I am currently working on LED to music sync circuit. The schematic is displayed below:
Mostly I am using this schematic image: . Because I was unable to find TIP31 transistor I used quite similar - BD243C. What I found out, I also needed an amplifier for my headphones signal, because the voltage is to low to activate transistor so I bought TDA2822M and build directly from documentation the amplifier: http://pdf.datasheetcatalog.com/datasheet/SGSThomsonMicroelectronics/mXqwxzy.pdf
After all of this unfortunately LED is barely blinking. To be honest I am not an expert in electric circuits and I have no idea what is wrong with it. Can someone please give me an advice what am I doing wrong.
I've edited my initial circuit due to the Spehro Pefhany answer. Now the outcome is quite interesting. When I plug in jack to the mp3 player the diode is turning off. When it is not connected it is turned on.
I suppose I might have just found an error. The amplifier isn't working. All the time I've been connecting my wire to the mp3 player and now I connected it to pc jack. With PC connected everything is working even without an amplifier. Even it is working better, because from amplifier I have outputs with resistors.
Now I need to check somehow my amplifier and probably get the new one. I'll update this questions when I'll know if my bet is correct.