the Jack
I drilled a hole 15/64 inch in diameter in the plastic TV back where I can reach it to insert the threaded crown on the jack and where it will be accessible for use. The plastic TV case is a bit too thick to catch threads with the nut for the headphone jack. I used a sanding drum on a Dremel tool to thin the plastic near the hole, but just enough for the nut to hold the jack well. In the photo you can see the Bluetooth adapter plugged into my new headphone jack.
Put the back on the TV. Attach all of the power and signal cables as they were.
How well does it work? The switching feature works well. I get a soft rushing or whoosh sound in the earbuds when using the Bluetooth adapter. There is some of the same sound when I connect the earbuds directly to the headphone jack without the Bluetooth adapter, too. But, when we use the TV with the built-in speakers as normally there is no extra noise. Everything is normal. I made my original hookup with two old ceramic disk capacitors I had in my junkbox. I thought quality mylar capacitors might get rid of the noise, but they did not. I have been doing some reading, and I need a ground loop isolator. Those involve a 1:1 transformer for each audio channel. I ordered one for less than $10 US. See the second photo. The rushing noise may be a little softer now, but it is still present. I will just ignore the extra noise. I do not use it to listen to music, but to voices speaking.