How to increase the volume of the headphones?

Probably many of you have encountered this problem when connecting your headphones to your MP3 player or phone, the volume was not enough, in other words, the power of the player or the phone is not enough to ensure loud, clear sound. And how to be in this case?
To do this, you can collect a headphone amplifier with your hands. His scheme is rather simple and any wireless enthusiast, whether a beginner or experienced, will be able to make it, showing care and attention.
In creating this amp I wanted to make it unusual, I wanted to get away from the classic plastic housing. Remembering that fans modding computers often make transparent housing for their PC, I decided to make a clear case of your amplifier. And as a highlight - to abandon the printed circuit board and do everything hinged mounting.
Development of the scheme was carried out in the program of Eagle. This is a classic twin opamp amplifier OPA2107.
Below is a diagram of a headphone amplifier with your hands.
List of parts needed for the power supply of the amplifier:
- power connector;
- LED 5 mm (any color);
- R1LED - resistor of 1K to 10K (1 W);
- CP1, CP2 - electrolytes 470 uF (voltage 35 or 50 V);
- RP1, RP2 - 4,7K (1 W).
Parts List for the amplifier:
- IC1 - dual operational amplifier OPA2107 (note - on the concept of an operational amplifier is designated as OPA2132, the fact is that in the beginning I planned to use it);
- C1L, C1R - 0.68 uF 63 V (for audio input);
- C2, C3 - 0.1 uF (film, to stabilize the operational amplifier);
- R2L, R2R - 100K (0.5 W);
- R3L, R3R - 1K (0.5 W);
- R4L, R4R - 10K (0.5 W);
- R5L, R5R - Jumper (optional);
- Stereo jack - 2 pcs.
So I decided to do everything hinged installation - started manufacturing the frame. Here you will need care and attention, as body will be transparent, and any shortcomings will be immediately visible.
For power bus I used solid copper wire, 1 mm thick, taken from the scraps of the cable used to house wiring.
As the power supply is perfect any transformer power supply with a voltage of 12 V and an output current of 300 mA. It is advisable to use a transformer power supply, since the use of pulse can lead to interference (you will hear a constant hum in the headphones).
To power connector, I used here is a connector (center pin - that's a plus power supply).
Just below you can see the power supply wiring. At the entrance of the power supply at 12 V, which are then using voltage divider (resistors RP1 and RP2, at 4.7 ohm) are converted to 6 volts and -6 volts. The fact that the operational amplifier must be power bipolar. The wire in the center - the so-called "virtual ground", which in any case should not be connected to this ground (in the power connector).
Two large capacitor 470 microfarads 50 volts paired with 0.1 uF capacitors are needed in order to minimize interference on the OS and increase the stability of its operation. To do this, try to place them as close as possible to the conclusions of the Shelter.
Once you have finished soldering, you can proceed to check the amplifier. A word of advice, do not need to test the use of your coolest headphones, some quite simple. The fact is that if you mess up somewhere and soldered parts are not under the scheme, it is possible option, in which you spoil your headphones. But I hope that when checking everything will be fine.
Since the amplifier will continue to be filled with epoxy resin, then I decided to raise it a little, so that when he was pouring the exact center of the body. To do this, I soldered a small findings below.
I thought it would be nice a little bit more to refine the design of the amplifier and therefore decided to print labels on audio connectors. I prepared them in Adobe Photoshop, and then printed on thin photo paper and glued to the connectors on the double sided tape.
For some time I was thinking on the design of the body and the material from which to make a form to fill. I opted for the 1.5 mm plastic, it is perfectly normal office cut with a knife, leaving a very smooth edge.
Then I developed a form to fill, using all the same Eagle. Cut out all the parts, I started to build. To facilitate this process, I first picked all angles using superglue, then two times each glued seam, ensuring full tightness.
The easiest way to check the amount of the epoxy resin to fill - a form fill with water and then pour the contents into the cup and found the resulting weight and volume. Of course, it is possible to measure the volume with a ruler - but the way the water seemed easier.
For the filling, I used a transparent epoxy resin. Specifically for this resin hardener and resin ratio should be 1: 50. It is difficult to measure such a small amount of hardener, for this useful jewelry scales. And generally the same for different brands of epoxy resin and hardener ratio is different, see the instructions.
When hardening epoxy excessive heat occurs (in my case, the temperature was 62 degrees). The mold is then covered in order to prevent dust and debris to the surface.
I left to harden epoxy resin for a day. After this time, it was dry, and I proceeded to the removal of the form. For this I used a belt sander.
Then use the router I Stoch chamfer and all sharp corners.
For polishing body I first used sandpaper with 600 grit, and spent the final polishing "the wet" 1200 th fine sandpaper.