I've inherited a TV with good picture and sound, but absolutely atrocious sound. I want to hook up some old PC speakers up, while retaining the ability to change the volume with the remote.

The TV has an aux input but it's not very good. It has a separate volume setting in a menu somewhere and sound still comes out the internal speakers.

I want to bypass the internal speakers completely to a female aux input which I can plug my PC speakers/headphones into.
Figured it would be pretty easy to bodge something together.

This is what I found inside:

Seems very simple, each speaker (ringed) receives 2 wires from the board, just like 2 phono cables.
I only unplugged the white (left) and red (right) wire from the speaker, the black cables are firmly clamped on.
I wired a female RCA/phono wire to each of the speaker wires, which I connected to my headphones, but the audio was drowned in hiss on both sides.
However, if I just wire the left or right individually, I hear it perfectly clear and crisply through my headphones, it's only when I have both that I get tons of hiss.
And if I connect both female phono wires to one side then I also get a perfectly crisp sound (albeit mono).

Can someone explain what's going on and how do I fix it for perfect stereo?

 

It may be that the audio output is a bridge circuit, with a DC bias on both the wires (you could measure that with a multimeter).
That could cause the hiss you hear.
Are the black wires connected together at the connector or do they go to separate PCB traces?
If they go to separate connections, then that's also a sign that it's a bridged amp.

Try using a coupling capacitor from each speaker wire to your RCA jack and see if that helps.
The size of the capacitor depends upon the load impedance. It should be ≥ 1/(6.28*20*R) for response down to 20Hz where R is your load .
You should find a separate ground connection for the jack, other than one of the black speaker wires if it has DC on it.

 

That's very similar to what others have suggested.

Bob @ ElectronicsPoint:

The outputs are probably bridged, which means neither of the wires are at ground. When you connect both channels to RCA jacks, you are shorting two wires together since each RCA jack has one side going to ground.​

I'm afraid I'm not very versed in circuitry though, so I'm not sure what much of this technically means.
On the main board are 4 connections, the 2 black wires connect to separate pins, so it is almost certainly a bridged amp.

I came across this hi-def image of the main board if it's any help (my picture shows it upside down):
https://spares2repair.co.uk/panason...PY4rnE6jGjQT8D6LEk5YTuyPV04PsvcaAm4IEALw_wcB&

Is there a module I could buy to link this bridged amp to a common ground output like a headphone jack?

BTW I'm currently using one of these to connect between the speakers and the headphones:

How would I find a separate ground connection for the jack, and what would happen to the 2 ground wires in the RCA cables?

 

This is a Bridged amplifier, as you can see both speaker terminals go to separate outputs, and so you cant put a single Ground output to it,.



The audio chip will be under the silver heatsink, unless you have an optical output on the tv your only option is to use the Red/White audio outputs into a separate amplifier.

 

Hello,

Just a caution, but you have to be careful when hooking up directly to a TV speaker. That is because the circuit that runs the speaker may not be isolated from the line voltage completely, so that means your headphone jack might be live with very high voltage like 120vac which could cause a very serious shock.

I ran into this when doing my TV several years ago, so what i did was i used an audio isolation transformer (iit was mono not stereo at the time). That gave my headphones electrical isolation from the line.

The test would be to measure from the ground of the headphone jack to BOTH sides of the line, one at a time, with a high impedance digital meter on the AC scale. Check for some higher voltage.

There is a chance that the TV uses a transformer for the low voltage but that's not always the case.

 

Try the capacitor circuit I mentioned.
If you can locate signal or power ground, you can use that for both output grounds.

Or one of these ground-loop isolators may also do the trick.
But note that you want one with separate inputs, not a single stereo plug, so the input commons are also isolated.
If you buy one, use a multimeter on the resistance range to insure there is no continuity between the input grounds, otherwise you could blow the output amps.
To insure input isolation you could also use two of them, one for each channel.

 

I think I'll try a ground loop isolator first.
I live in the UK, amazon is not so kind here.
I figured I can't use a 3.5mm one as it'll join the left and right grounds on the input, so how about one of these? :

https://www.ebay.co.uk/itm/Gold-Pla...154029?hash=item283ee9132d:g:beQAAOSwrQRZr9nA

 

as it'll join the left and right grounds on the input

Which "grounds" are you joining?
As I previously noted, if it's a bridge output you can't join the two black lines, as they are not really ground, but likely biased at a DC level.
The output of a bridge amplifier looks rather like a differential signal with the opposite polarity AC signal (to ground) on each output.

 

I think I'll try a ground loop isolator first.
I live in the UK, amazon is not so kind here.
I figured I can't use a 3.5mm one as it'll join the left and right grounds on the input, so how about one of these? :

https://www.ebay.co.uk/itm/Gold-Pla...154029?hash=item283ee9132d:g:beQAAOSwrQRZr9nA

Hi,

Dont forget to check for the line isolation as mentioned previously. You dont want your head so close to 120vac when you put the headphones on. There was a girl that was killed because of this in the past. Part of the metal of the headphone contacted here ear or something and she touched something else at the same time and that was it.

Also note that coupling capacitors do not provide the proper kind of isolation needed for this kind of protection. That is because the transient response is considered non isolating. They are better than nothing though i suppose