Op Amp Understanding + Holiday Lights Tutorial I am following Jeremy Blum's tutorial for Holiday Lights: http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds

I am just trying to set up the circuit for one of the audio channels. I believe I followed the breadboard schematic. However, when I connect the Arduino the power, but without any audio input, the LED lights up. I would've thought that would not be the case.

Can someone help me correct my understanding here? Thanks.

Image of my breadboard: http://postimg.org/image/ibqfvezqp/
Per Jeremy Blum:


  If the input doesn’t have a audio input plugged in, then it’s said to be “floating” and you >can’t really count on the circuit to do what you would expect. The audio input connection >introduces a known voltage (0 when no sound is playing) connection between the positive op->amp input and GND that we then amplify. Try connecting the input to GND and you should see >the LED turn off.


Source: http://www.jeremyblum.com/2011/12/25/tutorial-14-for-arduino-holiday-lights-and-sounds/comment-page-2/#comment-1373392