Earphone Output

[blindsjc]

Hi friends,
Someone knows about earphones output schematics or any other information.
I just finished a amplifier with a Tonemender and a TDA2050 but to get sound
directly from the preamp doesn't show good quality.

Every schematic that I know do not show a earphone connection. How the
big ones like Fender and marshall do this outputs?

again, sorry about the bad English.

Thanks
Ronaldo

[teemuk]

Put a voltage divider to the output (the usual method) or build a lower power amp for headphones.

[blindsjc]

Hi teemuk,
Thanks again, I'll try it today.

Ronaldo

[teemuk]

I was so haste to answer so I almost forgot few points:

You'd probably want to switch off the speaker when using headphones. You will need a jack with internal switch to do it. There are many types of switching jacks but what you need is a stereo jack equipped with a DPDT switch (douple, pole double throw). If you can find one with SPDT (single pole) it's OK too but I guess no one manufactures those.



http://img50.imageshack.us/img50/7103/headphoneswitchvu2.gif

The switches are normally fixed to one position but they have a spring mechanism that toggles the other position when plug is inserted. I attached a schematic of the switching arrangement since pictures are easier to interpret: The black circles depict jack's pins. The arrows depict orientations or "throws" of two internal switches. The wires that end to small "lump" are the "poles" of the switches. So, a pole will make contact with one of the throws depending on whether the plug is inserted or not. You need to test the continuity of the switch to find out the correct pinout.

You connect the amplifier output (speaker send) to either one of the poles.

The pole connects the bottom "throw" when no plug is inserted. A wire from it runs to the speaker.

The pole connects the upper throw when headphone plug is inserted. It is connected to resistor that forms a voltage divider together with the impedance of the headphones. The other two resistors are "mixing" resistors for stereo operation. They connect jack's pins for "tip" and "ring".

Yes, one switch is left unused and that's why I told SPDT switch would work as well. It doesn't hurt either to have that extra switch. For example, you could use it to toggle a led when the headphones are on or perhaps something more useful.

[blindsjc]

Oh yes,
I found some like this on runoffgroove faq,
http://www.runoffgroove.com/phones.png
and I think it will solve the problem.

Thanks again friend, people like you makes
newbies projects possibles. Thank you.