I got this car radio replacement module mp3 media player but it did not come with a car. So, I used a pull box to provide housing for the mp3 player. The result is a Mini Boombox MP3 Player and FM Radio. The speakers are powered by a single mono LM386 IC 20x-gain amplifier minimal circuit.
I have a modded phone charger with a 2.1mm DC plug but I also created a USB-to-DC cable to power the boombox from a PC USB port. The module is rated at 12 volts but it can boot up at 5v from a USB port.
I can also power the boombox with a 9v battery. For that, I have created a modded battery clip with a you-guessed-it 2.1mm DC plug.
The boombox can play MP3s from SD cards, pen drives or any storage device with a USB port. It also plays FM radio. (I fashioned an aerial out of the antenna of an old RC toy remote.) The mp3 module had a line input connector and I added a 3.5 mm stereo plug for plugging in an external audio source such as a phone or a tablet.
The speaker parts that I had used are not the best or the loudest that I have. I had to settle for smaller ones that would fit inside the pull box. Still, they are quite loud. (If I had used a cap on pins 1 and 8 of the LM386 IC, I would have had 200x gain!) The MP3 player module provides very good pre-amplified sound and I did not want do meddle with with it. The car radio module cost me around 500; the pull box was 70 and rest of the parts (accessories not included) should have been less than 100.
UPDATE 1 (20-October-2013)
Front Panel Stereo Input/Output Connectors
I went to Chennai and got 3.5mm stereo panel jack connectors. I added two of them – one for audio input and another for output. I also added a switch so that the speakers are silent when the amplified signal is sent out.
UPDATE 2 (23 October 2013)
Now that I have a line input, I decide to create a powered mike with an electret microphone.
When combined with my 200x-gain LM386 speaker-in-a-box, the microphone becomes extra sensitive and can be held at a foot or two away for regular use.