Step 4: Setup the Receiver
Solder long leads onto the phototransistor (or photodiode). Attach these to an 1/8th inch audio jack (a headphones cable is perfect). Plug this into the MIC port on a laptop or PC or other MIC preamp/amp and turn up the gain and volume to a moderate level. Try to mount the whole setup (with room for a magnifying glass) on a sturdy but portable material (like a wooden board).
For this project the GAIN of the amplifier is critical. It must be very high to pick-up slight variations in input signal (light) to pull out the music. Therefore I build a breadboard preamp from RadioShack's 50-in-1 Sensor Lab breadboard kit, which I highly recommend. Check out the photos and schematics from the included book.