You can plug any light in (with the right voltage ofc) and it will work.
A Vu-Meter is simply measuring the volume of the sound, the bigger the voltages, the higher the light will go on the bar. :)
Though, getting it accurate takes calibrating and such, and I will not go over that.
This is as simple as it gets, and it's pretty awesome!
Step 1: Gather your parts!
Standard transistor, cheap and easy to find.
Use as many as you want!
Then you need just as many diodes + a few spares. (take note of the Vf drop they have, too high, and you can't use many leds with low voltage)
A pcb board.
a pin-breakable thing :^) -- The same thing you use to build shields with.
A potentiometer (100k for this one) To adjust sensitivity on the bar.
A simple switch.
And last but most important, a lunchbox.
Step 2: Step 1, or step by step, or step, or ..
Then you solder a Diode (shown on the picture) as a starting rectifier for the BASE-pins.
Connecting another diode onto the end, with another diode, and so on. so you "split the voltages, the further away you go.
Since there is a Forward-voltage, you drop, in this case 0,6V per diode. Making the LED's shine less the further away it is in the bar.
Continue adding a diode, then connecting the end to a base with a resistor (10k ohm)
(view the picture)
Trying to view from below just makes my eyes hurt.
Step 3: Connectors
And not necessary, but done here, a simple passive low-pass filter done with a 1k ohm resistor and a 1µf capacitator.
(sorry for poor documentation here)