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I'm trying to understand how I would add a headphone jack (audio out) to a TV of mine. The board on the TV looks like so:

enter image description here

And the headphone jack I have is the following:

https://www.adafruit.com/product/1699

I've tried connecting the L+ to the far left of the jack and R+ to the far right of the jack and then the middle ground port running to L- or R-

This works but results in right channel bleeding into the left channel when panning the audio. I've also tried to connect the ground wire on the jack to a common ground on the board but this blows the headphones (checking it with a voltmeter shows about 120V).

I thought I understood how a stereo jack works but this is the first time seeing a L+/L- and R+/R-. Can someone explain to me whats going on and what I should be doing? I would assume also that this port is after a gain/amp stage does that require any additional components to protect the output jack?

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    \$\begingroup\$ Besides anything else, you should NEVER connect a speaker output straight into a pair headphones! No surprise they blew up. You need to put in some attenuation for the headphones. First, what sort of wattage are the TV speakers? And impedence? From there, you can work out the size and value of the resistors. Doing that may cure the bleed, but your major problem, as mentioned already, is that the TV amp is most probably 2 bridge mode, Class D amplifiers that do not share a common earth. What surprises me, is that the amp IC didn´t go up in smoke already! \$\endgroup\$ – F. Bloggs Oct 4 '17 at 18:24
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A headphone jack uses 3 connections because the L- and R- are common (shorted).

This connector has 4 connections.

Only if L- and R- are also shorted on the TV's PCB can you connect a headphone. Probably the connector connects to speakers, these do not require L- and R- to be shorted.

Not shorting them allows for a bridge amplifier or class-D amplifier to be used. My guess is that this is a class-D amp as I'm seeing 4 inductors and a chip just above the connector.

Conclusion: you cannot use this output with a 3-pin headphone connector.

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  • \$\begingroup\$ That makes sense, I did a test with a voltmeter and L- + R- do not connect to a common ground and they do both, in fact, run to the speakers. Do I need a different audio jack (I'm actually using a 5 pin jack, see above link) or are you saying I need to find a different spot to tap into the audio? \$\endgroup\$ – Mikeb Oct 4 '17 at 15:03
  • \$\begingroup\$ @Mikeb A class-D amplifier (and I agree that it looks like it is one) is basically just a synchronous buck converter with an analog input signal in place of a fixed voltage reference. You'd have to dig backwards a ways to find and get at the audio and you probably would need to add circuitry at that point, as well. It's "non-trivial." \$\endgroup\$ – jonk Oct 4 '17 at 15:50
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Consider getting a switched stereo jack and wire directly from speaker wires. This will isolate the speakers when the headphones are plugged in. Simply splice into the common and connect to jack. Then cut the hot side of each speaker and connect to the appropriate pin on the jack. Then run two additional wires back to the speaker output.

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    \$\begingroup\$ The board photo shows L+/L- R+/R- so the chances are that this has bridge mode outputs. There is no "cold" side so connecting any two wires together will no end well. \$\endgroup\$ – Transistor Dec 6 '18 at 7:34

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