Headphone jacket sensing

[Umfriend]

OK, wierd Q:

My dad-in-law bought a new LCD TV. It has a headphone socket. When he plugs in the plug, audio is output to the headphone and not to the speakers. This is fine.

The prob is, he isn't really able to plug the plug (don't ask). So now I am wondering, if I soldered a switch in the wire, would the TV switch audio to the speakers if the switch was turned off? Or would the TV still sense the headphone and direct it to the headphone?

Thx and knid ragerds.

[VJ]

OK, wierd Q:
So now I am wondering, if I soldered a switch in the wire, would the TV switch audio to the speakers if the switch was turned off? Or would the TV still sense the headphone and direct it to the headphone?

FWIW, if I plug in an adapter to change the size of the headphone plug, the audio mutes. Even if no headphone is connected on the other side of the adapter...

So my guess is that it won't work. My parents TV as a configuration menu that allows one to define what audio is transmitted to the headphone out (i.e. it is possible to show a TV station while listening via headphone to an external source). So if the TV has this, the headphone jack behaviour can be changed (but not many TVs have this).

A possible alternative could be to connect the headphone to a scart connector:
SCART -> cinch (audio+video) -> jack for audio
The downside is that you'll most likely have no volume control, but if the headphone has this (or if you put a volume button in the wire) it is easily overcome.


Jörg

[VJ]

Oh, some TVs simply have a line out as well. This would overcome the need of using a SCART. Bear in mind that this line out can also be muted when the mute button is pressed, but doesn't change volume when volume control is changed (this is the case on my parents TV).


Jörg

[Umfriend]

Yeah well, my DIL doing anythign on the remote aside from on/off, volume and changing channels is a long shot I'm afraid. But the line out option is actually a very good idea? The HP is connected via an extension (?) wire which does have a volume control on it already! Wahee!

Thx for the heads up!

[az]

The switch in headphone jacks just closes a contact when something of appropriate size is plugged in. You could just cut the wire to that switch (a headphone jack doesn't have that many contacts, trial and error will do in a pinch, you can't destroy anything if you solder the wrongly cut wires together again), and it will never mute the speakers. Depending how the device works though, there may also never be a signal to the headphone then. Just soldering a single pole switch into the line which you've cut should provide you with a nice manual control of whether you want headphone or speaker out.

[az]

I don't really understand what you try to achieve though, I must admit. Do you want to still have audio from the speakers if phones are plugged in?

[VJ]

and it will never mute the speakers

Careful: Chances are you cannot mute the speakers at all: if the volume settings for the speakers and headphone are linked, you cannot turn down the volume of the speakers, but keep audio in the headphones.

I don't really understand what you try to achieve though, I must admit. Do you want to still have audio from the speakers if phones are plugged in?

Perhaps, but IMO he wants to be able to switch to headphone without having to plug it in.
If you use the headphone jack, you have to plug it in if you want to use it, and remove it when not.
Going via a scart allows you to just leave the headphone plugged in; it works when you need it. And you can still choose whether or not you want audio through the speakers.


Jörg

[VJ]

Umfriend:
If the TV is connected to an audio amplifier (home cinema or so), you could also prefer to have the headphones connected to the amplifier... That way, you can use the headphones also for music, without having to change connections.
(configuration at my parents place)


Jörg

[az]

Got it. My solution allows this - it switches between speakers and headphone, just like plugging a headphone in and out does. Depending on how you wire it, it automatically switches the speakers back on when you unplug the phones, regardless of switch position, or keeps the speakers muted if the switch is in headphone position. Material cost is about $1, the huge downside is of course that you'll have to open the TV, and if the headphone jack is soldered to a PCB, you have to scratch a circuit track (the equivalent of cutting a wire) and solder some wire to both sides of the cut to solder the switch in line. All this is not easy and you run a high risk of destroying your TV if you're not careful. Easier would be to just rip out the headphone jack (carefully, of course), solder wires, switch and a new jack to the solder points the old jack was attached to, and let the new jack and switch dangle out of the old headphone jack hole. Still voids your warranty, still poses the risk of destroying your TV, and doesn't look very neat.

[az]

I was also wrong: They don't close a contact, they open the signal contacts when something is plugged in. This means your switch must be three-pole, wired in parallel to the headphone jack. It will either let the signal pass to the jack or direct it around (where it then goes to the speakers). Sorry for the confusion.

[Umfriend]

I'm not going to solder in the TV. And yes, I want to be able to switch between speakers and headphone without having to plug in the plug.

The TV does have seperate volume control for speakers and headphone: whichever is used as output is controlled by the remote (kewl feature BTW). Assuming the line-out has a fixed output levev, the exisitng volume control on the headphone will manage though.

Of course, he'll have to mute the speakers, but that's not a prob.

[VJ]

A true line out on a TV doesn't always have a fixed output level (depends on the TV), but the audio lines on a scart do have a fixed output level and are never muted.


Jörg