Not all audio devices allow direct connection of headphones. Some of them are equipped with line outputs only. Headphones can be connected to them only through intermediate low-power amplifiers.
Instructions
Step 1
Use any suitable plastic box as a housing for your homemade headphone amplifier. It should be easy to open and fit in your pocket.
Step 2
Take two cinch plugs and a standard headphone jack. Solder short two-wire cords to the plugs. Fasten the socket on the wall of the case.
Step 3
Purchase dedicated headphones with a built-in volume control. They are not much more expensive than conventional ones, but they allow you not to put such a regulator on an amplifier.
Step 4
Fasten the compartment for two AA batteries inside the case.
Step 5
Take any two low-power, low-frequency junction transistors. They must be the same, otherwise the sound volume in the headphones will differ.
Step 6
If using NPN transistors, connect the common pin of the headphone jack to the positive of the battery compartment, and the emitters of both transistors to the negative of the battery compartment. If pnp transistors are used, do the opposite. Remember that this amplifier has a common lead from the headphone jack not connected to the common wire, but to the power bus. Do not try to put the tulip ring contacts on the common terminal of this socket, as this will cause a short circuit.
Step 7
Connect the collector of one transistor to the output of the jack corresponding to one stereo channel, and the collector of the other to its output corresponding to the other stereo channel.
Step 8
Connect the ring contacts of both cinch plugs to the junction point of the emitters of the transistors. Connect the pins of these plugs to the bases of the transistors, but not directly, but through capacitors with a capacity of several tenths of a microfarad.
Step 9
Connect a 10 kilohm fixed resistor and a 1 megohm variable resistor between the base and the collector of one of the transistors. Set the maximum resistance of the variable resistor. Turn on the amplifier, apply a signal, and slowly begin to decrease the resistance. Reduce it until the wheezing disappears, then increase it slightly.
Step 10
Turn off the power, unsolder the chain, then measure its resistance. Replace it with the nearest larger fixed resistor from the standard series. Solder the same resistor between the base and the collector of the second transistor.
Step 11
In the future, to turn on and off the power of the amplifier, simply, respectively, connect headphones to it and disconnect them from it.
