This circuit uses two quad op-amps to form an eight LED audio level meter. The op-amp used in this particular circuit is the LM324. It is a popular IC and should be available from many parts stores. The 1K resistors in the circuit are essential so that the LED`s turn on at different audio levels. There is no reason why you can`t change these resistors, although anything above 5K may cause some of the LED`s to never switch on.
This circuit is easily expandable with more op-amps, and is not limited to use with the LM324. Pretty much any op-amp will work as long as you look up the pinouts and make sure everything is properly connected. The 33K resistor on the schematic is to keep