matth3w

I am glad you like the project. The 1 and 8 pins on the LM386 control the gain of the amplifier. Look at the datasheet and you will see various configurations of resistors and capacitors strung between pins 1 and 8 to create various levels of gain. Usually I have just left these pins unconnected (lowest gain). With an older or weaker MP3 player you will probably want some gain. A wire connecting the pins will create the highest gain. Experiment with configurations. You can also put a potentiometer in to give something of a volume control. The GNGN8 is actually the names I gave to the pins, except that they overlap and mask each other. They are GN1 and GN8 (GN for gain). Hope this helps. Let me know if you have other questions.

Good catch on both. The +9 for the battery is left over from when the ATS was powered directly from a 9V battery. The upper half of the schematic is for the circuit that bumps a single AA (1.2V for rechargeable) battery up to the 5V necessary to run the amplifier portion. The whole thing is now just powered from the AA battery. Similarly, the D2 1N4001 diode was in place when the ATS had a 9V supply to prevent reverse current if someone put the 9V battery in backwards. Since (I believe, hope, and it has been my experience) that the MAX756 chip outputs 5V and deals responsibly if you put a battery in backwards, I replaced the diode with a jumper (see note in step 5 Soldering Parts to PCB). This eliminates the voltage drop by diode which supplies slightly higher voltage to the amplifier. Hope this helps. Let me know if you have other questions.