Switching off speakers when plugging in headphones?

[Christian]

I would like my amp to turn off the speakers when I plug in my headphones. So I bought a headphone plug/contact with an internal switch. But, because I don’t have a separate headphone amp ( just running them on the power amp, 330 Ohm resistor from speaker terminal) this switch now becomes useless. This, because the switch really is just a plate that contacts the signal pin.

I can’t make the switch turn on relay, which in turn turns off the speakers, because I can’t put a signal for the relay on the channel-pin.

Any bright ideas? The contact looks like this illustrated on a drawing and a pic.

Best Regards,
Chris V

 

[Christian]

.

 

[Bill Fitzpatrick]

Cut off the old headphone plug and install a new one with the 330 resistors inside of it.

 

[Electro]

Or

Put it after the pre-amp, but before the main amplifier.

 

[Bill Fitzpatrick]

Electro:

I doubt that his pre-amp can drive the phones.

This whole deal is out of desperation anyway. Using a phone jack as a speaker on-off switch is not a particularly good idea in any arena except low-fi.

 

[ThingyNess]

I'd just use the switch contacts inside the headphone jack to open an NC (normally closed) DPDT relay connected at the speaker output.

It'll cost a bit, but it should be relatively bulletproof.

 

[Bill Fitzpatrick]

The switch contacts inside the jack have the audio signal. As Christian originally said, they are not available for anything else.

 

[Peter Daniel]

Why don't you get a regular headphone jack, connect 330 ohm resistors to it from speakers output and install a switch at the back of your amp which can disconnect the speakers. It may be mechanical (like double pole AC switch) or toggle switch controlling a relay. Do you really need convenience of automatic speakers shutoff when you plug your phones?

 

[Christian]

Hi,

Well, I'd really like to be that convenient, but it seems it doesn't work.

Maybe I'll have to go with the switch anyways, or find some other phone-jack.

/Chris,

 

[Duo]

You can easily pass the necesarry voltage through the contacts in the jack to fire a relay to the speakers and use caps to bypass this voltage from getting into phones and the amp. I don't see why it wouldn't work, perhaps even very well... If you guys want a diagram of what I'm thinking, I'll happily supply it!

 

[Peter Daniel]

Better than using caps is to get a different headphone jack. I've seen jacks with one switch at the end, which is pushed by the phone plug (this could control the relay).

 

[paulb]

Heh. Try this (it's quick and cheap and may be okay). Use a single 330 ohm resistor in series with the ground of the headphone jack, and get rid of the other two resistors. The left and right channels will blend somewhat, but you may like this effect. You can play with the resistor value a bit. The speakers will cut off when you plug in the headphones, but the resistor will not affect the speakers, just the headphones.
THEN, build yourself a decent headphone amp. See www.headwize.com.

 

[Christian]

Yeh, that be a really good idea actually. But why would the channels blend a bit? Seems like that would work just perfect putting twice the value resistor on the ground instead.

Or, I'll go with Peter D. suggestion. I've seen larger (not 3,5 mm but 6mm or so) phone plugs with a separate switch, which would be ideal.

Then I'll just make it draw a relay when plugged in, which disconnects the speaker. There will probably be some kind of click in the speakers, but I'm sure it can be fixed somehow.

/Chris

 

[paulb]

But why would the channels blend a bit? Seems like that would work just perfect putting twice the value resistor on the ground instead.
/Chris

Actually, working through the algebra it looks like it won't blend, but actually separate the two channels more. The summing currents through the ground resistor modulate the "common" voltage that both channels of the headphone see. So you end up subtracting some left channel information from the right channel, and vice-versa. A super-stereo effect.
I like Peter's suggestion better too but if you want a quick fix so you can work on a Real Headphone Amplifier...

Gee I like these new Smilies. I'd like to buy one of these glasses that keeps filling itself.

 

[Duo]

You can't get any wider a stereo image, you'll just get a monoural difference from both speakers in the headphones which appears to be similar to the sound of a Hafler Matrix. However, this may only muddle the sound on certain pieces of music.

 

[Duo]

Think of this, if you were to connect both head phones positive wires to the speaker O/Ts and couple the negatives together without any link to ground... What would happen?? You would get a total Hafler Matrix effect with the audio being completely the same in both headphones since they're in series. Thus, as a Hafler Matrix, you get only sounds that are different between the channels and nothing that's the same, similar to running the amp bridged without using the right kinds of inputs. Now, if you place a resistor from the headphone grounds to the amp ground and you reduce the subtraction effect a certain amount and begin to hear center sounds and some difference between channels. By now you guys must realize that there is a very big problem with running the headphones with only a resistor to ground! Think what would happen if you had only sound coming into the right channel of the amp? Then the headphones would get all of that using the other channel's ground level as a reference because of the direct connection. In other words, if you have a song that starts with music on one channel or there are lot's of stereo differences, then you'll be feeding audio right from the amps through the headphones and fry them quickly!

If you don't believe me, just try this and you'll see instantly how weird it sounds and how easy it is to fry your headphones with stereo sound occurances!

 

[Duo]

Well, does anyone see what I mean yet?

 

[Electro]

Duo, you are saying you want a device that is designed for headphones to produce surround sound. There are many on the internet if you know where to look.

Try looking at ePanorama.net

 

[Duo]

You obviously didn't clearly read what I said.
I don't want a device to produce surround sound into headphones... ( I already know how to do that)
My point is about the previous remarks in this thread about running a pair of headphones off an amp's speaker o/t's by using a common ground resistor and direct connections to the channel o/t's. Please read back a bit and you'll see what I'm getting at.




EDIT: BTW, I also know of Epanorama already, it's a great page and I hope you continue to recommend it to other people who may not know of it!

 

[paulb]

In other words, if you have a song that starts with music on one channel or there are lot's of stereo differences, then you'll be feeding audio right from the amps through the headphones and fry them quickly

Right you are. You'd need resistors on each channel as well as the one in common. Also, signals appearing on only one channel or the other would appear out of phase on your two ears. That would be weird. Maybe there are hidden messages out there that we can decipher using this.