I'm at the beginning stages of making an LED visualizer for live music. My ideal end product will most likely be a wearable device that has the arduino switching transistors to connect different led configurations that will get their supply voltage from an anolog signal (ultimately for vocals, but I have a guitar and not a nice microphone, so right now with a guitar)
Where I am right now is a simple circuit with the guitar input to a LM386 OP amp IC and an LED out. It works fine when I have a 8 Ohm speaker (from a Hallmark card) attatched as an output also. When I have no speaker, and just the LED is when I run into trouble. The led starts off working but fades out in like a second. I'm not sure why this is, but hopefully someone can point me in the right direction.
Also, what can I do to make the LED brighter? It works at a reasonable brightness, but nothing close to what I would get if I fed 3V straight into the LED. The difference appears greater when instead of a standard LED I use one of the 8000mcd jumbo 10mm LEDs from RadioShack. This is the LED that I ultimately want to use (it's super bright and big).
Here is the circuit I have set up as of right now (forgive the sloppy mspaint):