Line level voltage to drive LED display
That diagram is a rich collection of errors, to long to fit in a comment, so I'll make it an answer.


your diagram shows PNP transistors, but wired the wrong way round. But the TIP31C that you show next to a PNP symbol is an NPN type...
you have no resistor in the base wire of the transistors to limit the current. Put a 1k resistor there (in each each line)
you have the LEDs pointing in the wrong direction, the arrow  must point towards the negative. The LED picture next to the symbol that is pointing in the opposite direction does not help for clarity.
you have no resistor to limit the current through the LEDs. For standard 20 mA leds put a resistor of ( 12 - ( 4 X 2 )) / 0.02 ~= 220 ohm in series with each LED string.
you used the symbol for a foto-transistor, which is a very different component than the power transistor you want (and should) use.


If you want to get this to work, either find a better instructable or dive into the theory yourself.